Esters are defined as molecules consisting of a carbonyl group which is adjacent to an ether linkage. They are polar molecules which are less polar than alcohols but more so than ethers, due to their degree of hydrogen bonding ability. Most often derived from reacting an alcohol with a carboxylic acid, esters are a unique, ubiquitous class of compounds with many useful applications in both natural and industrial processes 1. For example, within mammals, esters are used in triglycerides and other lipids as they are the main functional group attacking fatty acids to the glycerol chain 2. A unique property of esters is their tendency to give off distinct aromas such as the scent of apples (Ethyl caprylate) and bananas (Isoamyl acetate). This is of a unique importance especially in industries that utilize flavors and aromas such as the tobacco, candy and alcohol industry. Consistent research is conducted in order to enhance and increase the effectiveness of esters in these products 3.
The most classic and standard procedure for producing esters is the Fisher-esterification reaction. Discovered in 1895 by German chemists Emil Fischer and Arthur Speier 4, this reaction involves refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. In order to drive the equilibrium towards the products, the water from the dehydration process must be removed and there must be an excess amount of alcohol. A vast range of carboxylic acids may be used for this reaction however the type of alcohols are limited. Primary and secondary alcohols are most frequently used in esterification reactions, tertiary alcohols are steric ally hindered usually resulting in poor yields5 and tend to undergo elimination reactions instead. In this reaction, the acid catalyst serves to increase reaction rate while at the same time remove water formed as a by-product within the reaction.
A common catalyst used in esterification reactions is sulfuric acid, however further research is being done on other potential catalysts such as alkyl amines to enhance yield of products as well as reducing waste and by-products6. In this experiment, the ester of interest will be one that produces the fragrance of grapes. In order to determine the ester that produces this fragrance, a combination of a variety carboxylic acids and alcohols will be subjected to Fischer esterification. In this way, a variety of esters with different fragrances will be made in the hopes that one or more may turn out to be the ester of interest. This experimental technique is known as parallel combinatorial chemistry. In parallel, a variety of compounds are synthesized simultaneously in order to prepare an array of molecules, or a library, from which the properties and usefulness of each compound can be determined.
In this experiment, a small library of esters will be synthesized from varying carboxylic acids and alcohols via Fischer Esterification. The focus of this study was the reaction of ethanol...