Selective C-methylation of phenol with methanol over borate zirconia solid catalyst

Abstract

Selective C-methylation of phenol to o-cresol and 2,6-xylenol in high yields has been carried out with methanol over borate zirconia solid acid catalyst. The maximum conversion of 70 and 65% selectivity for corresponding ortho-alkylated products (o-cresol and 2,6-xylenol) was obtained with 1–2% anisole as O-alkylated product. A series of borate zirconia catalysts with 5–30 mol% B2O3 loading were prepared and calcined at different temperatures. The XRD results reveal the formation of single phase cubic zirconia after addition of B2O3. The cubic structure was stable up to 650 °C, above which it transformed to monoclinic structure. Borate zirconia containing 5 mol% B2O3 calcined at 650 °C was found to be the most active catalyst among the series indicating the influence of composition and structure on the conversion and selectivity. The FTIR results provided the evidence for the vertical orientation of phenol aromatic ring on the catalyst surface, which explains the selective C-alkylation of phenol. The influence of various experimental parameters on phenol conversion and product selectivity has been investigated. The catalyst was active for 150 h time on stream without any deactivation showing its longer life. The catalytic activity and selectivity is correlated with its acidity and structure.