Anisole acylation catalysis

This does not occur in the case of catalyst and reactants here described. With Bronsted-type catalysis, the reaction between the benzoyl cation, Ph-C" =0, and the hydroxy group in phenol is quicker than the electrophilic substitution in the ring. This hypothesis has been also confirmed by running the reaction between anisole and benzoic acid in this case the prevailing products were (4-methoxy)phenylmethanone (the product of para-C-benzoylation) and methylbenzoate (obtained by esterification between anisole and benzoic acid, with the co-production of phenol), with minor amounts of phenylbenzoate, phenol, 2-methylphenol and 4-methylphenol. Therefore, when the 0 atom is not available for the esterification due to the presence of the substituent, the direct C-acylation becomes the more favored reaction. 

Catalysis by Bronsted acids requires very strong concentrations (refs. 4-6), and is restricted to the more stable reagents and substrates. In this respect, anisole is not acylated with a good yield in presence of 1 % of triflic acid (ref. f 16). 

As far as catalysis of acylation is concerned, BiCl3 has been little studied. Two references report the use of this salt for the acetylation of toluene (ref. 38) and for the benzoylation of anisole (ref. 39), with average results for the latter, but poor for toluene. More recently, Le Roux and al. showed that BiCl3-metallic iodide systems efficiently catalyze the acylation reaction of enoxysilanes and allylsilanes for which they represent the first known catalysts (refs. 30b, 40). 

The acylation of anisole appears to be heterogeneously catalysed no contribution of homogeneous catalysis by HPA is observed. The H3[PWi204o] catalyst is reusable, although gradual decline of activity was observed due to the coking of the catalyst. 

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