Oxymercuration of Alkynes

by James

Description: Alkynes treated with mercury (usually HgSO4) and water will be hydrated to give ketones, via an enol intermediate.
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{ 6 comments… read them below or add one }

Andrew Ross April 8, 2013 at 1:43 am

If I remember organic I correctly HgSO4 is only required for terminal alkynes so that the reaction is carried out under more mild acidic conditions, and that for internal alkynes it isn’t necessary but often is carried out in this manner as well (the HgSO4 component, that is)?

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james April 10, 2013 at 9:56 pm

With HgSO4 the reaction is milder than with straight acid (e.g. H3O+) although in truth more advanced methods these days avoid mercury and use late metal cations such as Au and Ag

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Seah October 25, 2013 at 11:43 am

Given that the cyclic mercuronium ion formed in step 2 has lone pairs of electrons on it and that resonance is possible, shouldnt the ion be anti aromatic and unstable? Is it possible that the intermediate in step 2 is a vinylic carbocation?

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James Ashenhurst October 27, 2013 at 6:21 pm

The C-Hg bonds are very long and orbital overlap between any empty p orbital on Hg with the carbon p orbitals is likely very poor. Antiaromaticity isn’t really a concern here.

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Carl Silverstein November 9, 2013 at 2:43 pm

Will HgSO4 have an effect on a double carbon bond?

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James Ashenhurst November 11, 2013 at 3:43 pm

Yes – it will work just as well as Hg(OAc)2 . For alkynes we generally use HgSO4 because the reaction is done in concert with H2SO4, which helps to remove the mercury from the substrate.

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