Industrial application of Nafion-systems in rearrangement-aromatisation, transesterification, alkylation, and ring-closure reactions

Nafion, a perfluorinated sulphonic acid ion-exchange polymer, is known to b e a very strong Bronsted acid. Thus, Nafion NR 50 and Nafion/SiO2 with 15 w t.% Nafion-loading were selected, in order to elucidate the potential for r earrangement-aromatisation of ketoisophorone (KIP) to 2,3,5-trimethylhydroq uinone diacetate (TMHQ-DA) in presence of acetic acid anhydride as acylatin g agent, transesterification of TMHQ-DA to 2,3,6-trimethylhydroquinone mono acetate (TMHQ-1-MA) and reaction of isophytol (IP) with trimethylhydroquino ne (TMHQ) to (all-rac)-alpha -tocopherol. For the rearrangement-aromatisati on of KIP to TMHQ-DA supported Nafion/SiO2 was markedly more active than th e unsupported Nafion NR 50. Both Nafion-systems generally revealed remarkab ly high selectivity, which ranged up to 94 GC-a% TMHQ-DA at high conversion . The major side-product was 3,4,5-trimethylcatechol diacetate. In case of Nafion/SiO2, pre-treatment under vacuum and especially grinding of the extr udates seemed to increase activity at comparably high selectivity. Recyclin g Nafion/SiO2 after filtering and rinsing with acetic acid anhydride led to gradually decreasing activity. Without intermediate isolation of TMHQ-DA, Nafion/SiO2 was active and selective for the formation of TMHQ-1-MA. Using the Nafion systems in the reaction of IP and TMHQ revealed that remarkably high conversion of IP (> 95%) and compared with zinc chloride/Bronsted acid or BF3-catalysed reaction good yields (approximate to 92%) and selectiviti es were obtained. We found a strong dependency on the solvent polarity. In further experiments, the recovery of the catalyst was tested. (C) 2001 Else vier Science B.V. All rights reserved.