Table 1 #38 standard procedure II
Procedure II - Only DCE and the hydride in 30 to 60% excess
"Procedures. 1. Direct Reductive Amination Methods.
General Notes. (a) The amine and the carbonyl compound
are mixed in 1,2-dichloroethane and treated with NaBH(OAc)3.
THF, CH2Cl2, or CH3CN may also be used as solvents.
(b) Acetic acid (1-2 mol equiv) may be used in reactions of
ketones but is not necessary with most aldehydes.
(c) Reactions are normally carried out using the free amines;
however, the amine salt may be used. In this case, 1-2 equiv
of Et3N is added to the reaction mixture. The Et3N must be
removed from basified product prior to salt formation."
"Method I. This procedure is used for most ketone reactions.
A representative example is the reductive amination of cyclopentanone
with hexamethyleneimine (Table 1: entry 4):
Hexamethyleneimine (1.0 g, 10 mmol) and cyclopentanone
(0.84 g, 10 mmol) were mixed in 1,2-dichloroethane (35 mL)
and then treated with sodium triacetoxyborohydride (3.0 g,
14 mmol) and AcOH (0.6 g, 10 mmol). The mixture was stirred
at rt under a N2 atmosphere for 24 h until the reactants were
consumed as determined by GC analysis."
I get the dry players going into this fight and being under dry n2 but not a mention of imine formation drying, in fact quite the opposite with all the "direct" not "stepwise indirect" written in the ref.
From looking at the tables one would infer that methylamine will be faster than #38 by quite a bit, as would additional acetic acid. You say this is a bad assumption and they are not mentioning parts of the tech?
So are these Docs liars? Or white lie tellers?http://www.rohmhaas.com/assets/attachments/business/process_chemicals/reducing_agents/reductive_aminations.pdf
says that it is even better to generate STAB in situ. Researchers were all geared up to to have NaBH4 pulverized under N2, add correct amount of AcOH with the excess for catalyzing, then add the methylamine gassed DCE and ketone, and stir like hell for a day under n2 even though it should be done in hours from the looks of the tables and the read.
Just a good read? That sucks.
So how about titanium salts?
I guess back to a-teaming the PtCl6/NaBH4 and hydrogenation rig. At least nitromethane to methylamine runs in the same rig and solvent, so that scratches that nightmare off the list. What does the peanut gallery think of waiting for the cat to settle then dropping a mesh bag of silica gel in to get the water produced after the nitro reduction? How sensitive is the hydrogenation to water from the imine formation?
There is a thing on Rhodiums back up about using aq. 40% methylamine and p2p, hydrogenating in denatured ethanol, that seems like a pile of water from where I'm sitting.
Sorry this isn't really short questions now, but it follows the last. It will probably only receive short answers. Move/delete/deathray at your leisure. Also sorry if this is too methy. These things are applicable to all the forbidden flavors and a bit beyond the shake and baker or whatever the matchbook scrapers are doing these days.