kangoo
Harmless
Posts: 5
Registered: 27-8-2019
Member Is Offline
|
|
methylamine from formaldehyde and NH4Cl won't complete
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
International Hazard
Posts: 2542
Registered: 26-12-2012
Location: Boston, MA
Member Is Offline
Mood: Double, double, toil and trouble
|
|
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
National Hazard
Posts: 570
Registered: 27-11-2016
Location: Minnesota
Member Is Offline
Mood: No Mood
|
|
NH4Cl + 2 COH2 = CH3NH2.HCl + HCO2H
You get CO, not CO2, from the decomp of the formic acid.
Phlogiston manufacturer/supplier.
For all your phlogiston needs.
|
|
|
S.C. Wack
bibliomaster
Posts: 2419
Registered: 7-5-2004
Location: Cornworld, Central USA
Member Is Offline
Mood: Enhanced
|
|
What do you expect at 100-102C without vacuum. Refluxing until CO2 stops evolving does not increase the yield.
|
|
|
Metacelsus
International Hazard
Posts: 2542
Registered: 26-12-2012
Location: Boston, MA
Member Is Offline
Mood: Double, double, toil and trouble
|
|
| 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
Harmless
Posts: 5
Registered: 27-8-2019
Member Is Offline
|
|
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
bibliomaster
Posts: 2419
Registered: 7-5-2004
Location: Cornworld, Central USA
Member Is Offline
Mood: Enhanced
|
|
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
National Hazard
Posts: 646
Registered: 11-8-2015
Location: Missouri, USA
Member Is Offline
Mood: No Mood
|
|
http://www.orgsyn.org/demo.aspx?prep=cv1p0347
This a preparation given in Organic Syntheses.
|
|
|
PirateDocBrown
National Hazard
Posts: 570
Registered: 27-11-2016
Location: Minnesota
Member Is Offline
Mood: No Mood
|
|
There is HCl present.
Phlogiston manufacturer/supplier.
For all your phlogiston needs.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
