The hydroxylation of the salicylate anion by a Fenton reaction and T-radiolysis: a consideration of the respective mechanisms.
The yield of 2,3- and 2,5-dihydroxybenzoates (dHB's) from the reaction of .OH radicals with salicylate (SA) ions has been measured as a function of pH and in the presence of oxidants. Under steady-state radiolysis conditions, the production of these products occurs via the reactions .OH + SA----HO-SA. (radical adduct) HO-SA. H+.OH+----2-carboxyphenoxyl radical (SA.) + H2O HO-SA. + SA.----2,3-/2,5-dHB + SA The addition of the oxidants O2, Fe3+ edta, or Fe(CN)63- increases the relative yield of 2,5-dHB/2,3-dHB from about 0.2 to 1. A model to account for this effect is presented. Steady-state radiolyses of 3- and 4-hydroxybenzoate give dihydroxybenzoate products consistent with the phenol group being an ortho-para director in the electrophilic attack of the hydroxyl radical on the aromatic ring. A comparison of product distributions from the reaction of ferrous edta with hydrogen peroxide using salicylate as a scavenger strongly suggests that the same hydroxyl radical adducts are formed as in the radiation experiments.
Maskos
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Department of Chemistry, Louisiana State University, Baton Rouge 70803-1800.
Rush
J D
JD
Koppenol
W H
WH
D001386:Azides / Q000032:analysis; D055598:Chemical Phenomena; D002621:Chemistry; D004492:Edetic Acid / Q000494:pharmacology; D005609:Free Radicals; D005720:Gamma Rays; D005841:Gentisates; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D062385:Hydroxybenzoates / Q000032:analysis; D006900:Hydroxylation; D007501:Iron; D007700:Kinetics; D010084:Oxidation-Reduction; D012459:Salicylates / Q000032:analysis* / Q000528:radiation effects
D001386:Azides; C045076:Fenton's reagent; D005609:Free Radicals; D005841:Gentisates; D062385:Hydroxybenzoates; D012459:Salicylates; C009135:2,3-dihydroxybenzoic acid; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D007501:Iron; C010925:2,5-dihydroxybenzoic acid