Friedel–Crafts alkylation of sodium salicylate with 4-tert butylbenzyl chloride performed in aqueous dispersions of mesoporous oxides

Reactant incompatibility is a common problem in organic chemistry. In this study we investigate the use of concentrated aqueous dispersions of mesoporous oxides to overcome incompatibility in the Friedel–Crafts reaction between sodium salicylate and 4-tert-butylbenzyl chloride. The mesoporous material was first impregnated with the water-soluble nucleophile, sodium salicylate, and the “loaded” particles were then dispersed in the apolar electrophile, 4-tert-butylbenzyl chloride. A range of different mesoporous oxides and one clay mineral, montmorillonite, were investigated as catalyst for the reaction. These were all characterised with small angle X-ray scattering (SAXS) and with nitrogen adsorption (BET and BJH methods). Their Lewis and Brønstedt acidities were determined by ammonia adsorption experiments using diffuse reflection infrared Fourier transform (DRIFT) spectroscopy as detection method. The reaction proceeded well and gave high yields provided proper stirring was maintained. Alumina, an aluminosilicate and montmorillonate were the most efficient catalysts. These were also the materials that showed the strongest Lewis acidity. In general, there was good correlation between Lewis acidity and efficiency of the material as catalyst for the Friedel–Crafts alkylation. Attempts to reuse the catalyst were not entirely successful. Deactivation occurred after the first run. ESCA indicated that the reduction in performance was due to adsorption of carbonaceous residues on the catalyst.

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► Solid acid catalyst reaction system for incompatible reactants developed.
► Clean Friedel–Crafts alkylation.
► Mesoporous catalysts are more effective than stoichiometric amounts of mineral Lewis acid.
► Mesoporous catalyst with the highest Lewis acidity had the highest catalytic activity.