Having worked with nitropropene reductions using NaBH4 / formic acid, i would like to share some comments on that reaction type.
First of all: To hell with LAH, these reactions are seriously nice to work with.
The borohydride reduction is well known to many people. It is really fast, and the workup is a breeze.
Reduction of the nitro group can be performed with formic acid, as described in
Indian Journal of Chemistry, Section B: Organic Chemistry (2001), 40B(1), 75-77.. Barium has tested the reaction with ammonim formate, so swim decided to test it with formic acid. The reaction is very vigorous and care must be taken when adding the formic acid, as it WILL boil over if added to fast(max. 5% of the formic acid can be added per time).
It is also very important to activate the zink with 5% hydrochloric acid before use. The first run was done without doing this, as swim thought the formic acid would eat through the oxide layer and activate it in-situ. It might have done that in time, but swim was not patient enough. On the second run activated zink was used and the formic acid was added without to much thought. Bad idea, 20% of the reaction mixture got splattered on the hot plate.
Here is the technical writeup, using 2,4,5-trimethoxynitropropene(which was prepared alá Barium):
6 grammes of 2,4,5-trimethoxynitropropene was reduced alá
Barium
(
https://www.thevespiary.org/rhodium/Rhodium/chemistry/nitrostyrene.nabh4.reduction.html) to give 5,6 grammes(93% yield) colorless crystals of 2,4,5-trimethoxynitropropane. The only difference was that chloroform was used in stead of toluene for the extraction of the nitroalkane.
5,6 grammes of the isolated crystals where dissolved in 22 mL methanol and mixed with 2,0 grammes of activated Zn. 12 mL 85% formic acid was added in small portions(the first portion caused a major boil over, be seriously carefull; it is even more agressive than LAH reductions). After addition, the mixture was allowed to return to room temperature and filtered to remove the Zn/salt slurry. The remaining liquid was slightly yellowish. The solvent was stripped, and the remains where acidified with HCl and dissolved in water. Afterwards it was washed once with chloroform. The water was basified with sodium hydroxide, which caused a clear oil to fall out(TMA-2). There was not enough time for work up, so yeilds will be posted later.
There is no obvious reason to go through the trouble of making a salt of formic acid, when that can be used straight away.
All in all:
-The reaction is faster than LAH reductions
-It's mega cheap
-It does not want to kill and destroy you like LAH with ethers.
-It's high yielding.
-It's less suspicious chemicals that are used.
-It seems more clean than LAH reductions.
The reaction is so cheap and easy, that swim will refer to it as the Joan Collins reaction from now on!
Swim is definately over his LAH days, that's for sure.
Regards
Bandil