Chemistry Reference
In-Depth Information
Examples of drugs susceptible to hydrolysis
Figure 8.17 lists examples of the types of drugs containing functional
groups prone to decomposition by hydrolysis. There is insufficient space
to consider each drug in detail, but a few important examples will be
considered.
Aspirin
Aspirin, the widely used analgesic, is the acetyl ester of salicylic acid and is
very susceptible to hydrolysis; moisture in the air is sufficient to bring about
significant decomposition. A bottle of aspirin tablets smells of vinegar
when opened; this is due to the reaction shown in Figure 8.20 taking place
to liberate salicylic and acetic acids. The rate of decomposition is increased
because members of the public often store medicines in a cabinet in the
bathroom, the one room in the house that is almost guaranteed to have a
hot, steamy atmosphere ideal for hydrolysis reactions.
O
O
CH
3
OH
O
H
2
O
COOH
COOH
+
CH
3
C
OH
Aspirin
Salicylic acid
Acetic acid
Figure 8.20
The hydrolysis of aspirin.
Diamorphine
Diamorphine (or heroin) is the diacetyl derivative of morphine and, like
morphine, is used as a narcotic analgesic (Figure 8.21). The two acetyl
groups are important for two reasons; first, they render the molecule more
lipophilic (increasing the partition coefficient), which means that diamor-
phine is absorbed into the central nervous system more rapidly than is
morphine, and in turn results in a faster onset of action than for morphine
(and, sadly, makes the compound a favourite with addicts). The second
aspect of the two acetyl groups is that they are susceptible to hydrolysis, to
yield morphine and two molecules of acetic acid (Figure 8.21).
