FORMATION OF PHENOXYL AND METHYLPHENOXYL RADICALS BY PULSE-RADIOLYSIS

In acidic (pH = 1,3-1,9) and alkaline (pH approximate to 11) aqueous s olutions the reaction kinetics of the OH. radical induced of (sic) of phenol, o-, m- and p-cresol were studied by pulse radiolysis. The form ation kinetics of phenoxyl and methylphenoxyl radicals, resp., are des cribed by two, consecutive reaction steps: the first is addition of OH . radicals to the aromatic ring, while die second H2O or OH- eliminati on. The rate constants of the addition of OH. radicals are the same, ( 1,4 (sic), 1) . 10(10) mol(-1) dm(3) s(-1) for phenol and the three cr esol isomers: this relates to diffusion controlled processed. The rate constant of the adddition is nearly index independent of the pH. The phenoxyl and methylphenoxyl radicals are produced from the adducts in acidic solutions (pH = 1,3-1,9) by H2O elimination with a rate constan t of (1,6+/-0,2) . 10(6) s(-1), but in alkaline systems (pH approximat e to 11) by OH- elimination with considerably faster reaction, (9-12) . 10(6) s(-1). The rate constants of production of methylphenoxyl radi cals from cresol isomers are practically the same as that of phenoxyl from phenol: it means that the methyl substitution and the position of it influences neither the rate of the OH-addition nor that of the H2O /OH- elimination.