Esterification

A carboxylic acid reacts with an alcohol to form an ester and water. This is esterification. The mixture is warmed with a strong acid catalyst, usually a few drops of concentrated sulfuric acid.RCOOH + R′OH ⇌ RCOOR′ + H₂OExample: ethanoic acid and ethanol form ethyl ethanoate:CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂OThe water is formed from the OH group of the carboxylic acid and the H atom of the alcohol's OH group. The two molecules are joined by the ester linkage, -COO-.Esterification is reversible, so an equilibrium mixture forms and the yield is never 100%. The ester can be separated from the mixture by distillation, since esters have lower boiling points than the acids and alcohols they come from (they cannot hydrogen bond to each other). Small esters have sweet, fruity smells.Worked example: 6.00 g of ethanoic acid (M_r = 60.0) is esterified with excess ethanol, and 5.28 g of ethyl ethanoate (M_r = 88.0) is collected. Moles of acid = 6.00 ÷ 60.0 = 0.100 mol, so the theoretical yield is 0.100 mol of ester. Moles of ester obtained = 5.28 ÷ 88.0 = 0.0600 mol. Percentage yield = 0.0600 ÷ 0.100 × 100 = 60.0%.