chpt. 22: some families of organic compounds (organic chemistry)
TRANSCRIPT
Chpt. 22: Some Families of Organic Compounds
(Organic Chemistry)
Previously studied organic families:AlkanesAlkenesAlkynesAromatic Compounds
This section involves the study of further organic families:
ChloroalkanesAlcoholsAldehydesKetonesCarboxylic AcidsEsters
All ten of these families can be split into two groups:
Group 1 – Tetrahedral
*Do Not Take Diagram
Group 2 – Planar
*Do Not Take Diagram
Group 1: Tetrahedral
Alkanes ChloroalkanesAlcohols
Group 2: Planar
Alkenes Alkynes Aldehydes Ketones Carboxylic Acids Esters Aromatic Conpounds
Tetrahedral Carbon Compounds
In saturated organic compounds, ALL of the carbon atoms are tetrahedral
CHLOROALKANES (Haloalkanes):
Chloroalkanes are compounds in which one or more of the hydrogen atoms in an alkane molecule have been replaced by a chlorine atom
The part of an alkane remaining after one hydrogen is removed is an alkyl group e.g. Methane CH4 minus a hydrogen group leaves methyl -CH3
Remember: Alkyl Radicals (R)Name Alkyl Radical
Methyl CH3
Ethyl C2H5
Propyl C3H7
Butyl C4H9
*Do Not Take This Slide
Chloroalkanes are named after the alkane from which they are derived with the prefix chloro- indicating the
presence of chlorine.
Chloroalkanes of METHANENumber
of Chlorine atoms
Name of Compound
Chemical Formula
Structural Formula
1 Chloromethane CH3Cl
2 Dichloromethane CH2Cl2
3 Trichloromethane(Chloroform)
CHCl3
4 Tetrachloromethane CCl4
*Important Note*
You must be able to name and draw the structure of all the chloroalkanes for the first four alkanes!!!
(methane, ethane, propane, butane)
Naming and Drawing structural formulas of Chloroalkanes:
1. Draw full structural formula of compound
2. Identify longest continous chain of carbon atoms - parent alkane
3. Number carbon atoms from the end that gives lowest number to the carbon atom to which the chlorine atom is attached
4. Indicate position of chlorine atom e.g 2-chloro-
5. Name compound
Example:Name the compounds:
a) CH3CH2CHClCH3
b) CH3CCl2CHClCH3
c) CH3CCl(CH3)CH3
Student Questions:
Workbook – pg 60 W22.1, W22.2, W22.3
Homework:
Book – pg 360 22.1,22.2, 22.3
Physical State and Properties of Chloroalkanes• Chloroalkanes are slightly polar
• Chloroalkanes are insoluble in water but are soluble in non-polar solvents e.g. cyclohexane, methylbenzene
• Chloroalkanes have low boiling points but because of the polarity of the carbon/chlorine bond chloroalkanes have higher boiling points than corresponding alkanes.
*Note: Boiling point depends on the strength of the intermolecular forces, so, because longer carbon chains have stronger van der Waals forces between molecules they will have higher boiling points.
• Most chloroalkanes liquid at room temperature, exception – chloromethane* and chloroethane are gaseous
• Main use is as solvents:- for removing oil and grease machinery, dry cleaning- paint stripper (dichloromethane)- Tippex*
*Ozone Layer
Functional Group (Active Group)
A functional group is an atom or group of atoms that defines the particular chemistry of a homologous series.
Homologous Series Functional Group
Alkanes C-C single bond
Alkenes C=C double bond
Alkynes C=C triple bond
ALCOHOLS
Alcohols form a homologous series of compounds of formula:
CnH2n + 1OH
• Functional group – OH group (V-shaped) called hydroxyl group
AlcOHol
• Alcohols are formed when the hydrogen atom in an alkane is replaced by the hydroxyl group (OH)
• Carbon atoms including that joined to the OH group are *TETRAHEDRAL*
• Named by replacing -ane at end of corresponding alkane with -anol
Primary, Secondary Tertiary Alcohols
*Do Not Take Diagrams
Pimary Alcohol:A primary alcohol is one where the carbon atom joined to the –OH group is attached to only one other carbon atom.
Ethanol*Do Not Take Diagram
Secondary Alcohol:A secondary alcohol is one where the carbon atom joined to the –OH group is attached to two other carbon atoms.
Propan-2-ol*Do Not Take Diagram
Tertiary Alcohol:A tertiary alcohol is one where the carbon atom joined to the –OH group is attached to three other carbon atoms
2-methylpropan-2-ol *Do Not Take Diagram
*Important Note*
You must be able to name and draw the structure of all the alcohols, primary and secondary, up to C4
(methanol, ethanol, propanol, butanol)
Type of Alcohol
Name Chemical Formula
Structural Formula
Primary Methanol(Methyl Alcohol)
CH3OH
Primary Ethanol(Ethyl Alcohol)
C2H5OH
Primary Propan-1-ol C3H7OH
Primary Butan-1-ol C4H9OH
Primary 2-methylpropan-
1-ol
C4 H9OH
Type of Alcohol
Name Chemical Formula
Structural Formula
Secondary Propan-2-ol(Isopropyl Alcohol)
C3H7OH
Secondary Butan-2-ol C4H9OH
Tertiary 2-methylpropan-
2-ol
C4H9OH
Members of alcohols up to C-4
Naming and Drawing structural formulas of Alcohols:
1. Draw full structural formula of compound
2. Identify longest continous chain of carbon atoms containing the carbon atom to which the –OH group is attached – parent alkane change ane
to anol
3. Number carbon atoms from the end that gives lowest number to the carbon atom to which
the -OH group is attached
4. Indicate position of –OH group e.g 2-butanol
5. Name compound
Example:Name the compounds:
a) CH3CH2CH(OH)CH3
b) CH3CH2CH2OHc) CH3CH(CH3)CH2OH
Student Questions:
Book – pg 360 W22.4Workbook – pg 60 W22.4
Physical State and Properties of Alcohols
Boiling Points:
Alcohols have much higher boiling points than alkanes of comparable relative molecular mass:
First 4 members of alkanes – gasesFirst 4 members of alcohols – liquids
WHY???
• An alcohol can be regarded as a compound similar to a water molecule with an alkyl group replacing a hydrogen atom
• The higher boiling points are due to the fact that the highly polar –OH group gives rise to hydrogen bonding between the alcohol molecules.
Oxygen, being more electronegative, has a partial negative charge, and hydrogen has a partial
positive charge. The oxygen in the hydroxyl group in one molecule attracts the hydrogen in the hydroxyl group on a neighbouring molecule .
• Because of this hydrogen bonding extra energy has to be supplied to break these bonds – hence higher boiling points than corresponding alkanes
Hydrogen Bonding in Ethanol
Hydrogen Bond
*Take Diagram
Solubility:
Methanol, ethanol and propan-1-ol are completely miscible with water. They are said to be infinitely soluble in water i.e. miscible in all proportions.
WHY???
• This solubility is possible because hydrogen bonding occurs between the alcohol molecules and the water molecules.
• It is impossible to separate ethanol from water by distillation gives a mixture called 95% ethanol thus to obtain an absolute alcohol sample water must be removed using a chemical drying agent e.g. calcium oxide
Hydrogen Bonding between Ethanol and Water
*Take Diagram
• Solubility of alcohols decreases with length of carbon chain.
• The tendency of the polar –OH group to make the alcohol soluble is counteracted by the insoluble alkyl (non-polar) portion of the molecule which becomes more significant as the carbon chain increases.
• Thus while the lower members of the alcohols, C1 – C3, are completely soluble with water the higher alcohols have poor solubility in water and readily dissolve in solvents like cyclohexane
Occurences and Uses of Alcohols
Ethanol is the most commonly known of all alcohols
• Ethanol is the alcohol found in alcoholic drinks and is produced by a process known as fermentation.
• Ethanol in alcoholic drinks is made by fermentation of sugars in fruits such as grapes – wine or apples – cider. This process involves a series of reactions brought about by enzymes (zymase) contained in yeast. Enzymes break down the sugar to give alcohol and CO2
• Fermentation is used in brewing industry to produce beer (malted grain) and cider (apples) – 7-8% v/v.
• To produce drinks of higher alcohol concentration fermented liquids are distilled e.g. distillation of wine produces brandy. Other distilled products include: whiskey, gin, vodka, brandy – 40% v/v.
• Ethanol (made by fermentation of sugar cane) mixed with petroleum products – used as a motor fuel instead of petrol.
• Ethanol is a very good solvent ( solubility properties). It is widely used as a solvent for perfumes, aftershaves, lotions, deodorants, hair sprays.
• Methanol is TOXIC. Methanol along with a purple dye are added to industrial alcohol (ethanol) to prevent people drinking it. Methanol added in this way is called a denaturing agent.
• Ethanol is the main component of methylated spirits which is burned in some types of camping stoves.
Planar Carbon Compounds
Planar carbon atoms feature in a number of organic families – those whose compounds have a carbon-carbon (C=C) or carbon-oxygen (C=O) double bond.
The atoms in the double bond are planar, while other carbon atoms in the molecule may be tetrahedral.
Presence of double bond means these compounds are unsaturated.
ALDEHYDES
AldeHydes form a homologous series of compounds of formula:
CnH2n + 1CHO
• Functional group –CHO group (V-shaped)
• Named by replacing -ane at end of corresponding alkane with –anal e.g. methane becomes methanal
Polar Double Bond
Important Note*
You must be able to name and draw the structure of the aliphatc aldehydes up to C-4 (incl. isomers)
(methanal, ethanal, propanal, butanal)
Name Chemical Formula
Structural Formula
Methanal(Formaldehyde)
HCHO
Ethanal (acetaldehye)
CH3CHO
Propanal (Propionaldehyde)
C2H5CHO
Butanal C3H7CHOISOMER
2-methylpropanal C3H7CHOISOMER
Members of aldehydes up to C-4
Naming and Drawing structural formulas of Aldehydes:
• Aldehyde functional group (-CHO) must always occur at the end of the carbon chain.
• Therefore naming aldehydes is easier as there is no need to use a number to indicate the position of the functional group.
• Molecular formula worked out by changing the last carbon in the chain of the alkane from being a part of a CH3 group, to being part of the aldehyde –CHO group
• Must use numbers to indicate position of substituents on carbon chain i.e. 2-methylpropanal
Example:Write the name, chemical formula and structural formula of the aldehyde containing three carbon atoms.
The Carbonyl Group (Aldehydes):The carbonyl group has a major effect on the physical
and chemical properties of the aldehydes
• Planar carbon atom – bond angle 120o
• Strongly polar – E.N. Carbon = 2.5E.N. Oxygen = 3.5E.N. Difference = 1
C = O δ+ δ-*Take Diagram
Physical State & Properties of AldehydesBoiling Points
• Due to the polarity of the carbonyl group (C=O) dipole- dipole attractions exist between adjacent aldehyde molecules.
• Boiling points are higher than those of corresponding alkanes (because of dipole-dipole forces) but less than those of the corresponding alcohols (which contain H – bonding) – graph pg. 348
e.g. Ethanol – boiling pt = 78OC Ethanal – boiling pt = 21OC (volatile)
• Methanal – gas at room temperature but other lower members of the series are liquids
SolubilityHigh solubility in water – hydrogen bonding takes place between the O atom of the carbonyl group and the H atom of the water molecule.
*Take Diagram
•The lower members of the aldehydes are very soluble in water and, like the alcohols, will dissolve both polar and non-polar substances.
• This solubility in water decreases with the length of the carbon chain i.e. the more non-polar the molecule becomes the less it dissolves
• Aldehydes are soluble in non-polar solvents
• Aromatic aldehyde: Benzaldehyde• found in almond kernels• manufactured to make almond essence for use in cooking
*Do Not Take Diagram
KETONES(Ketones are Higher Level Only!!!)
Ketones form a homologous series of compounds of formula:
RCOR’
where, R and R’ are two alkyl groups which can be the same or different.
• Functional group – C=O group (carbonyl group)
*Take Diagram
Aldehyde Vs. Ketone
*Take Diagram
• Carbonyl carbon – planar carbon
• Named by changing the final –e of the parent alkane to –one e.g. propane becomes propanone, butane becomes butanone
• Since functional group in ketones has two alkyl groups attached it cannot be located at end of chain i.e. located in middle of chain so must be at least 3 carbon atoms present.
• Most common ketone – propanone (acetone) – organic solvent – nail varnish remover
Important Note*
You must be able to name and draw the structure of the Ketones up to C-4 i.e. first two members
(propanone and butanone)
Name Chemical Formula
Structural Formula
Propanone(Acetone)
CH3COCH3
Butanone(methylethyl ketone)
CH3COC2H5
Members of ketones up to C4
Physical State and Properties of KetonesPhysical properties of ketones very similar to those of
aldehydes – both contain carbonyl group
Boiling Points•Lower ketones are liquids at room temperature
•Due to the polarity of the carbonyl group (C=O) dipole-dipole attractions exist between adjacent ketone molecules
•Ketone boiling points are higher than those of corresponding alkanes due to dipole-dipole forces:
Propane – -42OC BUT Propanone – 56OC Butane – -0.5OC BUT Butanone – 800C
• Ketone boiling points are lower than those of corresponding alcohols due to lack of hydrogen bonding in ketones:
Propanone – 56OC BUT Propan-1-ol – 97OCButanone – 80OC BUT Butan-1-ol – 117OC
Solubility• Similar to aldehydes - due to the polarity of the C=O
group hydrogen bonding will take place between the O atom of the carbonyl group and the H atom of the water molecule – lower ketones are very soluble in water e.g. propanone and butanone are very miscible in water
• All ketones are soluble in organic solvents but since propanone and butanone can act as solvents for both polar and non-polar substances they are widely used as solvents in industry
CARBOXYLIC ACIDSCarboxylic acids form a homologous series of compounds of the formula:
CnH2n+1COOH
•Functional group – COOH called carboxyl group - contains an OH group (hydroxyl grp) and a polar C=O group (carbonyl grp = polar double bond).
*Take Diagram
• Carboxyl carbon atom – in effect is a carbonyl carbon i.e. it is a planar carbon
• Carboxylic acids are formed when the last methyl group in the chain of the alkane is replaced with the carboxyl functional group
• Carboxylic acids are named by replacing the final –e at the end of the corresponding alkane with –oic acid e.g. methane becomes methanoic acid, ethane becomes ethanoic acid
*Important Note
You must be able to name and draw the structure of the carboxylic acids up to C-4
(incl. isomers)
Name Chemical Formula
Structural Formula
Methanoic Acid(Formic Acid)
HCOOH
Ethanoic Acid (Acetic Acid)
CH3COOH
Propanoic Acid C2H5COOH
Butanoic Acid C3H7COOHISOMER
2-methylpropanoic Acid
C3H7COOHISOMER
Members of carboxylic acids up to C-4
Naming and Drawing structural formulas of Carboxylic Acids:
1. Draw full structural formula of compound
2. Identify longest continuous chain of carbon atoms containing the COOH group – parent alkane
change -e to -oic acid.
3.Number carbon atoms from the –COOH end. The carbon atom of the carbonyl group is always carbon atom 1.
4. Indicate position of substituents by a number
5. Name compound
Example:Name the compounds:
a) CH3CH(CH3)COOHb) CH3CCl2CH2COOH
Student Questions – AFTER ESTERS!!!
Physical State and PropertiesPhysical properties of carboxylic acids are governed by
their ability to form hydrogen bonds!!!
Melting and Boiling Points
•Due to INCREASED hydrogen bonding the melting point of pure carboxylic acids is much higher than those of corresponding organic families
Ethane -183OCEthanal -124OCEthanol -117OCEthanoic Acid 17OC
• These relatively high melting points result from the formation of dimers, where two carboxylic acid molecules are held together by two hydrogen bonds. These arise due to the polarity in the C=O bond and the O-H bond.
*Note: Dimer – groups of two molecules joined together
• Each H atom (partial positive charge) forms a hydrogen bond with the carbonyl oxygen (partial negative charge) on the neighbouring acid molecule. The reverse also happens resulting in the formation of two hydrogen bonds
*Take Diagram
• Pure ethanoic acid is a liquid at room temperature but if temperature drops below 17OC the ethanoic acid turns into a solid (room now too cold to melt pure ethanoic acid). In its solid from ethanoic acid looks like ice and is known as glacial acetic acid.
• Similarly due to INCREASED hydrogen bonding the boiling point of carboxylic acids is even higher than those of corresponding alcohols
Ethanol 78OCEthanoic Acid 118OC
• Lower carboxylic acids – methanoic, ethanoic, propanoic, butanoic acid are all liquids at room temperature
• Lower carboxylic acids - colourless liquids usually with sharp or distinctive smell - vinegar
• Long chain carboxylic acids – unpleasant odoursOld smelly socks – butanoic acid *Tracker Dogs
Stench of goats – decanoic acid
Solubility
• Hydrogen bonding can also occur between water molecules and the lower carboxylic acids.
Hydrogen bonding between ethanoic acid and water (note two water molecules will form two hydrogen bonds)
* Do Not Take Diagram
• As a result of this hydrogen bonding acids containing up to four carbon atoms are highly soluble in water. However, as the carbon chain increases in length, the molecule becomes less polar and solubility in water decreases e.g. benzoic acid not very soluble in cold water
• Higher carboxylic acid members become more soluble in organic solvents - cyclohexane
Occurrence and Uses of Carboxylic Acids
•Methanoic acid is an irritant fluid emitted by ants and also found in nettle stings (Antidote – apply a weak base to affected area – sodium hydrogencarbonate/bread soda)
•Ethanoic acid – best known carboxylic acid! Principal acid found in vinegar. It is usually made by the oxidation of ethanol by air. Also used to make cellulose acetate which is used in varnishes and photographic film (Undrinkable wine!!!!)
Higher Level Only•Propanoic acid, benzoic acid (C6H5COOH) and some of their salts (isodium benzoate) are widely used in the preservation of food
ESTERS(Esters are Higher Level Only!!!)
Esters form a homologous series of compounds of formula:
RCOOR’
where, R could be a hydrogen atom or an alkyl group and R’ is an alkyl group.
• Functional group – -COO- group (contains planar carbon in the form
C=0)
• Consist of two parts – R’ alkyl group derived from an alcohol
- RCOO- derived from a carboxylic acid
Methyl Ethanoate
Ethanoic Acid
Methanol*Take Diagram
• Esters may be prepared in the laboratory by the reaction between an alcohol and a carboxylic acid – condensation reaction ( results in loss of water molecule this reaction will be studied in greater detail in next chapter)
*Take Diagram
Naming Esters
2 parts to the name:
- first part is alkyl group derived from the alcohol - second part is the name of the acid, with the ending –oic replaced with -oate
*Important Note
You must be able to name and draw the structure of the carboxylic acids up to C-4
Name Chemical Formula
Structural Formula
Methyl Methanoate HCOOCH3
Ethyl Methanoate HCOOC2H5
Propyl Methanoate HCOOC3H7
Methyl Ethanoate CH3COOCH3
Name Chemical Formula
Structural Formula
Ethyl Ethanoate CH3COOC2H5
Methyl Propanoate C2H5COOCH3
Naming and Drawing structural formulas of Esters:
1. Draw full structural formula of ester
2.Divide structural formula into two parts:- alcohol part- carboxylic acid part
3.Write down name of alkyl group attached to bridging oxygen atom
4.Identify carboxylic acid and change -oic ending to -oate
5.Name compound putting name of alkyl group first.
Example:Name the compound:
a) HCOOCH2CH3
Student Questions:Book – pg 360 22.6Workbook – pg 61 W22.6
Physical State & Properties
Boiling Points:• The carbon-oxygen double bond (C=O) in esters is polar leading to dipole-dipole forces but NOT hydrogen bonds, between adjacent molecules.
• Thus esters have low boiling points which are similar to those of aldehydes and ketones of similar relative molecular mass.
Ethyl ethanoate - 77OC
• Lower members of ester family are volatile liquids.
Solubility:
• The polarity of the C=O group allows hydrogen bonding to occur with water molecules.
• The lower members of the ester family (up to C-5) are fairly soluble in water.
• However, the solubility of the esters decreases as the length of the carbon chain increases.
• Esters are soluble in organic solvents (non-polar)
Occurence and Uses of Esters
• Members of the ester family have strong and often pleasant, fruity smells. Many esters occur naturally and are responsible for the flavour in fruits and the smells of flowers
• Polyester – refers to a type of fabric used in clothing etc. – consists of millions of esters linked together.
• Fats and oils are naturally occurring esters. They are used by plants and animals for storing energy.
Fat - solid esterOil - liquid ester
• Fats and oils are esters which are insoluble in water but soluble in organic solvents. They usually consist of an alcohol named glycerol and various long chain carboxylic acids (fatty acids) e.g.
Ester - Glycerl Tristearate
* Note: Glycerol is the only alcohol with more than one OH group on this course
• Fats and oils – used in manufacturing soap
Alcohol - Glycerol Fatty Acid – Stearic Acid (3)
• Ethyl Ethanoate- used as a solvent for printing inks and paints.
Short Experiment: Test – Tube Preparation of Esters
Aromatic Compounds
In chapter 21 we learned that any compound containing a benzene ring is called an aromatic compound, with benzene itself being the most
important.
Benzene
Bonding in Benzene (Brief):Although it was expected that benzene would have three double bonds its lack of reactivity suggested otherwise. It was discovered that the bonds are actually intermediate between single and double bonds. When bond lengths were measured it was expected that:
C-C - 0.154nmC=C - 0.13nm
However, all carbon –carbon bond lengths were the same measuring 0.139nm i.e. between that of a double and single bond.
Hence, it was suggested that the 6 valence electrons, one from each carbon atom, belonged to the whole molecule (delocalised) rather than being localised in 3 double bonds.
Remember:
Sigma Bond – head on overlap of two atomic orbital's
Pi Bond – sideways overlap of two atomic orbital's
*Do Not Take Diagrams
Bonding in Benzene – Detail:
The benzene molecule consists of six carbon atoms joined to form a hexagonal planar ring.
Each carbon atom (1s2,2s2,2p2) has four electrons in its outer shell:
1 e-- used to bond with hydrogen - sigma1e- - used to bond carbon and its adjacent carbon (left) – sigma1e- - used to bond carbon and its
adjacent carbon (right) - sigma
Sigma – Head on Overlap
Two S orbitals
P orbital & S orbital
The one electron remaining in the outer shell of each carbon atom is in a p orbital.
Each p orbital overlaps sideways with its two neighbouring orbital's to form two doughnut shaped electron clouds
*Do Not Take Diagrams
These two electron clouds give rise to a pi bond in the molecule of benzene.
*Do Not Take Diagram
The six electrons in the pi bond do not belong to any particular atom. These six electrons are said to be delocalised i.e. they are not restricted to any particular carbon atom but can move freely around the ring within the pi-bonded system
Physical Properties:Benzene is a planar, non-polar molecule.
Benzene is a carcinogenic.
Methylbenzene (benzene substitute) is widely used:
- as an industrial solvent- in manufacture of plastics and explosives- added to petrol to improve octane rating
While benzene is a carcinogenic there are many aromatic compounds that are not and which play an important
role in our everyday lives
Aromatic Compounds and their Uses:Aromatic compounds are in widespread use in a range of different applications. They are used in manufacture of:
- medicine - painkillers- dyes- detergents- insecticides- herbicides- disinfectants- acid-base indicators – methyl orange
- phenolphthalein
Examples of Aromatic CompoundsFormulas/diagrams do not need to be known but you must be able to name a variety of aromatic compounds and their area of use.
Insecticides & Herbicides
DDT
Narcotics
Heroin
*Do Not Take Diagrams
Pharmaceutical Compounds
Aspirin Ibuprofen
Food Colourings Disinfectants
` TCP (2,4,6- trichlorophenol)
*Do Not Take Diagrams
Demonstration: To Investigate the Solubility of Organic Compounds
Organic Natural Products(Know 2 examples)
A natural product is any chemical produced in nature, either by plants or by animalsExamples:
- Benzaldehyde – almomds- Caffeine – tea/coffee- Nicotine – tobacco- Opium – poppies- Limonene – orange peel- Quinine – bark of cinchona trees- Penicillin – bread mould
Many of these natural products were isolated for their use as valuable medicines:
- quinine (malaria)- morphine- paracetamol
While others were isolated for their poisonous properties:
- strychnine (rat poison)
Natural products may also be isolated for their fragrant oils which can be used in perfume making
At the initial time of discovery of many of these substances it was not possible to determine the structure of their molecules and therefore they could not be synthesised in the lab. With modern developments in analytical techniques it is now possible to determine the molecular structure and to synthesise these compounds in the laboratory
Synthesis of these natural products is important as they may be difficult to obtain otherwise due to seasonal nature of plants, weather conditions etc. and the fact that their medicinal properties may be improved upon.
Remember: Natural products may also be isolated for their fragrant oils which can be used in perfume making.
Steam DistillationDefinitionSteam Distillation: is a technique used to separate organic oils from plants themselves e.g. – extracting oil from roses, lavender, cloves (eugenol)
This technique allows organic substances to be isolated that, if heated on their own to higher temperatures, might partially decompose.
The principle of this technique is that the boiling points of a mixture of two immiscible liquids is below the boiling points of both pure liquids allowing organic substances to be isolated at temperatures below 100O C.
Steam Distillation – How it Works???
• If the pressure on a liquid changes so does its boiling point
• If two immiscible liquids A & B are kept stirred, the vapour pressure above the mixture is the total of the two separate vapour pressures i.e.
Total Vapour = Vapour Pressure + Vapour Pressure Pressure of A of B
• When this mixture is heated the vapour pressure of both liquids (total vapour pressure) will increase and when the total vapour pressure reaches atmospheric pressure the mixture will boil.
*Do Not Take Diagram – on handout
Liquid Boiling Point Vapour Pressure@ 25OC
A 100oC 3kPa
B 126OC 2.3kPa
Mixture of A & B 89OC 5.3kPa
*Note: Atmospheric Pressure = 100kPa
Hence, the presence of the water in the mixture reduces its boiling point and the organic liquid will distil at a lower temperature preventing decomposition at higher boiling points.
*Do Not Take Diagram – on handout
• The distillate produced is a mixture of the isolated organic component A and liquid B (water).
• The mixture obtained is called an emulsion. An emulsion is a mixture of normally immiscible liquids where tiny particles of one liquid (A) are dispersed throughout the other but not dissolved.
• To obtain a pure sample of the organic component A, a technique called solvent extraction is used (see experiment notes for details)
Mandatory Experiment: The extraction of clove oil from cloves by steam distillation.
Please see handout re: important points to note!!!!