Hydroxylation of phenol over Sn-sillicalite-1 molecular sieves; solvent effects

Abstract

Tin-silicalite-(MFI) prepared by hydrothermal synthesis has been used as catalyst in the hydroxylation of phenol with aqueous Hz02. Isolated Sn 4f ions which are probably attached to the defect silanols are active in this reaction. At optimum conditions, a H102 efficiency of 70% and a ortho to para product ratio of 1.6 have been achieved. The solvent used has a strong influence on the activity. The UV-Vis spectral studies indicate that acetone and acetonitrile probahly coordinate strongly with Sn4+ centers preventing the solvolysis of the Si-0-Sn units and the formation of peroxo intermediate. Methanol probably causes the cleavage of Si-0-Sn bond to form Si-OH and Sn-OMe species. Water was found to be an efficient solvent. The formation of EPR active radical ion in presence of H2O2 and H20 and its attenuation in presence of acetone, acetonitrile and methanol support the above conclusion.