Esters: preparation, properties and uses
Substances formed from a carboxylic acid and an alcohol with loss of water are esters; the general formula is R–COO–R′. Esterification is reversible and goes with concentrated H₂SO₄: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. The systematic name is the alcohol radical name plus the acid name with “-oate”: ethyl ethanoate (ethyl acetate), methyl methanoate (methyl formate); the traditional name is “ethyl ester of acetic acid”. Esters are interclass isomers of carboxylic acids with the same carbon number: C₂H₄O₂ — acetic acid and methyl formate; C₃H₆O₂ — propanoic acid, ethyl formate, methyl acetate. Lower esters are fragrant volatile liquids lighter than water: ethyl butanoate smells of pineapple and isoamyl acetate of banana, so they are used in food, perfumery and as solvents. The main chemical property is hydrolysis: reversible in acid (CH₃COOC₂H₅ + H₂O ⇌ CH₃COOH + C₂H₅OH), irreversible in alkali, giving the salt of the acid and the alcohol (CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH); alkaline hydrolysis is called saponification.
Discuss what gives fruits their smells: make a table of esters (name, smell, formula). No chemical experiments; concentrated sulfuric acid is handled by the teacher only.