# Mechanism for an Étard reaction (chromium complex)

In the following reaction, a chromium complex is formed during the Étard reaction:

I have the following questions:

1. How is this complex formed?
2. How does its hydrolysis take place? (What's the mechanism?)

Wikipedia gives a different mechanism for the same reaction. I am in doubt which is correct?

@Jan is this the correct mechanism?

• Wikipedia’s mechanism is basically the same. – Jan Sep 3 '16 at 9:11
• How ? There is disubstitution in book and mono substitution on Wikipedia. I am unable to figure out how after disubstitution hydrolysis takes place? I understand hydrolysis when monosubstituted. – JM97 Sep 3 '16 at 9:13
• Ooooh, now I see it, the two escaped me. But you can think of $\mathrm{S_N2}$ type attack of a water molecule to chromium, displacement of one alcoholate which then rearranges to displace the second one. I’m not in a place where I can draw compounds now though (and won’t be until in a few days). – Jan Sep 3 '16 at 9:16
• 1) pubs.acs.org/doi/abs/10.1021/ic200877f . The proposed mechanism is radical, though it is yet to be proven experimentally. However, the mixture of products is in agreement with this proposal. 2) The mechanism would be extremely hard to prove, but I suppose it should be an addition/dissociation type mechanism, similar to nucleophilic substitution at $sp^2$ carbon atoms. – permeakra Sep 3 '16 at 9:53
• @Jan I am uploading the picture of hydrolysis please check it in the answers column. – JM97 Sep 3 '16 at 10:21