Esters in Nature and Society

Organic chemistry, the chemistry of carbon containing compounds, has played a major role in our society throughout the years. Most of the common drugs used in the medical profession today, from aspirin to AZT, owe their beginnings to synthetic organic chemistry. Organic synthesis is that branch of organic chemistry that deals with building large, often complex molecules from smaller ones.

Esters encompass a large family of organic compounds with broad applications in medicine, biology, chemistry and industry. The structure is represented by the following arrangements of atoms:
 

Atom arrangement in an Ester (R and R'represent different arrangements of carbon and hydrogen)

Esters are widespread in nature. They occur naturally in plants and animals. Small esters, in combination with other volatile compounds, produce the pleasant aroma of fruits. In general, a symphony of chemicals is responsible for specific fruity fragrances; however, very often one single compound plays a leading role. For example, an artificial pineapple flavor contains more than twenty ingredients but ethyl butyrate is the major component that accounts for the pineapple-like aroma and flavor. It is amazing that so many fragrances and flavors can be prepared by simply changing the number of carbons and hydrogens (the R groups) in the ester.

The following table gives some ester flavors and fragrances (notice the similarities/differences in the R groups):
Name Chemical Structure Flavor or Fragrance
Propyl acetate
Pears
Octyl acetate
Oranges
Isoamyl acetate
Banana
Ethyl Butyrate
Pineapple
Butyl acetate
Apple
Methyl trans-cinnamate
Strawberry

Some esters play an important role in insect communication. Isoamyl acetate, the main component of banana aroma, is also the alarm pheromone of the honeybee. (Z)-6-dodecen-4-olide, a circular ester, is the "social scent" of the black-tailed deer. Circular esters (called lactones) are also found in the oily poisonous secretion of termites.

Esters also have remarkable applications in everyday life. Plexiglas is a stiff, transparent plastic made of long chains of esters. Dacron, a fiber used for fabrics, is a polyester ('many esters').
 
Plexiglas
Dacron

Esters derived from p-aminobenzoic acid (PABA) have local anesthetic properties. Benzocaine and procaine are chemicals used in medicinal preparations to alleviate pain caused by skin burns.
 
Benzocaine
Procaine

Hopefully this brief overview of Esters will help you appreciate the diverse nature of aromas and flavors.  We will prepare some of these compounds in the laboratory and compare them to the flavors and fragrances that comprise candies and fruits.  We will be examining the esters using state-of-the-art chemical techniques.  For more information regarding these techniques please visit the following web site - Mass Spectrometry.