Saponification

Under hydrolysis ( saponification lat ) is defined as the hydrolysis of an ester by the aqueous solution of a hydroxide, such as by sodium hydroxide, or by special enzymes esterases. It is in contrast to the acidic ester hydrolysis ( the reverse reaction of esterification) irreversible because the quantity needed for the esterification of the carboxylic acid proton lacking. As products of the reaction caused the alcohol and the salt of the acid ( carboxylate ion ), which composed of the esters. In a broader sense, each hydrolysis is called saponification.

Mechanism of the hydrolysis of carboxylic esters

The saponification is part of the addition-elimination mechanism.

The hydroxide (1) engages the ester (2) to nucleophilic. It forms an ortho-carboxylic acid monoester anion ( 3). The alkoxide ion ( 5) is cleaved to form a carboxylic acid ( 4). Finally: proton transfer from the acid to the alkoxide ion to form the carboxylate (6) and the alcohol ( 7) ( irreversible step of saponification). When the hydroxide (1) is derived from the sodium hydroxide solution, a sodium cation, the counter ion of 6, starting from potassium hydroxide would be analogous to the potassium salt form of the carboxylic acid.

Use

Originally, the saponification described merely the basic ester hydrolysis of triglycerides, such as animal fats or vegetable oils with alkali, especially sodium hydroxide solution or potassium hydroxide solution, in the soap making. Here, the trivalent alcohol glycerol and the respective alkali metal salts of esterified fatty acids in the fats occurring arise. The salts of the fatty acids are called soaps. The saponification with sodium hydroxide solution provides core soap (a soap sodium, so the sodium salts of fatty acids) with caustic potash soft soap ( a potassium soap, so potassium salts of fatty acids).

A chemical indicator in the fat analysis is the saponification number.