Nafion-H Perfluorinated Resin Sulfonic Acid

Nafion-H is a registered trademark of E. I. DuPont de Nemours Co. and has been shown to be a useful and versatile acid catalyst for organic 

Nafion resins are copolymers of tetrafluoroethylene and monomers such as perfluoro-3,6-dioxa-4-methyl-7-octensulfonic acid and were first synthesized by DuPont chemists. 

A convenient solid of perfluorinated-sulfonic acid can be made readily from DuPont s commercially available Nafion brand ion membrane resins. Powder granules of the 1200-EW polymer, Nafion 501, have been used most frequently in catalytic applications the price in the K+ form of the perfluorosulfonic salt, 501X, was 650/kg in 1981. Because only the potassium salt derivative is commercially available, the salt is converted to the free sulfonic acid by treatment with mineral acid. A standard procedure for the conversion is described below. This procedure also serves to regenerate the resin in various catalytic cycles. 

A slurry of 100 g of perfluorinated ion-exchange polymer in 130 ml concentrated HC1 (36%) and 400 ml distilled water is stirred at 50-60°C for 2 h. The aqueous acid is decanted away from the resin and fresh acid/ water solution added. The mixture is heated and stirred for another 2 h. After the third exchange, the resin is isolated by filtration and washed with distilled water until the washings are neutral. The resin is dried in a vacuum oven under N2 at — I I0°C for 6 h. Conversions 95% are obtained with this procedure. 

TheNafion-H given above exhibits acidic character comparable to 100% H2S04. The physical and chemical properties of the resins as reported by the manufactures are summarized in Table IV (55). It has been suggested that Nafion-H has an acidity between -11 and - 13 (8, 9), and we also determined it to be -12 by the visual color change method of the 

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Alkylation of aromatic hydrocarbons such as toluene or xylenes with styrene over Nafion-H (perfluorinated resin-sulfonic acid) and Amberlyst 15 has been reported. 

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