PHOTOCHEMISTRY OF DIBENZO-1,4-DIOXINS - INTRAMOLECULAR REARRANGEMENT-REDUCTION THROUGH OBSERVABLE 2,2'-BIPHENYLQUINONES

The photochemistry of dibenzo-1,4-dioxin (7) and 2,3,7,8-tetramethyldibenzo-1,4-dioxin (15) - both of which have the parent ring system of the well-known environmental contaminant dioxin - has been studied in aqueous solution and in selected organic solvents. It is shown that a novel intramolecular photorearrangement is the major mode of reaction for 7 and the exclusive reaction for 15, giving rise to observable (by UV-Vis spectrophotometry) intermediate 2,2'-biphenylquinones. Subsequent reduction by the organic co-solvent gives rise to 2,2'-biphenols as major or exclusive product. Thus, photolysis of these compounds generates oxidizing agents in the biphenylquinones. Photolysis in the presence of added NaBH4 resulted in greatly enhanced yields of biphenols along with more than 90% material balance. These findings have relevance to dioxin photodecomposition, which can be used as a method for its destruction.