lab+manual+2014 cbe 2207
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The University of Western OntarioFaculty of Engineering Science
DEPARTMENT OF CHEMICAL AND BIOCHEMICAL ENGINEERING
INDUSTRIAL ORGANIC CHEMISTRY II
CBE2207
LABORATORY MANUAL
Prepared by P. Charpentier, E. R. Gillies and J. Herrera
8th Edition
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TABLE OF CONTENTS
1 INTRODUCTION .................................................................................... 31.1 CONVERSIONFACTORS .................................................................... 31.2 COMMONITEMSOFGLASSWAREAND APPARATUS ...................... 5
1.3 ANOTETOTHESTUDENT ................................................................... 91.4 SAFETYGUIDELINES ........................................................................... 91.5 GENERALHOUSEKEEPINGANDLABORATORYWORK ................. 141.6 GUIDELINESFORPREPARATIONOFLABORATORYREPORTS .... 16
LABORATORY1-ANATTEMPTATTHESYNTHESISOFASECONDARYALCOHOL:THEUNCERTAINREDUCTIONOFAKETONE.......................22
LABORATORY 2- REACTIONS OF ALCOHOLS: SYNTHESIS, PURIFICATIONAND STRUCTURE ELUCIDATION OF AN ORGANOLEPTIC MOLECULE......27
LABORATORY 3 -THE ALDOL CONDENSATION - SYNTHESIS OFBENZYL AND DIBENZYLACETONES...............................................................32
LABORATORY 4- ALDOL CONDENSATION, BENZYNE FORMATION AND THEDIELS-ALDER REACTION : A MULTI-STEP REACTION SEQUENCE39
APPENDIX ..47
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INTRODUCTION
1.1 CONVERSION FACTORS FOR SOMECOMMONLY USED UNITS OF MEASUREMENT
Acceleration m/s2 ft/s2 3.281X100 3.048X10-1
g (accel. of gravity) 1.020X10-1 9.807X100
Area m2 ft2 1.076X101 9.290X10-2
inch2 1.550X103 6.452X10-4
yard2 1.197X10
08.361X10
-1
Density kg/m2
g/cm 1.000X10-3
1.000X103
lb/gallon 8.345X10-3
1.198X102
lb/ft3 6.242X10-2 1.602X101
Energy J btu 9.484X10-1 1.054X103
(includes work) calorie 2.387X10-1
4.184X100
(thermochemical)erg 1.000X107 1.000X10-7
ft-lb 7.375X10-1
1.356X100
kW-hr 2.778X107 3.600X10
-6
Force N dyne 1.000X105 1.000X10
-5
pound force 2.248X10-1 4.448X100
Heat capacity J/kg*K btu/lb*oF 2.390X10-4 4.184X103
(includes entropy) cal/g*oC 2.390X10
-4 4.184X10
3
Length m 1.000X1010 1.000X10-10
in 3.937X101 2.540X10
-2
ft 3.281X100 3.048X10
-1
micron 1.000X106 1.000X10-6mile 6.213X10
-4 1.609X10
3
yard 1.094X100 9.144X10
-1
Mass kg ounce 3.527X102 2.835X10
-1
lb 2.205X100 4.536X10-1
Power W btu/hr 3.414X100 2.929X10-1
btu/sec 9.484X10-4 1.054X101
cal/sec 2.390X10-1
4.184X100
ft-lb/sec 7.376X10-1
1.356X100
horsepower 1.341X10-1 7.457X102
(550 ft*lb/sec)
Pressure Pa atm 9.869X10-6
1.013X105
(76cm Hg)bar 1.000X10-5 1.000X105
cm of Hg 7.506X10-3
1.333X103
dyne/cm2 1.000X10
1 1.000X10
-1
in of Hg 2.961X10-4 3.337X103
kg force/cm2 1.020X10-5 9.807X104
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CONVERSION FACTORS FOR SOME
COMMONLY USED UNITS OF MEASUREMENT CONTD
lb/in2(psi) 1.450X10
-4 6.895X10
3
torr 7.501X10
-3
1.332X10
2
(mm of Hg)
Volume m3 ft
3 3.531X10
1 2.832X10
2
(includes capacity) in3 6.102X10
-1 1.639X10
-5
gallon (U.S.) 2.642X102 3.785X10-3
L 1.000X103 1.000X10-3
ounce (U.S.) 3.381X104 2.957X10
-5
psig =pounds per square inch gaugepsia =ponds per square inch absolute
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1.2 COMMON ITEMS OF GLASSWARE AND APPARATUS
Most of the apparatus used will be familiar to you, but the following notes may help
you in identifying and using specific pieces.
The ERLENMEYER or CONICAL FLASK is used for handling
solutions, and for titrations. It is designed with a narrow neck to
minimize loss of solution through splashing or evaporation.
The FILTER or BUCHNER FLASK is used in conjunction with the
Buchner funnel for vacuum-assisted filtration. It is heavy-walled to give pressure
resistance; for this reason, a Buchner funnel should never be
used to heat a solution. Attach it to the vacuum line or water
aspirator with heavy-wall rubber tubing. For any operation
involving vacuum, always use heavy walled rubber tubing -
never use soft tubes like Tygon. If a water aspirator is used,
an empty flask should come between the filter and the pump to
avoid suck-back if the water pressure falls. The Buchner
assembly is top-heavy and should be supported when in
operation.
The BUCHNER FUNNEL is used for filtration. It fits through a rubber
bung or cone into the Buchner flask. To use, assemble the flask and
funnel, place a filter-paper flat across the perforated porcelain plate,
and wet the paper with the solvent being used (usually distilled
water). Turn on the vacuum and make sure the paper is correctly seated in thefunnel; the filter paper should be cut slightly smaller than the funnel, but make sure it
covers all the holes. Stir the suspension to be filtered and quickly pour it onto the
center of the paper, using a glass rod to guide it. Filtration will go more quickly if you
keep liquid in the funnel. If all of the liquid is filtered off, the residual solid will pack
down into a solid cake, slowing filtration. To empty the funnel after the solid cake has
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been washed and sucked as dry as possible, loosen the cake around the edge with
a spatula, carefully invert the funnel onto a watch-glass and tap it gently.
The EVAPORATING DISH is used to provide a large surface area to
speed up evaporation. It can be heated on the steam-bath but should
never be heated with a direct flame.
The BURETTE accurately measures volumes to 0.1ml accuracy. When titrating,
always fill the burette to the zero milliliter marking. Your eye should be level with the
bottom of the meniscus in order to take a proper reading of the liquid level.
The TRANSFER PIPETTE accurately deliversone volume (e.g. 5 or10 or25ml).
The PASTEUR or DROPPING PIPETTE is for transferring a few drops.
The SEPARATORY FUNNEL is used for the separation of
liquids with differing densities and for washing. The funnel
should have a properly working stopcock and a stopper of the
correct size. The solution to be separated is poured into the
funnel with the stopcock closedand the funnel stoppered. It is
then shaken vigorously with two hands; one holding the bottom
of the flask between first and second fingers and the other on
the stopper so it does not fall out. This maneuver is performed
with the flask upside down and the stem directed away from
people standing by in case of any splashing. The pressure
which may build up inside the flask is released by holding the funnel upside down
and opening the stopcock. Next, the funnel is placed in a proper size support ring.
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Enough time is given for the solutions to separate into two distinct layers after which
the bottom layer can be removed and the procedure repeated until necessary. (It is
assumed that one knows which layer is to be kept!)
GAS CYLINDERS with the safety cap off need to be securely strapped to the wall or
a desk in order to prevent them from falling. There is considerable pressure in these
cylinders and care must be taken to control the flow of gases from them. The main
cylinder or tank valve should be closed when not in operation. This valve measures
the pressure present in the tank (i.e. how much gas is left in the tank). The control
valve, usually the second one, gives the pressure reading present in the line
connected to the tank. This is usually a backwards valve, meaning that to
reduce pressure it needs to be turned in the counterclockwise direction. A
BUBBLER is usually inserted in the gas line between the cylinder and the
connection to the apparatus to be filled with the gas. This is advantageous for
two reasons: 1) the flow of gas is actually seen as it bubbles through the oil in
the bubbler and 2) this is an outlet for the gas if the pressure becomes too high so
that it exits via the bubbler rather than blowing the glassware or connecting tubes.
When working with gas cylinders it is very important that you know and understand
how everything is connected and what function each piece of equipment has.
There are many different shapes of
CONDENSERS available for use. All of them
serve the same purpose in conjunction with
distillation apparatus. Their purpose is to cool
the vapors inside the condenser usually with
water as coolant. The condenser is placed
before and is tilted toward the receiving
flasks. The glass is blown so that the cooling
liquid is separated from the vapors which are
to be condensed. To have good cooling cold
water should flow through the condenser at
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all times. This is achieved by connecting the water inlet to the bottom end of the
condenser and the outlet to the top so the water flows from the bottom up the
condenser and out the top.
ERROR DATA
Volumetric flasks Volumetric pipettes
Volume (ml) Error Volume (ml) Error
10 0.04 1 0.006
25 0.06 2 0.006
50 0.10 5 0.01
100 0.16 10 0.01
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1.3 A NOTE TO THE STUDENT
The objective of this laboratory is to introduce the student to basic organic reactions
and analytical instrumentation, as used in industrial operations and processes. By
performing the prescribed experiments the student will become familiar with a typical
organic chemical laboratory and the operation of typical analytical instruments.
She/he will also obtain a feeling and routine for generation of analytical results and
the technical capabilities of various instruments. The generated knowledge will
enable the student to better understand the basic chemical principles and control of
industrial processes, which is essential for proper operation of individual units in the
plant and the management of processes for optimum performance and product
quality, and environmental effects. Whether in management, processing, design or
laboratory, an engineer should have good knowledge and understanding of the
chemistry, measurements and instrumentation being used in the plant. The
important decisions and modifications that an engineer must make in industry will be
based on the results obtained from the laboratory. A good understanding of possible
errors in procedures and instruments is also required and particularly a good
understanding of variables that could affect a result. A lack of this understanding
very often results in erroneous judgments that can affect considerably bothproduction and quality of the final product.
1.4 SAFETY GUIDELINES
Although this laboratory does not involve extensive manipulation of hazardous
chemicals, some of the materials that will be used are often flammable and volatile
as well as toxic. Each student must therefore follow strictly all safety procedures and
not perform any unauthorized manipulations with these chemicals prior to
consultation with the instructor or the demonstrator. Although most of laboratory
safety is common sense, this is a general guideline, and therefore may be
incomplete. If you are ever unsure about safety, please ask.
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Remember: ACCIDENTS ARE CAUSED AND CAN BE PREVENTED!
VIOLATION OF ANY OF THE REGULATIONS DESCRIBED BELOW WILL MEAN
THAT YOU WILL NOT BE PERMITTED TO WORK IN THE LABORATORY AND
THEREFORE RECEIVE A MARK OF ZERO FOR THE LABORATORY REPORT.
1.4.1 Laboratory Apparel Rules
-Safety goggles are required in the laboratory AT ALL TIMES! Eyes are extremely
sensitive and delicate to minimum amount of most chemicals. You are responsible to
provide your own goggles.
-Contact lenses should not be worn in the laboratory. Goggles protect the eyes from
spill hazards, but do nothing to protect them from fumes, which can easily dry or
dissolve contact lenses and may result in the necessity of eye surgery for their
removal. Moreover contact lenses can also absorb chemicals from the air (especially
those breathable lenses), concentrate and hold them against the eye, and/or
prevent proper flushing of the eye should a chemical be splashed into the eyes.
-Laboratory coats must be worn at all times inside the laboratory. If you need to step
outside the laboratory for a while, your coat must be removed and left behind in the
laboratory.
-Sandals, open-toed shoes and high heels are not permitted in the lab. Shorts or
skirts cut above the knee are not permitted either. If a spill occurs, your clothing will
protect you from direct exposure. Open toe and shorts or skirts are prohibited to
protect your feet from splashes and spills. The restriction on high heels is for
balance. If you must wear some of this gear for a later appointment or situation you
should consider carrying with you a pair of sneakers and sweat pants to wear during
the lab.
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- Careful consideration should be given before wearing any jewelry into the lab.
Some chemicals can get beneath a ring, watch or some other form of jewelry, this
prevent them from evaporating and hold them against the skin increase the risk of
injury. If you decide to wear jewelry to the laboratory be particularly mindful of
itching, burning or any other irritation under or around your jewelry. Some gems and
precious metals might be easily damaged by the laboratory environment (for
instance silver and opal jewelry). If you decide to ear jewelry you do it at your own
risk.
- Never wear clothes that hang, such as loose sleeves. Ties and scarves must be
tucked inside your laboratory coat
- A good suggestion is to wear only very old clothes to the laboratory. Some
students might consider bringing lab-suitable clothing with them in a gym bag and
change right before and after lab. If you have a very tight schedule (must be
documented) and decide to change into suitable clothes before the lab we can
arrange for 10 minutes for you to change clothes.
- Long hair is to be constrained at all times.
1.4.2 Safety rules
- Eating and drinking in the laboratory is strictly forbidden.
- No radios, tape players, CD players, iPods or any other devices of this type will be
permitted in the laboratory at any time.
-Use of cell phones is not permitted in the laboratory.
-Identify all of the laboratory safety equipment, and keep their location in
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your mind at all times. We might ask you to close your eyes any time during a lab
and point to such safety equipment as the fire extinguisher, the emergency eyewash
stations, the safety shower, the nearest exit etc. This exercise might save you from
a big injury. For instance if you were to splash a chemical in your eyes, you'd better
be able to find that eyewash station without your eyes well before permanent
damage can occur (which can be seconds depending on the nature of the chemical).
- Develop good working habits. Keep your area clean and tidy. Your working area
reflects your working habits and also the quality of your work and results. A clean
and tidy environment decreases the probability of a laboratory accident.
- ALL FLASKS, BEAKERS AND CONTAINERS WITH ANY CHEMICALS OR
SYNTHESIS PRODUCTS THAT YOU LEAVE BEIND AFTER A LABORATORY
SESSION MUST BE CLEARLY LABELED WITH THE NAME OF THE CHEMICAL,
THE OWNER AND DATE! UNLABELED VIALS CONTAINING CHEMICALS WILLL
BE DISCARDED.
1.4.3 Handling Chemicals and Equipment
Students will work in groups of two or three and enough time will be provided to
finish all the prescribed experiments. If any piece of equipment fails or does not
function properly, students are required to report the problem immediately to the
demonstrator or the instructor and are not allowed to attempt to fix the instrument on
their own.
1. Do not taste chemicals.
2. Do not pipet any chemicals by mouth. Use rubber bulb (propipette).
3. Do not pour liquids that are flammable or that do not mix with water into sinks.
Pour them into the provided and labeled containers.
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4. Do not mix incompatible chemicals. If you do not know their compatibility ask.
5. Do not heat flammable liquids with an open flame.
6. Operations involving volatile or toxic materials are to be conducted in the fume
hood.
7. Dispose of solid wastes in garbage pails. Do not use the sinks.
8. Clean up spills (solid or liquid) at once.
9. Return chipped or broken glassware to the laboratory TAs or technician.
10. Be sure the apparatus is placed properly. Do not move instruments without
proper consultation with the laboratory TAs or technician.
11. When heating a test tube make sure that it is not pointing towards yourself or
other people in the vicinity, so no damage will result if the contents suddenlydump out.
12. Never apply force to any glass apparatus. Many serious cuts are caused by the
sudden fracture of glass under strain from misuse. In particular, never use force
in an attempt to push a thermometer or glass tube through a hole in a cork or
rubber.
13. Never heat a tightly sealed flask even if it is empty-----it will explode.
14. Do not attempt to buttress a laboratory assembly with makeshift supports such
as books, pencils and the like. Use several ring stands if necessary. Round
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bottom flasks cannot stand freely on the bench----use a special cork support or
place the flask into a beaker.
15. Do not attempt to break up a solid in the bottom of a flask by punching the solid
with a glass stirring rod. The rod may either fracture in your hand or puncture the
bottom of the flask.
16. Avoid shortcuts! If you have an idea for an improvement talk it over with your
demonstrator; if no objections, try it; if it is successful, tell us about it, you will
get extra marks.
17. There are certain necessary precautions associated with particular chemicals or
experiments. Your demonstrator will point these out when required.
18. If you are not familiar with a piece of apparatus or an experimental procedure
ask for help. Dont just try to muddle through without knowing what you are
doing.
19. Chemical waste should be disposed of in the labeled waste containersprovided.Halogenated chemicals must be disposed of separately from non-
halogenated chemicals. Nothing should go down the drain! Dispose of all
chemicals in the bottles marked for the specific lab.
1.5 GENERAL HOUSEKEEPING AND LABORATORY WORK
ALL STUDENTS MUST HAVE A LABORATORY BOOK IN WHICH TO RECORD
ALL LAB DATA DURING THE LABORATORY PERIOD. The lab book used in
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industry is a legal document. Loose papers for recording of data or comments are
not allowed and will be removed from the lab.
Each student must read the instructions for the particular experiment PRIOR to
coming to the laboratory. He/she should understand the whole procedure and what
must be done in the experiment. This knowledge will be checked periodically by the
instructor or the demonstrator and it will be evaluated.
Equations for all reactions should be written out in your lab notebook before coming
to the laboratory. Also, any calculations required (e.g. theoretical yield, preparation
of solutions) should be written in full in your laboratory notebook before coming to
the laboratory. Record all observations in the lab book including any color changes,
unexpected events, smells, etc. The notebook will be marked from time to time
during the term. Plan your working time in the laboratory! By doing this your
laboratory will be a useful and pleasant experience rather than a frustrating one.
ALL LABORATORY EXPERIMENTS MUST BE DONE DURING THE ALLOCATED
TIME PERIOD. THERE WILL BE NO EXTENSION OF THE LAB AND NO
ADDITIONAL TIME PERIOD AVAILABLE FOR THE EXPERIMENTS, except underspecial circumstances such as illness verified by a doctors note.
1. Keep benches clean and orderly and sinks clean. You must leave your portion of
the bench and all glassware and equipment clean at the end of the lab period.
2. Aisles and floors are to be kept free of obstructions. Keep cupboard doors and
drawers closed when not in use.
3. Hang coats on the rack. No coats are permitted on tables or benches.
4. Laboratory doors MUST be unlocked during lab period.
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1.6 GUIDELINES FOR PREPARATION OF LABORATORY REPORTS
Laboratory reports should be written as though they were short technical reports.
Thus Tables and Figures should always be referred to in the prose text of the report,
i.e. they should not appear on their own.
The report should be written in the past tense, since it is a description and a
correlation of past observations. The present tense may be used in referring to laws
of nature, properties of materials etc. which are independent of time. Thus, for
instance, in a particular experiment The ambient temperature equaled 22C; on
the other hand, The ambient temperature equals about 20 C .
TITLE PAGE
Title of experiment
Name of person writing the report
Name of experimenters
Date when the experiment was performed
All Formal reports must be TYPED
ABSTRACT
The Abstract should summarize the entire report. It should state clearly and briefly
the objectives, methods, results and conclusions of the lab.
Objective: State the objective or purpose of the lab
Method: In one or two sentences, summarize the methods, including scientific
and common names of chemicals and techniques used.
Results: Summarize what was found in the study
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Conclusions: State the significance of the results in relation to the objective.
INTRODUCTION
The Introduction should describe the scope and the purpose of the lab and include
any background information necessary to understand the experiment.
State the general problem. Give a brief statement of why the general topic is
relevant and important. Define any specialized terms or concepts (e.g. the concept
of distillation) likely to be encountered later in the lab report. Supply sufficient
background (historical and theoretical) information to allow the reader to evaluate
and understand the results of the study without needing to refer to other
publications. The introduction to each experiment in this manual can be used as a
guide but must not be copied and cannot be used as the backbone of the
introduction in the report.
State the specific objective or purpose of the lab and the approach to be used. The
purpose states what you are investigating and why; how you perform theinvestigation should be described later in the Methods and Materials.
MATERIALS AND METHODS
The Methods section should describe what was done and how it was done. It should
be written in the past tense with active voice, and in paragraph form.
The Materials and Methods section should provide only enough detail to permit a
competent worker to evaluate the validity of the experiment and to repeat it, if
necessary. It should not be simply a recipe of all the steps involved. State the names
(IUPAC if possible) of the chemicals used, the instruments, equipment and pattern of
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replication. Describe any unusual numerical calculations and state the statistical
technique used to analyze the data.
RESULTS
The Results section should present the data collected in a summarized form and
describe only the key features of these data, emphasizing trends or patterns that are
relevant to the hypotheses being tested. Interpretation of the data is reserved for the
discussion section.
Do not present the same data in both a table and figure i.e. place table of raw data in
an appendix and place figure in the results section. Titles of tables and figures
should contain enough information to understand the contents without reference to
the text. The number and title are placed at the top of a table, and at the bottom of
figure.
Guide the reader through your figure (s) and table (s) in a logical and systematic
manner, pointing out trends and differences that pertain to the objective (s) of the
report. Simply state what you found in your study, without inference or reference to"expected" results.
DISCUSSION
The Discussion section should provide an explanation and interpretation of your
results and indicate the significance of the results to the hypothesis being tested.
Results of previous studies on the same topic should be compared with yours, with
an explanation of why your results are different from previous studies, if necessary.
State how and why your results either support or do not support the objectives and
hypotheses. REMEMBER: results are results, they are never wrong simply by being
different from either your expectations or from other investigations.
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CONCLUSIONS
Draw conclusions about the hypotheses (objectives) of your study, based on all
data available in the current studies.
APPENDIX
Includes all raw experimental data, e.g. time vs. temperature data points, sample
calculations, and any other information or data used for the experiment and
calculations.
REFERENCES
The Reference section should be a list of all books, journals, and other materials
cited in the body of the paper. Please notice that all reference sources must be peer
reviewed and scientifically validated. Wikipedia or other non-refereed materials
available on the World Wide Web are not acceptable as reference sources in a
technical report.
The surname of the author(s) and the year of publication should be inserted in the
text at an appropriate place:
"Smith (1991) compared..." or "... have been recently compared (Smith, 1991)."
If the reference has more than 2 authors, include only the surname of the first
author, followed by "et al."
"Smith et al. (1991) compared..." or "... have been recently compared (Smith et al.,
1991)."
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When listing more than one citation at a given point in the text, list them in
chronologically by first author, but for 2 (or more) papers, published in the same
year, list these alphabetically:
"(Jones, 1978; Black et al., 1989; Smith, 1989; Jones and Smith, 1991)"
If an author or group of authors has published more than one article in a given year,
you can distinguish between these articles by placing a letter postscript after the
publication year:
"(Black and Smith, 1990a; Black and Smith, 1990b)"
List all references in alphabetical order, sorted by the author(s)' last name(s). In
cases where the same author or group of authors has/have published multiple
papers that you have cited, then arrange these references in chronological order.. All
authors must be given in the reference list - the abbreviation "et al." Is used only in
the text. The following are examples of the punctuation, style and abbreviations that
may be used for references (note: the headings given here are not to be included in
your reference list).
Journal article:
Jones, R.S., E.J. Gutherz, W.R. Nelson and G.C. Matlock. 1989. Burrow utilization
by yellowedge grouper, Epinephelusflavolimbatus, in the northwestern Gulf of
Mexico. Env. Biol. Fish. 26: 277-284.
Chapter in a Book:
Gross, M.T. 1984. Sunfish, Salmon and evolution of alternative reproductive
strategies and tactics in fishes. Pp. 55-57. In: G.W. Potts and R.J. Wooten (eds.)
Fish reproduction: strategies and tactics. Academic Press, London.
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Book:
Siegel, S. 1956. Nonparametric statistics for the behavioral sciences. McGraw-Hill,
New York. pp. 312.
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LABORATORY 1
AN ATTEMPT AT THE SYNTHESIS OF A SECONDARY
ALCOHOL: THE UNCERTAIN REDUCTION OF A KETONE(2 lab periods)
ABSTRACT
During this laboratory session you will attempt to reduce a ketone. Somegroups will be using sodium borohydride and some sodium chloride. Sodiumchloride is not a reducing agent so the ketone will not transform into the alcohol.However, even if sodium borohydride is used the reaction should be carefully carriedout to obtain the alcohol. You will find out whether your synthesis was successful
using IR spectroscopy.
INTRODUCTION
As you have learned in class, aldehydes and ketones can be converted to
alcohols by a process known as reduction. In this case the reduction process
involves the creation of a new set of C-H and O-H bonds.
CH3 CH2
O
C H CH3 CH2 CH2 OH
CH3
O
C CH3 CH3 CH3CH
OH
(1)
(2)
There are several reagents available for this reaction. For example, lithium
aluminum hydride (LiAlH4) is a commonly used reducing agent; however, it is
extremely reactive with water and rapidly decomposes in air, making it difficult tohandle. Sodium borohydride (NaBH4) is also a commonly used reducing agent and
is easier to handle safely. The reaction of sodium borohydride with water is
sufficiently slow at room temperature to allow its use as a reducing agent in an
aqueous medium. However, many organic compounds are insoluble in water, so it is
frequently necessary to use ethanol as a solvent.
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Sodium borohydride serves as a source of H- (hydride, a very powerful
nucleophile), which attacks the electrophilic carbon of the carbonyl group in the
ketone. However, sodium borohydride does react to some extent with the solvent
ethanol and it is therefore necessary to use excess sodium borohydride to overcome
this effect so that the reducing agent does not become the limiting factor in this
experiment.
The product benzhydrol is soluble in the ethanol-water mixture which was
used for the reaction but is insoluble in water. Thus, if the reaction mixture is diluted
with cold water the product precipitates. However, if the reaction was unsuccessful
unreacted benzophenone will precipitate as well. Sodium borate remains in solution
since it is a salt and is very soluble in water. Following the precipitation of your
reaction product, you will purify it further by recrystallization (Appendix 1A).
In order to evaluate the success of your experiment, you will use infrared
spectroscopy. The most important aspect to understand is that the bonds in the
molecules stretch and bend and that this stretching and bending is linked to the
absorption of infrared light. The wavelength of the infrared light absorbed in these
processes depends on the specific atoms and bonds (ie. single, double, or triple)involved. The absorbed wavelengths for a given sample can be determined using an
instrument called an infrared spectrometer and plotted to provide a spectrum. As
different functional groups absorb light of characteristic wavelengths, leading to
characteristic peaks in the spectrum, this technique can be very useful in
determining which functional groups are present in a molecule. This aids in verifying
the identity of the compound. More details on infrared spectroscopy can be found in
the text (Wade Ch. 12-1 12-12) and your lecture notes.
MATERIALS
125mL Erlenmeyer flask
Ceramic Boiling chips
50mL, 500mL beakers
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Buchner funnel and filtering flask
Whatman #4 Filter paper
Disposable Pasteur pipette
6.0 g Benzophenone
50mL 96% EtOH (ethanol)
0.60 g of Reactant A or B (these will be either sodium borohydride or
sodium chloride but you will not know the exact identity of the reactant you
are using).
5mL 6N NaOH
Hot Plate/ Magnetic stirrer
FT-IR Spectrophotometer
METHODS
Lab One
1. In a 125 ml Erlenmeyer flask dissolve 6.0 g of benzophenone in 50 ml of ethanol.
You will need to use a magnetic bar and stir plate.
2. In a 50 ml beaker dissolve 0.6 g of Reactant A or B in 25 drops of distilled water,
and using a Pasteur pipette add this solution drop-wise, with stirring, to the solution
of benzophenone. Continue stirring the reaction for 15 minutes.
3. Using a 10ml graduated pipette add 4 ml of a 6N NaOH solution and a boiling chip
to your flask, and boil the reaction mixture on a hot plate for 10 minutes.
4. Being cautious, pour the reaction mixture into 400 ml of cold water and ice and stir
with a glass rod until the ice is all melted. Collect the resulting precipitate on filter
paper using a Buchner funnel.
6. Wash the crude product with 100ml cold H2O, and let the product sit on the filter
for 5 minutes to remove as much water from the crude product as possible. Using a
metal spatula carefully transfer your product to a tared plastic weighing boat and
place it in the dessicator until next lab period.
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Lab Two
1. Weigh your dried crude product and assuming a successful synthesis determine
the percentage yield.
2. Weigh out 1.0g of your crude product and recrystallize it using an appropriate
solvent (ask your TA which one to use) Do this recrystallization in a 250 ml
Erlenmyer flask. Suspend your product in approximately 50 mL of solvent, heat it
gently using a hot plate (do not boil) and swirl until complete dissolution. You will
need to add more solvent (use 10 mL aliquots) until the solid is dissolved. Be
patient. After cooling, first at room temperature and then on ice, filter your
recrystallized product on a Buchner funnel, air dry the crystals for 10 minutes on
the filter paper, weigh the product to calculate yield and do a melting point
determination.
3. Obtain an infrared spectrum of your purified final product (benzhydrol if the
synthesis was successful), compare it with the one of bezophenone provided.
PRE LAB QUESTIONS Week 1
1. Draw Lewis structures for benzophenone, benzhydrol, and sodium borohydride.
2. Draw the reaction mechanism (arrow diagram) for the reduction benzophenone to
benzohydrol.
3. Calculate the theoretical yield of benzohydrol assuming 100% reduction of
benzophenone. You should include your calculations.
PRE LAB QUESTIONS Week 2
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1. What do you expect to be the main change in the infrared spectrum as you go
from the benzophenone starting material to the benzhydrol product?
2. What was the purpose of using 6N NaOH during the benzophenone reduction
experiment last week?
SUMMARY OF SPECIFIC REQUIREMENTS FOR THE REPORT
1. Assuming a successful synthesis, show calculations of the % yield for the crude
and recrystallized product.
2. Compare the infrared spectra of the starting material benzophenone and that one
of your product. Which peaks are common and which are different? Using the data
in the text book (Wade sec 12-1 12-12) assign the major peaks that correspond to
the functional groups in benzophenone and benzhydrol. Does the spectrum indicate
that your reaction was successful or unsuccessful?
3. Establish the identity of Reactants A and B.
4. Propose and discuss (using a minimum of 200 words) another way, besides anyform of spectroscopy, to evaluate whether your reaction was successful.
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LABORATORY 2
REACTIONS OF ALCOHOLS: SYNTHESIS, PURIFICATIONAND STRUCTURE ELUCIDATION OF AN ORGANOLEPTICMOLECULE.
( 2 lab periods )
ABSTRACTDuring this laboratory session you will run a common reaction of alcohols tosynthesize a molecule that is used in the food and flavours industry. You willelucidate the structure of the molecule using IR and NMR.
INTRODUCTION
Organoleptic substances are commonly used in the industry to fabricate consumer
products. In general an organoleptic material is defined as a substance that has
sensory properties, such as odour, colour, taste or feel. Specifically in the food
industry organoleptic refers to substances used to improve or impart odours and
flavours to materials, making the product more appealing to consumers. While a
wide range of organoleptic substances are used in the flavours and fragrances
industry (for instance, orange extract or lavender oil); it is more desirable to use
single molecules with strong organoleptic properties rather than the very expensive
and complex mixture obtained as oil extract from a natural product.
During this laboratory you will synthesize a molecule with high organoleptic
properties. The procedure in based on an equilibrium reaction involving a carboxylic
acid and an alcohol. Since this is an equilibrium reaction, an excess of reactants isrequired to drive the reaction to completion. In our case the carboxylic acid will be
used in excess since it is less expensive than the alcohols we are using and more
easily removed from the reaction mixture. In the isolation procedure, the excess
acetic acid and the unreacted alcohol is removed by extraction with water since the
product has a low water solubility. Any remaining acid is removed by extraction with
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aqueous sodium bicarbonate (NaHCO3). The resulting product is dried over
Na2SO4.
MATERIALS AND METHODS
An alcohol (you will not know the structure of the alcohol you are using).
Either one of these acids:
Glacial Acetic Acid
Formic Acid
H2SO4 (conc.) (CAUTION : highly corrosive )
Sodium Sulfate (anhydrous)
5% aqueous Sodium Bicarbonate
Saturated NaCL solution
100 ml Round bottom boiling flask
Reflux condenserShort path Distillation head with thermometer and condenser
Boiling stones
Heating mantle
250 ml separatory funnel
Glass funnel and filter paper
Sample vial
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Synthesis and purification steps
1. Place 15 ml of the alcohol in a 100 ml RB flask and add 20 ml of the
carboxylic acid
2. Swirl to mix and carefully add 4 ml of conc. H2SO4.
3. Add a few boiling stones, attach a reflux condenser, start the cooling water,
and reflux the mixture for 1 hour. Cool to room temperature.
4. Transfer the mixture to a separatory funnel and add 55 ml of cold water.
Rinse the 100 ml RB flask with 10 ml of cold water and add it to the contents
of the separatory funnel. Mix the two phases by inversion 20 30 times. If
you shake the mixture too vigorously it will form an unbreakable emulsion.
5. Allow the phases to separate and drain off the lower aqueous layer.
6. Add 25 ml of 5% NaHCO3to the separatory funnel. Do this carefully as there
will be gas evolved. Mix by inversion, drain, and check the pH of the aqueous
phase with litmus paper. If it is not basic you will have to repeat the 5%
NaHCO3 washing step.
7. A final extraction with 20 ml of saturated NaCl will remove residual water from
the product.
8. Fold a piece of filter paper, put it in a glass funnel, and add 1 g ofanhydrous Sodium Sulfate ( Na2SO4) to the filter. Clean, dry, and weigh a
100 ml RB flask and filter your product into it. The Na2SO4 will complete the
drying process. Weigh your product and then seal the flask with a stopper and
some parafilm and label it clearly.
Week 2 - Spectroscopic analysis of the product.
1. Obtain the infrared spectrum of your product.
2. Obtain the 1H-NMR of your product. (These will be provided).
3. Obtain the MS of your product. (These will be provided)
4. Using the spectroscopic information and the synthesis protocol used,
elucidate the structure of your product. You must solve this structure before
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leaving the lab. Feel free to bring any reference materials you think will help
you in this task.
PRE-LAB QUESTIONS Week 1
1. Provide an example of an organoleptic molecule used in the food insdutry
2. Which gas in evolving during step 6 of the synthesis and purification protocol?
PRE-LAB Questions Week 2
1. What will be the position of the infrared O-H stretching band for carboxylic acid
and the alcohol. Would you expect to see a difference between the two bands?
2. What are the typical MS fragmentation patterns of alcohols and acetic acid? How
would those differentiate form the MS fragmentation pattern of your product?
SUMMARY OF REQUIREMENTS FOR YOUR LAB REPORT
1. Show step by step how you elucidated the structure of the molecule you
synthesized. These should include assignment of each 1H-NMR peak and main
infrared bands. Indicate how the MS spectrum contributes to structure elucidation.
2. Clearly identify the reaction and mechanism involved in the synthesis procedure.
2. Calculate your yield. Suggest possible reasons why your yield might be less than
100%.
3. Sulphuric acid is also a strong oxidizing and dehydrating agent, what do you
predict as by products of the reaction between the alcohol and sulphuric acid? Will
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all these by-products remain in liquid phase? Propose an analytical technique to
identify these.
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LABORATORY 3
THE ALDOL CONDENSATION - SYNTHESIS OF
BENZYL AND DIBENZYLACETONES
INTRODUCTION
The Aldol condensation is perhaps one of the most important and versatile
organic reactions that leads to the formation of a new carbon-carbon bond. In it
simplest form the aldol condensation combines two carbonyl compounds (ketones
and/or aldehydes) to yield a new -hydroxy- aldehyde or ketone (know also as
aldol)
Under the basic conditions required to run the condensation reaction the aldol
product normally undergoes water elimination, to yield the final ,unsaturated
aldehyde or ketone:
The mechanism for the aldol condensation requires the formation of the enolate ion
of the ketone or aldehyde under strong basic conditions. This step involves the
abstraction of a proton (H+) from the alpha position in the carbonyl compound. The
resulting ion is resonance stabilized in the form of an enolate:
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Enolate ions are strong nucleophiles and will add to a molecule containing a
carbonyl group:
The resulting aldol undergoes base-catalyzed dehydration
In this experiment we will perform a cross-aldol condensation. A cross condensation
is a reaction in which one aldehyde or ketone adds to the carbonyl group of a
different compound. It is very important that for a cross aldol condensation the
electrophile (the carbonyl compound being attacked by the enolate) cannot form
enolate ions itself. Otherwise a mixture of products can be obtained.
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To avoid a mixture of products usually one of the reactants chosen should not have
the ability of forming an enolate ion. In other words, the reactant should not have
protons available in the alpha position.
Another complication arises when the resulting product has also protons available in
the alpha position, in this case a double condensation can occur:
In this experiment you will use acetone as the enolate forming nucleophile and
benzaldehyde as the electrophile. As in the previous example, acetone has alpha
hydrogen on both sides of the carbonyl group, so acetone can add either one or two
molecules of benzaldehyde to yield benzalacetone (4 phenyl -3 penten-2-one) or
dibenzalacetone (1,5-diphenyl-1,4 petadien-3-one) respectively.
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You will synthesize both products and characterize them using UV spectroscopy and
melting point measurements.
MATERIALS AND METHODS
95 % Ethanol
Acetone
Benzaldehyde
600 ml beaker to use as an ice bath
125 ml Erlenmyer flask
16 x 100 test tube
Pasteur pipette
Thermometer
Buchner funnel, filter paper, and vacuum flask
Melting point apparatus
UV spectrophotometer
Week 1 Synthesis of dibenzal acetone.
1. Half fill a 600 ml beaker with crushed ice
2. In a 150 mL Erlenmeyer mix 30mL of Ethanol (95%) and 40mL of a 10%
NaOH. Put a thermometer into the reaction mixture and place the flask into
the ice bath. Stir the mixture occasionally by swirling.
3. In a 16 x 100 test tube mix 4mL of benzaldehyde and 1.5mL of acetone, mix.
4. Using the Pasteur pipette add the benzaldehyde acetone mixture to the
ethanolic NaOH solution drop by drop stirring frequently. The addition should
be done over a period of 20 min. Keep track of the temperature of the
reaction mixture. By moving back and forth between the ice bath and the
bench you can keep the mixture greater than 20 C but less than 28 C.
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Cloudiness of the solution indicates formation of the product. If cloudiness is
not observed let the mixture reach room temperature.
5. After finishing the addition stir manually for 10 minutes and then let the
reaction mixture stand for 10 minutes at room temperature. Slowly add 2 ml
of ice water to the mixture to force precipitation of product. Put the reaction
mixture in the ice bath for 10 more minutes.
6. Filter the reaction mixture using a Bchner funnel and vacuum, wash the
mixture with cold water until the pH of the filtrate is neutral (basic pH will
interfere with recrystallization), and continue to draw air through your product
to partially dry it.
7. Weight your crude product
8. Recrystallize your product from ethanol. You should obtain yellow , needle-
like crystals.
9. Weight your recrystallized product and determine its melting point.
10. Use a single crystal dissolved in 20mL of ethanol to obtain the UV spectra
(400 to 200nm). This solution might be too concentrated for the UV so it might
be necessary to dilute in ethanol even more.
Week 2 Synthesis of benzal acetone.
1. Half fill a 600 ml beaker with crushed ice
2. In a 150 mL Erlenmeyer mix 30mL of Ethanol (95%) and 40mL of a 10%
NaOH. Put a thermometer into the reaction mixture and place the flask into
the ice bath. Stir the mixture occasionally by swirling.
3. In a 16 x 100 test tube mix 4mL of benzaldehyde and 6mL of acetone, mix.
4. Using the Pasteur pipette add the benzaldehyde acetone mixture to the
ethanolic NaOH solution drop by drop stirring frequently. The addition
should be done over a period of 20 min. Keep track of the temperature of
the reaction mixture. By moving back and forth between the ice bath and
the bench you can keep the mixture greater than 20 C but less than 28 C.
White cloudiness of the solution indicates formation of the product. If the
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mixture begins to turn brown this indicates product decomposition and that
the reaction temperature is too high. If cloudiness is not observed let the
mixture reach room temperature.
5. After finishing the addition stir manually for 10 minutes and then let the
reaction mixture stand for 10 minutes at room temperature. Slowly add 2
ml of ice water to he mixture to force precipitation of product. Put the
reaction mixture in the ice bath for 10 more minutes.
6. Filter the reaction mixture using a Buchner and vacuum. Discard the liquid
filtrate and rinse the vacuum flask.
7. Using 100mL of 50 % Ethanol wash the precipitate. In this step we are
extracting benzalacetone (that becomes an oily suspension) and goes to
the filtrate from the dibenzalacetone (that remains as solid in the Buchner).
Benzalacetone has low melting point (close to 40, 42oC) therefore it is very difficult
to recrystallize. We will extract it to get the UV spectra
8. Take 5mL of the aqueous oily suspension and put it in a 16 x 100 test tube .
9. Add 3mL of chloroform and vortex the mixture to extract the oily
suspension into the organic phase.10. Take one drop of the chloroform phase (bottom phase), mix it with 5mL of
EtOH, and obtain the UV spectra of this mixture (400 - 200 nm ). Dilution
or concentration might be required to get good quality spectra.
PRE-LAB QUESTIONS
Week 1
1. Do you think is possible to run the Aldol condensation in acidic instead of basic
conditions?
2. Write four possible products that can result from an attempt to run a crossed
aldol condensation between acetone and 2-propanal.
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Week 2
1. In the last step, chloroform is used to extract benzalacetone from water. Do you
anticipate that the organic phase (chloroform) will sit above or below the aqueous
phase? Justify your answer.
2. Recrystallization of benzalacetone is very difficult due to its low melting point,
suggest another method of purification for the product. Justify your answer
SUMMARY OF REQUIREMENTS FOR YOUR LAB REPORT
1. Calculate your yield of dibenzalacetone. Suggest possible reasons why your yield
might be less than 100%.
2. Based on the scientific literature(available in the library and the web) propose
a method for the isolation from the reaction mixture and purification of
benzalacetone .
3. The UV/Vis spectrum of Benzaldehyde is shown below. Compare this spectrum
with the spectra you obtained for your products, discuss the differences and
similarities in terms on conjugation of pi systems.
benzaldehyde
0
1
2
3
4
5
6
200 220 240 260 280 300 320 340 360 380 400
w avelength (nm)
Absorbance
benzaldehyde
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LABORATORY 4
ALDOL CONDENSATION, BENZYNE FORMATION AND
THE DIELS-ALDER REACTION : A MULTI-STEP
REACTION SEQUENCE
( 2 lab periods )
ABSTRACT
In this laboratory experiment you will run an Aldol condensation reaction tosynthesize Tetraphenylcyclopentadienone. Then, you will usetetraphenylcyclopentadienone in a Diels-Alder reaction to obtain 1,2,3,4-tetraphenylnaphthalene. Since this is your last laboratory, you are expected toclearly understand the chemistry involved on each of the synthetic steps and befamiliar with all techniques. These will be evaluated during the laboratory session.There will not be written report required for this laboratory; instead you will beevaluated on your knowledge of reactions and procedures involved and the finalyield of your product.
INTRODUCTION
In this laboratory experiment you will again utilize the Aldol condensation to
synthesize a highly coloured organic molecule; Tetraphenylcyclopentadienone.
Then, you will use this compound in a Diels-Alder reaction to obtain 1,2,3,4-
tetraphenylnaphthalene. During this last step you will be constructing a new aromatic
ring structure utilizing benzyne, an unusual and unstable reactant that must be
generated in situ.
In the first part of this experiment you will use diphenylacetone as the enolate
forming nucleophile and benzil as the electrophile. Diphenyl acetone has alpha
hydrogens on both sides of the carbonyl group, while benzyl has two carbonyl
groups. If the stoichiometry and reaction conditions are carefully controlled, a cross
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double Aldol condensation takes place, and the product obtained is a highly
substituted cyclopentadienone:
Notice that in his case a very strong base is needed (potassium ethoxide). The
resulting product is an aldol, however under the very strong basic conditions the
aldol undergoes dehydration to yield the unsaturated, highly conjugated ketone.
In the second part of the experiment you will react the tetraphenylcyclopentadienone
obtained with benzyne in a Diels Alder reaction to form 1,2,3,4-
tetraphenylnaphthalene.
Since benzyne is very unstable it is necessary to generate it in situ. Our strategy will
be then to form benzyne from the unstable diazonium salt of anthranilic acid:
To obtain the diazonium salt of anthranilic acid it is necessary first to run a
diazotization reaction on anthranilic acid. Diazotation reactions often involve the use
of sodium nitrite and HCl to generate nitrous acid (HONO). HONO protonates and
loses water to give the nitrosonium ion (NO+) used as electrophile that attacks the
Diazonium salt of anthranilic acid
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amino group to yield the diazonium salt. In this case, however we will use isopentyl
nitrite to form the nitrosonium ion:
Then, the sequence for the formation of the diazonium salt is:
Once the diazonium salt is formed, it rapidly undergoes decomposition, losing CO2
and N2 to yield benzyne:
Benzyne is a very reactive molecule and extremely difficult to isolate. In our case
benzyne will react with the tetraphenylcyclopentadienone obtained in the first part of
the laboratory session. The process is a DielsAlder reaction that in turns gives
another unstable intermediate:
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The intermediate readily loses carbon monoxide (CO) to yield the fully aromatized
1,2,3,4-tetraphenylnaphthalene:
Please refer to the next page for a full synthetic pathway for this experiment.
In the first part of the experiment you will synthesize tetraphenylcyclopentadienone,
characterize it by FTIR, UV and melting point measurement. In the second part you
will synthesize 1,2,3,4-tetraphenylnaphthalene through a Diels Alder reaction
between tetraphenylcyclopentadienone and benzyne. You will characterize the
product by by FTIR, UV and melting point measurements.
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Figure 9.1Synthetic diagram for the synthesis of 1,2,3,4-tetraphenylnap
tetraphenylcyclopentadienonetetraphenylcyclopentadienone
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MATERIALS AND METHODS
Benzil
1,3-Diphenyl Acetone
Ethanol (anhydrous)
Anthranilic acid
1,2-Dimethoxyethane ( DME )
Isoamyl Nitrite
Methanol
Dichloromethane
1.25 % KOH in Ethanol
50 and 100 ml RB flasks
Reflux condenser
Claisen adapter
Heating mantle and controller
Hirsh funnel and vacuum flask
Screw cap vialsMelting point apparatus
FT IR and UV/VIS spectrophotometers
Part 1 Synthesis of tetraphenylcyclopentadienone.
1. In a 50 ml round bottom flask dissolve 1 g of Benzil and 1 gram of 1,3-
diphenyl acetone in 30 ml of Ethanol (abs). A little heat may be necessary to
help dissolution.
2. Slowly add 20 ml of 1.25 % KOH/Ethanol to the reaction mixture. Add a few
boiling chips, attach a reflux condenser to the flask, start the cooling water,
and heat the mixture at reflux for 15 min. The mixture should change color to
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a dark purple (might be dark brown). After 15 minutes stop the reflux, and
allow the reaction flask to cool to room temperature, and then cool down in
an ice bath.
3. Set aside 50 mL of ethanol and put it in an ice batch, this will be used for
washing the product.
4. After reaction mixture is cold, filtrate it using vacuum and a Hirsh funnel.
Wash the crystals using ice cold ethanol. Keep washing until the filtrate is
transparent or light pink. Keep sucking air over the crystals in the filter to dry
them. Crystals are very dark purple with a slightly metallic sheen. There is not
need to recrystallize as the product is quite pure.
5. Weight the tetraphenylcyclopentadienone obtained and calculate your yield.
6. Obtain a UV spectrum for your product. For the UV dissolve a few crystals in
hexane (a very light pink solution) and scan from 650 nm down to 200 nm.
The FTIR of the product will be provided.
Part 2 Synthesis of 1,2,3,4-tetraphenylnaphthalene.
1. In a 50ml RB flask dissolve 0.5g of the tetraphenylcyclopentadienoneobtained in the first part and 0.23g of anthranilic acid in 10mL of 1,2
dimethoxy ethane (DME). Warning DME is toxic, it should be measured in
the fumehood, transported in a stoppered flask and uncapped only under the
elephant trunks located over your lab bench. Attach the flask containing the
reaction mixture to a reflux condenser and heat up to reflux.
2. Add 4 ml of DME to a screw cap vial and place the vial in an ice bath. After
the DME is cold and right before the next step add 0.5ml of isopentyl nitrite to
the vial and reseal it. IMPORTANT - if mixture is not ice cold and/or is
exposed to air for long time the nitrite will decompose and no reaction will
occur.
3. Once reflux is established carefully add the DME solution containing the
isopentyl nitrite through the top of the condenser. The solution should be
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added slowly (over a period of 2 minutes) If the addition is too fast foaming
might occur and the reaction mixture can boil over.
4. Keep the reaction mixture at reflux for 15 more minutes; the reaction mixture
should change to an orange-yellow color. If color change is not observed
prepare a new mixture of isopentyl nitrite in DME with a higher concentration
and add it slowly to the reaction mixture following the same procedure.
5. Set aside 50 ml of ethanol, mixed with 10 ml of water , in a ice bath.
6. Cool the reaction mixture to room temperature. In a 250 ml beaker mix of 25
ml of water and 10 ml of ethanol. Add the reaction mixture to the beaker
slowly using a dropper. A precipitate should form.
7. Use a Hirsh vacuum filter to separate the solid 1,2,3,4
tetraphenylnaphthalene. Wash the solid with the cold ethanol/water mixture.
8. Recrystallize your crude product from 2-propanol. If not all the solid is
dissolved at the boiling point of the solvent the mixture might need to be
filtrated hot to remove insoluble impurities.
9. Needle like crystals should be obtained
10. Measure the melting point and obtain the IR spectra. Compare it to the
spectrum obtained for tetraphenylcyclopentadienone.
11. Obtain the UV spectra using 2-propanol as solvent. Compare it with thespectrum obtained for tetraphenylcyclopentadienone.
PRE-LAB QUESTIONS
There are not prelab questions, on this session all questions will be asked orally and
will heavily influence the mark assigned to the lab.
.
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APPENDIX: RECRYSTALLIZATION, MELTING POINT DETERMINATION, AND
EXTRACTION
A. RECRYSTALLIZATION
1. Theory
(a) General Methods of Recrystallization
Chemical transformations lead invariably to mixtures of products, and therefore
various techniques of separation or purification must be employed to isolate
individual components in pure form, from the crude reaction mixtures. In the case of
solid substances the most commonly employed technique, at least until the advent
of chromatographic methods, was that of recrystallization (or more simply
"crystallization").
As commonly practiced, purification by recrystallization depends upon the fact that
most solids are more soluble in hot than in cold solvents. The solid to be purified is
dissolved in the solvent at its boiling point, the hot mixture is filtered to remove all
insoluble impurities, and then crystallization is allowed to proceed as the solutioncools. In the ideal case, all of the desired substance separates nicely in crystalline
form and all the soluble impurities remain dissolved in the mother liquor. Finally, the
crystals are collected on a filter, washed and dried. If a single recrystallization
operation does not yield a pure substance, the process may be repeated with the
same or another solvent.
(b) Nature of Suitable Solvents
The single most important factor contributing to a successful recrystallization is the
proper choice of solvent. In general, the most "suitable" solvent for recrystallization
purposes is one in which the compound to be purified is only very slightly soluble at
low temperatures but very soluble at higher temperatures (e.g. at the boiling point of
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the solvent). Most compounds exhibit positive temperature coefficients of solubility.
Ideally of course, the impurities to be removed should be readily soluble in the cold
solvent in which they will remain after the crystallization process or almost
completely insoluble even at elevated temperatures.
It should be realized that the solvent selected must be inert and not enter into
chemical reaction with the sample. In addition, it is desirable that the solvent be
reasonably volatile (low boiling point) so that it can be fairly easily removed from the
crystals by evaporation. Where two or more solvents are comparable with respect to
the properties already cited, factors such as inflammability, toxicity and cost are to
be considered.
The lower the solubility of the compound to be purified in the cold solvent, the
greater will be the recovery of purified material from the crude mixture. The fact that
the solubility of the impurities may be comparable to that of the desired compound
does not preclude the use of a particular solvent, since most impurities are present
in relatively small amounts. As an example, consider the recrystallization of a
mixture of solids consisting of 10 g of A and 1 g of B from a solvent in which the
solubility of each is 1.5 g per 100 ml at room temperature and 10 g per 100 ml at the
boiling point. One hundred milliliters of hot solvent would be required to dissolve themixture, and upon cooling the solution would precipitate 8.5 g of A (i.e. 85%
recovery) and no B because the solubility of B had not been exceeded. Only if there
were more than 1.5 g of B and 10 g of A would any B crystallize, and even then a
second recrystallization would complete the separation of up to 2.5 g of B.
(c) Choosing a Suitable Solvent
If no information concerning the solubility characteristics of the substance to be
recrystallized is available, the choice of solvent becomes an experimental problem. It
is necessary to test various solvents for their suitability according to the criteria
outlined above. As a rule, solvents of decreasing polarity are tried in succession and
the solubility behavior in each case observed. To do this, small-scale trial
recrystallizations are carried out rapidly in micro (10 X 75 mm) test tubes. A few
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drops of various common solvents (see table below) are added to small portions of
the crude, finely divided solid mixture and the crystals are stirred and crushed under
the cold solvent with a stirring rod. If solution occurs at room temperature the solvent
is obviously unsuitable. If solution does not occur, the test tube is heated gently on a
steam bath or over a small flame with stirring or shaking. A few more drops of
solvent are added if only partial solution has occurred. (Transfer of solvent is most
conveniently done with small clean dropping tubes drawn out at the end like
pipettes). If a homogenous solution is obtained it is cooled, and the inside walls of
the test tubes are scratched if crystallization does not occur readily. If no crystals
can be obtained or if solution does not occur on warming, the solvent is unsuitable
and another should be tried. To avoid misleading observations, some care and
judgment must be exercised in choosing the relative amounts of solid and solvent to
be used in these solubility tests.
Choosing a Suitable Solvent
The ultimate proof of the suitability of a particular solvent is in achieving a separation
of the desired component from the unwanted impurities. This can be established by
collecting the crystals which precipitate from the solvent being tested and
determining their melting point.
In many cases it is difficult to predict a suitable solvent. In general, it is said that "like
dissolves like" -that is, a substance will dissolve in a solvent containing similar
groups -or better, that polar solvents will dissolve polar molecules and nonpolar
solvents will dissolve nonpolar molecules; but a good recrystallization solvent cannot
be too like the compound being purified. The accompanying table lists, in order of
decreasing polarity, some of the common solvents used for recrystallization.
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2. DETAILED DESCRIPTION OF EXPERIMENTAL STEPS AND APPARATUS
(a) Preparation of Hot Solution
At this stage the key words are saturated and minimum. Since the compound to be
purified will invariably be soluble in cold solvent to some extent, however small, the
recovery of pure material will be a maximum only by employing no more solvent than
is absolutely essential to obtain a complete solution at the elevated temperature. By
working at or near the boiling point of the solvent, full advantage is taken of the
temperature coefficient of solubility for that particular solute/solvent combination.
Quantitative solubility data are not essential, and the following general approach
may be applied to any solute/solvent combination. The solid is placed in a flask of
suitable size and just covered with a small quantity of solvent (use a volume
comparable to that of the solid phase, but certainly less than will be required
ultimately). The flask and contents are heated gently on a steam bath, shaking or
swirling, to a temperature just below the solvent's boiling point. Heating may then be
interrupted, an additional small quantity of solvent added, and heating resumed. This
procedure is repeated until the last bit of solid just dissolves or until no further
decrease in the amount of undissolved material is apparent. In many instances it willnot be possible to obtain complete solution because of the presence of insoluable
impurities in the mixture.
For this and all subsequent operations in the recrystallization sequence, it is
convenient to use the conically shaped Erlenmeyer flask, but never beakers. This
particular design offers many practical advantages. It minimizes both solvent loss
(the upper walls acting as a condenser) and the distribution of crystals on the vessel
walls out of reach of the solvent phase. It is also particularly convenient for handling
in the transfer operations or for corking or fitting with a condenser. In this way, hot,
ascending solvent vapor does not escape but is condensed and continuously
returned to the solution flask. This is particularly important with solvents such as
ethyl ether, benzene, and petroleum ether, but in practice it is advantageous with
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any solvent because loss of solvent over the period of time taken by the subsequent
filtration step will cause the solution to become supersaturated prematurely. In fact, it
is often desirable to have the solution slightly below saturation at this point to
minimize difficulties in the hot filtration (see below). This is especially true for highly
volatile solvents (e.g., b.p.
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the results of the single trial. In practice, one seldom uses more than 20 mg of
charcoal per gram of dry compound.
(c) Hot Filtration
The hot solution must be filtered to achieve separation from any insoluble impurities
or other undissolved materials. If charcoal is used for decolorization the necessity for
filtration is obvious. If no undissolved material is evident (which is very seldom) this
step may be omitted. The chief difficulty encountered in this operation is that of
keeping the solution hot enough to avoid premature crystallization in the filter. This
means that the filtration must be done as rapidly as possible with minimal cooling of
the solution.
Rapid filtration of small quantities of solution is best done by gravity through a fluted
filter paper supported in a stemless glass funnel. Fluting of the filter paper (the
technique of folding will be demonstrated in the laboratory) increases the rate of
filtration by presenting a much larger surface area to the solution. If a regular funnel
with a stem is used, there is a good possibility of filtrate cooling in the stem, with
crystallization resulting. The relatively narrow stem thus becomes clogged and
filtration is impeded. It is often advantageous to preheat the glass funnel simply by
briefly heating it in a flame or by pouring a quantity of hot solvent through itimmediately prior to filtration. If water is used as the solvent, the filter funnel may be
warmed conveniently on a steam bath.
When working with particularly volatile solvents or with solids having very large
temperature coefficients of solubility, it is particularly difficult to avoid premature
crystallization. In these cases it is usually better to prepare the hot solution with
excess solvent (i.e. the solution is not saturated at the boiling point). After the hot
solution has been filtered the excess solvent must, of course, be removed by
evaporation before inducing crystallization.
It should be emphasized that the hot filtration is done by gravity (at least in an
elementary laboratory) and not by suction filtration as described below for the
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collection of the crystallized product. The use of suction for filtering a hot, nearly
saturated solution is nearly always highly unsatisfactory, because the reduced
pressure in the filter flask causes rapid evaporation of the hot solvent; consequently,
the solution is not only more concentrated but it is cooled by the heat of vaporization
and becomes supersaturated.
Crystallization in the funnel is then almost inevitable and the funnel may become
completely plugged by the deposited crystals.
In carrying out the actual filtration, the fluted paper is inserted into the stemless
funnel so that the lower tip of the paper projects into the opening at the bottom of the
funnel. The hot solution is decanted quickly but carefully into the paper, keeping the
level of solvent well below the top of the paper. When all of the solution cannot be
put into the funnel at once, the remainder is kept warm on the steam bath or hotplate
until it can be transferred to the funnel.
After the solution has run through the paper, a crust of crystals often remains around
the tip of the funnel and ill-formed crystals often form in the body of the cooling
filtrate. It is common practice to rinse the original flask with a little hot solvent and tofilter this through the filter paper to redissolve the crystals adhering thereto. The
filtrate which has been collected in an Erlenmeyer flask should be reheated to
redissolve any material that has crystallized and, if significantly diluted below the
saturation point, should be concentrated to its original optimal volume prior to
cooling and crystallization.
If the various precautions outlined above fail to prevent excessive crystallization of
the solute in the filter paper, the simplest expedient is to return the complete filter
paper and its contents to the original flask, add additional solvent, boil briefly to
ensure complete solution, and begin a new filtration.
(d) Cooling/Crystallization
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Crystallization is accomplished by allowing the hot filtrate to cool slowly, undisturbed,
to room temperature (or at least until crystallization has begun) and then chilling the
mixture in ice or cold water to complete the precipitation. The objective is, of course,
that the desired substance be deposited as pure crystals while any "insoluble"
impurities remain dissolved in the "mother liquor". The lower the temperature to
which the solution is cooled, the more the desired substance will crystallize;
however, at some point the impurities may also begin to separate from solution. The
size of the crystals which separate will vary with the rate of cooling and the degree of
agitation of the solution. Rapid cooling with stirring tends to produce small crystals,
while slow cooling of an undisturbed solution tends to give larger crystals. In general,
either very large or very small crystals are undesirable. There are problems
associated with the collection of very fine crystals because of clogging of the pores
in the filter paper and of adhesion of the small particles to the walls of the
crystallization flask. Moreover, if the solubility of the impurities is comparable to that
of the desired compound, sudden chilling may result in the co-deposition of the
impurities; whereas, with slow, undisturbed cooling these tend to remain in
supersaturated solution and more complete separation is effected. On the other
hand, with very large crystals there is a tendency for the mother liquors to be
occluded within the crystals. In the subsequent drying operations, evaporation of thesolvent will leave a deposit of impurities on the crystals.
Yet another problem associated with too rapid chilling of the solution, especially in
the case of low melting solids, is the tendency for the solute to separate first from the
solution as an "oil" which subsequently solidifies to a crystalline cake. If this
happens, it is possible for impurities to be distributed between the solvent layer and
the "oily" layer (see discussion of principles of extraction). The impurities will then be
entrapped when the oil solidifies. For this reason it is often desirable to choose a
solvent for recrystallization whose boiling point is lower than the melting point of the
solid being purified.
(e) Collection of Crystals -Cold Filtration
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The important objective in the collection of a purified product is complete separation
of the crystals from the "mother liquor" containing the dissolved impurities. This is
achieved most effectively by employing suction filtration. The necessary apparatus
consists of a Buchner funnel attached to a heavy-walled filter flask which is
connected through a "trap" bottle to the source of suction (water aspirator or vacuum
pump) -see accompanying illustration.
The Buchner funnel is prepared for filtration by attaching it to the filter-flask by
means of a cork or rubber adapter, inserting a piece of filter paper whose diameter is
just sufficient to cover the holes in the filter plate (the paper must not fold up against
the sides of the funnel), wetting the paper with a-small quantity of the solvent being
used, then smoothing the paper snugly against the filter plate by the application of
gentle suction.
The cold contents of the crystallization flask are stirred to break up any lumps and
swirled to obtain suspension of crystals. The suspension is decanted quickly into the
funnel in such a way that a layer of uniform thickness is obtained across the whole
surface of the filter bed. This is essential for obtaining complete separation of the
mother liquor. It is important, particularly in the early stages, to use only sufficientsuction to obtain a steady flow of filtrate. Very strong suction at this stage will draw
the finer particles into the pores of the paper, clogging them, and slowing the rate of
filtration unnecessarily. The bulk of the crystals remaining in the flask may be
transferred to the funnel with the aid of a metal spatula. Any crystals still remaining
are most efficiently transferred to the funnel by rinsing the flask with a portion of the
filtrate (which is already saturated with solute) rather than using fresh solvent.
When the bulk of the mother liquor has drained through, the cake of crystals is
pressed down quickly with a spatula or glass stopper and the suction is interrupted
by removing the rubber tubing from the filter flask. It is particularly important at this
stage not to draw air through the crystal cake, because this will cause evaporation of
the mother liquor and the impurities that were dissolved therein will be deposited on
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the surface of the crystals. If it is intended to use the mother liquor to obtain a
second "crop" of crystals after concentration to a suitable volume, it should be
transferred at this point to a separate vessel (or the Buchner funnel attached to a
clean filter flask).
(f) Washing the Crystals
To complete the separation of the mother liquor, the crystalline cake must be
washed with small quantities of fresh, clean solvent. This is done conveniently by
covering the filter cake completely with a thin layer of solvent, with the suction
disconnected. If possible the crystalline cake should be loosened with a spatula to
ensure complete wetting by the wash solvent, but care must be exercised not to
disturb the filter paper. The suction is reapplied and the wash solvent drawn down
through the crystals, which are then pressed down firmly as before to remove the
wash liquid as completely as possible. For complete removal of the mother liquor
from the crystals two or three such washes are recommended; however, to minimize
loss of product, the wash portions should be small in volume and the solvent should
be cold. After the last wash, full suction is applied to draw air through the filter cake
to suck it as dry as possible.
(g) Drying the Crystals
The final operation in the recrystallization of a product, is the drying of the solid. If
the solvent employed in the recrystallization is rather volatile, it is possible that it will
have evaporated completely during the last stages of the suction filtration.
Otherwise, further drying is necessary. As used here the term "drying" refers to the
complete removal of solvent, be it organic or aqueous.
The cake of crystals is transferred, with the aid of a spatula, to a sheet of glazed
paper, a watch glass, or any suitable container having a relatively large surface
area. The solid sample should be spread out and permitted to stand in air with
periodic stirring with a spatula. In many instances, however, simple "air-drying" as
just described will be inadequate or much too slow. The last traces of solvent (and/or
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atmospheric moisture) are removed most conveniently by using a drying oven, a
dessicator, or by evaporation under vacuum. A dessicator is simply a closed vessel
with a lower compartment containing an anhydrous salt such as phosphorus
pentoxide which can remove water vapor by forming a hydrated salt. When using
either an oven or a dessicator the rate of drying can be enhanced even further by
reducing the pressure in the system. The temperature at which the crystalline solid is
dried in an oven should, of course, be significantly lower than the melting point.
B. MELTING POINT DETERMINATION
1. Use of Melting Points for Analysis
Most crystalline organic compounds have characteristic melting points that are
sufficiently low (50 300 C) to be conveniently determined with simple equipment.
Organic chemists routinely use melting points to a) get an indication of the purity of
crystalline compounds and b) help identify such compounds.
Pure crystalline compounds usually have a sharp melting point. That is, the melting-point range or the difference between the temperature at which the sample begins to
melt and the temperature at which the sample is completely melted, is relatively
small (narrow). Impurities, even when present in small amounts, usually depress the
melting point and broaden the melting point range. A wide melting-point range (more
than 5 C) usually indicates that the substance is impure, while a narrow melting
point range of about 0.5 2 C usually indicates that the substance is fairly pure.
However, there are some exceptions to both of these generalizations. Small
differences in melting point (on the order of 2 3 C
top related