workshop for secondary school teachers
DESCRIPTION
Experiments of Microscale Organic Chemistry. Workshop for Secondary School Teachers. Dr. W M TSUI Department of Chemistry, HKUST. Outline. Introduction of Microscale Organic Chemistry Introduction of designing experimental procedures Microscale Organic Glassware - PowerPoint PPT PresentationTRANSCRIPT
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Dr. W M TSUI
Department of Chemistry, HKUST
Workshop for Secondary School Teachers
1
Experiments of Microscale Organic Chemistry
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Department of Chemistry
Outline2
Introduction of Microscale Organic Chemistry Introduction of designing experimental
procedures Microscale Organic Glassware Techniques in Microscale Organic Experiments:
Solvent /Reagent Dispensing, Reaction Setup Liquid-Liquid Extraction, Filtration Purification methods
Characterization Method of Organic Compounds Experiment highlights
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Department of Chemistry
Organic synthesis & natural products synthesis
3
Complex and fascinating molecular structures can be assembled from simple starting materials.
Designed molecular frameworks containing carbon atoms in combination with H, O, N, S, and halogens, can be synthesized on demand and tested for various applications.
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Department of Chemistry
Organic synthesis & natural products synthesis
4
These useful compounds range from biological tools and medicines to high-value materials for cosmetics, computers and useful devices
OH
CO OH
O
CO OH
CO
CH3
OH
CO2
NaOH (CH3CO)2O
aspirin
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Department of Chemistry
Introduction of Microscale Organic Chemistry
5
Had been gradually recognized and adopted at secondary school level
Handle with small quantities of chemical substances
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Department of Chemistry
Macroscale vs. Microscale6
Macroscale Microscale
Quantities of chemicals
5-100 g 0.005-0.5 g
Glasswares 25 - 500 mL Microscale kit (<5mL)
Cost per experiment
$100-1000 $10-100
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Department of Chemistry
Advantages7
1. Require smaller storage area2. Save laboratory space3. Reduce amount of chemical waste4. Improve laboratory safety (smaller amount of
…)5. Shorter reaction time (efficient heat
transfer…)6. Save time for preparation and work up7. More time for evaluation and communication8. ………….
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Department of Chemistry
Microscale Organic Glassware8
Various designs
http://www.sigmaaldrich.com/labware/glassware-catalog/glassware-kits-microscale.html
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Department of Chemistry
9
Microscale Organic Glassware
All-purpose kit:
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Department of Chemistry
Designing experimental procedures
10
Stage 1: Setup reaction Experimental setup, Temperature, Time,
Catalyst, Solvent
Stage 2: Isolation of crude product Solvent extraction, Filtration, Precipitation
Stage 3: Purification of crude product Distillation, Recrystallization, Sublimation
Stage 4: Characterization Melting point, Boiling point, IR, MS
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Department of Chemistry Technique: Transfer of reagent/dispensing of solvent11
1.0 mL Syringe
Macroscale: Measuring cylinder Beaker Conical flask Dropping funnel
Microscale: Syringe Needle Septum
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Department of Chemistry
Technique: Setup for Organic Synthesis
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Organic Synthesis: Formation and breaking of C-C bond, C-O bond, C-H bond, C-X bond, etc.
Reflux: for long reaction time
Macroscale reflux setup
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Department of Chemistry
Technique: Microscale Experiment Setup
13
Microscale Round-Bottom Flasks, Threaded
Microscale Condenser, Threaded
Water in
Water out
Microscale reflux setup
Microscale Organic Synthesis: Water condenser
Sand bath
Reagents (+ catalyst)
Anti-bumping granules
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Department of Chemistry
Technique: Microscale Experiment Setup
14
Microscale Organic Synthesis: Air condenser
Reagents (+ catalyst)
Anti-bumping granules
Mic
roscale
R
ou
nd
-Bott
om
Fla
sks,
Th
read
ed
Microscale reflux setup
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Department of Chemistry
Isolation Technique: Filtration15
Vacuum filtration: Probably the most
common type of filtration used by chemists. The funnel used for this method is called Hirsch funnel. This funnel has a flat disc inside which is made from porous ceramic materials
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Department of Chemistry
Isolation Technique: Filtration
Pipette filtration: For small quantity
of crystals
16
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Department of Chemistry
Isolation Technique: Liquid-liquid Extraction
17
Partition coefficient Solubility in solvents
Screw capTest tube
Separatory funnel
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Department of Chemistry
Purification Technique: Distillation
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For liquids with various volatilities
Macroscale distillation setup
Microscale distillation setup
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Department of Chemistry
Purification Technique: Sublimation
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For solids
Macroscale sublimation setup
Microscale sublimation setup
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Department of Chemistry
Purification Technique: Recrystallization
20
For solids Various Solubility
Macroscale 250mLConical flask
Microscale 5mLConical flask
Temperature controlled by depth in sand
Microscale 5mLReaction tube
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Department of Chemistry
Purification Technique: Recrystallization
21
Steps in Recrystallization:1. Dissolution (various choice of Solvent)2. Hot Filtration3. Decolorization4. Crystallization5. Collection
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Department of Chemistry
Purification Technique: Recrystallization
22
The general idea is to follow the “like dissolves like” principle, e.g. compounds containing hydroxyl groups are best recrystallized from hydroxy-containing solventsClass of compound Suggested solvents
Hydrocarbons Light petroleum, pentane, cyclohexane and toluene
Ethers Diethyl ether and dichloromethane
Halides Dichloromethane
Carbonyl compounds Ethyl acetate and acetone
Alcohols, acids EthanolSalts Water
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Department of Chemistry
23
Methods for crystallization
2Ice Ice bathbath
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Department of Chemistry
Purification Technique: Recrystallization
24
Crystallization Slow cooling: the easiest method and works for
most cases Scratching: induced crystallization by scratching
the inside of the beaker or flask with a glass stirring rod. This will produce microscopic fragments of glass that may act as surfaces on which crystal growth can begin
Seeding: taking a small crystal from the original solid or the other groups and dropping them into the solution
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Department of Chemistry
Characterization of organic compound
Melting point / melting point apparatus
Simplest and most common characterization method for solid organic compounds
Purity check Affordable
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Department of Chemistry
Characterization of organic compound
Boiling point / distillation apparatus Simplest and most
common characterization method for liquid organic compounds
Purity check Affordable
26
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Department of Chemistry
Characterization of organic compound Infrared spectrum
Infrared spectrophotometer
Absorption of infrared electromagnetic radiation
Information of functional groups
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Department of Chemistry
Characterization of organic compound• To allow passage of IR, most sample
cuvettes have mineral salt windows [Caution! Avoid high humidity.]
• Transmission limit:– NaCl 650cm-1
– KBr 350cm-1
– CsI 56 μm (200cm-1)
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Department of Chemistry
Characterization of organic compound
29
BondBase Value
Strength / Shape
Comments
1 C=O 1715 s, "finger"Exact position depends on type of carbonyl
2 O-H 3600 s, broad Broad due to hydrogen bonding
3 N-H 3500 m Can tell primary from secondary
4 C-O 1100 s Also check for O–H and C=O
5 C=C 1650w alkene m-s aromatic
Alkene w due to low polarity Aromatic usually in pairs
6 CΞC 2150 w, sharp Most obvious in terminal alkynes
7 C-H 3000 sAs hybridisation of C changes sp3-sp2-sp, the frequency increases
8 CΞN 2250 m, sharpCharacteristic since little else around this value
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Department of Chemistry
Characterization of organic compound Functional groups can be identified
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Infrared spectrum of acetone
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Department of Chemistry
Characterization of organic compound Mass spectrum / mass spectrometer mass-to-charge ratio of molecular ion
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Picture from http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch13ms.html
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Department of Chemistry
Characterization of organic compound Mass-to-charge
ratio: Molecular ion Fragmentation
pattern of molecular ion
32
Molecular ionThe ion obtained by the loss of an electron from the molecule
M+ Symbol often given to the molecular ion
Radical cation
+ve charged species with an odd number of electrons
Fragment ions
Lighter cations formed by the decomposition of the molecular ion. These often correspond to stable carbcations.
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Department of Chemistry
Characterization of organic compound
33
Decane (C10H22)
Molecular ion at m/z = 142
142-29 = 113 113-14 = 99 etc
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Department of Chemistry
Characterization of organic compound Acetone (C3H6O) Molecular ion at m/z =
58
34
–15
–28
58
43
15
CH3 CH3
C
O
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Department of ChemistryExperiment 1: Microscale separation of components
in a mixture35
caffeine p-dimethoxybenzene acetaminophen
Separation based on their different physical and chemical properties
3 components
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture36
Step 1: Solubility test Technique: Solid-liquid extraction
(Filtration)
Step 2: Acid-base chemistry Technique: Liquid-liquid extraction, Pipette
filtration, Evaporation
Step 3: Purity check Technique: TLC analysis
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture37
Step 1: Solubility test water, dichloromethane, hexane
Powder
Insoluble
Slightly soluble
soluble
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture38
Solid-liquid extraction (Filtration)
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Department of ChemistryExperiment 1: Microscale separation of components
in a mixture39
Step 2: Acid-base chemistry
basic neutral
HCl
NaOHaq orgorg
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture40
Liquid-liquid extraction Release pressure Which layer on the top? Test by adding water
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture Some water will be
transferred into the organic phase because of the partial miscibility of the organic phase and water Organic solution contaminated with traces of water.
41
Water
brine works to pull the water from the organic layer to the water layer
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Department of ChemistryExperiment 1: Microscale separation of components
in a mixture42
Dry by anhydrous Na2SO4 (Preliminary purification)
Pipette filtration
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture43
Evaporation
Needle
Compressed air
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture44
Step 3: Purity check Thin layer chromatography (TLC)
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Department of Chemistry
Thin layer chromatography (TLC)45
Chromatography: Separation of compounds by the distribution between two phases – Mobile phase & Stationary phase
Experiment 1: Microscale separation of components in
a mixture
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture46
stationary phase(TLC plate: Silica gel)
Sample mixture
mobile phase (solvent)
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Department of ChemistryExperiment 1: Microscale separation of components in
a mixture47
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Department of ChemistryExperiment 2:Catalytic Hydrogenation of Methyl
Oleate48
Organic Synthesis by Hydrogenation Microscale Experiment Setup
Reagents: Methyl oleate, H2, Palladium on charcoal,
Methanol
methyl oleate methyl stearateH2(g)
Catalyst: Pd/C
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Department of Chemistry
Catalytic Hydrogenation of Methyl Oleate
Setup: Generation of
hydrogen gas as reagent
Use of septum Use of needles Use of syringe
49
HCl(aq)
Zn metal in 5mL flask
5mL flask
H2(g)
Syringe instead of dropping funnel
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Department of Chemistry
Catalytic Hydrogenation of Methyl Oleate
Collect H2
into a
inverted measuring cylinder
50
HCl(aq)
Zn metal in 5mL flask
5mL flask
H2(g)
Syringe instead of dropping funnel
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Department of Chemistry
Catalytic Hydrogenation of Methyl Oleate
51
Beginning of synthetic reaction
Use of syringe + needle
H2(g)
Meth
yl ole
ate
+ m
eth
an
ol
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Department of Chemistry
Catalytic Hydrogenation of Methyl Oleate
52
Use of parafilm to prevent leakage
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Department of Chemistry
Catalytic Hydrogenation of Methyl Oleate
53
Workup: Filter off Pd/C Evaporate excess CH3OH Purification of methyl stearate
Isolation of second crop of product (by adding H2O to filtrate)
Characterization Melting point determination