Carboxylic Acids
Carboxylic acids with up to 4 carbon chains are soluble in
water. Highly polar C=O and O-H bonds allow the
carboxylic acid molecules to form hydrogen bonds with
polar water molecules.
Solubility decreases as the number of carbon atoms
increases. This is because longer hydrocarbon chains of
the molecules do not form hydrogen bonds with water –
they are hydrophobic. They prevent the formation of
hydrogen bonds between water and hydrophilic carboxylic
acid functional group.
δδ+
δδ+
Reactions of Carboxylic Acids
Acid + Base  Carboxylate Salt + Water
Acid + Metal  Carboxylate Salt + Hydrogen
Acid + Carbonate  Carboxylate Salt +Water +Carbon Dioxide
Esters
Esters contain the functional group ‘COOC’. They are formed in esterification
reactions. Esterification reactions are condensation reactions because water is
released. There are 2 ways in which an ester can be formed:
Conc.
1. Carboxylic Acid + Alcohol  Ester + Water
H2SO4
Reflux
+
+
Example: Propanoic Acid + Ethanol  Ethyl Propanoate + Water
2. Acid Anhydride+ Alcohol  Ester + Carboxylic Acid
+
Warm
+
Example: Butanoic Anhydride + Ethanol  Ethyl Butanoate + Butanoic Acid
Hydrolysis of Esters
Hydrolysis uses water to split an ester. It is the reverse reaction of esterification.
1. Acid Catalysed Hydrolysis - Reflux, Sulphuric Acid (Hot Aqueous Acid)
Ester + Water  Carboxylic Acid + Alcohol
+
+
Ethyl Propanoate + Water 
Propanoic Acid + Ethanol
2. Alkaline Catalysed Hydrolysis
[Reflux, Sodium Hydroxide(Hot Aqueous Alkali]
Ester + Hydroxide  Carboxylate Salt+ Alcohol
This reaction occurs in 2 steps:
the ester is hydrolysed with
water from NaOH (aq) and
then the acid is neutralised by
the alkali to produce the salt.
Triglycerides
Animal and vegetable fats and oils are esters of long chain carboxylic acids. The
simplest is a triester known as a triglyceride. Triglycerides are triesters of
glycerol and fatty acids.
Triglyceride
+
Glycerol is an
alcohol– its
systematic name is
propane-1,2,3-triol
Fatty acids are long change
carboxylic acid. Fatty acids can
be saturated (containing C-C
single bonds only) or
unsaturated (containing at least
one C=C double bond)
+ 3 H2O
Triglycerides are
formed in condensation
reactions – when each
fatty acid joins to the
glycerol molecule, 1
water molecule is
release – so 3 are
produced in total.
Triglycerides can be saturated or unsaturated:
 Saturated fats are triglycerides
containing only carbon-carbon
single bonds.
 Saturated fats are derived from
fatty acids that are saturated containing single C-C bonds only
 Saturated fats tend to be solid at
room temperature because they
have stronger intermolecular
forces between molecules which
require more energy to break and
so they have a higher melting
point.
 Animal fats are rich in saturated
fatty acids
 Unsaturated fats are triglycerides
containing at least 1 carbon=carbon
double bond.
 Unsaturated fats are derived from
fatty acids that are unsaturated
- containing at least one C=C double
bond.
 Unsaturated fats tend to be oils at
room temperature because they
have weaker intermolecular forces
between molecules which require
less energy to break and so they
have a lower melting point.
 Vegetable fats are rich in
saturated fatty acids
 Foods high in saturated fats are known to
increase the risk of heart disease by
raising blood cholesterol levels.
 Unsaturated fats are often believed to be
better for us than saturated fats.
Unsaturated fats however can exist in 2
isometric forms: cis and trans.
Trans fats are thought to behave like
saturated fats in the body: they raise Low
Density Lipoprotein levels and so increase the
risk of coronary heart disease and strokes.
Biodiesel is made in a process called
transesterification: Triglycerides in fats
and oils are reacted with methanol or
ethanol in the presence of a sodium or
potassium hydroxide catalyst. Biodiesel
and glycerol are formed:
Lipoproteins are particles that
carry lipids, such as cholesterol
and fats, through the blood.
High Density Lipoproteins (HDLs)
are ‘good’ lipoproteins – they
transport cholesterol out of the
blood
Low Density Lipoproteins (LDLs)
deposit lipids onto the artery wall,
building up fatty acids and
restricting blood flow.
Making Biodiesel
Biodiesel is easily produced suing
waste cooking oil, but naturally
sources of suitable oils also occur in
crops like palm or soya bean and
rapeseed.
Soaring oil prices, the nonrenewable nature of fossil fuels and
the desire to protect the
environment have lead to an increase
in biodiesel, because it is a renewable
source of fuel.
Isomerism
Unsaturated fats can display stereoisomerism.
Stereoisomers are molecules with the same
structural formula but a different arrangement
of atoms in space.
This is dec-4-enoic acid. It can
display cis-trans isomerism
because:
 There is restricted rotation
about a C=C double bond
 There are 2 different atoms or
groups attached to each carbon
in the C=C double bond
 Two of the substituent groups
are the same
There is a difference in melting points of the cis and trans isomers:
 Trans isomer of the unsaturated fatty acid is more linear
 Molecules can pack closer together
 Stronger Van der Waals’ intermolecular forces
 More energy required to break forces between molecules
 Trans form has a higher melting point
 In the cis form, unsaturated fatty acid molecules are more likely to exist as a
liquid at room temperature as they have a lower melting point.