Tetrabutylammonium chromate oxidant

A modern version of dichromate oxidation in aqueous media is a phase-transfer reaction carried out in a two-phase system. Alkaline di-chromate is converted into tetraalkylammonium dichromate, which is soluble in organic solvents such as dichloromethane, chloroform, or benzene ( orange benzene ). The treatment of alcohols with a solution of potassium dichromate in acetic acid in the presence of Adogen 464 (Aldrich s trade name for methyltrialkyl [Cg-Cio] ammonium chloride) and benzene gives aldehydes at 55 °C [651. Similar results are obtained with a chloroform solution of tetrabutylammonium chromate at 60 °C [618]. ... 

The addition of chromium trioxide to solutions of alcohols in ether and dichloromethane in the presence of Celite furnishes ketones in 71-93% yields after 35 min at room temperature [535]. Oxidation can also be performed by refluxing the alcohols in solvents such as chloroform, ether, hexane, or benzene with chromium trioxide on an anion exchanger, Am-berlyst A26 [571]. Very good results are obtained when chromium trioxide is converted into tetrabutylammonium chromate by addition of catalytic amounts of tetrabutylammonium chloride in dichloromethane [617. ... 

QCC)385 is able to regioselectively oxidize primary alcohols in the presence of secondary ones. Tetrabutylammonium (TBACC),386 387 butyltriphenyl-phosphonium (BTPPCC) and benzyltriphenylphosphonium chloro-chromates, as they possess no acidic protons, behave as very mild oxidants able to perform selective oxidations on allylic and benzylic alcohols. 

Another chromium reagent for the oxidation of secondary alcohols to ketones is tetra-n-butylammonium chromate which is readily prepared by the addition of tetrabutylammonium chloride to an aqueous solution of CrOa. This reagent is very soluble in chloroform and, although only a limited number of substrates were studied, yields were good (80%) using only a small excess of oxidant. 

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