Browsing by Author "Clark, K. P."

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Photochemistry and Radiation Chemistry of 9,10-Anthraquinone-2-sodium Sulphonate in Aqueous Solution: Part 2.—Photochemical Products 1
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Clark, K. P.; Stonehill, H. I.
Anthraquinone-2-sodium sulphonate in “aqueous” solutions within the range pH 14 to 100% H2SO4(and also in oleum) is both reduced and hydroxylated when irradiated with u.v. or visible light. The major hydroxy-photoproducts were isolated and identified as a 3 : 2 mixture of isomeric α-and β-hydroxy derivatives of the starting material in the range 40 % H2SO4 to pH 9; outside this region the relative amount of α isomer produced falls off rapidly and in strong acid or alkali only the β-hydroxy product is obtained. Prolonged irradiation produces also small amounts of polyhydroxy derivatives. The pH-dependence of the ratio of α- and β-hydroxy product yields is correlated with ionization of hydroxyl radical adduct intermediates.
Photochemistry and radiation chemistry of 9,10-anthraquinone-2-sodium sulphonate in aqueous solution. Part 3.—Pulse and gamma radiolysis
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (05), 1977) Clark, K. P.; Stonehill, H. I.
Electron-pulse and gamma radiolysis of “aqueous” solutions of the title compound (D) in the range pH 14 to > 100 % H2SO4 give the same products as photolysis (mainly α- and β-monohydroxyderivatives ROH with some polyhydroxylated D, and in the absence of oxygen, semiquinone and quinol), and the same variation with pH or acidity of the α : β ROH isomer ratio. Of the following rate constants (all in dm3 mol–1 s–1) the first three were determined by pulse radiolysis, the others by scavenger competition during gamma radiolysis : 2 DOH˙→ DHOH + ROH, 2 k=(1.41 ± 0.17)× 109; DOH˙+ O2→ DOH˙ O2., k=(1.39 ± 0.17)× 107; 2 D–˙→ D + D2–, 2 k=(1.33 ± 0.18)× 109; D + OH·→ DOH·, k=(2.68 ± 0.25)× 109; D + O·–→ DO·–, k= 6.1 × 107; D + O.–→ products other than DO.–, k= 1.63 × 108[this reaction is postulated to explain the fall in G(ROH) at pH > 12]. The effect of individual scavengers and of high alkalinity on the yield of ROH is different in photolysis and radiolysis. This suggests that since OH· is known to be the precursor of DOH· in radiolysis, any photolysis mechanism involving intermediate free OH· production is invalid.
Photochemistry and Radiation Chemistry of Anthraquinone-2-sodium-sulphonate in Aqueous Solution: Part 1.—Photochemical Kinetics in Aerobic Solution
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (4), 1972) Clark, K. P.; Stonehill, H. I.
When aqueous solutions of anthraquinone-2-sodium-sulphonate (D) are photolyzed the quinone becomes hydroxylated and (in the absence of oxygen) reduced. On the basis of the kinetics of the photohydroxylation in air or oxygen saturated solutions (pH 2–14), two alternative mechanisms are proposed, the 3D*/S (S = H2O or OH–) and the 3D*/D. In the former, D attacks S to produce an adduct DOH– which is converted by ground-state D to the radical DOH·. In the latter, 3D* attacks D to form a solvent caged radical pair {D·+ D·–}, the D·+ constituent then reacting with S to give OH· radicals which with D yield DOH·. This intermediate is converted by oxygen to hydroxy product. Neither continuous irradiation kinetics nor conventional µs flash photolysis permits discrimination between these schemes. The thermodynamic feasibility of OH· production by the 3D*/D reaction is demonstrated.