ACIDITY STUDIES OF EATON CATALYST, METHANESULFONIC ACID-PHOSPHORUS PENTOXIDE

The acidity of Eaton's regent, methanesulfonic acid-phosphorus pentoxide, was determined by C-13 NMR using mesityl oxide as indicator extrapolated to infinite dilution. It was found that addition of P2O5 decreases the strength of MeSO3H. The mixed anhydrides and the polyphosphoric acids identified by C-13 and P-31-NMR behave, therefore, as weak bases in methanesulfonic acid solution. Addition of small amounts of water produces a steep decrease in acidity of MeSO3H but has little effect on the acid strength of MeSO3H-P2O5 acid mixture. Phosphorus pentoxide is thus able to delay the deactivation by the strong base water, when this is a product of the reactions catalyzed by Eaton's catalyst.