The control of regioselectivity in the liquid-phase hydroxymethylation of 2-methoxyphenol with aqueous formaldehyde. A comparison between zeolites and basic catalysts

The heterogeneous hydroxyalkylation of 2-methoxyphenol (guaiacol) with ail aqueous solution of formaldehyde was carried out using either zeolites or solid bases as catalysts. The reaction is aimed at the production of vanillic alcohols (methoxyhydroxybenzyl alcohols), which are intermediates for the synthesis of the corresponding aldehydes. In the case of H-Mordenites, the catalytic performance was governed by the hydrophobic properties of the zeolite (which were in turn affected by the Si/Al ratio), rather than by the number of acid sites. With H-beta zeolites, instead, hydrophobic properties had a smaller influence on the conversion and selectivity. It was found that the regioselectivity of the hydroxymethylation is greatly affected by the catalyst characteristics; while zeolites gave mainly the product of methylation in the para position with respect to the hydroxy group in guaiacol, oxides having basic Surface features gave predominantly o-vanillol, the product of ortho-C-hydroxymethylation.