Physicochemical Studies of Vitamin B₁ and Related Substances. III

Quantitative Studies on the Behavior of Thiol-Type Thiamine in Aqueous Solution. (1)

Abstract

The reaction whereby thiamine transits reversibly to the thiol type by alkali in aqueous solution was followed by the potentiometric method. The reaction rate of thiamine salts with alkali or acid is extremely rapid at below pH 7 and slow at above that pH. The rate is greater at higher temperatures and is independent of the thiamine salt used or the kind of acid added. pKa values of various pure thiamine salts were measured at 0° to 50° and the values were found to be smaller at higher temperatures, and independent of the kind of thiamine salts used. From these results, it was found that the equilibrium of thiamine and its thiol type is extremely dynamic and it was assumed that there is a possibility of the presence of the thiol-type thiamine under physiological conditions.