Photohydroxylation of anthraquinone in concentrated sulphuric acid

Abstract

In concentrated sulphuric acid 9,10-anthraquinone gave solutions exhibiting absorption in the visible range which remained stable indefinitely in the absence of light. Treatment of such solutions with near-u.v. or visible radiation caused an efficient and clean phototransformation into a product, which was recovered and proved to be 2-hydroxyanthraquinone. Because of the remarkable photostability of the product and the relatively high efficiency of conversion, the reaction readily approaches completion. The reaction was carried out in dilute solutions for time-lapse spectroscopic measurements and in concentrated solutions for preparative purposes. The mechanism is discussed.