Fe-substituted molecular sieves as catalysts in liquid phase pinacol rearrangement

Pinacol-type rearrangement reactions in toluene were catalyzed by iron-substituted molecular sieves of different porous structures, including AlPO4-5, ZSM-5 of micropores and MCM-41 of mesopores, Iron(III)-substituted in the framework of the molecular sieves was found to be the active center for pinacol rearrangement reaction. The catalytic activity was found to have no correlation with the acidity. Ten vicinal diol reactants with various alkyl or aryl substitution were examined. The results showed that AlPO4-5 molecular sieve containing 0.5-2% Fe was most active in catalyzing the pinacol rearrangement of 2,3-dimethyl-2,3-butanediol. On the other hand, Fe-substituted MCM-41 with relatively large pores was most active in catalyzing the rearrangement of large molecules such as 2,3-pinanediol and 2,3-diphenyl-1,2-ethanediol. All these molecular sieves were not catalytically active in the rearrangement of the vicinal diol compounds of high polarity. This was attributed to the fact that polar molecules would cover the catalyst surfaces and deactivate the catalysts. The migrating preference of the substitution groups was dependent on the catalysts and was different from that observed on acid-catalyzed reactions. (C) 2002 Elsevier Science B.V. All rights reserved.