REACTION OF HYDROXYL RADICALS WITH ALKYL PHOSPHATES AND THE OXIDATIONOF PHOSPHATOALKYL RADICALS BY NITRO-COMPOUNDS

The rate constants for reactions of hydroxyl radicals with a number of alkyl phosphates have been determined by competition with KSCN. Hydro xyl radicals react with alkyl phosphates preferentially by H-abstracti on at the alpha-position of the phosphate functions. The resulting alp ha-phosphatoalkyl radicals are not very efficient one-electron reducin g agents towards nitro compounds. They react with tetranitromethane (T NM) by addition to form adduct intermediates with absorption maxima at about 300 nm. The rate constants for decay of these TNM adducts to pr oduce the nitroform anion (NF-) and the corresponding alpha-phosphato- alcohols have been determined by optical and/or conductance detection. The stability of these TNM adducts varies considerably with the chain length (methyl > ethyl > isopropyl) and number (trialkyl > dialkyl > monoalkyl) of the alkyl substituents. Additional formation of proton d uring or after the decay of the TNM adducts has been tentatively attri buted to the hydrolysis of the alpha-phosphato-alcohols. alpha-Phospha toalkyl radicals derived from trimethyl, triethyl, triisopropyl, and d iethyl phosphates react with p-nitroacetophenone (PNAP) very slowly (k < 5 X 10(7) dm(3) mol(-1) s(-1)) possibly forming adducts. One-electr on reduction of PNAP by these radicals to PNAP(-) was not observed und er pulse radiolysis conditions. The rate constants for the reactions o f (OH)-O-. with glycerol 1-phosphate and glycerol 2-phosphate have bee n redetermined by competition with KSCN. Using the radical scavengers N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and TNM, the percentag e of (OH)-O-. attack at each carbon atom was obtained. Contrary to the simple alkyl phosphates described above, the alpha-position to the ph osphate function is the least favoured (10-15% in glycerol 1-phosphate and 6% in glycerol 2-phosphate). These so-formed alpha-phosphatoalkyl radicals react with TNM also by forming adducts. The beta-phosphatoal kyl radicals in both;cases eliminate inorganic phosphate on formation (k > 10(6) s(-1)). The gamma-phosphatoalkyl radical from glycerol 1-ph osphate undergoes base-catalysed water elimination (k(obs) = 1.8 X 10( 5) s(-1) at pH 10.6) to give an oxidizing radical. Products in the gam ma-radiolysis of N2O-saturated solutions of glycerol 1-phosphate and g lycerol 2-phosphate have been identified and their yields determined. The mechanisms for their formation are discussed.