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
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