Chapter 16 Carboxylic Acids
Various dilute solutions of ethanoic acid
A carboxylic acid contains a carboxyl group,
which is a carbonyl group (C═O) attached
to a hydroxyl group (—OH);
the carbon of the carboxyl group is numbered
position 1
To write the IUPAC names of a carboxylic acid
STEP 1 Replace the e in the alkane name with oic acid.
CH4
Methane
HCOOH
Methanoic acid
CH3-CH3 Ethane
CH3—COOH Ethanoic acid
STEP 2 Locate and name substituents, counting
from the carboxyl carbon as carbon 1.
Alpha hydroxy acids (AHAs)
occur naturally in fruit, milk,
and sugarcane;
they are used in skin care
products
2-hydroxyethanoic acid
2-hydroxypropanoic acid
2,3-dihydroxybutanedioic
acid
2-hydroxybutanoic acid
Benzoic acid is the carboxylic acid that is attached to a benzene ring
the –NH2 group is called amino; 4-aminobenzoic acid is an example of an amino acid
Some common carboxylic acids used as analgesics
Carboxylic acids
are strongly polar
have two polar groups: hydroxyl (−OH)
and the carbonyl (C═O)
Carboxylic acids form very strong hydrogen bonds
with themselves in the absence of water
The smaller carboxylic acids (1-4 carbons) are
quite soluble in water
Carboxylic acids are weak acids that ionize in water to produce carboxylate ions and
hydronium ions
A weak acid is an acid that undergoes the reaction shown above to the extent of about 5%
but will react completely with stronger bases. For example:
C
H
3
—
C
O
O
H
CH3COOH + NaOH
CH3COO– Na+ + H2O
Esters:
HCl + NaOH
CH3CO2H + CH3CH2OH
NaCl + H2O
CH3CO2CH2CH3 + H2O
Aspirin
is used to relieve pain and
reduce inflammation
is an ester of salicylic
acid and acetic acid
Oil of wintergreen
is used to soothe sore
muscles
is an ester of salicylic
acid and methanol
Naming esters
The name of an ester contains the names of the alkyl group from the alcohol
the carbon chain from the acid with -ate ending
Fats are esters of 1,2,3-trihydroxypropane (glycerol) and a long chain fatty acid
O
O
O
CH3(CH2)16
C
O
CH2O
C
CH
O
CH2O
C
Na+
(CH2)16CH3
CH3(CH2)16
C
NaOH
CH2OH
(CH2)16CH3
HO
CH
CH2OH
The fatty acids are not necessarily all the same;
some differ in the number of carbons, some
have double bonds in them (unsaturated fats);
upon hydrolysis they yield the salt of a fatty
acid known as a soap
Soaps have a polar end and a non-polar tail and self
assemble in water in a spherical fashion with the
non-polar ends pointing inward and the polar ends
on the outside. The non-polar ends are good for
dissolving grease and oil. These small spherical
balls are called micelles
O
-