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Esters

Esters

Background:


Esters are to carboxilic acids and alcohol, what table salt is to hydrochloric acid and sodium hydroxide. They are the organic salts formed when a carboxilic acid exchanges the loosely held hydrogen ion on its carboxyl group, for the alkyl group of a reacting alcohol. In spite of the parallel between the salts and esters, esters do not dissociate in solution into anion/cation pairs as inorganic salt tend to do.

Esters are widespread in nature. They occur both in plants and in animals. Small esters, in combination with other volatile compounds, produce the pleasant aroma of fruits. Many chemicals in combination are responsible for specific fruity fragrances; however, often a single compound plays the leading role. For example, pineapple flavouring contains more than twenty ingredients but ethyl butyrate is the major component that accounts for what we think of as the pineapple-like aroma and flavor.

Physical Properties:


These salts are non-polar and hence more volatile than the acids from which they formed. In addition they have a tendency to have distinctive odors, many similar to the familiar odors of the fruits and flowers we find in nature.

Uses and Applications:


The relative high volatility of esters make them useful in organic analytical chemistry. Unknown organic acids with low volatility can very often be esterified into a volatile ester. The ester in turn can be analysed using gas or liquid chromatography, or mass spectrometry.

Many esters are used as artificial flavourings and fragrances due to their have distinctive odors.

Naming Conventions:


Esters can be produced by an equilibrium reaction between an alcohol and a carboxylic acid. The ester is named according to the alcohol alkyl group and then the name of the acid while changing the from "-ic acid" to "-onate." For example:

H-COO-CH3 is either as methyl formate or methyl methanoate.

Esters derived from the simplest carboxylic acids use the traditional names as recommended by IUPAC,for example, formate, acetate, propionate, butyrate. For esters derived from larger chain acids, it is preferable to use the alkane name with an "-oate" ending.

Bibliography:


Wikipedia article on esters
An article on esters in nature

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