Abstract
It was found that vitamin B6 is not so stable as had been believed in acid range, in the presence of oxygen, and that it colored with passage of time. The degree of coloration increased with passage of time, the rate constant of coloration was affected by pH of the solution, and the maximum rate constant of coloration in the range of pH 4.5-7 was indicated at around pH 5.5. Coloration of aqueous solution of vitamin B6 due to the hydroxyl in 3-position in its molecule and the maximum coloration at pH 5.5 is believed to be due to vitamin B6 taking a different structure in a solution of that pH.
