What is the mechanism for the following oxidation of toluene with $\ce{CrO3}$ in acetic anhydride?

Use of chromic oxide ($\ce{CrO3}$): Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be hydrloyzed to corresponding benzaldehyde with aqueuous acid.

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    $\begingroup$ This appears to be the Étard reaction, which proceeds via a 2,3 Sigmatropic rearrangment. You can read about it here. $\endgroup$ Sep 3, 2016 at 7:00
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    $\begingroup$ In etard reaction Chromylchloride is used and if it were like etard reaction then methyl of toluene will not get disubsituted. $\endgroup$
    – JM97
    Sep 3, 2016 at 7:04
  • $\begingroup$ I don't see why CrO2Cl2 would behave any differently than chromic oxide. Can you explain why you would expect a different outcome? $\endgroup$ Sep 3, 2016 at 7:10
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    $\begingroup$ wikipedia mechanism is based on papers of 1950-60s .. pubs.acs.org/doi/abs/10.1021/ic200877f this is a recent mechanism proposed $\endgroup$ Aug 27, 2019 at 8:34
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    $\begingroup$ What is the evidence that the Etard reaction is [2,3]-sigmatropic rearrangement? Read this: chemistry.stackexchange.com/questions/140039/… $\endgroup$
    – user55119
    Sep 17, 2020 at 20:15

1 Answer 1


The following mechanism is based on the findings made in The Mechanism of the Etard Reaction[1].

Etard like reaction


(1) Necsoiu, I.; Balaban, A. T.; Pascaru, I.; Sliam, E.; Elian, M.; Nenitzescu, C. D. The Mechanism of the Etard Reaction. Tetrahedron 1963, 19 (7), 1133–1142.


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