Reducing ketone to alkane

[vegan1]

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Can someone briefly explain to me the mechanisms behind the Clemmensen (Hg(Zn) and HCl) and Wolf-Kishner (hydrazine + base + heat) Reductions of a ketone or aldehyde to an alkane? 😕

I can't visualize what the reactants are doing here, and would rather not blindly memorize these.

Thanks!

 

[rls303]

Hi,
I believe they just reduce the C=O to CH2 as you stated in your post. I don't believe we have to know the mechanism and we just have to memorize the reaction.

Somebody please correct me if I'm wrong.

Thanks

 

[vegan1]

It would just personally help me remember these to understand why, for instance, zinc and mercury cause a ketone to be reduced. Is there a nucleophilic attack going on and then a leaving group that leaves?

 

[loveoforganic]

Pretty sure Clemenson mechanism is unknown.

Wolff Kishner: http://www.organic-chemistry.org/namedreactions/wolff-kishner-reduction.shtm

The reaction is driven by the formation and release of the incredibly stable diatomic nitrogen.

 

[orgohacks]

Pretty sure Clemenson mechanism is unknown.

Wolff Kishner: http://www.organic-chemistry.org/namedreactions/wolff-kishner-reduction.shtm

The reaction is driven by the formation and release of the incredibly stable diatomic nitrogen.

Yeah, the Clemmensen mechanism is obscure. I had to look it up. Essentially it occurs at the surface of the zinc metal.

In a way the mech of the Clemmensen is like the mechanism of the Grignard - you're breaking bonds by pumping electrons into the system from an easily reduced metal. Since the Clemmensen is run in acid you end up protonating the ions that result.

Here's one mechanistic proposal FWIW:
http://www.organic-chemistry.org/namedreactions/clemmensen-reduction.shtm