Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L-ascorbic acid

✍ Scribed by Lu-Ming Lin; Ming-Huei Lien; Andrew Yeh

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 155 KB
• Volume: 37
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20052

✦ Synopsis

Abstract

The reduction of Fe(CN)~5~L^2−^ (L = pyridine, isonicotinamide, 4,4′‐bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1–7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H~2~A(k~0~), HA^−^(k~1~), and A^2−^ (k~2~), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given K____a~1~ and K____a~2~, the rate constants are k~0~ = 1.8, 7.0, and 4.4 M^−1^ s^−1^; k~1~ = 2.4 × 10^3^, 5.8 × 10^3^, and 5.3 × 10^3^ M^−1^ s^−1^; k~2~ = 6.5 × 10^8^, 8.8 × 10^8^, and 7.9 × 10^8^ M^−1^ s^−1^ for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO~4~/LiClO~4~, T = 25°C. The kinetic results are compatible with the Marcus prediction. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 126–133, 2005