Methylamine From Hmta2
Methylamine From Hmta2
Methylamine From Hmta2
Figure 5: A part of the liberated formic acid is oxidized to water and carbon
dioxide
Most of the formic acid which is formed above, is evolved during the reaction
as carbon dioxide during the heating of the solution.
This was misinterpreted by Eleusis, who thought the reaction proceeded like
HMTA + 4 HCl => 4 MeNH2*HCl + 2 CO2.
Here is an excerpt from a letter I got from him, when I told him that the
byproduct formed was ammonium chloride:
Not when I did it. NO Formaldehyde smell was ever noticed. In fact, the
mixing of Hexamine with HCl, if done *slowly* is fairly docile with no real
smell elicited. However when you heat the filtered mixture on the stove, it
*definitely* stinks to high heaven, but the smell at first is more like an
*isocyanate*. If one immediately dumps the reaction mixture onto the stove
(skipping the filtering) it takes *hours* (almost days!) to evaporate but 4
moles of methylamine are produced. If you wait for the precipitate to form,
then filter it, you get 240-270g of methylamine HCl from 140g of Hexamine.
Methylamine HCl weighs 67.5, and 4 times that is, not-so-coincidentally,
270g. I have only the slightest idea what the white precipitate that forms is,
but it smells like an isocyanate (very nasty, very poisonous).
I *do* have a text copy of the translation I did of the original french journal
article and it was by R. Cambier and A. Brochet [6]. In their article they state:
They also state, and I quote my own translation here (from 1800's french):
Unfortunately, Eleusis was wrong here. The reaction between Hexamine and
hydrochloric acid is the same as between ammonium chloride and
formaldehyde, and also the same as between ammonium chloride and
paraformaldehyde.
Synthesis
A standard run, from 250 grams ammonium chloride and 500g 37%
formaldehyde (containing 15% methanol), gives 100-134 grams methylamine
hydrochloride, 27 grams dimethylamine hydrochloride and 81 grams of
recovered ammonium chloride. The distillate contains methylal
(formaldehyde dimethyl acetal) and methyl formate, which after treatment
with NaOH can yield 25g of sodium formate and 30 grams of methylal, as the
compound cannot be separated by fractional distillation, neutralization is the
way to go. Ammonium chloride is very sparingly soluble in a concentrated
solution of methylammonium chloride, making the separation of the
compounds pretty sharp.
140 grams HMTA (1 mole) was slowly dissolved in 400 ml water and 400ml
37% HCl (4 moles) was added. If the hydrochloric acid is added directly to the
HMTA, a lot of it is lost, as ammonium chloride starts to separate almost
immediately. The mixture was heated on a temperature controlled heating
plate, and the contents was slowly distilled while the temperature slowly rose
from 100C to 109C during 1-2 hours, during which time a lot of CO2 was
evolved, and approx 75ml of formaldehyde-smelling distillate was collected.
The solution was concentrated under vacuum until a lot of solids precipitated,
which were filtered off, and the solution was further concentrated, filtered etc
until everything was crystallized. The last crop of crystals was very hard to
crystallize, and care must be taken not to burn the contents of the flask, it
must not be allowed to rise over, say 75C. The white solids were placed in
150ml warm methanol (cheaper than denatured ethanol), and was filtered.
The insoluble portion was recrystallized from water, to give 40 grams of pure
ammonium chloride, which looked like very large snowflakes. The methanol
solution was evaporated, recrystallized from methanol and washed with
acetone, to give a deliquescent crystalline mass, which was dried in a
desiccator over CaCl2, to give XX grams of methylamine hydrochloride (XX
moles) as a fluffy soft powder. Calculated on the two moles of amine nitrogen
put into the equation, XX% became methylamine, and 37% (0.75 mole)
became ammonium chloride. The net yield of methylamine is therefore XX%
of the processed nitrogen.