Dichromate, polymer supported

An effective oxidation of a,p-unsaturated primary alcohols and benzylic alcohols, but not saturated alcohols, to the corresponding aldehydes has been achieved using polymer-supported quaternary ammonium dichromate [14],... 

One research group has exploited the concept of polymer site-isolation in a multistep/one-chamber solution-phase synthesis in which all the reagents, catalysts, and downstream reactants required for a multistep synthesis were combined in one reaction chamber. For instance, a one-chamber/three-step synthesis of substituted acetophenones has been reported (Scheme 10).84 An a-phenethyl alcohol was introduced into a reaction chamber containing the polymer-supported reagents and reactants necessary to accomplish oxidation by polymer-supported pyridinium dichromate 60 bromination by the A-26 perbromide resin 61 and nucleophilic displacement by the A-26 phenoxide resin 62. Filtration afforded the... 

A compound prepared and first described as nicotinium dichromate (NDC) by Palomo et al.,379 was later shown by X-ray-crystal analysis380 to be a betainic mixed anhydride of nicotinic and chromic acid (NACAA). Because of its unique structure, it deserves a close scrutiny of its oxidative properties.381 Replacement of the chloride anion in the quaternary ammonium resin, Dowex 1-X8, for the dichromate anion, leads to a polymer supported dichromate, which is able to make selective benzylic oxidations.382 Finally, poly[vinyl(pyridinium dichromate)] (PVPDC), a polymeric analogue of PDC, must be mentioned whose use in the oxidation of alcohols allows for a very easy work-up.383... 

A series of transformations was also accomplished by the simultaneous use of different polymer-supported reagents (Fig. 10). Parlow [28] published a multistep synthesis from sec-phenethyl alcohol using resin-supported dichromate, perbromide and pyrazol-3-ol. 

Y,7-Dimethylallyl bromide and geranyl bromide are converted into the corresponding aldehydes in 75 and 82% yields, respectively, by heating at 100 °C with sodium dichromate in hexamethylphosphoramide in the presence of dicyclohexyl-18-crown-6 ether [614]. Similar results are achieved with polymer-supported chromic acid [540] (equation 192). 

Several other polymer-bound oxidizing reagents have recently been reported in the literature (reaction 14). A polyethyleneimine-supported silver dichromate 35 has been shown to be a stable, mild, and efficient oxidizing agent for the conversion of alcohols to carbonyl compounds.51 A... 

Goudarzian, N. Ghahramani, P. Hossini, S. Polymeric Reagents. (1). Polyethyleneimine-Supported Silver Dichromate as a New Oxidzing Agent, Polym. Int. 1996, 39,61. 

Alternative approaches have been proposed over the years. In none of these cases is there sufficient experimental evidence for truly heterogeneous catalysis. Frechet et al. (55) used a polyvinylpyridinium (PVP) material for supporting chlorochromate [Cr(IV)02Cl ] or dichromate [CrCVI Oy-]. Cr3+ can be immobilized by simple ion exchange on polymers such as Nation or on a Y zeolite (59, 60). However, it is doubtful whether these methods ensure complete Cr anchoring when the material is brought into contact with oxidants. Clark et al. (61) advocated the use of alumina-anchored dichromate. Particularly when a neutral alumina is used, surface-anchored species are formed ... 

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