Chapter 11. POLY- AND HETEROFUNCTIONAL COMPOUNDS

Organic compounds of biological importance contain very often not one, but several functional groups. These groups can be identical or different. For example, ethylene glycol, HOCH₂CH₂OH, and glycerol, HOCH₂CH(OH)CH₂OH, contain two and three hydroxyl groups, respectively. Dicarboxylic acids, such as oxalic, malonic, succinic, have been discussed in the preceding chapter. These compounds are referred to as polyfunctional ones.

A significant importance in living systems belongs to heterofunctional compounds that involve different functional groups in the same molecule.

11.1. TYPES OF HETEROFUNCTIONAL COMPOUNDS

Hydroxyl, amino, oxo, and carboxyl groups are encountered most widely in heterofunctional compounds. A combination of different functional groups results in the formation of mixed classes of organic compounds, some of them are given in Table 11.1 (other combinations are possible, of course).

Table 11.1. Some types of combining functional groups in heterofunctional compounds

At the first approximation, the chemical behavior of heterofunctional compounds can be represented as a sum of properties of separate monofunctional classes. For instance, pyruvic acid (an oxo acid) can be esterified and transformed into derivatives on its carbonyl group. Salicylic and lactic acids (hydroxy acids) form esters in the reaction with alcohols, as well as their hydroxyl group can be acylated or alkylated. The reaction of salicylic acid with acetic anhydride is used to synthesize aspirin (Sec. 9.3.2). Esterification of the same acid with methanol results in the formation of methyl salicylate.

In consideration of various combinations of functional groups we will mainly attend to new properties arising in such combinations without resort to familiar reactions of individual functional groups.