Dowex MSA

One important factor to consider in the preparation of the organic phase is the presence of inhibitors in the monomers. Some formulae call for the removal of inhibitors, primarily TCB, from the monomers. The TCB inhibitor forms highly colored complexes with metallic salts rendering the final product colored. Styrene has about 50 ppm of TCB. DVB, being more reactive, contains about 1000 ppm of TCB. There are several options for the removal of inhibitors. Columns packed with DOWEX MSA-1 or DOWEX 11 ion-exchange resins (Dow Chemical Company) can be used. White drierite or activated alumina also works well. 

Figure 4.2—Stationary phases in ion chromatography. Schematic of a polystyrene sphere used as a cation exchanger. The polystyrene matrix is transformed into a resin that can exchange cations (e.g. DOWEX 4) or into an anion exchange resin (e.g. DOWEX - MSA-l, or Permutite" if R = CH,).

Figure 8. Scanning electron photomicrographs of anion exchange resin Lett, Dowex MSA-1 (11,000 X) Right, Dowex 1-X2 (21,000X)-...

Because of supply problems in the past few years, resins from other manufacturers have been investigated. Ionao A-641 has been used for some applications at SRP and results approximate those obtained with production-grade Dowex MSA-1. 

Figure 4.4 Stationary phases in 1C. Cross-section of a spherical particle of polystyrene used as a cation exchanger. The polystyrene matrix is transformed either to a cation (ex. DOWEX 4) or to an anion (ex. DOWEX MSA-1) exchange resin. For anion separation the resin is usually a quaternary ammonium group.

F -Anion exchange resins. Fluoride ion immobilized on strongly basic anion exchange resins, particularly Amberlyst A27 and Dowex MSA-1, promote the various reactions that have been found to be promoted by alkali metal or tetraalkylammonium fluorides, such as C- and O-alkylation, sulfenylation, and Michael additions. 

The catalysts applied include sodium hydroxide [689], polymer-supported catalysts such as Dowex MSA 1 [690] or the polymer from styrol and 4-(4-chlorobutyl)styrol [691], zeolites [692], Boehmite [693], and metal-based catalysts such as Y2O3 [694], Na2W04 [695], M0O3 [696], CoYO [697], ZnO [698], and MnO [699]. 

Alkylation of j8-diketones using polymers as supports for the intermediate enolate anion has also been reported (Gelbard and Colonna, 1977). Reaction of several cyclohexyl j3-diketones with Amberlite IRA-9(K) formed a resin-linked j8-diketonate that could be readily alkylated. Similarly, it was shown that alkylation of phenoxide anions can be readily effected when the anions are supported via an ionic bond with the resin (Gelbard and Colonna, 1977). Alkylations of /3-diketones were also shown to occur if a fluoride-substituted, strongly basic resin (Amberlyst A26, A27, or Dowex MSA-1) is used (Miller et at., 1978). In this case, the presence of the fluoride ion was necessary before reaction would proceed. Considering the report on the use of Amberlite IRA-900— a very similar resin— the necessity for a fluoride ion is puzzling. In the same publication, the 0-alkylation of phenols, the sulfenylation of /3-diketones, and the Michael addition of a thiol to an ot,/8-unsaturated ketone were also investigated. 

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