Nuclear magnetic resonance study of the interaction between cation exchange resins and alcohol and water-alcohol mixtures

Abstract

Nuclear magnetic resonance data are reported for hydrogen-form, strongly acidic, cation exchange resins in water, methanol, ethanol, n-propanol, n-butanol, and water-alcohol mixtures. Gel and macroreticular (porous) type resins were investigated. The effect of crosslinking was considered in the gel type resin. A downfield shift in the peak for internal solvent was observed as a function of type of solvent. This behavior is discussed in terms of solvation of the sulfonic acid exchange sites on the resin. An observed shift for the interior solvent NMR peak in mixed solvent is discussed as a function of solvent composition. Comparison is made to p-toluenesulfonic acid in mixed solvent. Supporting data collected in mixed solvents were solvent uptake and solvent preference. Effects due to particle size, type of resin, and broadening are discussed. of these investigations, mixed solvents have been considered (9-11). Macro water levels in ion exchange res-1 Present address, American Machine and Foundry Company,

Ion Exchanger-Solvent Interactions: Properties and Methodology

“…A similar relationship is found for the Dowex exchanger in MeOH, EtOH, n-PrOH, and n-BuOH, where the downfield shift increases in the order n-BuOH > n-PrOH > EtOH > MeOH > H 2 O. 48 These experiments suggest that the alcohol molecules solvate the sulfonic acid group in a manner similar to the water molecules. Hence, the solvation can be represented by The internal peak represents a summation of the species -SO 3 H, ROH, R(or H)OH2, since exchange occurs.…”

“…4 8 ' 1 9 7 This observed trend is consistent with the interior solvent composition. 48 It should be noted that the NMR data on the macroporous exchanger suggest that the exchanger shows a preference for water over the alcohol solvent at higher water concentrations, just as in the case of the microporous exchanger. This was confirmed by determining the interior composition of the exchanger.…”

“…148 Solvent uptake by macro-and microporous cation exchangers in the H-form was determined for alcohol-water mixtures by a centrifugation-Karl Fischer titration procedure. 48 Furthermore, these researchers were able to determine the exchanger's internal and external solvent composition by NMR measurements. In these experiments the macroporous cation exchangers, like the microporous exchangers, preferentially take up water.…”

“…If it is assumed that the -SO 3 H and ROH contributions are nearly the same for all the systems, the observed trend is consistent with the acidity that would be exhibited by the solvated proton; that is, BuOHj is the most acidic and H 3 O + is the least acidic. 48 If a water-alcohol mixture is used, the internal and external resonance peaks in the presence of the cation exchanger are still observed. 4 8 ' 1 9 7 -1 " However, five species will now contribute to the system: -SO 3 H, ROH, ROHz, H 2 O, and H 3 O + .…”

“…(The original article should be consulted for additional data and for a discussion of the experimental conditions and conclusions. 48 ' 198 ) The linear downfield shift in the model system results because of the increased acid molality and because of the larger contribution from the more acidic alcohol-solvated proton species (MeOH^). A similar trend, although not linear, was found for the system containing the ion exchanger, water, and alcohol (see Figure 6).…”