Photolysis of Aqueous Solutions Of 9,10-Anthraquinone-2-Sulfonate. Part II. Dependence of Rates of Hydroxylation on Reaction Conditions

Abstract

. Can. J. Chem. 53, 826 (1975).The rates of formation of hydroxy-9,lO-anthraquinone-2-sulfonates, produced by irradiationof neutral and alkaline aqueous solutions of 9,lO-anthraquinone-2-sulfonate (A) at 365 nm, have been measured for solutions with initial [A] rangingfrom 5 x to 8 x m~l d m -~, saturated with either 02, air, or Nz. The rate of monohydroxylation was independent of the saturating gas and, for neutral solutions absorbing all the incident light, increased with increasing initial [A] reaching a constant maximum quantum yield of 0.08 above 2 x rnol dm-J. In 0.1 mol dm-J aqueous NaOH solution, the rate was about three times largerbut had not attained a limiting value at the maximum a 8 x mol dm-', saturees soit en 0,, en air ou en N2, les vitesses de formation des hydroxyanthraq~~inone-9,10 sulfonates-2 produits par irradiation de solutions aqueuses, neutres ou alcalines d'anthraquinone-9.10 sulfonate-2 (A). Le taux de monohydroxylation est independant du gaz produisant la saturation et dans des solutions neutres absorbant toute la lumikre incidente, la vitesse augmente avec I'augmentation de la vitesse initiale de [A] approchant un rendement quantique maximum constant de 0.08 au dessus de 2 x mol dm-J. Dans des solutions aqueuses de NaOH aO.l mol dm-j, la vitesse est environ trois fois plus grande mais elle n'avait pas atteint une valeur limite a la concentration maximum de [A] imposee par sa solubilitk. On propose que les dihydroxyanthraquinone-9,10 sulfonates se forment par reaction de 0 2 avec un intermediaire plut6t que par une hydroxylation ulterieure des produits monohydroxyles. Le taux de dihydroxylation diminue lorsque la concentration de [A] augmente au dessus de 5 x mol dm-' et cette vitesse devient pratiquement zero a haute concentration.[Traduit par le journal]

Reduction of the polynuclear quinonoiddyes16,17-dihydroxy- and dimethoxyviolanthrone with photogenerated radicals

“…Thus U isc of the quinonoid dyes under examination is too low to trigger a reduction step, in contrast to AQ or other quinones. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The measurements were therefore performed in the presence of donors under sensitized conditions. Appropriate H-atom and electron donors are 2-propanol (or 1-phenylethanol) and TEA, respectively, and acetophenone, benzophenone or acetone were used as sensitizers.…”

“…The donor radical can also be formed by reaction of the ketyl radical (6); the opposing reaction is also possible. 20 This can be neglected due to a much lower sensitizer concentration of <1 mM, at least in the cases of acetophenone or benzophenone.…”

“…1,2 For 9,10-anthraquinone (AQ) the mechanism of photoreduction is known in great detail. [3][4][5][6][7][8][9][10][11][12][13][14][15] For AQ the quantum yield of intersystem crossing (U isc ) is substantial and in 2-propanol or in the presence of triethylamine (TEA) the quantum yield of photoreduction is close to unity. [1][2][3] This is in contrast to the case of 1-or 2-aminoAQs.…”

Photohydroxylation of 1,4‐Benzoquinone in Aqueous Solution Revisited

“…[32,52,53,58,64,70] However, it has been calculated that the reduction potential of the relaxed triplet state of Q is insufficient to oxidize water, and it has been suggested that the water oxidation (formation of 1,4-benzosemiquinone CQH observed by time-resolved Raman spectroscopy) must be due to the reaction of an unrelaxed triplet state. [35] As another potential route to COH, electron transfer from a ground-state quinone to an excited quinone and oxidation of OH À or water by the ensuing quinone radical cation has been considered.…”

Photoreactions of 1,4‐Naphthoquinones: Effects of Substituents and Water on the Intermediates and Reactivity¶

“…For MeNQ, a similar but smaller dependence of φ d on pH was obtained. In comparison, the yield of photoconversion of AQ‐2‐sulfonate into the corresponding hydroxyanthraquinone is low, φ= 0.08 (40). On the other hand, photodecomposition of L‐NQ is not sensitive to the presence of a donor; instead φ d is moderate in all solvents examined (Table 3).…”