Learning Objectives To identify and describe the substances from which most esters are prepared. Some esters can be prepared by esterification, a reaction in which a carboxylic acid and an alcohol, heated in the presence of a mineral acid catalyst, form an ester and water: The reaction is reversible. As a specific example of an esterification reaction, butyl acetate can be made from acetic acid and 1-butanol. A Closer Look: Condensation Polymers A commercially important esterification reaction is condensation polymerization, in which a reaction occurs between a dicarboxylic acid and a dihydric alcohol (diol), with the elimination of water. Such a reaction yields an ester that contains a free (unreacted) carboxyl group at one end and a free alcohol group at the other end. Further condensation reactions then occur, producing polyester polymers. The most important polyester, polyethylene terephthalate (PET), is made from terephthalic acid and ethylene glycol monomers: Polyester molecules make excellent fibers and are used in many fabrics. A knitted polyester tube, which is biologically inert, can be used in surgery to repair or replace diseased sections of blood vessels. PET is used to make bottles for soda pop and other beverages. It is also formed into films called Mylar. When magnetically coated, Mylar tape is used in audio- and videocassettes. Synthetic arteries can be made from PET, polytetrafluoroethylene, and other polymers. Reactions to Prepare Esters Esterification : Description : This is the most common method, involving the reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst (usually concentrated sulfuric acid). Example : Ethyl acetate can be prepared by reacting acetic acid with ethanol: CH 3 ​COOH + CH 3 ​CH 2 ​OH → CH 3 ​COOCH 2 ​CH 3 ​+ H 2 ​O Acyl Chloride Method : Description : Esters can also be synthesized by reacting an alcohol with an acyl chloride (acid chloride). This method is often faster and more efficient than esterification. Example : Ethyl acetate can be prepared by reacting ethanol with acetyl chloride: CH 3 ​COCl + CH 3 ​CH 2 ​OH → CH 3 ​COOCH 2 ​CH 3 ​ + HCl Acid Anhydride Method : Description : Another method involves the reaction of an alcohol with an acid anhydride. This method is useful for preparing esters without producing water as a byproduct. Example : Ethyl acetate can be prepared by reacting ethanol with acetic anhydride: (CH 3 ​CO) 2​ O + CH 3 ​CH 2 ​OH → CH 3 ​COOCH 2 ​CH 3 ​+ CH 3​ COOH Transesterification : Description : This reaction involves exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. It is commonly used in biodiesel production. Example : Methyl acetate can be converted to ethyl acetate by reacting with ethanol: CH 3 ​COOCH 3 ​+ CH 3 ​CH 2 ​OH → CH 3 ​COOCH 2 ​CH 3 ​ + CH 3​ OH These methods highlight the versatility in ester synthesis, allowing for the preparation of a wide range of esters with varying properties and applications 1 2 3 .