Friedel-Crafts reactions induced by heteropoly acids. Regioselective adamantyl substitution of aromatic compounds

• Published in: Catalysis letters Vol. 48; no. 1-2; pp. 83 - 87
• Main Authors: BEREGSZASZI, T, TÖRÖK, B, MOLNAR, A, OLAH, G. A, SURYA PRAKASH, G. K
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01-01-1997; Springer Nature B.V
• Subjects: Acids; Anisole; Aromatic compounds; Catalysis; Catalysts; Catalytic reactions; Chemistry; Dependence; Exact sciences and technology; Friedel-Crafts reaction; General and physical chemistry; Halobenzenes; Heat treatment; Isomerization; Isomers; Reaction time; Regioselectivity; Selectivity; Silicon dioxide; Substitution reactions; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Toluene; Heteropolyacid; Catalysis; Catalysts; Regioselectivity; Toluene; Friedel-Crafts reaction
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1023/a:1019058516695

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.