




An alkane molecule such as ethane has a
‘backbone’ consisting of a chain of single C-C
bonds.
An alkane molecule is non-polar as carbon
and hydrogen have similar electronegativity.
Therefore they are insoluble in water, but are
soluble in non-polar solvents.
The stability of the C-C bonds and the nonpolar nature means that alkanes are quite nonreactive.
Most reactions involving alkanes are either
combustion or substitution reactions.
Alkanes can be used as fuel.
 Combustion reactions involving alkanes
release large amounts of heat energy.
 Combustion of methane

› CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + energy

Combustion of methane
› 2C8H18(g) + 25O2(g) → 16CO2(g) + 18H2O(g) + energy
One or more hydrogen atoms in an
alkane is replaced by a different atom or
functional group.
 This involves breaking the C-H bonds and
making new bonds with the substituting
atom or group.
 Chloroethane is a gas at room
temperature and is used in a local
anaesthetic spray.

Heat or light

CH3CH3(g) + Cl2(g)
CH3CH2Cl(g) + HCl(g)
Page 146
 Questions 1 and 2


Alkenes:
› Are unsaturated
› Are non-polar
› Are insoluble in water
› Participate in addition reactions
› Polymerises to produce polymers.
The double covalent bond in ethene
molecules has a significant effect on its
chemical properties.
 Ethene reacts more readily, and with
more chemicals than ethane.
 The reactions of ethene usually involve
addition of a small molecule to produce
a single product.
 For example it reacts with bromine
solution.

Involve the C=C bond being converted
to a single bond.
 Ethanol can be produced by an
addition reaction of ethene and water
using a catalyst to speed up the
reaction.






A type of addition reaction of ethene is involved in
making polyethene.
The number n in this reaction is very large (several
thousand or more).
A molecule made by linking a large number of small
molecules, is called a polymer.
The small molecule (in this case ethene) is called a
monomer.
This type of reaction is known as addition
polymerisation
When the polymer is being formed the
ethene molecules add to the end of
growing polymer chains.
 Ethene is used as a base for other
addition polymerisation reactions. For
example to make PVC and polystyrene.

Page 149
 Question 1-3

Once a more electronegative atom
such as chlorine has been substituted for
a hydrogen atom in an alkane, the
molecule becomes polar.
 Electrons in the carbon-chlorine bond
are attracted towards the more
electronegative chlorine atom.
 This makes the carbon atom at the other
end of the bond susceptible to attack by
negatively charge ions.

For example chloromethane is
converted to methanol when it is
reacted with hydroxide ions.
 The chlorine atom is substituted by an
OH functional group to form methanol.



Alkanols can be produced by addition
reactions of alkenes or substitution reactions of
chloroalkanes.
Ethanol has very different properties from
ethane or chloroethane.
› It is liquid at room temp.
› It is widely used as a solvent in cosmetics and
pharmaceuticals
› It is the active ingredient in alcoholic drinks
› It can act as a depressant on the human body,
slowing reactions and responses.
› Excess ethanol consumption also blocks the
production of antidiuretic hormones, increasing
urination and resulting in dehydration.
Ethanol is soluble in water as a
consequence of its highly polar OH group,
which readily forms hydrogen bonds with
water molecules.
 Alkanols can be turned into amide groups
by reacting ethanol with ammonia.

alumina

CH3CH2OH(g) + NH3(g)

What type of reaction is this?
400°C
CH3CH2NH2(g) + H2O(g)

Alkanols can also be oxidised to form
carboxylic acids:
› CH3CH2OH(aq)

O2 (g)
CH3COOH(aq)
Not all alkanols will oxidise to form
carboxylic acids. Carboxylic acid
synthesise only occurs from primary
alkanols.
Primary
Secondary
Tertiary


Carboxylic acids are weak acids,
reacting with water to form weak acidic
solutions.
CH3COOH(aq) + H2O(l)↔ CH3COO-(aq) + H3O+(aq)
Page 151
 Questions 8, 9 and 10



Esters are a group of organic compounds
responsible for some of the natural and
synthetic flavours and smells in ice-creams,
lollies, flowers and fruits.
Ester
Smell or flavour
Pentyl propanoate
Apricot
Ethyl butanoate
Pineapple
Octyl ethanoate
Orange
2-methyl methanoate
Raspberry
Ethyl methanoate
Rum
Pentyl ethanoate
Banana
Esters composed of small molecules are
volatile and smelly. Esters of larger molecular
size are oils and waxes
Esters are made by a condensation
reaction between carboxylic acids and
an alkanol.
 Reactions that involve the combination
of two reactions and the elimination of a
small molecule, such as water, are
called condensation reactions.

Gently heating a mixture of ethanol and
pure ethanoic acid, with a trace amount
of sulfuric acid as a catalyst, produces
an ester (ethyl ethanoate) and water.
 Ethyl ethanoate is more commonly
known as ethyl acetate, it is used as a
solvent in paints and nail varnish


Below is the general equation for the
esterification reaction involving a
carboxylic acid and an alkanol.
Esters have two-part names.
 The first part derived from the name of the
alkanol from which it is made

› The ‘anol’ part is replace with ‘yl’
› Ethanol becomes ethyl

The second part comes from the carboxylic
acid.
› Where ‘ic acid’ is replace with ‘ate’
› Ethanoic acid becomes ethanoate.

Therefore we have ethyl ethanoate
Read pages 153 – 155 on polyesters
 Page 156
 Questions 11 and 12


Which pathway is the most effective to
make ethanol???
Production chemists need to find the most
efficient pathway for making certain
materials.
 To do this there are certain areas to
consider:

›
›
›
›
›
›
›
How readily available is the starting material
The yield (how much will it produce)
The purity of the final product
Can they minimise any unwanted side products
Can they minimise waste materials
Cost
How long will it take.

What is ethyl propanoate made out of?

Suppose we only had alkanes and
alkenes on hand how could we make
ethyl propanoate?

Ethanol is a two carbon compound that
can be synthesised directly from ethene,
or from ethene via the intermediate
product chloroethane.





Propanoic acid is a carboxylic acid containing
3 carbon atoms.
It is prepared by the oxidation of the primary
alkanol propan-1-ol.
This in turn can be formed by the reaction of 1chloropropane with NaOH.
1-chloropropane is formed by reacting
propane with chlorine.
A number of products will be formed which are
separated by fractional distillation.
The substitution reaction of propane is
chosen rather than an addition reaction
of propene because the addition of HCl
to propene will result in the formation of
unwanted 2-chloropropane.
 Having synthesised ethanol and
propanoic acid we can now prepare
the ester using a condensation reaction.

The purity of the product needs to be
evaluated. For this a lot of companies will
use some of the analysis techniques
looked at in first term.
 The yield must be taken into account, as
not all of the reactants are necessarily
converted to product

% Yield =
Actual mass of product obtained
Theoretical mass of product
Page 159
 Question 15, 17 and 18

A technique used to separate liquids that
have different boiling points.
 Commonly used in a laboratory to separate
volatile liquids from a reaction mixture.
 Industrial application of fractional distillation
include:

› Separation of the fractions from crude oil
› Production of oxygen and nitrogen by the
fractional distillation of liquid air
› Extraction of ethanol from water in the
fermentation of sugar.
The column is packed with glass beads or
has glass shelves, providing a large surface
area upon which the vapours condense.
 There is a temparature gradient up the
fractionating column; the column is cooler
at the top than at the bottom.

Looking at our example of synthesis of
the ester ethyl ethanoate.
 Pure ethyl ethanoate can be extracted
from the reaction mixture by fractional
distillation. Look at the boiling points of
components in the reaction mixture

Component
Boiling Point
CH3COOCH2CH3
57°C
CH3CH2OH
78°C
H2O
100°C
CH3COOH
118°C
The reaction mixture is heated in the
distillation flask.
 The vapour rises up the fractionating
column.
 The temperature at the top of the column
slowing increases until it stabilises at about
57°C, which is the boiling point of ethyl
ethanoate.
 The fraction condensing over a small range
of temperature near the boiling point of
ethyl ethanoate, 55°C - 59°C is collected.

Page 161
 Question 19





Pharmaceutical products are often developed
from substances found in a plant that has been
used as a traditional medicine.
Aspirin is one such substance.
Its origins are from a naturally occurring
substance called salicin found in the leaves
and bark of willow trees and in the herb
medowsweet.
As long ago as 400BC people have
recommended ‘an infusion of willow leaves
and bark to relieve aches, pains, inflammation
and fever.’
The body converts salicin into salicylic
acid and this is the active substance that
helps to reduce fever and acts as a pain
killer.
 Salicylic acid is more effective than
salicin and by 1870 doctors were
prescribing salicylic acid directly.
 A lot of people could not tolerate
salicylic acid directly and it tasted bad.

In 1897, Felix Hoffmann, synthesised an
improved modification of salicylic acid.
 Once he had made salicylic acid he
replaced the hydroxy functional group
with an ester functional group to form
acetylsalicylic acid.
 This is the compound known
commercially as aspirin.

To make aspirin we could add a
carboxylic acid and an alcohol.
 This would form acetylsalicylic acid
 However this is a slow reaction, with a
low yield, as the water formed tends to
drive the reaction backwards.

In an alternative reaction pathway,
which is faster and produces higher
yields, the ethanoic acid is replaced with
ethanoic anhydride (acetic anhydride).
 This is the preferred pathway for aspirin
synthesis


The products, acetylsalicylic acid and
acetic acid have to be separated and
the product purified before it can be put
into tablet form and packaged for sale.
Although aspirin has a –COOH functional
group, pure acetylsalicylic acid is not
very soluble in water.
 Converting the carboxylic acid
functional group into the sodium salt
changes the molecule into an ion and
makes it much more soluble.
 It is used in many headache and cold
remedies in this form.



A recent development is to make a polymer
structure using a condensation reaction
between salicylic acid and 1,8-octanedioic
acid
Pretty much a polymer of aspirin which has a
number of potential advantages:
› It can be used as a controlled-release pain killer
because the polymer breaks down slowly
› Because it is a polymer with a similar molecular
structure to polyesters it can be made into thread
and used to stitch cuts or wounds together.
› It has the potential to be used as a plastic coating
for an injured bone or joint.
Page 225
 Question 1
