The Investigation of the Redox Reactions between Ascorbic Acid and Pentacyanoferrate(III) Complexes

• Main Authors: MingHuiLien, 連明惠
• Other Authors: 葉玉堂
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/42078847441605534467

碩士 === 東海大學 === 化學系 === 92 === The oxidation of ascorbic acid by [Fe(CN)5L]2‾(L=py, isn) complexes undergoes outer-sphere electron transfer mechanism. The rate of the reduction depends on the pH of the solution for the reason that ascorbic acid exists in different forms, namely H2A, HA‾ and A2‾, at various pH values. The kinetic studies of the reactions at [H+]= 0.01~0.10 M and pH=4~7.5 yield specific rate constants of reduction as k0(H2A)= 1.8 ( L=py ),7.0 (L=isn)；k1(HA-)=1.6×103 ( L=py ),4.5×103 (L=isn)；k2(A2-)=6.5×108 ( L=py ),8.8×108 (L=isn)M-1s-1,respectively at m=0.10 M HClO4/LiClO4 and T=25℃. Our kinetic results conform with Marcus theory for outer-sphere electron transfer. Moreover, the detailed theoretical analysis indicates that, the tremendously large rate difference with k0:k1:k2~1:103:108, arises predominantly from the equilibrium barrier and the intrinsic reactivities of the different acid forms of the ascorbic acid, and is rather insensitive to the charge effect of the reactants. The stoichiometry for the reduction of [Ru(NH3)5isn]3+ complexes by the quercetin, shows that sure the quercetin is a three electron reductant. The kinetic studies of the reactions at pH＝5.0 yield specific rate constant of reduction k = (1.57±0.02)×104 M-1s-1 at m =0.10 M LiCl and T=25℃.