Formic acid reduction - comments

[Bandil]

Hi!

While using formic acid, the final mixture should get quite acidic, as there is quite alot of acid in the reaction broth. Isn't it the formic acid salt or something, of the PEA/amphetamine, that's in the mixture, after the reaction?

If that is the case, couldn't one expect that some of the product would fall out of the solution(as the salt is not very soluble in methanol)?

Regards
Bandil

[dr_mabuse]

Hi!  

I don't think that the amine formate will crash out of the MeOH, I suspect that it is quite soluble in alcohols. The precipitate seen is probably Zn formate?

Well, even if it would, I just slowly basified the mixture using cold 20% NaOH, extracted with toluene, vac filtered off the precipitated Zn(OH)₂, washed this with some toluene, and extracted the mother liquor again 2x with toluene. So even if the salt precipitated, it should be basified and all go into the toluene after the  NaOH addition.

Bandil, you said you had a runaway reaction. I placed the mixture in a cold waterbath (5-10°C), and still after adding the first small portion the temp of the contents rose to 25°C. After this the temperature was easily kept below 20°C.

I really suspect this is where the mistake is. With Zn/AcOH a raised temperature is also used IIRC, and I also suspect that the formic acid needs this to decompose efficiently, and thus be a hydrogen donor to the activated Zn.

I think placing a mixture of activated Zn and the nitroalkane in methanol in a large enough flask equipped with a reflux condensor and magnetic stirrer, and adding the HCOOH dropwise from an addition funnel might do the trick here. If the exothermic reaction is not enough to consume all Zn, some external heat from a waterbath may be applied.

This is how a next trial will be, in the nearby future. Wish me luck   .