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 Bronsted sites. Both materials were tested in the synthesis of (all-rac)-alpha-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)-alpha-tocopherol (> 99.9%, for an IP conversion of 100%) whereas high surface area aluminium fluoride is a poor catalyst for this reaction.