Tetra-n-butylammonium Chlorochromate1


[54712-57-1]  · C16H36ClCrNO3  · Tetra-n-butylammonium Chlorochromate  · (MW 377.98)

(mild and selective oxidizing agent for benzylic and allylic alcohols;2 can oxidize thiols2)

Alternate Name: TBACC.

Physical Data: mp 184-185 °C.

Solubility: sol ethyl acetate, THF, CHCl3, CH2Cl2.

Form Supplied in: orange crystalline solid; widely available.

Handling, Storage, and Precautions: the dry solid is nonhygroscopic, but must be stored in the absence of light, since it slowly darkens within weeks, although without losing its oxidizing power. Reaction solvents must be anhydrous and free of reducing impurities. Tetrabutylammonium chlorochromate is reported to be a toxic agent. Use in a fume hood.

Oxidation of Benzylic and Allylic Alcohols.

As is well known, the oxidizing power of heterocycle-chlorochromate salts is inversely proportional to the basicity of the amine counterpart of the chlorochromate anion. Consequently, tetrabutylammonium chlorochromate is described as a neutral, mild, and selective oxidant for benzylic and allylic alcohols. The reagent (3 equiv) very slowly oxidizes these alcohols into the corresponding carbonyl compounds at rt in 68-88% yield (eqs 1-3).2a No (E)/(Z) isomerization is generally observed.

In refluxing chloroform, the oxidation of benzylic and allylic alcohols is achieved in a reasonable period of time (1-24 h) and in good yields. Using 3 equiv of oxidant, saturated aliphatic alcohols are oxidized to a minimum extent both at rt and in refluxing chloroform. For example, treatment of 1-phenyl-1,3-propanediol with TBACC at 70 °C for 1 h affords 3-hydroxy-1-phenyl-1-propanone in 52% yield (eq 4).2

With a large excess of oxidant (6 equiv), primary and secondary aliphatic alcohols can be oxidized slowly in refluxing chloroform to carbonyl compounds in 50-75% yields.2a

Oxidation of Thiols.

TBACC can rapidly perform oxidative coupling of thiols to disulfides in good yield. The reaction can be applied to both alkanethiols and arenethiols, and appears to be superior to Pyridinium Chlorochromate for this transformation (eq 5).2

1. (a) Haines, A. H. Methods for the Oxidation of Organic Compounds; Academic: London, 1988; p 39. (b) Ley, S. V.; Madin, A. COS 1991, 7, 283.
2. (a) Santaniello, E.; Milani, F.; Casati, R. S 1983, 749. (b) Luzzio, F. A.; Guziec, F. S. OPP 1988, 20, 533.

Giovanni Piancatelli

University of Rome La Sapienza and CNR, Italy

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.