Temperature and pressure effects on the kinetics of the Bromate ion-iodide ion-L-ascorbic acid clock reaction

✍ Scribed by István Fábián; Rudi Van Eldik

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 480 KB
• Volume: 27
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550270507

✦ Synopsis

The kinetics of the bromate ion-iodide ion-L-ascorbic acid clock reaction was investigated as a function of temperature and pressure using stopped-flow techniques. Kinetic results were obtained for the uncatalyzed as well as for the Mo(V1) and V(V) catalyzed reactions. While molybdenum catalyzes the Br0;-I-reaction, vanadium catalyzes the direct oxidation of ascorbic acid by bromate ion. The corresponding rate laws and kinetic parameters are as follows. Uncatalyzed reaction: i-2 = kz[Br0,][I-][H+]2, k2 = 38.6 2 2.0 dm9 mol-3 s-l, A H * = 41.3 ? 4.2 kJmol-', A S * = -75.9 t 11.4 Jmol-lK-', A V * = -14.2 2 2.9 cm3 mol-l. Molybdenum-catalyzed reaction: )], kv = 9.1 2 0.6 dm3 mol-I s-', A H * = 61.4 ? 5.4 kJmol-l, A S * = -20.7 5 3.1 Jmol-lK-l, A V * = 5.2 2 1.5 cm3 mol-'. On the basis of the results, mechanistic details of the Br03-I-reaction and the catalytic oxidation of ascorbic acid by BrO, are elaborated.