Mechanistic studies on oxidation of L-ascorbic acid by an oxo-bridged diiron complex in aqueous acidic media.
[Fe2(micro-O)(phen)4(H2O)2]4+ (1) (Fig. 1, phen = 1,10-phenanthroline) equilibrates with [Fe2(micro-O)(phen)4(H2O)(OH)]3+ (2) and [Fe2(micro-O)(phen)4(OH)2]2+ (3) in aqueous solution in the presence of excess phen, where no phen-releasing equilibria from 1, 2 and 3 exist. 1 quantitatively oxidizes ascorbic acid (H2A) to dehydroascorbic acid (A) in the pH range 3.00-5.50 in the presence of excess phen, which buffers the reaction within 0.05 pH units and ensures complete formation of end iron product ferroin, [Fe(phen)3]2+. The reactive species are 1, 2 and HA- and the reaction proceeds through an initial 1 : 1 inner-sphere adduct formation between 1 and 2 with HA-, followed by a rate limiting outer-sphere one electron one proton (electroprotic) transfer from a second HA- to the ascorbate-unbound iron(III).
Bhattacharyya
Jhimli
J
Department of Chemistry, Jadavpur University, Calcutta 700 032, India.
Das
Suranjana
S
Mukhopadhyay
Subrata
S
D000143:Acids; D001205:Ascorbic Acid / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007202:Indicators and Reagents; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction
D000143:Acids; D007202:Indicators and Reagents; D058085:Iron Compounds; D001205:Ascorbic Acid