propanoates

Propanoates are the salts or esters of propanoic acid (propionic acid). The propanoate anion has the formula CH3CH2COO− and forms salts with metals such as sodium, potassium, and calcium. When propanoic acid reacts with alcohols, propanoate esters are formed, including methyl propanoate, ethyl propanoate, and longer-chain esters such as propyl propanoate. The term propanoates therefore covers both propionate salts and propanoate esters.

Properties and nomenclature: Propanoic acid is a weak acid, with a pKa around 4.87. Propanoate salts are generally water-soluble, depending on the counterion, while many propanoate esters are relatively nonpolar and volatile. The salts are used as food preservatives; esters are used as solvents, flavors, and fragrance ingredients.

Production: Propanoate salts are prepared by neutralization of propionic acid with bases such as sodium hydroxide or calcium hydroxide. Propanoate esters are obtained by esterification of propionic acid with alcohols in the presence of acid catalysts, or by reaction of acyl chlorides with alcohols.

Applications: In food, calcium propionate and sodium propionate act as mold inhibitors in bread and other baked goods. Propanoate esters such as ethyl propanoate and propyl propanoate are used as flavors or solvents in food and fragrance industries.

Biology and metabolism: Propionate is produced in the gut and during the metabolism of certain amino acids and odd-chain fatty acids. In human metabolism, propionyl-CoA is carboxylated to methylmalonyl-CoA and ultimately converted to succinyl-CoA, feeding into the citric acid cycle. Propanoates thus have both industrial and physiological relevance.