Azoxybenzene rearrangement catalyzed by solid acids

For the first time, the potential of acidic cation-exchange resin (sulfonated polystyrene) to catalyze the Wallach rearrangement of azoxybenzene into 4-hydroxyazobenzene has been proved. This finding reveals an alternative reaction path possible in a heterogeneous process using solid acids and may help to clear some doubts concerning the rearrangement mechanism postulated so far. The resin-induced reaction was found to proceed exclusively in a non-polar medium. Reasonable yield was obtained particularly in isooctane due to favorable distribution of azoxybenzene throughout the resin's matrix. On the contrary, the HY type zeolite did not activate the rearrangement, most probably because of steric hindrance. Experimental results favor the hypothesis of a quinoid intermediate controlling the chemistry of azoxybenzene conversion, which also follows from thermodynamic considerations involving DFT calculations. (C) 2008 Elsevier B.V. All rights reserved.