Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 3177 - 3188 (1987)
Update date:2022-08-16
Topics:
Anderson, Robert F.
Patel, Kantilal B.
Stratford, Michael R. L.
The distribution of electrophilic OH. radical addition to 4-hydroxybenzoic acid (HBA) has been determined by oxidizing the radical intermediates (substituted hydroxycyclohexadienyl radicals) with quinones and viologens, to yield products.It is deduced from product analysis using high-performance liquid chromatography that the fractions of OH. attack at the 1:2:3:4 positions of HBA are 0.16:0.04:0.65:0.15 respectively.Pulse radiolysis studies show that the rate of electron transfer from the radical intermediate formed by OH. addition to position 3 of HBA is dependent on the one-electron reduction potential of the oxidant.This electron-transfer process is in competition with the elimination of water by general acid-base catalysis to yield the phenoxyl radical.Catalysis by OH- proceeds through the formation of the deprotonated species, pKa=8.4+/-0.2, followed by the elimination of water, ke=3.0+/-0.3*105 s-1.The addition of an OH. radical ipso to the hydroxy group of HBA also gives rise to the phenoxyl radical through rapid water elimination, k=2*107 s-1.The addition of an OH. radical to position 3 of HBA gives rise to an absorption band centred at 365 nm.
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