The chemistry of hydroxy-quinones. Part VI. Formation of 2-hydroxy-semiquinones during the autoxidation of benzene-1,2,4-triols in alkaline solution

By using a technique of stepwise oxidation of benzene-1,2,4-triols at pH > 12 it has been demonstrated, spectrophotometrically, that hydroxy-semiquinone intermediates are formed in appreciable quantities and that their stability increases with pH. In the absence of a C-5 substituent C–C coupling occurs with the ultimate formation of appreciable quantities of 2,2′-bi-p-benzoquinones, together with other products. C-5 Substituted triols give the 2-hydroxybenzoquinones which react rapidly with the hydrogen peroxide formed during the oxidation to give cyclopentanetriones or acyldihydroxycyclopentanediones.