Home > Chemistry > Core > The acidic environment > The acidic environment: 5. Esterification
9.3 The acidic environment: 5. Esterification
Extract from Chemistry Stage 6 Syllabus (Amended October
2002). © Board of Studies, NSW.
Background: Living things store much of
their energy as esters, known as fats or oils. Many of the
flavours and odours of fruits are esters. The formation and
breakdown of esters are reactions that occur frequently in
the differences between the alkanol and alkanoic acid
functional groups in carbon compounds
A functional group is an atom or group of atoms that
reacts in a characteristic way in different carbon
- The hydroxy functional group,-OH, in alkanols provides
their characteristic properties, such as high melting
points and boiling points.
- The carboxylic acid functional group, -COOH, in
alkanoic acids can lose a hydrogen ion and behave as a weak
- The diagram below shows a common way to illustrate the characteristic structure of the members of a homologous series. The R group represents a carbon chain of unspecified length. This is a skeletal formula as the carbon atom within the functional group (COOH) is not labelled with a C. In this type of formula the junction of bonds with no letter indicating the atom present is assumed to be a carbon and hydrogens bonded directly to carbon atoms are not shown. Note: it is best in HSC Chemistry to always draw full structural formulae but it is useful to be able to interpret other representations.
the difference in melting point and boiling point caused by
straight-chained alkanoic acid and straight-chained primary
Straight-chained structures do not have any branches on
the hydrocarbon chain.
A primary alkanol has the -OH group at the end of
the hydrocarbon chain.
The high melting points and boiling points in alkanols is
due to hydrogen bonding between the O in one molecule and
the H of an-OH in a nearby molecule.
The ability of the-COOH group to be involved in two
hydrogen bonds gives an alkanoic acid an even higher
boiling point than that of a similar sized alkanol. Two
hydrogen bonds can occur between a pair of alkanoic acid
data, plan, select
equipment and perform a
first-hand investigation to prepare an ester using
- Use a chemical data book to identify
the boiling points of the alkanol, alkanoic acid, ester and
- Plan the investigation by considering
if the boiling points of the reactants and products are
sufficiently different for you to easily separate the ester
from the rest of the reaction mixture by fractional
distillation. Consider the effect of using more than a few
drops of concentrated sulfuric acid catalyst and how this
might complicate the separation. Consider if you would be
better off using differences in densities and water
solubility of the components to separate the ester.
Choose suitable reflux equipment:
A large test tube fitted with a cork through which a
pipette has been passed upside-down. The test tube could
be heated in hot water; air circulating around the
pipette acts as a condenser.
Ground-glass joint equipment, including a water-cooled
condenser, positioned vertically, and a reaction vessel
heated by an electric heater.
- Perform the investigation, making sure
you identify and use safe work practices. For instance, if
using the first method above, make sure the pipette is not
blocked by pieces of cork, otherwise you risk an
esterification as the reaction between an acid and an alkanol
using equations, examples of esterification
- An acid, containing the-COOH functional group, can
react with an alkanol, containing the-OH functional group,
to produce an ester and water.
- If an oxygen-18 isotope, O, is used in
the alkanol only, it is found in the ester, but not in the
water product. Use of this tracer shows that the O in water
comes from the acid.
- The reaction is reversible and comparable quantities of
alkanol, acid, ester and water are present at equilibrium.
- Common names, rather than systematic names, are often
used to obtain the ester name:
Common: methyl alcohol acetic
methyl acetate water
Common: ethyl alcohol
the IUPAC nomenclature for describing the esters
produced by reactions of straight-chained alkanoic acids from
C1 to C8 and straight-chained primary alkanols from C1 to
The naming of esters follows a straight forward pattern
using IUPAC nomenclature.
The table below will give you a start. Copy it and attempt
to complete it.
There is no need to learn all the ester names. Just
remember the naming pattern you used.
Did you note that the alkanol always forms the first part
of the ester's name having its ending changed from
'...anol' to '...yl' and the alkanoic acid
forms the second part of the ester's IUPAC name with its
ending changing from '...oic acid' to '...
naming Alkanols AUS-e-TUTE
the purpose of using acid in esterification for
the need for refluxing during esterification
Esterification requires heat for the reaction to reach
equilibrium within an hour, rather than after many days.
When the reaction mixture is heated, volatile components,
such as the reactant alcohol and the product ester, could
escape. This problem is overcome by refluxing the
- A condenser is placed on top of the reaction vessel so
that any volatile components pass into the condenser. The
condenser can be water or air-cooled and causes the
volatile components to condense back to liquid and fall
back into the reaction mixture.
- Refluxing also improves the safety of the operation, as
the volatile components are flammable.
information from secondary sources to identify
the uses of esters as flavours and perfumes in processed
foods and cosmetics
You can process information from the
labels on processed food containers and cosmetics. You
should be able to recognise and record the names of
esters they contain. Remember the name of an ester is
usually in two words:
- the first word is derived from the alcohol and ends
- the second word is derived from the acid and ends
- Alternatively, you could look in a list of food
additives or cosmetic ingredients and try to recognise
- Having identified the names of some esters, you should
then use a chemical dictionary, chemical encyclopedia or
Internet search engine to find uses of those esters.
some examples of the occurrence, production and uses of
- Use a chemical dictionary, chemical encyclopedia or
Internet search engine to find occurrence, production and
uses of esters.