Uses

The essentials

Aldehydes, ketones and carboxylic acids are important in industry, in the home and in medicine. Many are used as solvents, as starting materials for plastics and polymers, and in food and perfume. Several occur naturally: for example vanillin (vanilla), cinnamaldehyde (cinnamon) and many fruit flavours are carbonyl compounds or their esters.

Key points

• Methanal (formaldehyde): a 40% aqueous solution, called formalin, preserves biological specimens. Methanal is used to make Bakelite (phenol–formaldehyde resin) and urea–formaldehyde resins.
• Ethanal (acetaldehyde): a starting material for making ethanoic acid, ethyl ethanoate, vinyl ethanoate and some polymers and drugs.
• Benzaldehyde: used in perfumery and in dye industries.
• Propanone (acetone) and butanone: widely used industrial solvents.
• Methanoic acid: used in the rubber, textile, dyeing, leather and electroplating industries.
• Ethanoic acid: used as a solvent and as vinegar in the food industry (vinegar is a dilute solution of ethanoic acid).
• Hexanedioic acid (adipic acid): a monomer for making nylon-6,6.
• Esters of benzoic acid: used in perfumery; sodium benzoate is used as a food preservative.
• Higher fatty acids: used for making soaps and detergents.

Exam tips

• Learn pairs: formalin–specimen preservation, adipic acid–nylon-6,6, sodium benzoate–preservative, acetone–solvent.

Common mistakes

• Confusing formalin (methanal in water) with formic acid (methanoic acid).