Cross polystyrene resins

Two classes of micron-sized stationary phases have been encountered in this section silica particles and cross-linked polymer resin beads. Both materials are porous, with pore sizes ranging from approximately 50 to 4000 A for silica particles and from 50 to 1,000,000 A for divinylbenzene cross-linked polystyrene resins. In size-exclusion chromatography, also called molecular-exclusion or gel-permeation chromatography, separation is based on the solute s ability to enter into the pores of the column packing. Smaller solutes spend proportionally more time within the pores and, consequently, take longer to elute from the column. 

Divinylbenzene. This is a specialty monomer used primarily to make cross-linked polystyrene resins. Pure divinylbenzene (DVB) monomer is highly reactive polymericaHy and is impractical to produce and store. Commercial DVB monomer (76—79) is generally manufactured and suppHed as mixtures of m- and -divinylbenzenes and ethylvinylbenzenes. DVB products are designated by commercial grades in accordance with the divinylbenzene content. Physical properties of DVB-22 and DVB-55 are shown in Table 10. Typical analyses of DVB-22 and DVB-55 are shown in Table 11. Divinylbenzene [1321 -74-0] is readily polymerized to give britde insoluble polymers even at ambient temperatures. The product is heavily inhibited with TBC and sulfur to minimize polymerization and oxidation. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

A typical system is a chlorome thy late d polystyrene resin cross-linked with 2 or 4% p-divinylbenzene and different amounts of chloromethylated sites (0.7—3.7 mequiv. of Cl per g of polymer) . The reaction is shown schematically in Eq. (6.19) and additional information may be found in Sects. 8.3 and 8.8. 

The relative selectivities of strongly acid and strongly basic polystyrene resins, with about 8 per cent DVB, for singly charged ions are summarised in Table 7.2. It should be noted that the relative selectivities for certain ions may vary with a change in the extent of cross-linking of the resin for example, with a 10 per cent DVB resin the relative selectivity values for Li+ and Cs+ ions are 1.00 and 4.15, respectively. 

Organic traps contain isoporous, macroporous, or other specifically designed resins (such as reticulated, cross-linked polystyrene resins devoid of ionic function) and take up organics by a combination of ion exchange, adsorption, and other mechanisms. They typically are installed to precede the DI plant. 

The pore structure of most cross-linked polystyrene resins are the so called macro-reticular type which can be produced with almost any desired pore size, ranging from 20A to 5,000A. They exhibit strong dispersive type interaction with solvents and solutes with some polarizability arising from the aromatic nuclei in the polymer. Consequently the untreated resin is finding use as an alternative to the C8 and Cl8 reverse phase columns based on silica. Their use for the separation of peptide and proteins at both high and low pH is well established. 

Rapid loading of cross-linked PS Wang resin (4-(benzyloxy)benzyl alcohol PS) with a selection of /3-ketoesters was shown to reach completion within 1-10 min if microwave irradiation at 170 °C was employed. The conventional thermal method for acetoacetylation of hydroxymethyl-functionalized polystyrene resins takes several hours therefore, microwave heating allowed for... 

The catalysts mentioned above are soluble. Certain cross-linked polystyrene resins, as well as alumina and silica gel, have been used as insoluble phase-transfer catalysts. These, called triphase catalysts, have the advantage of simplified product work up and easy and quantitative catalyst recovery, since the catalyst can easily be separated from the product by filtration. 

Devaky and Rajasree have reported the production of a polymer-bound ethylenediamine-borane reagent (63) (Fig. 41) for use as a reducing agent for the reduction of aldehydes.87 The polymeric reagent was derived from a Merrifield resin and a 1,6-hexanediol diacrylate-cross-linked polystyrene resin (HDODA-PS). The borane reagent was incorporated in the polymer support by complexation with sodium borohydride. When this reducing agent was used in the competitive reduction of a 1 1 molar mixture of benzaldehyde and acetophenone, benzaldehyde was found to be selectively reduced to benzyl alcohol. 

As far as polymer supports for microwave-assisted SPOS are concerned, the use of cross-linked macroporous or microporous polystyrene (PS) resins has been most prevalent. In contrast to common belief, which states that the use of polystyrene resins limits reaction conditions to temperatures below 130 °C [14], it has been shown that these resins can withstand microwave irradiation for short periods of time, such as 20-30 min, even at 200 °C in solvents such as l-methyl-2-pyrrolidone or 1,2-dichlorobenzene [15]. Standard polystyrene Merrifield resin shows thermal stability up to 220 °C without any degradation of the macromolecular structure of the polymer backbone, which allows reactions to be performed even at significantly elevated temperatures. 

M3. Moore, S., and Stein, W. H., Procedures for the chromatographic determination of aminoacids on four per cent cross-linked sulfonated polystyrene resins. J. Biol. Chem. 211, 893-906 (1954). 

A number of modifications of the structure of the allylstannane have been prepared with the aim of facilitating the removal of tin from the product. These include Curran s fluorous allylstannane (see Section 3.14.04.1), Pereyre s monoallylstannane AllylXSn[N(TMS)2]2 (Equation (92) above),258 allylstannanes with a polar (oligoethylene oxide) tail (e.g., 23 and 24), and the allylstannyl group bonded to a soluble or insoluble (cross-linked) polystyrene. The reaction using the allylstannane bonded to a soluble, uncross-linked, polystyrene resin occurs about 100 times faster than that on the cross-linked, insoluble resin, and the polymer can be recovered by recrystallization from methanol. 

The separation takes place in a column of sulphonated cross-linked polystyrene resin, which is a strong cation exchanger. The matrix of the resin is strongly anionic in nature (S03 ) and at the low pH used initially, the amino acids will be positively charged and will be attracted to the negatively charged sulphonate groups. 

Spoly(vinylbenzylchloride). -Cross-linked using divinylbenzene. Chloromethylated, cross-linked polystyrene resins were obtained coiranercielly from Bio-Rad Laboratories. Percent chloromethylation js based on the available phenyl groups in the polymer that is minus the percent cross-linking. =D=dioxane E ethanol. Percent of available chloromethyl croups reacted with donor. —Percent reaction x percent chloromethylation. Polymer prepared by free-radical polymerization of 60.00 para-neta chloromethylated sytrene (Dow Chemical). Reaction heated at 50-55°C. 

Shibasaki et al. developed a polymer-supported bifunctional catalyst (33) in which aluminum was complexed to a chiral binaphtyl derivative containing also two Lewis basic phosphine oxide-functionahties. The binaphtyl unit was attached via a non-coordinating alkenyl Hnker to the Janda Jel-polymer, a polystyrene resin containing flexible tetrahydrofuran-derived cross-Hnkers and showing better swelling properties than Merifield resins (Scheme 4.19) [105]. Catalyst (33) was employed in the enantioselective Strecker-type synthesis of imines with TMSCN. 

In a similar way, Mizota et al. grafted polymer chains functionalized with sulfonic sites over a polystyrene-type polymer. As observed above, the flexibility of the polymer chains allowed better accessibility of the catalytic sites and this solid acid catalyst was ten times more active than the conventionally used cross-linked resin in the hydrolysis of sucrose (Scheme 2) [27]. 

Aiming at easier workup conditions, immobilization of several transition metal catalysts, which show activity for the epoxidation of allylic alcohols, on polymer support has been investigated. For example, Suzuki and coworkers incorporated an oxo-vanadium ion into cross-linked polystyrene resins functionalized with iminodiacetic acid or diethylenetri-amine derivatives (Scheme 57), which afforded a heterogeneous catalyst that can promote... 

Attachment of Compound 11 onto an Aminomethylated Polystyrene Resin 1 3141 A 1% cross-linked aminomethylated polystyrene resin (0.83 mmol of amino group per gram of resin, 2.41 g, 2 mmol) was placed in an ATC Model 90 reaction vessel (capacity 200 mL) and the resin washed successively with NMP, 10% DIPEA in NMP, and NMP. Then, 11 (1.41 g, 3 mmol, 1.5 equiv), HBTU (1.14 g, 3 mmol), and HOBt (0.41 g, 3 mmol) were dissolved in NMP (20 mL) in a flask, and DIPEA (0.78 mL, 4.5 mmol) was added to the soln immediately. The mixture was introduced into the reaction vessel containing the resin within 2 min after addition of DIPEA, and the entire mixture was agitated for lh at rt. The soln was drained from the reaction vessel and the resin washed well with NMP. The completion of the coupling reaction was confirmed by a ninhydrin test. 

The oxidative hydrolysis and acetylation of olefins in the presence of palladium(II) salts are well-established as commercial routes to acetaldehyde and vinylacetate (46). Both processes have been investigated using supported catalysts. The oxidative hydrolysis has been briefly studied using palladium(ll) chloride supported on a cross-linked polystyrene resin containing cyano groups (64). Oxidative acetylation was effected using palladium(II) chloride supported on phosphinated silica (5). 

The intramolecular C-H insertion reaction of phenyldiazoacetates on cyclohexadiene, utilizing the catalyst Rh2(S-DOSP)4, leads to the asymmetric synthesis of diarylacetates (Scheme 8). Utilizing the phenyl di azoacetate 38 and cyclohexadiene, the C-H insertion product 39 was produced in 59% yield and 99% ee. Oxidative aromatization of 39 with DDQ followed by catalytic hydrogenation gave the diarylester 40 in 96% ee. Ester hydrolysis followed by intramolecular Friedel-Crafts gave the tetralone 31 (96% ee) and represents a formal synthesis of sertraline (5). Later studies utilized the catalyst on a pyridine functionalized highly cross-linked polystyrene resin. ... 

Low cross-linked polystyrene resins (1% divinylbenzene) is probably the most popular solid support. These resins swell to 2-6 times their original volume depending on the solvent used. Swollen resin, after removal of solvent and without excessive drying, remains in a rubbery state and can be easily flattened for FTIR study in the transmission mode. The support-bound compound should be washed free of reagent and solvent. 

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