Hydrolysis, esterification, interesterification, etc

Ester or lipid hydrolysis is most conveniently effected in the laboratory by refluxing with aqueous ethanolic alkali. Acidification of the hydrolysate liberates fatty acids which can be extracted with hexane or other organic solvent. Non-acidic compounds (unsaponi-fiables) such as hydrocarbons, long-chain alcohols, sterols and glycerol ethers will also be present in the organic extract, but glycerol remains in the aqueous phase. The hydrolysis may be effected quantitatively for determination of saponification equivalent or saponification value (Section 6.2.10). 

The production of soap by alkaline hydrolysis (saponification) is usually carried out around 100 °C, with glycerol being recovered as a second commercial product. Sodium and potassium salts are used as soaps (Section 5.9). Salts of other metals are used to promote polymerization of drying oils, in the manufacture of grease and lubricants, and as ingredients in plastics formulations. 

Partial hydrolysis of lipids occur during digestion under the influence of lipases (Sections 11.2 and 11.3). Lipases present in seeds also promote hydrolysis, so that most extracted lipids contain some free acid and some partial glycerides. This is an undesirable change, since removal of free acid during processing is accompanied by some loss of fat. Lipolysis can be minimized by inactivation of the lipase before extraction. Enzymic deacylation is also the basis of some valuable analytical techniques (Section 6.2.17). 

Esters can be prepared by interaction of a carboxylic acid or an acyl derivative with an alcohol or its equivalent (esterification) or by reaction of an ester with an alcohol (alcoholysis), an acid (acidolysis) or 

Alternative esterification procedures include the interaction of alkyl halide with the anion of the acid in the form of a salt (silver, sodium, potassium, calcium, tetramethylammonium). 

---