containing,? have been reported. However, the usefulness of these sensitive organometallic reagents under ordinary laboratory conditions is limited by the rigorous inert conditions required and the relatively high cost of the metal catalysts used in these reactions. On the other hand, although protic acids such as anhydrous HF and concentrated H2SO4 have also been successfully used in the alkylation of the aromatic nucleus using simple olefins,8 the notoriously corrosive, highly toxic, and hazardous nature of these agents has precluded their common use under ordinary laboratory conditions.
Various organic sulfonic acids4'9 including perfluorosulfonic acids sa,1(superacids), methanesulfonic acid," and benzenesulfonic acid9d have, on occasion, been used as catalysts in Friedel-Crafts alkylations. In addition, p-toluenesulfonic acid (TsOH) has also been occasionally used as a Friedel-Crafts alkylation catalyst9f-n (mainly for the alkylation of phenols9i_7 and other highly activated aromatic nuclei9g,h). However, to our knowledge the chemistry and the scope of these reactions for common use have never been exploited in detail. For example, TsOH has not been described as a useful catalyst for the alkylation of the aromatic nucleus with haloalkanes, haloalkenes, alkyl sulfonates, or cycloalkenes. The lack of the popularity of TsOH as a Friedel-Crafts alkylation catalyst is also quite apparent from the fact that the most recent review by Olah et al.4a on the subject has not even cited TsOH as a catalyst for the reaction.
In the present study we have carried out a systematic characterization of the alkyl substitution of the aromatic nucleus using commercially available p-toluenesulfonic acid monohydrate (TsOH) as a catalyst. Our results demonstrate that TsOH is a very effective environmentally friendly catalyst for the alkylation of the aromatic ring with activated aliphatic halides, alkenes, and sulfonic esters. While this reaction could be carried out in an open atmosphere to produce high yields of the desired products, most of the catalyst could be recovered by simple filtration and reused. The scope and mechanism of the reaction is discussed in detail.
Results and Discussion
Alkylation of the toluene nucleus by various alkylating agents was chosen as a model reaction for our study. The
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