4.3.13 Carboxylic acid derivatives
Carboxylic acid derivatives are compounds that possess an acyl group
(RÀ ÀCÀ À
À À O) linked to an electronegative atom, e.g. À ÀCl, À ÀCO 2 R, À ÀOR
or À ÀNH 2 . They can be converted to carboxylic acids via simple acidic or
basic hydrolysis. The important acid derivatives are acid chlorides, acid
anhydrides, esters and amides. Usually nitriles are also considered as
carboxylic acid derivatives. Although nitriles are not directly carboxylic
acid derivatives, they are conveniently hydrolysed to carboxylic acids by
acid or base catalysts. Moreover, nitriles can be easily prepared through
dehydration of amides, which are carboxylic acid derivatives.
R C N
R C O
O
C
O
R
R C Cl
O
R C OR'
O
R C NHR'
O
Ester
RCO 2 R'
Amide
RCONH 2
Nitrile
RCN
Acid anhydride
(RCO) 2 O
Acid chloride
RCOCl
Reactivity of carboxylic acid derivatives
The carboxylic acid derivatives vary greatly in their reactivities in the acyl
substitution reactions. In general, it is easy to convert more reactive
derivatives into less reactive derivatives. Therefore, an acid chloride is
easily converted to an anhydride, ester or amide, but an amide can only be
hydrolysed to a carboxylic acid. Acid chlorides and acid anhydrides are
hydrolysed easily, whereas amides are hydrolysed slowly in boiling alkaline
water.
R C OH
O
R C Cl
O
R
C
O
R C O
O
R C NH 2
O
NaOH, heat
H 2 O
Fast
Slow
Carboxylic acid
or
Acid chloride
Acid anhydride
1 o Amide
The reactivity of carboxylic acid derivatives depends on the basicity of the
substituent attached to the acyl group. Therefore, the less basic the
substituent, the more reactive is the derivative. In other words, strong
bases make poor leaving groups. Carboxylic acid derivatives undergo a
variety of reactions under both acidic and basic conditions, and almost all
involve the nucleophilic acyl substitution mechanism (see Section 5.5.5).
R C Cl
O
R C O
O
C
O
R'
R C OR'
O
R C NH 2
O
R C O
O
Less basic
leaving group
More reactive
derivative
RO
_
Cl
_
RCO 2
_
NH 2
_
94
CH4 ORGANIC FUNCTIONAL GROUPS
Carboxylic acid derivatives are compounds that possess an acyl group
(RÀ ÀCÀ À
À À O) linked to an electronegative atom, e.g. À ÀCl, À ÀCO 2 R, À ÀOR
or À ÀNH 2 . They can be converted to carboxylic acids via simple acidic or
basic hydrolysis. The important acid derivatives are acid chlorides, acid
anhydrides, esters and amides. Usually nitriles are also considered as
carboxylic acid derivatives. Although nitriles are not directly carboxylic
acid derivatives, they are conveniently hydrolysed to carboxylic acids by
acid or base catalysts. Moreover, nitriles can be easily prepared through
dehydration of amides, which are carboxylic acid derivatives.
R C N
R C O
O
C
O
R
R C Cl
O
R C OR'
O
R C NHR'
O
Ester
RCO 2 R'
Amide
RCONH 2
Nitrile
RCN
Acid anhydride
(RCO) 2 O
Acid chloride
RCOCl
Reactivity of carboxylic acid derivatives
The carboxylic acid derivatives vary greatly in their reactivities in the acyl
substitution reactions. In general, it is easy to convert more reactive
derivatives into less reactive derivatives. Therefore, an acid chloride is
easily converted to an anhydride, ester or amide, but an amide can only be
hydrolysed to a carboxylic acid. Acid chlorides and acid anhydrides are
hydrolysed easily, whereas amides are hydrolysed slowly in boiling alkaline
water.
R C OH
O
R C Cl
O
R
C
O
R C O
O
R C NH 2
O
NaOH, heat
H 2 O
Fast
Slow
Carboxylic acid
or
Acid chloride
Acid anhydride
1 o Amide
The reactivity of carboxylic acid derivatives depends on the basicity of the
substituent attached to the acyl group. Therefore, the less basic the
substituent, the more reactive is the derivative. In other words, strong
bases make poor leaving groups. Carboxylic acid derivatives undergo a
variety of reactions under both acidic and basic conditions, and almost all
involve the nucleophilic acyl substitution mechanism (see Section 5.5.5).
R C Cl
O
R C O
O
C
O
R'
R C OR'
O
R C NH 2
O
R C O
O
Less basic
leaving group
More reactive
derivative
RO
_
Cl
_
RCO 2
_
NH 2
_
94
CH4 ORGANIC FUNCTIONAL GROUPS