Thiophenes acylation kinetics

Finiels, A., Calmettes, A., Geneste, P. and Moreau, P. Kinetic study of the acylation of thiophene with acyl chlorides in liquid phase over HY zeolites, Stud. Surf. Sci. Catal., 1993, 78, 595-600. 

Kinetic studies of acylation reactions are somewhat limited by the insolubility of the acyl halide-Lewis acid complexes in many of the solvent systems that are used. However, useful results have been obtained and, as far as we are concerned, relative rates of reactions are of greater importance than absolute values. In any case it is not possible to distinguish between the two mechanistic extremes on the basis of the observed kinetics." Friedel-Crafts acylations are generally characterized by high substrate selectivity and frequently by high positional selectivity. Relative rate data show, as expected, that toluene is more reactive than benzene and that /n-xylene is the most reactive of the dimethylbenzenes. Values, relative to benzene, for benzoylation catalyzed by aluminum chloride were r-butylbenzene (72), toluene (1.1 X 10 ), p-xylene (1.4 x 10 ), o-xylene (1.12 x 10 ), and m-xylene (3.94 x 10- ). Competition data for the trifluoroacetylation of a number of heterocycles using trifluoroacetic anhydride at 75 "C gave the relative rates thiophene (1.0), furan (1.4 x lO ), 2-methylfuran (1.2 x 10 ) and pyrrole (5.3 x 10 ). ... 

Kinetic study of the acylation of thiophene with acyl chlorides in liquid phase over HY zeolites... 

The kinetic study of the acylation reaction of thiophene with acyl chlorides over dealuminated HY zeolites, in chlorobenzene as solvent, has been shown to follow a Langmuir-Hinshelwood type kinetic law. In liquid phase conditions, thiophene is slightly more adsorbed than the acyl chloride. Moreover, the study of the reaction with various substituted benzoyl chlorides X-CgH4-COCl shows that the nature of the substituent has very little influence on the initial rate. 

Dealuminated HY zeolites have been shown to be efficient catalysts for the selective preparation of 2-acyl thiophenes in the reaction nf thiophene with various acyl chlorides. The acylation reaction of thiophene with butyroyl chloride over HY (Si/Al =15) zeolite, in chlorobenzene as solvent, follows a Langmuir-Hinshelwood kinetic law, which involves the adsorption of the two reactants on identical sites of the catalyst surface. ... 

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