A perhaps helpful modification of the synthesis is to use zincdust as catalyst. Lower reaction temperatures and significantly higher yields as all formaldehyde is available for forming the methylamine and gets not used up as reducing agent forming formic acic (which is partly decomposed whereby CO2 evolves).
An 50% to 100% overfold (of theory) of ammmoniumchloride suppresses here the formation of dimethylamine virtually completely. A polymerisation of methyleneimine to the trimer was never encountered. If thus had taken place then only in amounts not important for the reaction.
The reaction runs best at ambient or lower temperatures
With Hexamine and ammoniumchloride:
100 gram HMTA are dissolved in 1 liter H2O at about 10°C. The flask is placed in a waterbath. Over about 5 hours under strong stirring slowly is added 30% HCl, 25 gram ammoniumchloride (salmiac) dissolved in 0,5 liters H2O and zincdust. During this time cold water runs through the waterbath cooling the flask. It should not get to hot now thats all. Done. The reaction is forgotten overnight (stirrer runs medium) and next day it is regretted to have used an open vessel. No harm but stink. This reaction forms methylamine and not methylamine HCl if done right. The amine freebase gets steamdistilled (basify if necessary, not worth to mention) and is collected in dil.HCl if the hydrochloride is whats wanted or in H2O if a aquesous solution is what one heart desires. It is advised to form the hydrochloride and wash with chloroform to remove possible dimethylamine residues at least the first times this is done. If the chloroform washes show that no or near to zero dimethylamine is present this may be skipped in future if the procedure stays otherwise unchanged.
Yields are up to 80% of theory counted on the used hexamine, the overfold on ammoniumchloride may be extracted from the residue and reused I guess.
A closed vessel and ventilation are recommended, also to setup the complete rig incl. steamdistillation from start on. It can be done without having to open the vessel once and no smell at all (ok, not absolute but no problems causing). Very brave ones may do this in a open beaker with a handmixer - they will have no friends for weeks.
The LEUCKART-WALLACH reaction is often better catalyzed by zinc/HCl than formic acid. It´s worth a look for all interested in this "good old style" reactions.
Zinc: For those who don´t have the possibility or don´t want to buy zincdust at a chemsupplyhouse there are two ways to aquire it as I know: Recovering the zincdust from spray or paint or milling metallic pure zinc. The metal is easy available as ingoy and not watched. (Only the dust for it´s impacts on health and the possible use in explosives maybe restricted - check your tribal rules for this). As zinc gets brittle at about 220°C it is astonishing easy to get the dust, the metal if pure nearly mills itself at this temperatures. (to use steelballs for milling is plain stupid - lead or ceramic/glass, nonsparking, the dust IS explosive).
Oh, I forgot the amounts of HCl an zinc?
No, I didn´t.
Edit by LT/ : see
Post 414873
(Rhodium: "Cyclic Methyleneamines. Part I.", Tryptamine Chemistry)Edit by Organikum/ : see also
Post 378615
(Organikum: "hexamine to methylamine a old new way?", Methods Discourse)In the post of Rhodium the reaction is to hot (reflux) and to much HCl ("excess HCl") is added at a time. If done right virtually only monomethylamine is the product and this is mostly in the form of the freebase - only small amounts of NaOH are needed to free all for steamdistillation. (so far I can judge this of course. Yields in first, not optimized runs seem to back it up).
But a highly interesting read this post of Rhodium hidden in the Tryptamines forum, for sure.
