Catalytic activity of iron-substituted polyoxotungstates in the oxidation of aromatic compounds with hydrogen peroxide

abstract

The tetrabutylammonium (TBA) salts of Keggin-type polyoxotungstates of the general formula [XW(11)Fe(III)(H(2)O)O(39)](n-), where X = P, B or Si, were evaluated as catalysts in the oxidation, under mild conditions, of ethylbenzene, cumene, p-cymene and sec-butylbenzene with aqueous H(2)O(2) in CH(3)CN at 80 degrees C. The influence of various factors, such as the substrate/catalyst molar ratio, the amount of oxidant added or the reaction time, was investigated in a systematic way. Generally, the system exhibited moderate conversion, with good selectivity towards the corresponding acetophenone and hydroperoxide. In order to understand the reaction pathways, the oxidation of several products and presumed intermediates was also carried out in the presence of TBA(4)[PW(11)Fe(H(2)O)O(39)]center dot 2H(2)O. Under the conditions used, the oxidation of styrene and styrene derivatives gave rise mainly to carbon carbon double-bond cleavage, affording the corresponding products in very high yields (81-87%). Possible reaction pathways are presented.

keywords

KEGGIN-TYPE POLYOXOTUNGSTATES; SELECTIVE OXIDATION; MOLECULAR-SIEVES; POLYOXOMETALATE; TUNGSTOPHOSPHATES; HYDROCARBONS; COMPLEXES; OXYGEN; ALKYLAROMATICS; CHEMISTRY

subject category

Chemistry

authors

Estrada, AC; Simoes, MMQ; Santos, ICMS; Neves, MGPMS; Cavaleiro, JAS; Cavaleiro, AMV

our authors

acknowledgements

Thanks are due to the University of Aveiro and FCT (Fundacao para a Ciencia e a Tecnologia) for funding. A.C.E. and I.C.M.S.S. also thank FCT for their grants.

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