Polystyrene catalysts, aminated

Dihydropyrroles have recently become readily available by ring-closing metathesis. For this purpose, N-acylated or N-sulfonylated bis(allyl)amines are treated with catalytic amounts of a ruthenium carbene complex, whereupon cyclization to the dihydropyrrole occurs (Entries 6 and 7, Table 15.3 [30,31]). Catalysis by carbene complexes is most efficient in aprotic, non-nucleophilic solvents, and can also be conducted on hydrophobic supports such as cross-linked polystyrene. Free amines or other soft nucleophiles might, however, compete with the alkene for electrophilic attack by the catalyst, and should therefore be avoided. 

Health and Safety Factors. Animal-feeding studies of DMPPO itself have shown it to be nontoxic on ingestion. The solvents, catalyst, and monomers that are used to prepare the polymers, however, should be handled with caution. Eor example, for the preparation of DMPPO, the amines used as part of the catalyst are flammable toxic on ingestion, absorption, and inhalation and are also severe skin and respiratory irritants (see Amines). Toluene, a solvent for DMPPO, is not a highly toxic material in inhalation testing the TLV (71) is set at 375 mg/m, and the lowest toxic concentration is reported to be 100—200 ppm (72). Toxicity of 2,6-dimethylphenol is typical of alkylphenols (qv), eg, for mice, the acute dermal toxicity is LD q, 4000 mg/kg, whereas the acute oral toxicity is LD q, 980 mg/kg (73). The Noryl blends of DMPPO and polystyrene have PDA approval for reuse food apphcations. 

Poly(phenylene ether). The only commercially available thermoplastic poly(phenylene oxide) PPO is the polyether poly(2,6-dimethylphenol-l,4-phenylene ether) [24938-67-8]. PPO is prepared by the oxidative coupling of 2,6-dimethylphenol with a copper amine catalyst (25). Usually PPO is blended with other polymers such as polystyrene (see PoLYETPiERS, Aromatic). However, thermoplastic composites containing randomly oriented glass fibers are available. 

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. 

Although phase transfer agents have been attached to clays, silica and alumina, the vast majority of studies have used organic polymers, especially polystyrene, as the support. The earliest of these triphase catalysts was prepared from 12% chloromethylated polystyrene crosslinked with 2% divinylbenzene by reaction with a tertiary amine. A wide range of triphase catalysts has since been reported, some examples of which are shown in Figure 5.16. 

Aminated Polystyrene-Copper Complexes as Oxidation Catalysts The Effect of the Degree of Substitution on Catalytic Activity... 

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... 

Polystyrene-bound pyridineboronic acid 5 is another example of an acylation catalyst which is easily recovered and reusable. Based on work by Yamamoto and coworkers [10] Wang et al. [11] developed an acylation protocol for amines, in which the carboxylic acid is... 

The synthesis of the polystyrene-supported biguanides was performed in the same way as for the soluble ones. The starting polymers were gel-type polystyrenes with chloromethyl or 6-bromohexyl groups prepared according to Merrifield or Tundo respectively.19. These new catalysts were obtained either by sequential syntheses on aminated polystyrene or by covalent grafting of ready made biguanides. 

Unsaturated polyesters (UPs) crosslinked with styrene are often used as a matrix of fiber reinforced plastics. Several reports treated the degradation of the crosslinked UPs with high temperature treatment in water (1,2), acetic acid (5), alcohols including glycols (4,5), and amines (6), often in the presence of catalysts. In these literatures, recovery of polymeric materials from the crosslinked UPs was not a main objective. However, in case we can hydrolyze polyester chains selectively, linear polystyrene derivatives can be obtained as recycled materials. 

The reduction proved to be chemoselective for aldehyde functions even in the presence of keto groups. The yield in homogeneous reactions varies between 9% and 30%. When aminated polystyrene is used as the basic component, the active anionic species [Rh6(CO)i5H] is immobilized via interaction with the supported ammonium eations and leads to an increase in the yields up to 91-99% [22, 23], while the catalyst can be recovered by simple filtration from the product. 

Polymer-supported chiral amine reagents represent an attractive extension of this methodology, since these catalysts can readily be recovered (Fig. 5). Succi-nated polystyrene-divinylbenzene (17) attached to 1 promoted the addition of 6 to 7 at a slower rate than the homogeneous reaction [17]. Although the absolute configuration of the adduct (S)-8 was identical, the enantiomeric excess was low-... 

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