University of British Columbia

CHEM 235

Our sense of smell is an important way of identifying items which may be safe to eator identifying
potential dangers(such as spoiled milk) and many industries are built around it. For example:
(1) The natural gas industry intentionally adds mercaptans as a scent warning of a potential gas
leak. It has a very strong smell similar to “rotten eggs” at very low concentrations (~1 ppb).
(2) The fragrance and flavor industries (includesaromatherapy, perfumes and essential oils) are
built on volatile compounds that are often isolated from natural products by (a) distillation,
(b) mechanical separation (pressing), or (c) solvent extraction. Worldwide, these industries
are estimated to be worthbillions USD.
Esters are a class of compounds which are found in natureand often contribute to the aroma of
nearly all fruits. Ester containing compounds are used as food additives and create a pleasing
fragrance for the consumer (Table 5.1).However, the yield ofisolating volatile oils from natural
products generally ranges from afew tenths of 1% to a few percent; so chemists have devised
synthetic methods to produce these fragrances.While there are many ways to synthesize an ester,
the most popular is the Fischer Esterification. In this reaction, a carboxylic acid and an alcohol
are mixed in the presence of a catalytic amount of strong acid(Scheme1).
Scheme 1. A General Fischer Esterification Reaction
Table 5.1: Common Esters used for Flavours and Fragrances
IUPAC Name Structure Perceived
Smell
Prepared from:
Alcohol Carboxylic acid
3-Methylbutyl ethanoate Bananas 3-Methylbutan-1-ol Ethanoic acid
Benzyl ethanoate Peaches Benzyl alcoho