CARBOXYLIC ACIDS & THEIR DERIVATIVES
Alkanoic (Carboxylic) Acids:
General Formula: R-COOH
Naming:
Suffix -anoic acid
CH3COOH ethanoic acid
CH2ClCH2COOH 3-chloropropanoic acid
General:
Organic acids contain a carbonyl group (C=O) and a hydroxyl group
(-OH) together on the end carbon.
 Low mass carboxylic acids are oily liquids with a strong smell and
are miscible with water.

Higher mass carboxylic acids are waxy solids with no smell and are
not miscible with water.

Carboxylic acids have significantly higher boiling points than their
corresponding alcohols or alkanes.
Preparation:
 can be made by the oxidation of primary alcohols (those alcohols
with the -OH group on the end carbon). An oxidising agent such as
acidified potassium dichromate or acidified potassium
permanganate may be used.
can also be prepared using certain bacteria. Vinegar is made by
fermenting sugar (from barley, apple juice or whey) to make
ethanol, then oxidising the ethanol to ethanoic (acetic) acid, using a
special bacteria.
Reactions:
Organic acids are weak acids. They react with bases, carbonates and
reactive metals like inorganic acids, only more slowly. The H from the -OH
group is lost forming RCOO - and H+. The name -oic acid changes to anoate ion. e.g. the ion formed from methanoic acid (HCOOH) is the
methanoate ion (HCOO -).
e.g.
 Carboxylic acids also react with alcohols to form esters and water:
methanoic acid
ethanol
ethyl methanoate
water
The reaction requires an acid catalyst. Usually a drop of concentrated sulfuric
acid is used (it also acts as a dehydrating agent, uses up the water & speeds
up the reaction).
Derivatives of Carboxylic Acids include acid (acyl) chlorides, esters, amides
and amino acids.
Acid (Acyl) Chlorides:




Derived from carboxylic acids with a chlorine atom replacing the
hydroxyl group (-OH) of the carboxylic acid COOH group.
COOH
COCl
Because of their high reactivity acyl chlorides are not found in nature.
They are formed by nucleophilic substitution of carboxylic acids using
PCl3, PCl5 or SOCl2.
the IUPAC name for acid chloride is alkanoyl chloride.
R
Acid chloride
functional group
C
Cl






O
naming follows the usual rules: e.g. CH3COCl is ethanoyl chloride,
CH3CH2COCl is propanoyl chloride.
Acid chlorides have low melting and boiling points as there is no
hydrogen bonding between molecules.
They exist as pungent smelling, fuming liquids.
They are highly reactive because the carbon of the acid chloride
group is attached to two very electronegative atoms, Cl and O. This
means there is a relatively large + charge on the carbon atom, and it
is therefore open to attack by nucleophiles.
The reactions that acid chlorides undergo are nucleophilic
substitutions.
With water: acid chlorides react violently with water to form a
carboxylic acid and hydrogen chloride. The hydrogen chloride
dissolves in moist air to form droplets of hydrochloric acid. This is the
fumes that are given off by acid chlorides.
CH3COCl + HOH

CH3COOH + HCl
With ammonia: acid chlorides react readily with ammonia to form
amides and ammonium chloride:
CH3COCl + HNH2 + NH3
CH3CONH2 + NH4Cl
Ethanoyl
chloride
2NH3
ammonia
ethanamide ammonium
chloride

with aminoalkanes: acid chlorides react with primary aminoalkanes
forming secondary amides and hydrogen chloride:
CH3COCl + 2CH3CH2NH2
CH3CONHCH2CH3 + C2H5NH3Cl

with alcohols: acid chlorides react readily with alcohols to form an
ester and hydrogen chloride. This is often a preferred way to prepare
an ester as it needs no catalyst.
CH3COCl + C2H5OH
CH3COOC2H5 + HCl

Reaction Summary for Ethanoyl Chloride:
Ethyl ethanoate
Ethanoic acid
Ethanoic acid
PCl5 or
SOCl2
Ethanoyl
chloride
Ethanamide
N-ethyl ethanamide
Esters:
Esters contain the functional group COO.
O
R
C
O
R'
R and R’ are alkyl chains. E.g. CH3COOCH2CH2CH3
Naming:
Name the part of the molecule that comes from the alcohol first,
like a side chain (e.g. ethyl). Then name the part that comes from the acid,
like an acid ion (e.g. methanoate)
CH3CH2CH2COOCH2CH3
ethyl butanoate
General:

Esters have lower melting and boiling points than the carboxylic
acid and alcohol from which they were formed.

Esters are not very soluble in water except for methyl
methanoate.

Low mass esters are volatile with distinctive, often fruity odours.

Used as solvents, perfumes and in flavourings. The scents of
many flowers are due to esters.

Higher mass esters are waxy solids with little odour. Complex
esters are contained in fats and oils.
Preparation of esters
Esters are produced by esterification reactions. These are condensation
reactions involving an alcohol and a carboxylic acid (with conc, H2SO4 as
catalyst) or an alcohol and an acid chloride.
a) carboxylic acid and alcohol – heated under reflux with conc. Sulfuric
acid as catalyst. Excess acid is then neutralised with sodium carbonate,
and anhydrous magnesium sulfate is added to remove excess water.
Because the esters are more volatile than the rest of the mixture they can
be removed by fractional distillation.
b) acid chloride and alcohol – acid chloride dropped into pure alcohol in a
fume cupboard. Reaction is fast and yield is high. No heat or catalyst
required. Most efficient way to prepare esters.
Hydrolysis of esters:
This is the reverse of esterification – the ester is split into two smaller
molecules. Under acidic conditions the product is an alcohol and a carboxylic
acid.
Under basic (alkaline) conditions the products are an alcohol and a
carboxylate ion/salt.
More product is favoured under alkaline conditions since the alkali shifts the
equilibrium in favour of the more unreactive carboxylate salt.
The alkaline hydrolysis of esters is known as saponification. Soap making is
the saponification of triesters of glycerol.
The carboxylate salt, sodium stearate is what we know as soap. Other long
chain carboxylate salts of sodium are also used as soap.
Amides:
The standard IUPAC naming system for amides uses the term alkanamides.
The functional group is:
O
R
C
Amide group
NH 2
Classification of amides:
Amides are classified as primary, secondary of tertiary, like amines,
depending on the number of carbons bonded to the nitrogen, in the amide
group.
 Primary – ethanamide - CH3CONH2
 Secondary – N-methylethanamide – CH3CONHCH3
 Tertiary - N,N-dimethylethanamide – CH3CON(CH3)2
General properties of amides:
Except for methanamide, all amides :
 Are white crystalline solids
 Have high melting points due to hydrogen bonding of the carbonyl
oxygen of one amide molecule to hydrogen on the nitrogen atom
of a neighbouring amide molecule.
 Tend to be soluble in organic solvents. The lower molecular mass
amides are water soluble.
 Are usually odourless – although pure methanamide smells like
‘mice’.
Preparation of amides:
Primary amides can be prepared by:
Heating a carboxylate salt e.g.
Reacting an ester with concentrated aqueous ammonia
CH3CONH2 + H2O
Reacting an acid chloride with concentrated aqueous ammonia
CH3CONH2 + HCl(g)
(This is the quickest way of preparing a primary amide)
Chemical Properties:
 Amides are such weak bases they are neutral to indicators and
are insoluble in hydrochloric acid i.e. no salt forms.
Hydrolysis of amides – amides are hydrolysed by heating in either acidic or
alkaline conditions
acid hydrolysis form the carboxylic acid and ammonium ions
alkaline hydrolysis produces the carboxylate ion and ammonia
Amino acids:
Amino acids contain two functional groups:
 An amino group -NH2

A carboxylic acid group –COOH
Naturally occurring amino acids always have the same basic configuration:
R = H, SH, CH3 etc
2
1
The amino group is attached
acid to the carbon atom (C2) that is next to the
carboxylic acid carbon. The carboxylic acid carbon is always the first carbon
when numbering for naming amino acids.
Biologists
refer to the C2 carbon as the alpha () carbon atom. Naturally
amino
occurring amino acids are all -amino acids. -amino acids have the amino
group attached to the third carbon.
Glycine – aminoethanoic acid
This amino acid has an H as the R group on the C2 carbon. In this molecule
the C2 carbon is bonded to :

One carboxylic acid group

One amino group

Two hydrogen atoms
Alanine – 2-aminopropanoic acid
This amino acid has CH3 as the R group on the C2 carbon. The C2 carbon in
alanine is bonded to four different groups or atoms:

One carboxylic acid group

One amino group

One hydrogen atoms

One methyl group
This means that the C2 carbon is
Alanine is a chiral molecule.
All amino acids, apart from glycine, form optical isomers or enantiomers.
In nature only one type of optical isomer of an amino acid can be used by
living organisms.
mirror
H
H
C*
H2N
C*
COOH
HOOC
CH3
NH2
CH3
mirror