Step 3. Loss of a proton from the arenium ion complex
H
SO 3
SO 3
+
Benzenesulphonate ion
+
+ H 2 SO 4
HSO 4
−
_
_
Step 4. Protonation of the benzenesulphonate anion
SO 3
H O
H
H
SO 3 H
Benzenesulphonic acid
+
+ H 2 O
_
+
5.6 Hydrolysis
The term hydrolysis comes from the word ‘hydro’ meaning water and ‘lysis’
meaning breakdown. A hydrolysis reaction is one in which a s bond is
cleaved by the addition of the elements of water to the fragments formed in
the cleavage. A hydrolysis reaction is catalysed by acid, base or hydrolysing
enzyme. For example, the analgesic drug aspirin (acetyl salicylic acid) is
easily hydrolysed in the presence of acid, moisture and heat to form salicylic
acid.
O
OH
O
O
OH
OH
O
Aspirin
(Acetyl salicylic acid)
Salicylic acid
Water, H +
Heat
Glucosidase is a hydrolysing enzyme, and can be used to hydrolyse
various glucosides. For example, salicin, found in willow barks, can be
hydrolysed to salicyl alcohol by enzyme.
CH 2 OH
O-Glucosyl
CH 2 OH
OH
Salicin
Salicyl alcohol
Glucosidase
5.6.1 Hydrolysis of carboxylic acid derivatives
All carboxylic acid derivatives yield parent carboxylic acids on hydrolysis,
catalysed by either an acid or a base. The reactivity toward hydrolysis varies
greatly amongst the derivatives.
260
CH5 ORGANIC REACTIONS