Methanesulfonic acid, sulfonylation with

Friedel-Crafts-type intermolecular sulfonylation of aromatics can also be conveniently carried out over Nafion-H by reacting aromatics with arenesulfonic acids at reflux temperature with azeotropic water removal465 [Eq. (5.168)]. Methanesulfonic acid also reacts with para-xylene to yield 2-methanesulfonyl-1,4-dimethylbenzene in much lower yield (30%). 

In Figure 11.2, a sulfonate ester is the leaving group, and reaction with a nucleophile breaks the weaker C-0 bond to generate a sulfonate anion (26). This anion is resonance stabilized and quite stable, which means it is relatively unreactive as a nucleophile. The combination of a weak C-0 bond and the stability and poor reactivity of the sulfonate anion makes sulfonate esters good leaving groups. The most common sulfonate esters (see Chapter 20, Section 20.11) are those derived from methanesulfonic acid, benzenesulfonic acid, or 4-methylbenzenesulfonic acid. Formation of sulfonate esters from sulfonic acids or sulfonyl chlorides will be discussed in Section 11.7.3 and in Chapter 20,... 

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