Acta Phys. -Chim. Sin. ›› 2005, Vol. 21 ›› Issue (03): 283-286.doi: 10.3866/PKU.WHXB20050311

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Kinetics of the Complex Reaction of Ascorbic Acid with Hydrogen Peroxide Catalyzed by CTAB

MENG Xiang-Guang; LI Jian-Mei; PANG Qin-Hui; ZHU Jie; ZANG Rong-Rong; ZENG Xian-Cheng   

  1. College of Chemistry, Sichuan University, Chengdu 610064
  • Received:2004-08-09 Revised:2004-10-19 Published:2005-03-15
  • Contact: ZENG Xian-Cheng E-mail:zengxc@scu.edu.cn

Abstract: Kinetics of the reversible-consecutive reaction of ascorbic acid H2A with hydrogen peroxide was studied in phosphate buffer(μ=0.1 mol•L-1) at pH 7 and 25 ℃ with conduction calorimeter. The apparent rate constants of this reaction, k1, k-1 and k2, were measured at different concentrations of cetyltrimethylammonium bromide(CTAB). The results indicated that the apparent rate constants of the reaction, k1, k-1 and k2, were remarkably affected by the cationic surfactant CTAB. k1 initially increased, up to a maximum, and then fell off with increasing CTAB micellar concentration, while k-1 was hardly affected by CTAB of low concentrations(< 2 mmol•L-1) and increased when the CTAB concentration was more than 5 mmol•L-1; with the increasing concentration of CTAB, k2 decreased before cmc, then increased up to a maximum, and at last fell off. CTAB micelles of low concentration had almost no influence on the activity of intermediate , but high concentrated micelles could promote the dismutation of and inhibit its oxidation reaction. Electrostatic effect, hydrophobic effect, and local concentration effect of CTAB premicelles and micelles were the main factors influencing this reversible-consecutive reaction.

Key words: Reversible-consecutive reaction, Thermokinetics, Ascorbic acid,  Micellar catalysis, Free radical reaction