SOME MECHANISTIC INSIGHTS INTO A MODEL BLEACHING PROCESS OF QUINONES BY BISULFITE AND DITHIONITE - AN ESR-CIDEP STUDY

The free radical mechanisms of a model bleaching system involving quin ones and bisulfite and dithionite in solutions were investigated by ti me-resolved ESR techniques. The major role of the radical anion, SO2.- , is established with a number of different parent ions, depending upo n the environment. The reduced colorless products are mainly the hydro quinone dianions which can effectively be photoionized into semiquinon e radical anions (thus the color reversal) and solvated electrons. The strongly polarized semiquinone radical anion and the solvated electro n confirm the mechanisms of the photoionization. Addition of calcium c arbonate to the system helps to stabilize the hydroquinone dianions by the formation of the Ca++/Q(2-) ion pairs and thus reduces the effect s of photoreversion.