Photochemistry of Aqueous Anthraquinone- 2-Sulfonate Solution

Department of Applied Chemistry, University of Calcutta, Calcutta-700 009

The aqueous photochemistry of anthraquinone-2-sodium sulfonate (D) has been studied. Under aerobic condition, mono-hydroxy derivative of D and hydrogen peroxide are the stable products of photolysis while in anaerobic medium mono-hydroxy derivative as well as semiquinone/semiquinolate ion are produced. In acid and neutral medium both α- and β-hydroxy derivatives of D are produced in the ratio 3 : 2, while in alkaline medium only the ß-isomer is detected. Quantum yields of hydroxy derivatives of D, semiquinone/semiquinolate ion and hydrogen peroxide are determined under both aerobic and anaerobic medium with (i) variation of initial concentration of D and (ii) variation of irradiation time.

The effect of some substrates namely sodium formate and sodium azide on the quantum yield of hydroxy derivative and the reduced product, semiquinone/semiquinolate ion has also been studied. The results indicate that the formate here is not acting as a scavenger of OH. radical, the precursor of hydroxy product, as suggested by some earlier workers but directly participates in the semiquinone formation. On the basis of the results a mechanism has been suggested.