Carboxylic Acids

Carboxylic Acids
The functional group in carboxylic acids is called the carboxyl group. A carboxyl group
is a carbonyl group (C = O) with a hydroxyl group (-OH) attached to the carbonyl carbon
atom.
C
O
Representation of a carboxyl group OH or COOH or CO2H
C
O
OH
(R = H, or aliphatic or aromatic hydrocarbon)
Carboxylic acid: R
9.2 Naming Carboxylic Acids
The names of carboxylic acids end in “-oic acid,” indicating the presence of the carboxyl
group, ie: propanoic acid, butanoic acid, pentanoic acid, etc. When naming carboxylic
acids, the “–e” is dropped from the alkane containing the carboxyl group and replaced
with “-oic acid”. The chain is numbered from the carboxylic acid group which is always
located on the first carbon. The location of the functional group is not included in the
name.
Examples:
CH3 - CH2 - COOH
CH3 - CH - CH2 - COOH
CH3
CH3 - COOH CH3 - CH2 - CH2 - COOH
COOH
ethanoic acid propanoic acid
3-methylbutanoic acid benzoic acid
butanoic acid
4 3 2 1
Some members of this class are widely known by their common names. Common names
of acids you should know:
HCOOH
Formic acid Acetic acid
CH3COOH
A solution of acetic acid and water is known as vinegar.
Acidity of Carboxylic Acids
Carboxylic acids are weak acids. When a carboxylic acid is placed in water, the following
equilibrium is established.
RCOOH + H2O RCOO - + H3O +
carboxylic carboxylate
acid ion
Carboxylate ions are named by dropping the –ic ending from the name of the parent acid
and replacing it with –ate.
+ H2O + H3O + CH3COOH CH3COO-
acetic acid acetate ion
Neutralization of Carboxylic Acids (reaction of acids with bases)
Carboxylic acids undergo neutralization reactions with strong bases as you have seen in
unit 6.in a manner similar to that of inorganic acids. Neutralization of carboxylic acids
produce a carboxylic acid salt and water.
CH3COOH + NaOH CH3COO-Na+ + H2O
acetic acid *sodium acetate
carboxylic acid carboxylic acid salt
*Note that carboxylic acid salts are named similarly to other ionic compounds (unit 4).
The cation is named first, followed by the name of the anion.