Highly cross-linked polystyrene

Figure 3.2. Chiral phosphine-phosphite ligands on a highly cross-linked polystyrene polymer...

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. ... 

Another kind of solid support that has gained more popularity is the surface-modified polypropylene, such as the Multipin crown and Microtubes. Reaction 3 was carried out on lightly and highly cross-linked polystyrene resins (1 % and >20% divinylbenzene, respectively), poly sty rene-PEG resin, and a surface-functionalized Microtube reactor.12 The reaction kinetics on these supports is compared in Figures 7.4 and 7.5. The reaction on the highly cross-linked polystyrene resin was shown to be slower than on other supports and the reaction on Microtube was faster than on polystyrene resins. 

The fact that macroporous, highly cross-linked polystyrene does not swell makes this support particularly interesting for continuous-flow synthesis in columns. This support has also been successfully used as an alternative to CPG for the solid-phase synthesis of oligonucleotides [90,91]. Furthermore, because reagents do not need to penetrate into the polystyrene network, enzyme-mediated reactions should also proceed smoothly on macroporous polystyrene [85]. 

Different forms of silicon dioxide have been used as supports for solid-phase organic synthesis. Silica gel is a rigid, insoluble material, which does not swell in organic solvents. Commercially available silica gel differs in particle size, pore size (typically 2-10 nm), and surface area (typically 200-800 m2/g). Like macroporous, highly cross-linked polystyrene, silica gel enables efficient and rapid transfer of solvents and reagents to its entire surface. Because the synthetic intermediates are only located on the surface of the support, enzyme-mediated reactions can be realized on silica [189,190], Silica gel is particularly well suited for continuous-flow synthesis because its volume stays constant and diffusion rates are high. 

In the latter half of the 1990s, porous, highly cross-linked polystyrene divinylbenzene (PS-DVB) resins with smaller, spherical particle sizes more suitable for SPE uses became available (Figure 2.23). The new generation of apolar polymeric resins is produced in more purified form, reducing the level of impurities extracted from the sorbent. Polymeric resins are discussed in more detail by Huck and Bonn [69], Fritz [73], Thurman and Mills [75], and Pesek and Matyska [87],... 

Shibahara F, Nozaki K, Hiyama T (2003) Solvent-free asymmetric olefin hydroformylation catalyzed by highly cross-linked polystyrene-supported (R, S)-BfNAPHOS-Rh(I) complex. J Am Chem Soc 125(28) 8555-8560... 

Asymmetric hydroformylation catalyzed by highly cross-linked polystyrene-sup-ported RS-BINAPHOS-Rh(I) complexes (phosphin-phosphite catalysts including dinaphtho-l,3,2-dioxaphosphepine ligands) 03YGK694. 

It is believed that the principal difference between the solid and liquid products is that the liquid is essentially a linear polymer, while the solid is highly cross-linked. Such a highly cross-linked polystyrene would be expected to have a lowdr ratio of aromatic C-H to aliphatic C-H bonds than would a linear polymer. Comparison of spectrum B or D with C in Figure 2 shows that the intensity of the aromatic and aliphatic C—H stretching vibrations agrees with this expectation. 

However, the Japanese group has noted partial cleavage of the diisopropylsi-lanediyl linkage under the acidic conditions needed for the DMTr group removal [245, 247]. To circumvent this nuisance, Kobori et al. [247] have prepared a highly cross-linked polystyrene-supported phenyldiisopropylsilyl ether linker that proved to be completely stable to detritylation and used it successfully for oligonucleotide synthesis without N-protection by O-selective phosphoramidite chemistry [246] and pyrophosphate formation on solid phase [248]. The anchor can be cleaved under almost neutral conditions by 1M TBAF-AcOH in THF (90% release after 1 h) or 0.2 M triethylamine trihydrofluoride in the presence of 0.4 M triethylamine for 4h. 

Hamilton PRP-XlOO 150x4.1 1-13 200 10 Highly cross-linked polystyrene divinyl benzene coated with quaternary ammonium groups. 

Surface-type supports. Many different materials are used for surface functionalization, including beads made from sintered polyethylene, cellulose fibers (cotton, paper, Sepharose, and LH-20), porous highly cross-linked polystyrene or polymethacrylate, controlled pore glass, and silicas. 

Highly Cross-Linked Polystyrene-Polyamide (Polyhipe)... 

Nozaki and coworkers recently disclosed the use of (i, S)-BINAPHOS-Rh(I) catalyst that is covalently anchored to a highly cross-linked polystyrene in the... 

When polystyrene is crosslinked using a peroxide, polystyrene can also undergo chain scission and coupling reactions that can lead to a low crosslink density. To achieve high crosslink density, copolymeiization with relatively small amounts of divinyl benzene can produce highly cross linked polystyrene beads. 

Figure 6.135 illustrates the increase of Tg of polystyrene when copolymerized with divinyl benzene for cross-linking (CH2=CH2- C6H4- CH2=CH2). All samples were gels (see Sect. 3.4.3), practically without extractable polystyrene. The decrease in the change of the heat capacity at Tj on cross-linking is shown in Fig. 6.136. The curve drawn in Fig. 6.136 is calculated from the heat capacities of the liquid and glassy polymers at the measured glass transition temperature of Fig. 6.135. Considerable deviations are observed, but one may still extrapolate the data to a point where ACp becomes zero (=50% divinyl benzene, Tj 500-550 K). Indeed, highly cross-linked polystyrenes with practically no ACp at Tj have been reported.

Fig. 5.3 The structure of the highly cross-linked polystyrene particle and its CO2/CH4 selectivity predicted by lAST for CO2/CH4 = 5/95 mixtures at 268 K (Reprinted with permission from Ref. [20]. Copyright 2012, American Chemical Society)...

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