Esters almost uniformly have pleasant odors, in sharp contrast to the pungent and rancid odors of carboxylic acids. Many of our natural and artificial flavorings and perfumes are esters, and some are represented at the beginning of the chapter.

The change that only a few atoms can make in taste or odor is remarkable. For example, methyl butyrate contributes to the taste of apples and pineapples, and ethyl butyrate to pineapples and peaches. Other butyric acid esters smell like pineapples, pears, and flowers in general. In contrast, the parent butyric acid has the stench of rancid butter. Amyl valerate has the odor of apples, but valeric acid smells like manure.

The odor or taste of any real fruit or flower comes from a blend of several esters, any one of which by itself seems artificial. Good natural flavors, like good wines, are complicated mixtures that the chemist is unable to duplicate perfectly in the laboratory.


Right (from top): Methyl salicylate (wintergreen), Amyl salicylate (clover)