FRIEDEL-CRAFTS REACTIONS INDUCED BY HETEROPOLY ACIDS - REGIOSELECTIVEADAMANTYL SUBSTITUTION OF AROMATIC-COMPOUNDS

Heteropoly acid catalyzed adamantylation of aromatic compounds (toluen e, anisole, fluoro-and bromobenzene) was studied. The catalysts applie d were various dodecaheteropoly acids of Keggin-type (H-n[XM12O40]; n = 3, 4; X = Si, P; M = Mo, W) and some of their derivatives (Cs2.5H0.5 [PW12O40] and heat-treated H-4[SiMo12O40]/SiO2) The reaction in each c ase took place in excellent yield, however, the selectivity strongly d epended on the experimental conditions applied. The para-isomer was sh own to be formed under kinetic control, whereas para to meta isomeriza tion occurred in the presence of acids with high acid strength (H-0 le ss than or equal to -13) during longer reaction time. As a rule, stron g acidity dependence was observed for the regioselectivity: the Mo-con taining acids yield the para-substituted isomers with high selectivity , whereas the W-containing catalysts result in high meta/para ratios. In addition, using halobenzenes as reactants the formation of adamanta ne was observed as a product of reductive side reaction. This transfor mation was found to be significant in the presence of Mo-containing ac ids due to the redox character of these compounds.