Reactions of the borate radical with para-substituted benzoic acids (photo-kolbe reaction)
01 Jun 1990-Journal of Photochemistry and Photobiology A-chemistry (Elsevier)-Vol. 52, Iss: 3, pp 451-459
TL;DR: In this paper, the rate constants for the reactions of the borate radical B(OH) 3 O with various para-substituted benzoic acids were measured by flash kinetic spectrophotometry.
Abstract: Rate constants for the reactions of the borate radical B(OH) 3 O⨪ with various para -substituted benzoic acids were measured by flash kinetic spectrophotometry. The product analyses and kinetic studies are consistent with an electron transfer mechanism followed by decarboxylation. In the case of the p -aminobenzoate anion the —NH 2 and —COO − groups react simultaneously with the borate radical providing two parallel pathways with different rate constants.
Citations
More filters
33 citations
TL;DR: The time-resolved resonance Raman spectra and acid−base properties of the transient prepared on the submicrosecond time scale by N3• oxidation of aqueous p-aminobenzoic acid (PABA) in near-neutral solutions identify it as the charge-neutral 4-O2C-aniline•+ radical as mentioned in this paper.
Abstract: The time-resolved resonance Raman spectra and acid−base properties of the transient prepared on the submicrosecond time scale by N3• oxidation of aqueous p-aminobenzoic acid (PABA) in near-neutral solutions identify it as the charge-neutral 4--O2C-aniline•+ radical. This zwitterion intermediate undergoes slow thermal dissociation (k ∼ 2.4 × 103 s-1) by intramolecular electron transfer and CO2 elimination. It reacts with common bases, such as OH-, N3-, and HPO42- ions, at the rate constants of 1.9 × 1010, 2.7 × 106, and 2.2 × 108 M-1 s-1, respectively, and converts into the nondissociative anilino radical form (pKa 6.7). In the •OH oxidation, formation of the zwitterion radical occurs via OH adducts (hydroxycyclohexadienyl radicals) of p-aminobenzoate anion, at a rate of 1.4 × 105 s-1 which is independent of the base concentration. In strongly acidic solutions the OH adduct of p-aminobenzoic acid reacts with H+, at a rate constant of 4.7 × 108 M-1 s-1, to form the 4-HO2C-aniline cation radical (pKa 1.1). T...
25 citations
References
More filters
TL;DR: In this article, rate constants have been compiled for reactions of various inorganic radicals produced by radiolysis or photolysis, as well as by other chemical means in aqueous solutions.
Abstract: Rate constants have been compiled for reactions of various inorganic radicals produced by radiolysis or photolysis, as well as by other chemical means in aqueous solutions. Data are included for the reactions of ⋅CO2 −, ⋅CO3⋅−, O3, ⋅N3, ⋅NH2, ⋅NO2, NO3⋅, ⋅PO32−, PO4⋅2−, SO2⋅ −, ⋅SO3 −, SO4⋅−, ⋅SO5⋅−, ⋅SeO3⋅ −, ⋅(SCN)2⋅ −, ⋅CL2⋅−, ⋅Br2⋅ −, ⋅I2⋅ −, ⋅ClO2⋅, ⋅BrO2⋅, and miscellaneous related radicals, with inorganic and organic compounds.
2,958 citations
992 citations
TL;DR: In this paper, the exact rate constants for.SO/sub 4/sup -/ with substituted benzenes and benzoates have been determined by pulse radiolysis.
Abstract: Absolute rate constants for reaction of .SO/sub 4//sup -/ with substituted benzenes and benzoates have been determined by pulse radiolysis. The values are found to range from about 5 x 10/sup 9/ M/sup -1/ s/sup -1/ for anisole to less than 10/sup 6/ M/sup -1/ s/sup -1/ for nitrobenzene. A correlation of the rate constants with the Hammett substituent constant sigma gave rho = -2.4 for both series of compounds. It is concluded that the reaction takes place by an electron transfer from the ring to .SO/sub 4//sup -/.
755 citations
TL;DR: In this article, the products of the reactions of SO/sub 4/sup -/ with some benzoic acid derivatives have been examined by ESR using steady-state radiolysis and photolysis to produce SO /sub 4//sup-/ and by optical absorption spectrophotometry in pulse radiolyisation experiments.
Abstract: The products of the reactions of SO/sub 4//sup -/ with some benzoic acid derivatives have been examined by ESR using steady-state radiolysis and photolysis to produce SO/sub 4//sup -/ and by optical absorption spectrophotometry in pulse radiolysis experiments. The optical absorption spectrum of the hydroxycyclohexadienyl radical following reaction of benzene with SO/sub 4//sup -/ is shown to be formed with <0.1 ..mu..s delay. Thus it appears that a cation is formed which reacts very rapidly with water. Similarly, pulse ESR methods have been used to show that the p-carboxyphenyl radical is formed within <1 ..mu..s of the reaction of SO/sub 4//sup -/ with terephthalate. With benzoate, most of the reaction leads to the phenyl radical but about 30% gives hydroxycyclohexadienyl radicals. The three isomeric toluates give different products. The ortho isomer gives mainly the o-carboxybenzyl radical while the para isomer gives approximately equal amounts of p-carboxybenzyl, p-methylphenyl, and a mixture of hydroxycyclohexadienyl radicals. The meta isomer gives mainly a mixture of hydroxycyclohexadienyl radical isomers. Several carboxyphenols were studied by ESR and all gave phenoxyl radicals. All reactions observed are consistent with the oxidation of the benzene ring to a cationic species which then reacts in parallel reactions by either hydroxylation,more » loss of a proton (from OH or CH/sub 3/ groups), or loss of CO/sub 2/.« less
56 citations
44 citations