Natural Science Forum / Chemistry / Organic Synthesis / February 2006

Well, this is the problem with using tin chloride as reducing agent.
That is why so many people prefers catalytic hydrogenation for the
reduction of nitrocompounds.

I would suggest to use catalytic hydrogenation if possible or to
perform an in situ derivatization of the aniline (acylation, or
protection as uretane), in case that you need to make later
nevertheless this derivatization.

I would not suggest the use of LiAlH4 because you might encounter
greater work up difficulties.

If you need to use tin chloride, it may help during the elaboration to
heat up the paste or to leave it stirring for some time. It might lead
to trituration resulting in bigger microcrystals and an easier work-up.

In fact, hopefully the microcrystals could grow by themselves with no
external help, resulting in an work up facilitated after a couple of
days. Sometimes procrastination works.

Another possibility is to elaborate by drying the reaction mixture and
performing a continous liquid-solid extraction on the resulting solid,
that hopefully would consist in a dust.

The solid could also be incorporated to a silica column, and hopefully
elution with a polar organic solvent could deliver the aniline.

The problem with these two proposal is that the aniline could remain as
an ammonium salt and result in a very polar molecule that would resist
elution with organic solvents.

One important point to consider during aqueous work ups of amines is
that many times a quite high pH is needed to deprotonate amines,
tipically ca. 10. Anilines normally are easier to deprotonate,
although. The point is not making the work up with K2CO3 or whatever.
The important point is the resulting pH. It must be basic enough to
allow the deprotonation of the amine, but not too basic to avoid
emulsions.

Hope it helps.

Gabriel Tojo

Consultant in Organic Synthesis

a soxhlet extraction wouldn't work?

I do think that a soxhlet extraction would work, as long as you are
able to convert the residue in a dust, rather than in a tar of sludge.
You need to remove the solvent, for example in vacuo. If it leads to
sludge because some water remains, you can dry it, for example by
azeotropic distillation with toluene.

Best regards and good luck

Gabriel Tojo

Consultant in Organic Synthesis