Protein Chemistry - Part 1 - General Protein Chemistry - Ashmarin, I. P. 1968

Chemical Composition of Proteins
Chemical Reactions of Amino Acids
Reactions of the Carboxyl Group

Preparation of esters. The most characteristic reactions of carboxyl groups are Esterification with methyl or ethyl alcohol, carried out in a solution of absolute alcohol in the presence of dry hydrogen chloride:

Class="center">

This reaction invariably yields hydrochloride salts of amino acid esters:

Amino acid esters can be distilled without decomposition. To achieve this, their salts are decomposed at low temperatures using an alkali:

Following this, the free amino acid esters are extracted with ethyl ether, which is subsequently distilled off, after which The amino acid esters undergo fractional distillation at a relatively low Temperature and reduced pressure. This method was first employed by Fischer to separate Amino Acids from protein hydrolysates.

Decarboxylation. Gentle heating of amino acids in an inert solvent typically results in decarboxylation—The formation of amines containing one less carbon atom:

H₂N—CHR—COOH → H₂N—CH₂R + СO₂

These amines are also produced through the action of specific Decarboxylases, synthesized by various Bacteria, on amino acids. Currently, decarboxylases are known for Lysine, Histidine, Tyrosine, Arginine, phenylalanine, and glutamic acid.