Kinetics of Decomposition of Aspartame Hydrochloride (Usal) in Aqueous Solutions

ABSTRACT A scheme of aspartame hydrochloride (Usal) decomposition in relation to the pH and temperature which takes into account the possibility of phenylalanyl‐aspartic acid dipeptide formation is suggested and experimentally confirmed. Aspartyl‐phenylalanine and diketopiperazine were found to be the main decomposition products. The concentration of diketopiperazine increases and that of aspartyl‐phenylalanine de‐creases with increasing pH. At pH 2.9 less aspartyl‐phenylalanine and more diketopiperazine is formed with increase in temperature; twice the concentration of phenylalanine methyl ester was found at 80° and 90°C when 50% of the Usal present in the medium was decomposed, as compared to that determined at 25° and 40°C. The distribution of the remaining products remained constant over the entire range measured.