Sulfonic acid resin

Esters. Most acryhc acid is used in the form of its methyl, ethyl, and butyl esters. Specialty monomeric esters with a hydroxyl, amino, or other functional group are used to provide adhesion, latent cross-linking capabihty, or different solubihty characteristics. The principal routes to esters are direct esterification with alcohols in the presence of a strong acid catalyst such as sulfuric acid, a soluble sulfonic acid, or sulfonic acid resins addition to alkylene oxides to give hydroxyalkyl acryhc esters and addition to the double bond of olefins in the presence of strong acid catalyst (19,20) to give ethyl or secondary alkyl acrylates. 

Fig. 2. Total capacity vs cross-linkage for polystyreae sulfonic acid resin in the form where A and B correspond respectively to dry and wet weight capacity in meq/g of resin, and C represents wet volume capacity in meq/mL of wet setded resin.

Both sulfuric acid and hydrofluoric acid catalyzed alkylations are low temperature processes. Table 3-13 gives the alkylation conditions for HF and H2SO4 processes. One drawback of using H2SO4 and HF in alkylation is the hazards associated with it. Many attempts have been tried to use solid catalysts such as zeolites, alumina and ion exchange resins. Also strong solid acids such as sulfated zirconia and SbFs/sulfonic acid resins were tried. Although they were active, nevertheless they lack stability. No process yet proved successful due to the fast deactivation of the catalyst. A new process which may have commercial possibility, uses... 

Another method of hydroxy-de-diazoniation with better yields was published by Satyamurthy et al. (1990). This method consists of the hydrolysis of l-aryl-3,3-di-ethyltriazenes in acetonitrile using a boiling mixture of the sulfonic acid resin BioRad AG 50W-X12 and water. For nine monosubstituted diethylaryl-triazenes, phenols were obtained in yields of 65-95% (Scheme 10-10). Other triazenes and the same sulfonic acid resin were also used for halo-de-diazoniations (see Sec. 10.6). 

MP borohydride catches one equivalent of the titanium catalyst, while the polystyrene-bound diethanolamine resin (PS-DEAM) can scavenge the remaining titanium catalyst. The borohydride reagent also assists in the reductive animation reaction. Final purification of the crude amine product is achieved with a polystyrene-bound toluene sulfonic acid resin scavenger that holds the amine through an ion exchange reaction, while impurities are washed off. The pure amine can be recovered with methanol containing 2M ammonium hydroxide. 

Nafion-H, a perfluorinated sulfonic acid resin, is another strongly acidic solid that has been explored as alkylation catalyst. Rprvik et al. (204) examined unsupported Nafion-H with a nominal surface area of 0.2 m2/g (surface area of a swellable polymer is difficult to define) in isobutane/2-butene alkylation at 353 K and compared it with a CeY zeolite. The zeolite gave a better alkylate and higher conversion than Nafion-H, which produced significant amounts of octenes and heavy-end products. The low surface area of the resin and questions about the accessibility of the sulfonic acid groups probably make the comparison inadequate. 

Alternatively, dissolve 220 g 4-benzyloxy-3-indoleacetic acid (or equimolar amount other indoleacetic acid) in 2 L absolute methanol and reflux six hours in the presence of 20 g Dowex 50X8 sulfonic acid resin. Filter (decolor with carbon if desired) and concentrate below 35° until precipitation starts then cool to precipitate and filter to get 200 g of the methyl ester. Add 200 g of the ester to 600 ml 40% aqueous methylamine over twelve hours with vigorous stirring. Filter, wash precipitate with water and dry to get 187 g of the N-methyl-acetamide (reflux two hours in 500 ml benzene to remove unreacted ester). 24 g of the acetamide in 300 ml tetrahydrofuran is added dropwise to 10 g lithium aluminum hydride in 300 ml tetrahydrofuran reflux ten hours, cool to 15° and add dropwise with stirring 50 ml ethyl acetate. Reflux two hours and proceed as above to get 15 g (II) or analog. 

Of interest is the metal ion selectivity of bifunctional exchangers having both sulfonic and phosphonic acid groups, since phosphonic acid resins prefer Pb(II) to Ba(II) but sulfonic acid resins show the reversed metal ion selectivity. 

At low temperatures, the activity of acid catalysts in transesterification is normally fairly low and to obtain a sufficient reaction rate it is necessary to increase the reaction temperature to >170 °C. Therefore, sulfonic acid resins can be used in esterification reactions where they perform well at temperatures <120 °C and particularly in the pretreatment of acidic oils. Under these reaction conditions, acidic resins are stable. Poly(styrenesulfonic add), for example, has been used in the esterification of a by-product of a vegetable oil refinery with a 38.1 wt% acidity at 90-120 ° C and 3-6 atm. It was not deactivated after the first batch and maintained a steady catalytic performance in the next seven batches [22]. 

In earlier investigations by the authors (2,3) solid sulfonic acid resins containing polyarylether and cyano substituents, (II) and (III), respectively, were prepared and used as proton-conductive membranes, electrode electrolytes, electrode paste, and in membrane electrode assemblies. 

MTBE is used on a large scale as an octane number boosting additive in unleaded gasoline. Sulfonic acid resins are applied as efficient catalysts for the industrial production of MTBE from methanol and isobutylene (222). Since 1987, investigations of the synthesis of MTBE with reactants in the gas phase have been performed with zeolites HY (223-225), H-Beta (226), HZSM-5 (224,225), and H-BZSM-5 (227) as catalysts. 

An interesting variant of cationic-resin capture has recently been reported wherein a strongly acidic cation exchange resin mediated sequential amine deprotection and resin capture (Scheme 6).78 Protected aminoalco-hols were reacted with an excess of isocyanates to form /V-BOC-amine carbamates in solution phase. Methanol was subsequently added to quench excess isocyanates as the neutral methyl carbamate byproducts. Sulfonic acid resin 51 was then used to affect amine-BOC group deprotection and resin capture of the deprotected amines. Washing of the resin bed and release (ammonia/methanol) afforded purified amine carbamate products. 

A very convenient method has been devised [40] for the conversion of thiols to ethyldithio derivatives as a routine procedure for protection of thiol-substituted organic acids. It uses a DMAP-catalysed exchange of the ethylthio group between a thiol and ethyl 2-pyridyl disulfide, prepared from the commercially available 2,2 -dithiobispyridine. Filtration through a macroporous sulfonic acidic resin and evaporation of the solvent yielded the disulfide directly. 

Chromium(III) and cerium(IV) impregnated Nafion K (a perfluorinated sulfonic acid resin) were used as catalysts f°r the themoselective oxidation of a variety of alcohols using TBHP or NaBr03 as tlie oxy9en donor A e.g. 

A palladium(II)-exchanged polystyrene sulfonic acid resin (Dowex 50W, H form) catalyzes the oxidation of 2-methylnaphthalene with 60% aqueous H2O2 (reaction 27), affording 2-methyl-l,4-naphthoqu1none (menadione) in 55-60% yield at 90-97% conversion. 3 Menadione is a commercially important vitamin K intermediate and these results compare favourably with those obtained in existing industrial processes that employ stoichiometric quantities of chromium trioxide in sulfuric acid. 

Ainberlyst-type catalysts were as active as and more selective than the best homogeneous catalyst, II2SO4. Amberlyst 15 and 3G are macroreticular type polystyrene sulfonic acid resins partially cross-linked with divinylbenzene. The absence of the N—benzyl product when solid acid catalysts were employed suggests the possibility that the reaction could be carried out in a single step. It is also expected to provide all the aforementioned advantages of solid catalysts over liquid catalysts. 

Fig. 2. Proposed reaction mechanism for methyl N—phenyl carbamate condensation in a liquid acid catalyst (a) and over a sulfonic acid resin(b).

There have been a number of reports of improved selectivity with sulfonic acid resin catalysts compared with conventional liquid acid catalysts[6—9]. Various explanations have also been proposed. If mechanisms usually postulated for condensation reactions with liquid Br0nsted acid [10] and solid acid catalysts [11] are adopted, the sequence of steps shown in Fig. 2 could be considered for the condensation of MFC. Both mechanisms incorporate the essential features of known carbenium ion chemistry, i.t., electrophilic attack on the aromatic ring by polar carbenium ion intermediates. Note that MDU is formed by this attack on the benzene ring of MPC, while the N—benzyl compound by the attack on nitrogen atom. 

The synthesis of methyl /-butyl ether (MTBE) from isobutylene and methanol on TS-1 has been investigated. This reaction is catalyzed by acids and the industrial production is carried out with sulfonic acid resin catalysts. It has been reported that at 363-383 K the reaction proceeds in the presence of the acidic HZSM-5, but also on TS-1, which is much more weakly acidic. However, the characterization of the catalysts used is not completely satisfactory for instance, the IR spectra reported do not show the 960-cm 1 band that is always present in titanium-containing silicas. It is therefore possible that the materials with which the reaction has been studied are not pufe-phase TS-1. The catalytic activity for MTBE synthesis is, in any case, an interesting result, and further investigations with fully characterized catalysts are expected to provide a satisfactory interpretation of these results (Chang et al., 1992). 

Polymeric resin sulfonic acids including sulfonic acid resins complexed with Lewis acids and perfluorinated polymer resin acids (Nafion-H and Nafion-silica nanocomposites). 

The following subchapters cover various solid superacids, including perfluorinated sulfonic acid resins (Nafion resins). Furthermore, in the past, various attempts have been made to obtain solid superacids by either (a) enhancing the intrinsic acidity of a solid acid by treatment with a suitable co-acid or (b) physically or chemically binding a liquid superacid to an otherwise inert surface. We will briefly review some of these attempts because most of these catalysts rapidly lose activity and need to be regenerated. 

The new Nafion-nanocomposite catalysts are produced by DuPont and marketed as Nation SAC materials with Nation loading between 10% and 20%. Additional information for perfluorinated sulfonic acid resin nanocomposites including characterization by a variety of physical and chemical methods can be found in a recent... 

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