NaBH4 isn't exactly cheep when you compair it to the amalgum routes and you will have to use that to reduce your Nitromethane to methylamine as well as having enough to reduce the imine.

It would be so much better and higher yeilding in BOTH versions of the synthesis to use MeNH2 and form the imine THEN reduce it instead of trying to cut corners. Even using nitromethane as the methylamine source during an amalgum reduction you would find it much harder to control then if you just dripped the imine into the reaction. Trying to control two concurrent reactions which both can be fairly violent in an amalgum can get hot and hairy as well as make it hard to determine your exact concentration of imine, methylamine,ketone ect.....

The the Methylimine Schiff base is stable in wet conditions hence the reason NaBH4 was a favorite means in days done past. I know I haven't exactly answered your question but I do pose the question of is it really economical to use MeNO2 as the MeNH2 source or is it just lazyness? Just something to think about.

I never thought about that Lugh I was more wrapped up in why someone would waste NaBH4 on such a thing to consider that fact that it might not even work. IIRC NaBH4 will just reduce a nitro to an alkane in an unsaturated compound under normal conditions. I could be wrong though. However it has been accomplish with the use of randy nickle in conjunction.

Rapid, efficient and selective reduction of aromatic nitro compounds with sodium borohydride and Raney nickel


I would suggest that the OP start searching around for NEW methods of reducing imines instead of trying to short cut established methods. Hell if some people looked more into Tungstic acid they may find that there favorite alkene could be aminated in a one pot in high yeilds. Thats something that needs to be researched.

Don't get me wrong now if you have access to NaBH₄ by all means add Alcoholic MeNH₂ and form the imine then reduce that with the borohydride because The Al/Hg sucks on so many levels. I have heard its excessively hot reaction, wants to run out of control without proper addition rate and is a bitch to filter and workup with so much toxic shit around.

As Lugh said use your Nitromethane to make MeNH₂ via Al reduction or Fe+HCl reduction and use that as your methylamine source. You will increase yeilds this way using methylamine instead of MeNO₂. Also look into ways of reducing imines as you may find there are alternatives to using either Al/Hg or NaBH₄.