Abstract
Heteropoly acid catalyzed adamantylation of aromatic compounds (toluene, anisole, fluoro- and bromobenzene) was studied. The catalysts applied were various dodecaheteropoly acids of Keggin- type (Hn[XM12O40]; n=3, 4; X=Si, P; M=Mo, W) and some of their derivatives (Cs2.5H0.5[PW12O40] and heat-treated H4[SiMo12O40]/SiO2). The reaction in each case took place in excellent yield, however, the selectivity strongly depended on the experimental conditions applied. The para-isomer was shown to be formed under kinetic control, whereas para to meta isomerization occurred in the presence of acids with high acid strength (H0≤ -13) during longer reaction time. As a rule, strong acidity dependence was observed for the regioselectivity: the Mo- containing 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 adamantane was observed as a product of reductive side reaction. This transformation was found to be significant in the presence of Mo-containing acids due to the redox character of these compounds.
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Beregszászi, T., Török, B., Molnár, A. et al. Friedel-Crafts reactions induced by heteropoly acids. Regioselective adamantyl substitution of aromatic compounds. Catalysis Letters 48, 83–87 (1997). https://doi.org/10.1023/A:1019058516695
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DOI: https://doi.org/10.1023/A:1019058516695