[tropane]

I reduced an oxime to the amine using LiAlH4 (lithal-for simplicity) and sulfuric acid in THF and quenched with water to give the amine but the paper I used is a patent and no chemical or mechanistic info is present and I can't find the info on the net. Does the nucleophilic Hydrogen of lithal attack the nitrogen centre of the oxime or the the adjacent carbon? I think its the Nitrogen and what role does the sulfuric acid play in this reaction. Does it provide an extra proton to the Nitrogen to form the amine as well as giving lithium sulfate? I will draw a mechanism once I start to understand the reaction better.

[Honclbrif]

If you treated the oxime with H₂SO₄ first, and LiAlH₄ second: you preformed a Beckmann Rearrangement and reduced the resultant amide.

[discodermolide]

I reduced an oxime to the amine using LiAlH4 (lithal-for simplicity) and sulfuric acid in THF and quenched with water to give the amine but the paper I used is a patent and no chemical or mechanistic info is present and I can't find the info on the net. Does the nucleophilic Hydrogen of lithal attack the nitrogen centre of the oxime or the the adjacent carbon? I think its the Nitrogen and what role does the sulfuric acid play in this reaction. Does it provide an extra proton to the Nitrogen to form the amine as well as giving lithium sulfate? I will draw a mechanism once I start to understand the reaction better.

LiAlH4 and H2SO4 will produce alane AlH3 which is pyrophoric and a strong reducing agent

[Kadabrium]

yeah H2SO4 first then LAH

[tropane]

Well I prepared Lithal and H2SO4 in THF first and left it overnight. I then added the oxime in 35 C and stirred for 4 h. I guess I would agree with you Discodermalide since formation of the alane, AlH3 would be the purpose of the reaction inorder to reduce the oxime but then would the alane then attack the nitrogen in a nucleophilic addition type reaction?

[jake.n]

I am guessing you are reducing the oxime to a primary amine?  Otherwise you would be looking at a Beckmann Rearrangement/Amide reduction as mentioned earlier.

It makes sense to me that a hydride would attack the nitrogen atom, displacing hydroxide and forming the imine, then the primary amine.

[tropane]

Yes it is a primary amine that I want....Here is what I think the mechanism is:  Is it right?

[Honclbrif]

I have to admit, I never would have thought of adding H₂SO₄ to LiAlH₄. Sounds like a great recipe for an exotherm/fire. However, upon looking up aluminum hydride, it seems like its got some interesting selectivity. Mind if I ask what your conditions were?

[tropane]

Yeah sure happy to tell you but do you think the mechanism looks right?

[Honclbrif]

Not at all. You've got H⁺ in what should probably be a reducing/basic environment. Then you've drawn the N-O bond breaking while the N lone pair attacks a proton. This should leave the nitrogen with one less e^- pair.

[tropane]

Yes I have missed a step but it is still wrong anyway. Does an alane hydrogen attack the nitrogen displacing the o-AlH2? Can you suggest a possible mechanism otherwise? Thanks

As for the reaction itself to 1 mmol of lithal in THF 10ml at -10C was added 1mmol of 0.5mmol of H2SO4 dropwise!! Leave overnight. Then at rt add the a solutionof dissolved oxime in THF and leave to stir for 4 h. Cool to 0C and add water 1mmol dropwise. Work up by filtration.

I will try and see overnight what the mechanism is but if you can suggest one then that it would be interesting to see.

[Honclbrif]

My best guess. I know I'm playing a little fast and loose with the charges. I'm assuming that Li⁺ is the common counter ion, and the disappearing hydrides (step 2) are used to convert the oximes to the oxime anion.