Photochemistry of 9,10-anthraquinone-2-sulfonate in solution. 1. Intermediates and mechanism

Journal Article · Thu Jul 07 04:00:00 EDT 1983 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100237a017· OSTI ID:5438236

Loeff, I ^[1]; Treinin, A; Linschitz, H

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1. Hebrew Univ., Jerusalem, Israel

The photochemistry of aqueous 9,10-anthranquinone-2-sulfonate (AQS) was investigated by using four different approaches: (1) laser photolysis of AWS in water as a function of concentration and pH; (2) laser photolysis of AQS in CH/sub 3/CN and CH/sub 3/CN/H/sub 2/O mixtures, combined with emission spectroscopy; (3) steady-state photolytic study of the effect of AQS concentration and pH on the yield of photohydroxylation in water; (4) quenching of intermediates in inhibition of photohydroxylation by inorganic anions. Our results lead to identification of triplet AQS (tau approx. 100 ns in water) and two other intermediates (B and C) which are formed by two parallel reactions of triplet AQS with H/sub 2/O. The nature of these intermediates is still uncertain, but evidence is presented to rule out H abstraction or net electron transfer (even in the case of OH/sup -/) leading to formation of free OH radicals. The possibility that B and C are two different water adducts is discussed. The role of referential solvation of AQS in CH/sub 3/CH/H/sub 2/O mixures in determining its photochemistry is also examined. Species C (lambda/sub max/ approx. 600 nm) is the only transient observed which appears to react with ground-state AQS, and this reaction is considered to be responsible for photohydroxylation. Our results provide direct evidence for the validity of the ''/sup 3/AQS/H/sub 2/O'' mechanism proposed by Clark and Stonehill (CS), in which the primary step is reaction of /sup 3/AQS with water (and not with ground-state AQS) to produce the hydoxylation agent. However, this mechanism is modified for pHgreater than or equal to11 by proposing another hydroxylating agent which may be AQS/sup -/.OH exciplex (or radical pair) produced by charge-transfer (CT) quenching of /sup 3/AQS by OH/sup -/. Evidence is presented to establish the charge-transfer nature of quenching of triplet AQS by various anions including OH/sup -/.

• OSTI ID: 5438236
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 87:14; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ADDUCTS
ANTHRAQUINONES
AROMATICS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
EMISSION SPECTROSCOPY
HYDROXYLATION
LASERS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PH VALUE
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHOTOLYSIS
QUENCHING
QUINONES
REACTION INTERMEDIATES
SPECTROSCOPY
SULFONATES