HYDROXYLATION OF PHENOL OVER SN-SILICALITE-1 MOLECULAR-SIEVE - SOLVENT EFFECTS

Tin-silicalite-1 (MFI) prepared by hydrothermal synthesis has been use d as catalyst in the hydroxylation of phenol with aqueous H2O2. Isolat ed Sn4+ ions which are probably attached to the defect silanols are ac tive in this reaction. At optimum conditions, a H2O2 efficiency of 70% and a ortho to para product ratio of 1.6 have been achieved. The solv ent used has a strong influence on the activity. The UV-Vis spectral s tudies indicate that acetone and acetonitrile probably coordinate stro ngly with Sn4+ centers preventing the solvolysis of the Si-O-Sn units and the formation of peroxo intermediate. Methanol probably causes the cleavage of Si-O-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 H2O and its attenuation in presence of ace tone, acetonitrile and methanol support the above conclusion.