[54712-57-1] · C16H36ClCrNO3 · Tetra-n-butylammonium Chlorochromate · (MW 377.98)
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.
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
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
University of Rome
La Sapienza and CNR, Italy