Benzyltriethylammonium dichromate

It has been claimed that chromium trioxide reacts with tetra-n-butylammonium chloride in water to produce tetra-n-butylammonium chromate, n-Bu4N+HCr04- [7], whereas benzyltriethylammonium dichromate is obtained from the closely analogous reaction of benzyltriethylammonium chloride with chromium trioxide in dilute hydrochloric acid [8]. 

The oxidative potency of dichromates and chlorochromates decreases under less acidic conditions. This is so, for example, when a less acidic ammonium salt is included as counter-ion of a dichromate or chlorochromate anion. Thus, a number of ammonium dichromates and chlorochromates possessing a milder oxidative potency has been described with the specific purpose of allowing very selective oxidations of unsaturated alcohols in the presence of saturated ones. These selective dichromates and chlorochromates include bis(benzyltriethylammonium)dichromate,135 tetramethylethy-lenediammonium dichromate (TMEDADC),136 imidazolium dichromate (IDC),137 N, A -dimeth y I a m i n o py r id i n i u m chlorochromate (DMAPCC),138 l-(benzoylamino)-3-methylimidazolium chlorochromate (BAMICC)139 and butyltriphenylphosphonium chlorochromate (BTPPCC).140... 

With only minor modifications it is possible to prepare a selective oxidant for benzylic alcohols benzyltriethylammonium chlorochromate under phase transfer conditions exhibits such a preference. The preparation of benzyltriethylammonium chlorochromate had been reported previously, but was initiidly assigned as the dichromate. It was demonstrated that this reagent (chromate or dichromate) shows good selectivity for benzylic and allylic alcohols, but unfortunately it was necessary to perform the oxidation in HMPT. 

Suitable mechanisms have been proposed following determination of the kinetic and activation parameters for oxidation of 2-naphthol and cyclic ketones by nicotinium dichromate some a-amino acids by tripropylammonium fluorochromate " distyryl ketone by quinaldinium fluorochromate methanol by benzyltriethylammonium chlorochromate catalysed by 1,10-phenanthroline substituted benzyl alcohols by tetraethylammonium bromochromate L-cysteine by pyridinium bromochromate lactic acid and 3,5-dimethyl-2,6-diaryl piperidin-4-one oximes by pyridinium chlorochromate allyl alcohol by IDC benzophenoxime by bispyridine silver(I) dichromate and alkyl phenyl sulfides by cetyltrimethylammonium dichromate. A non-linear Hammett plot obtained for the oxidation of substituted benzyl alcohols by IDC has been attributed to the operation of substituent effect on two steps of the proposed mechanism. " Kinetic and activation parameters for oxidation of o-toluidine and of A-methyl-2,6-diphenyl piperidin-4-one oxime and its 3-alkyl derivatives by sodium dichromate have been determined and suitable mechanisms have been suggested. Micellar catalysis in the 1,10-phenanthroline-promoted chromic acid oxidation of propanol... 

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