Effects of reaction parameters on self-degradation of L-ascorbic acid and self-degradation kinetics.

The degradation behavior of L-ascorbic acid (ASA) was investigated under different parameters of temperature, time, and pH. Higher temperatures and longer times accelerated the ASA degradation. Degradation product distributions changed with different pH values. As solution pH of 4.5 was beneficial for formation of uncolored intermediate products with an absorbance maximum at 294 nm. Formation of brown products was promoted at pH values from 5.8 to 6.8 with an absorbance maximum at 420 nm. Under different pH conditions, volatile products formation varied. Furfural and derivatives of furan were primary products due to the effects of pH. The non-enzymatic selfdegradation behavior of ASA was characteristic of first-order kinetics based on a classic dynamic model. Activation energy values varied under different pH values. An ASA degradation mechanism and pathway are proposed.