Study on amino acids by using a thermobalance

Abstract

Thermal decompositions of 21 compounds in-cluding refined amino acids derived from proteins, their derivatives and betaine were clarified by use of a “Tokoshi” type thermobalance and the following results were found: (1) On each compound, the loss in weight was represented by a typical curve as indicated in Fig. 2 and carbonization began after passing through 5 steps or more. Namely, aliphatic amino acids, aliphatic hydroxyamino carboxylic acids, aromatic aminocarboxylic acids and sulfur-con-taining aminocarboxylic acids were found more stable when they have short side chains and straight formula. They maintained a stable stage after removal of water, followed by the loss of 2% in weight, passed through another stable stage, then melted at 220°C or above and thereafter decomposed with a rapid loss in weight and finally carbonized. (2) The thermal decomposition of L-Valine and L-aspartic acid showed slower carbonization than the other amino acids. (3) Such compounds as L-lysine hydrochloride dihydrate, sodium L-glutamate monohydrate, L-histidine hydrochloride monohydrate, etc. having the water of crystallization, lost their water at a certain temperature and turned into a stable anhydrate. (4) The thermal decomposition temperatures of all amino acids examined were lower than heretofore reported values. (5) Although L-histidine hydrochloride mono-hydrates recrystallized from different solvents showed the same [α]D20, they showed different aspects of thermal decomposition. © 1960, The Japan Society for Analytical Chemistry. All rights reserved.