Catalytic performance of nanoscopic, aluminium trifluoride-based catalysts in the synthesis of (all-rac)-α-tocopherol

A novel nanoscopic, partly hydroxylated aluminium fluoride was prepared in a sol-gel fluorination synthesis and characterised by IR probe molecules. It was shown that this material has, in contrast to high surface area aluminium fluoride (HSAlF₃) which is one of the strongest Lewis acids, a low amount of strong Lewis acid sites combined with weak and medium strength Brønsted sites. Both materials were tested in the synthesis of (all-rac)-α-tocopherol through the condensation of 2,3,6- trimethylhydroquinone (TMHQ) with isophytol (IP). The activity data indicate the partly hydroxylated aluminium fluoride to be a very efficient and highly selective catalyst for (all-rac)-α-tocopherol (>99.9%, for an IP conversion of 100%) whereas high surface area aluminium fluoride is a poor catalyst for this reaction.