Hi!
Based on my reflections about the *real* advantage of adding ethanol to a hexamine/NH4Cl/HCl methylamine leuckart (in fact its a leuckart with formaldehyde!), I just decided to give the procedure outlined in
Patent DE468895
another try, and tried to modify the rxn parameters to challenge the following statements:
- According to the patent, one of the benefits would be that the reaction already succeeds at below 75°C, whereas normally >90°C are required.
- Also (and maybe far more important), the formaldehyde, upon oxidation, does result in formic acid - and this formic could normally serve as a methylating reducing agent for MeAm, resulting in diMeAm formation. But with ethanol being present, the acid should ideally be completely converted to its ester (ethylformate), and through removal by distillation, all formed formic acid should (ideally) be removed as it is formed.These two main statements in the original text can be well taken to the test: by quickly heating the reaction exactly to the point at which ethylformate
begins to come over (based on previous runs, I know this point is 85°C on my variac/heating mantle), then holding it there for a
long time to make sure all formaldehyde has reacted, all formic was esterified and all formed ethylformate has been removed by distillation (i.e. let it run overnight).
If the above claimed benefits are correct, the reaction should be finished at this stage, as the temperature was held above 75° for many hours
and in theory, all "harmful" formic acid should've been removed completely, i.e. from 48g hexamine, one should get 2.05mol of HCHO which in turn can act on 1.63 mol NH4Cl - therefore, ~131ml ethylformate should be formed in theory...
(..and this is well in accordance with the following observation: even far below 80°C, formaldehyde obviously reacts readily with "something" to produce formic which in turn esterifies to EtCOOH - at least there is ethylformate formed long before this temp. is reached! In fact, the threshold for its formation to occur was observed being ~43°C rxn temp...)
And as there are excess ethanol and NH4Cl present, the reaction should ideally give almost quantitative yields (calculated from formaldehyde) of pure methylamine hydrochloride (and the remaining excess of NH4Cl of course)
without any di- or even trimethylamine impurities... theoretically at least, or so to say, if the inventors knew what they got patented back then...
So far the theory.
As already said, I wanted to challenge this. The following procedure was used:
48g hexamine (fuel tabs) were dissolved in 100ml warm tap water and filtered through a pad of celite with the aid of vacuum in order to remove any waxes and binders. The resulting clear solution was put in a 500ml two-neck RBF along with a big ass stirbar. Then were added 14g NH4Cl, followed by 90ml EtOH. The RBF was fitted with a distillation rig and 160ml 31% HCl were added through the side neck which afterwards was equipped with a (second) thermometer submerged into the rxn liquid for measuring the rxn temp. HCl addition caused a bit of white smoke to travel down the condenser and the exothermic hex hydrolysis caused the rxn temp to climb to 40°C and everything became slightly milky.
Using a heating mantle equipped w/variac, the rxn was then brought to 80°C (internal rxn temp.) over the course of exactly 1 hour, causing the formation of a clear ethylformate top layer and, upon reaching the said temp., a slight reflux. At this point, the cloudiness had disappeared completely (waterlike, clean).
When the variac controller setting was raised to >80°C (82.5° internal rxn temp.), the ethylformate slowly started to distill with a steam temp. of 42-58°C (I didn't allow it to climb higher but cooled it if it happened; as the proper separation of ethanol and formate isn't warranted anymore if this happens).
The upper layer disappeared quickly within one hour, but formate still came over at a rate of 1 drop every 5-6 seconds while steam temp levelled of at 53°C (rxn. temp. 80.5° C). This is now heated at 85°C overnight...I'll get back with the results tomorrow!
(just in case...: anyone impeaching above procedure before results are in is immediately catalogued on my "personal asshole N°1"-list as one of the top ranks forever... So control your temper until you can fully judge about it please!!)
[EDIT] exactly 9 hours and 20 minutes of careful heating have passed since I combined the reagents, the internal rxn temp. is still 85°C with ethylformate coming over at a steam temp. of 49°C at a rate of 1 drop every 10 seconds - and interestingly, the solution has become slightly greenish tinted, although the amount of distillate collected is only about 60ml... Just cranked the variac up to 90°C - think I'll let it run for a few more hours.
I'll be back soon...
BTW did you realize the similarities to a leuckart? Slow heating over long time, resulting in faint bubbling due to *slow* decomposition of the reducing agent (only that it decomposes just to formic rather than complete decomposition to CO2 - like would be the case with *real* leuckart - but faint bubbling can be seen in both cases....)
[/EDIT]Greetz A