Transcript Chpt. 22: Some Families of Organic Compounds

Chpt. 22: Some Families of
Organic Compounds
(Organic Chemistry)
Previously studied organic families:
Alkanes
Alkenes
Alkynes
Aromatic Compounds
This section involves the study of further organic
families:
Chloroalkanes
Alcohols
Aldehydes
Ketones
Carboxylic Acids
Esters
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
Group 2: Planar
 Alkanes
 Alkenes
 Chloroalkanes
Alcohols
 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been replaced by a chlorine atom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 METHANE
Number
of
Chlorine
atoms
Name of
Compound
Chemical
Formula
1
Chloromethane
CH3Cl
2
Dichloromethane
CH2Cl2
3
Trichloromethane
(Chloroform)
CHCl3
4
Tetrachloromethane
CCl4
Structural
Formula
*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-chloro5. 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
Primary
Methanol
(Methyl Alcohol)
CH3OH
Primary
Ethanol
(Ethyl Alcohol)
C2H5OH
Primary
Propan-1-ol
C3H7OH
Primary
Butan-1-ol
C4H9OH
Primary
2methylpropan1-ol
C4 H9OH
Structural
Formula
Type of
Alcohol
Name
Chemical
Formula
Secondary
Propan-2-ol
(Isopropyl
Alcohol)
Butan-2-ol
C3H7OH
2methylpropan2-ol
C4H9OH
Secondary
Tertiary
C4H9OH
Members of alcohols up to C-4
Structural
Formula
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) CH3CH2CH2OH
c) CH3CH(CH3)CH2OH
Student Questions:
Book – pg 360 W22.4
Workbook – 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 – gases
First 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
Bond
Hydrogen Bonding in
Ethanol
*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 carboncarbon (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)
Polar Double
Bond
• Named by replacing -ane at end of corresponding
alkane with –anal e.g. methane becomes
methanal
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
Methanal
(Formaldehyde)
Chemical
Formula
HCHO
Ethanal
(acetaldehye)
CH3CHO
Propanal
(Propionaldehyde)
C2H5CHO
Butanal
C3H7CHO
Structural
Formula
ISOMER
2-methylpropanal
C3H7CHO
ISOMER
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 = 2.5
E.N. Oxygen = 3.5
E.N. Difference = 1
*Take Diagram
δ+
δ-
C = O
Physical State & Properties of Aldehydes
Boiling 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
Solubility
High 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
Propanone
(Acetone)
Butanone
(methylethyl ketone)
Chemical
Formula
CH3COCH3
Structural
Formula
CH3COC2H5
Members of ketones up to C4
Physical State and Properties of Ketones
Physical 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
Butane – -0.5OC
BUT
BUT
Propanone – 56OC
Butanone – 800C
• Ketone boiling points are lower than those of
corresponding alcohols due to lack of hydrogen
bonding in ketones:
Propanone – 56OC
Butanone – 80OC
BUT Propan-1-ol – 97OC
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 ACIDS
Carboxylic 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
Methanoic Acid
(Formic Acid)
Chemical
Formula
HCOOH
Ethanoic Acid
(Acetic Acid)
CH3COOH
Propanoic Acid
C2H5COOH
Butanoic Acid
C3H7COOH
Structural
Formula
ISOMER
2-methylpropanoic
Acid
C3H7COOH
ISOMER
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)COOH
b) CH3CCl2CH2COOH
Student Questions – AFTER ESTERS!!!
Physical State and Properties
Physical 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
Ethanal
Ethanol
Ethanoic Acid
-183OC
-124OC
-117OC
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
Ethanoic Acid
78OC
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 odours
Old 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.
* Do Not Take Diagram
Hydrogen bonding between ethanoic acid and water (note two
water molecules will form two hydrogen bonds)
• 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
*Take Diagram
Methanol
• 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
Methyl Methanoate
HCOOCH3
Ethyl Methanoate
HCOOC2H5
Propyl Methanoate
HCOOC3H7
Methyl Ethanoate
CH3COOCH3
Structural
Formula
Name
Ethyl Ethanoate
Chemical
Formula
CH3COOC2H5
Methyl Propanoate
C2H5COOCH3
Structural
Formula
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 22.6
Workbook – 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 ester
Oil - 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
Alcohol - Glycerol
Fatty Acid – Stearic Acid (3)
* Note: Glycerol is the only alcohol with more than
one OH group on this course
• Fats and oils – used in manufacturing soap
• 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 - 0.154nm
C=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 - sigma
1e- - used to bond carbon and its
adjacent carbon (left) – sigma
1e- - 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 Compounds
Formulas/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
*Do Not Take Diagrams
Heroin
Pharmaceutical Compounds
Aspirin
Food Colourings
`
Ibuprofen
Disinfectants
TCP (2,4,6trichlorophenol)
*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 animals
Examples:
- 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 Distillation
Definition
Steam 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
A
100oC
Vapour Pressure
@ 25OC
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!!!!