Photochemical rearrangement of azoxybenzene

Abstract

Direct irradiation of azoxybenzene lead to both isomerization and photochemical rearrangement to 2-hydroxyazobenzene and photoisomerization is faster than the photorearrangement. Because the rate constant and yield of the rearrangement increase in polar protic solvent as the reaction temperature increases the photorearrangement is occurring more favorably from trans-azoxybenzene than cisazoxybenzene. The electron withdrawing groups at the 4,4`` positions disfavor photorearrangement and electron releasing groups facilitate it. The proton donating ability of solvent affects the photorearrangement and proton of solvent accelerates the formation of 2-hydroxyazobenzene and base depresses this reaction. In the protic condition, the least polar solvent is the best solvent in this reaction.