DETAILED CHARACTERIZATION OF P-TOLUENESULFONIC ACID MONOHYDRATE AS A CONVENIENT, RECOVERABLE, SAFE, AND SELECTIVE CATALYST FOR ALKYLATION OF THE AROMATIC NUCLEUS

Alkylation of the aromatic nucleus, an important reaction in industry and synthetic organic chemistry, has traditionally been carried out by the well-known Friedel-Crafts reaction employing Lewis acid catalysts such as AlCl3 and BF3 or by using highly reactive organometallic reag ents. Although protic acids such as anhydrous HF and concentrated H2SO 4 have also been used in the alkylation of the aromatic nucleus, the n otoriously corrosive, highly toxic, and hazardous nature of these agen ts has precluded their common use under ordinary laboratory conditions . Various organic sulfonic acids have, on occasion, been used as catal ysts in Friedel-Crafts alkylations, but to our knowledge the chemistry and the scope of these reactions for common laboratory use have never been exploited in detail. In the present study we have characterized commercially available p-toluenesulfonic acid monohydrate (TsOH) as an efficient catalyst for the intermolecular coupling of the aromatic nu cleus with activated alkyl halides, alkenes, or tosylates under mild c onditions in an open atmosphere. In comparison to conventional Friedel -Crafts catalysts such as AlCl3, BF3, HF, and concentrated H2SO4, the extent of the formation of undesired products from side reactions such as transalkylation, polymerization, etc. was minimal with the TsOH-ca talyzed reaction. The ability to recover and reuse the catalyst from t he reaction mixtures, minimal generation of environmentally unfriendly waste, high specificity of the reaction, and the low cost of the cata lyst are important advantages of the TsOH catalyst over the other conv entional Friedel-Crafts catalysts.