Chromates, alkylammonium oxidation

Gelbard et al. have prepared a numbor of neutral and acidic supported ammonium chromates. Neutral resins woe found to be generally more effective dian acidic resins. The large differences in leactiviQr between different unbound, soluble alkylammonium chromates (Section 2.7.6.1) are not so pronounced with the polymer-supported oxidants. Some commoits about the reactivity of these supported oxidants woe made (i) quaternary ammonium salts are more reactive than the tertiary pyridinium chromates (ii) the reactivity of a conqilex chromate XCtOr was found to increase as the basicity of X decreases. Best... 

Two papers this year have described the use of chromate ions for the conversion of alkyl halides or alcohols into aldehydes or ketones (Equation 4). The reaction can be conducted in HMPA in the presence of a crown ether, and although yields are good for allylic and benzylic halides (ca. 80%) they are not so high for saturated halides. " The chromate ion, however, can be supported on an insoluble polymer matrix as the tetra-alkylammonium salt and this both enhances the nucleophilicity of the ion and simplifies the work up procedure. Using the polymer-supported reagent a variety of primary and secondary alcohols were oxidized to the corresponding aldehyde or ketone in excellent yield (ca. 90%). ... 

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