Sciencemadness Discussion Board

methylamine from formaldehyde and NH4Cl won't complete

kangoo - 6-10-2019 at 18:59

There are a number of writeups of the synthesis of methylamine from formaldehyde and ammonium chloride, which are, in summary - reflux at about 104C for 3-4 hours, after which point CO2 evolution stops. Further steps are about the workup/isolation of MeAm.

I have run the reaction at 100-102C (in a boiling brine bath) for 16 hours ( with nearly no stirring I should add) and the reaction continues to evolve CO2, distinguished by quite small bubbles that occur simultaneously with a few larger boiling bubbles. These smaller bubbles also remained as temperature was finally dropped until about 85C.

There is no longer an obvious smell of formaldehyde, but I'm confused as to what's happening

Metacelsus - 7-10-2019 at 04:55

Quote: Originally posted by kangoo  
There are a number of writeups of the synthesis of methylamine from formaldehyde and ammonium chloride, which are, in summary - reflux at about 104C for 3-4 hours, after which point CO2 evolution stops. Further steps are about the workup/isolation of MeAm.

I have run the reaction at 100-102C (in a boiling brine bath) for 16 hours ( with nearly no stirring I should add) and the reaction continues to evolve CO2, distinguished by quite small bubbles that occur simultaneously with a few larger boiling bubbles. These smaller bubbles also remained as temperature was finally dropped until about 85C.

There is no longer an obvious smell of formaldehyde, but I'm confused as to what's happening



Wait . . . why would there be CO2 produced at all? NH3.HCl + COH2 -> CH3NH2.HCl + H2O

PirateDocBrown - 7-10-2019 at 05:35

NH4Cl + 2 COH2 = CH3NH2.HCl + HCO2H

You get CO, not CO2, from the decomp of the formic acid.

S.C. Wack - 7-10-2019 at 16:02

What do you expect at 100-102C without vacuum. Refluxing until CO2 stops evolving does not increase the yield.

Metacelsus - 8-10-2019 at 14:20

Quote: Originally posted by Metacelsus  
Quote: Originally posted by kangoo  
There are a number of writeups of the synthesis of methylamine from formaldehyde and ammonium chloride, which are, in summary - reflux at about 104C for 3-4 hours, after which point CO2 evolution stops. Further steps are about the workup/isolation of MeAm.

I have run the reaction at 100-102C (in a boiling brine bath) for 16 hours ( with nearly no stirring I should add) and the reaction continues to evolve CO2, distinguished by quite small bubbles that occur simultaneously with a few larger boiling bubbles. These smaller bubbles also remained as temperature was finally dropped until about 85C.

There is no longer an obvious smell of formaldehyde, but I'm confused as to what's happening



Wait . . . why would there be CO2 produced at all? NH3.HCl + COH2 -> CH3NH2.HCl + H2O


Dang, I'm an idiot and it's too late to edit this. PirateDocBrown's answer is better.

kangoo - 16-10-2019 at 11:25

Sorry to have abandoned the thread. PirateDocBrown - yeah, that seems to make sense that it would be CO, though in actual point of fact I think the thing I thought was CO may just have been formic acid boiling, not sure.
S.C. Wack, it's not that I had expected it to distill over, I was surprised by the continued evolution, that's all.
Anyway, I distilled under vacuum until ammonium chloride precipitated, filtered, did that once more, and heated until methylamine began to sublimate, with yields just around 45%. Thanks all, and I will be more on top of the thread next time.

S.C. Wack - 16-10-2019 at 13:35

The identity of the gas is determined easily enough with Ba or Ca salts or a CO detector. My prediction is a heavy white precipitate, because formic acid is not converted to CO at 102C or even 107 without strong acids.

BTW none of the known procedures are summarized above; this is not how the reaction is performed. There is something similar, but the reflux until CO2 stops forming is done under aspirator vacuum. There is a good reason why 104C cannot be reached with reflux.

CharlieA - 16-10-2019 at 16:45

http://www.orgsyn.org/demo.aspx?prep=cv1p0347
This a preparation given in Organic Syntheses.

PirateDocBrown - 16-10-2019 at 17:37

Quote: Originally posted by S.C. Wack  
formic acid is not converted to CO at 102C or even 107 without strong acids.


There is HCl present.