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Benzyl from polystyrene oxidation

Taylor and Flood could show that polystyrene-bound phenylselenic acid in the presence of TBHP can catalyze the oxidation of benzylic alcohols to ketones or aldehydes in a biphasic system (polymer-TBHP/alcohol in CCI4) in good yields (69-100%) (Scheme 117) °. No overoxidation of aldehydes to carboxylic acids was observed and unactivated allylic alcohols or aliphatic alcohols were unreactive under these conditions. In 1999, Berkessel and Sklorz presented a manganese-catalyzed method for the oxidation of primary and secondary alcohols to the corresponding carboxylic acids and ketones (Scheme 118). The authors employed the Mn-tmtacn complex (Mn/168a) in the presence of sodium ascorbate as very efficient cocatalyst and 30% H2O2 as oxidant to oxidize 1-butanol to butyric acid and 2-pentanol to 2-pentanone in yields of 90% and 97%, respectively. This catalytic system shows very good catalytic activity, as can be seen from the fact that for the oxidation of 2-pentanol as little as 0.03% of the catalyst is necessary to obtain the ketone in excellent yield. [Pg.497]

Until now, the chemistry of radicals on solid supports has been investigated mostly in respect to intramolecular radical cyclizations and radical chain reactions. One reason for refraining from free radical transformations is the chemical nature of the polystyrene with its abundance of benzylic positions that are prone to H-radical abstraction and oxidation. [Pg.384]

Although there is dispute about the exact oxidation state of titanium in the active species [Ti(III) or Ti(IV)], it was suggested, from the results of ESR measurements, that Ti(III) species form highly active sites for producing syndiotactic polystyrene in styrene polymerisation systems with the TiBz4—[Al(Me)0]x catalyst [50]. The moderately low catalyst activity is attributable to the stability of the benzyl transition metal derivatives towards reduction. [Pg.254]

Most polymeric redox reagents have been developed on microporous polystyrene, typically cross-linked with 1% divinylbenzene. Few examples have been reported for macroporous polystyrene, silica or other supports such as high-loaded cross-linked polyethylene imine (Ultraresins). Some problems specific for redox reactions can also arise from the reactivity of the polymer support itself. In cross-linked polystyrene, for example, benzylic positions can be oxidized at elevated temperatures and thus can account for a competing reaction pathway [8], Further reactivities are found for other solid supports as well. [Pg.84]

Benzyl- and methyltriarylphosphonium salts bound to 2% and 8% cross-linked, and to 20% cross-linked macroporous, polystyrene undergo Wittig reactions in good yield with both aldehydes and ketones. The Wittig reaction has been carried out under gas-liquid phase-transfer catalytic conditions using solid potassium carbonate as the base. An advantage of the procedure is that the alkene product separates from the phosphine oxide. Unprotected phenolic aldehydes can be converted into alkenes by Wittig reactions provided two moles of base are used. ... [Pg.225]

The grafting-from approach is based on the mitial immobilization of initiators onto the nanotube surface, followed by in situ polymerization with the formation of the polymer molecules bound to the nanotube. The benefit of this technique is that polymer-functionalized nanotubes with high grafting density can be prepared. However, this method requires a strict control of the amoimts of initiator and substrate [53, 54]. The grafting- from technique is also used for the preparation of styryl-grafted nanotubes [55]. In this work, the carboxylic acid groups on the surface of oxidized MWNTs have been reacted with 4-vinyl-benzyl chlorides via an esterification reaction followed by the polymerization to produce polystyrene (PS)-grafted CNTs [34,36-38]. [Pg.99]


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