Perfluorosulfonic Acid Resins

Many other polymerization processes have been patented, but only some of them appear to be developed or under development in 1996. One large-scale process uses an acid montmorrillonite clay and acetic anhydride (209) another process uses strong perfluorosulfonic acid resin catalysts (170,210). The polymerization product in these processes is a poly(tetramethylene ether) with acetate end groups, which have to be removed by alkaline hydrolysis (211) or hydrogenolysis (212). If necessary, the product is then neutralized, eg, with phosphoric acid (213), and the salts removed by filtration. Instead of montmorrillonite clay, other acidic catalysts can be used, such as Fullers earth or zeolites (214—216). 

Osmium is unrivalled as catalyst for the asymmetric cis-dihydroxylation of olefins. However, Sato and coworkers reported that the perfluorosulfonic acid resin, Nafion (see Chapter 2) is an effective catalyst for the trans-dihydroxyla-tion of olefins with H202 [86]. The method is organic solvent-free and the catalyst can be easily recycled (see Fig. 4.33). The first step of this reaction is epoxi-dation which is probably carried out by resin-supported peroxysulfonic acid formed in situ. This is followed by acid-catalyzed epoxide-ring opening. 

TABLE 1. Summary of terepolymers produced when catalyzed by the solid perfluorosulfonic acid resin NAFION NR-50. 

Measurements of the 120, 214 and 295 duPont Nafion films and also fully converted ethylene diamine films are considered to be typical. The 120 polymer is a homogeneous film 10 mils thick of 1200 equivalent weight, (ew), perfluorosulfonic acid resin. The 214 and 295 films are each of 7 mils thick resin of 1150 ew having one surface facing the cathode that has been chemically modified to 1.5 mils depth, and having T-24 backing. The 295 films are the same as the 214 except that they are modified to a 1.5 mil depth and have T-900 backing (17) (18). 

Figure 2. Crown ethers identified by chemical ionization mass spectroscopy for EO/THF polymerization using Nafion perfluorosulfonic acid resin as catalyst.

In view of these considerations and the limitations of polystyrenesulfonic acids, we studied superacidic Nafion-H perfluorosulfonic-acid-resin-caialyzed nitration of aromatics with nitric acid under conditions of azeotropic removal of water (azeotropic nitration) [12]. The azeotropic removal of water in Nafion- H -catalyzed nitration allows utilization of nitric acid to a significantly greater extent than do conventional conditions of nitration. Both fuming and concentrated nitric acid are effective (Table VII). 

Du Font s Nafione membranes are perfluorinated ion exchange resins fabricated into reinforced and unreinforced membranes. Nafione Membrane 425, which we used in some of our tests, is a homogeneous film 5 mils thick of 1200 equivalent weight perfluorosulfonic acid resin laminated with T-12 fabric of Teflone TFE resin to make a 50 mil membrane. Properties and characteristics of Nafione membranes are given in reference 2. 

Naftion 425 (perfluorosulfonic acid resin) 1-decene oligomers 933... 

Figure 7. Electric resistance, ion exchange capacity (meq/g dry resin) and concentration of NaOH, for perfluorosulfonic acid membrane.

Bronsted acids can also be fixed to the surfaces of many common support materials. Surface attached perfluorosulfonic acids have been reported123 as well as the perfiuorinated sulfonic acid resin (Nafion)-silica composites reported a year earlier.124 The former are prepared by reacting... 

Naflon (a perfluorosulfonic acid type ion exchange resin, Du Pont) have also been synthesized from CH3Br and CF3Br, respectively, with Nafion-Br in a similar way102 (equation 77). 

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. 

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