Sciencemadness Discussion Board

N-methylformamide problem, can any brains solve??

organicmadness - 13-6-2013 at 18:55

To all Organic chemists, which one of you has the brains to figure out this one?

So I was doing my research into N-methylformamide, and realised that there are two forms that exist. One boils at 180-185 degrees, and the other boils at 199-201 degrees.

With reference to the N-meth that boils at 199-201:
There are two resonance structures. There is a partial double bond that exists between the carbonyl carbon and the nitrogen which gives rise to a high rotational barrier. This molecule is not able to rotate around its main axis. The positive charge on the nitrogen is due to the double bond, which makes it useless to work with.
Something has been done to the higher boil point nmf that keeps it in the non active state. For it to react, the nitrogen needs to have a spair pair of electrons, which it doesn't.


Is there a way to reverse this to get to the 180 degree boiling point n-methylformamide FROM the 199-201 degree n-methylformamide?

NB:

The reaction used from the industrial company to create the 199-201 N-methylformamide:

Methylamine (CH5N) + Methyl formate (C2H4O2) ----->
N-methylformamide (C2H5NO) + Methyl alcohol (CH4O)



[Edited on 14-6-2013 by organicmadness]

[Edited on 14-6-2013 by organicmadness]

ScienceSquirrel - 14-6-2013 at 05:27

Do you have any references?

KrysHalide - 14-6-2013 at 06:37

Seems like archaic alchemie to me.. There can't be two "forms" of the same molecule, except for enantiomeres.. Which isn'rt the case here.

There are tautomeric forms, but these are in equilibrium. You cannot seperate one form from the other, so IMHO, there no "active" N-methylformamide vs "inactive" N-methylformamide.

All there is N-methylformamide, which can tautomerize in two different formal representations, the "enolate like" and the carbonyl form.

Please prove otherwise


A hydrated derivative might account for seperate bp, but then again we are not talking of the same molecule.

[Edited on 14-6-2013 by KrysHalide]

Dr.Bob - 14-6-2013 at 10:28

I concur, there are not two isomers of N-methylformamide. N-methylformamide has a BP of ~200C. Not sure what the other material might be, but it is not N-methylformamide.

Nicodem - 14-6-2013 at 12:08

Quote: Originally posted by organicmadness  
So I was doing my research into N-methylformamide, and realised that there are two forms that exist. One boils at 180-185 degrees, and the other boils at 199-201 degrees.

Seriously? Two liquid forms of the same compound? And you don't even bother to give the reference for this extraordinary thing?
Quote:
With reference to the N-meth that boils at 199-201:There are two resonance structures. There is a partial double bond that exists between the carbonyl carbon and the nitrogen which gives rise to a high rotational barrier. This molecule is not able to rotate around its main axis. The positive charge on the nitrogen is due to the double bond, which makes it useless to work with. Something has been done to the higher boil point nmf that keeps it in the non active state. For it to react, the nitrogen needs to have a spair pair of electrons, which it doesn't.

Sounds like you might be trolling, but just in case you are serious: Formamides do not form stable rotamers (atropisomers). Their rotamers interconvert easily at way bellow their boiling point. And resonance structures have nothing to do with isomeric substances - they are only a pedagogic tool to teach students the bond delocalization.

KrysHalide - 14-6-2013 at 12:15

Detritus?

wackojacko - 14-6-2013 at 18:12

The Merck indeax states bp of 180-185 yet once checked various companys MSDS they vary some are 180-185 while others are 199-201 both CAS 123-39-7

wackojacko - 15-6-2013 at 00:54

also i have a friend who tried both the 180-185 and 199-201 with p2p and only the 180-185 worked

wackojacko - 15-6-2013 at 03:28

could it be that they have treated it to concerve the double bonded nitrogen???

unionised - 15-6-2013 at 03:56

Which is more likely?
A mistake in recording the BP, or a weird situation where one liquid has two boiling points?

organicmadness - 15-6-2013 at 16:26

None of the information has been really helpful. The question is not whether or not resonance structures exist.
There are for a fact, two forms of n-methylformamide that exist in the industrial industry. Take my word for it. Some manufacturers sell the nmf that boils at 199-201. And others the one that boil at 180-185.

The 199-201 definitely DOES NOT work or react.

My question is, does anyone know a way of potentially changing the nmf that boils at 199-201 TO 180-185?? That is the question...

Any brains?

AndersHoveland - 15-6-2013 at 16:41

Quote: Originally posted by Nicodem  
Formamides do not form stable rotamers (atropisomers). Their rotamers interconvert easily at way bellow their boiling point.

I do not know if this is true. Nicodem, are you absolutely sure about this?

The structure of formamides contains a somewhat delocalized bonding, since they are electron-donating. In fact, it would be more accurate to draw a diagram with the double bond between the carbon and nitrogen atom, with a positive charge on the nitrogen and a negative charge on the oxygen atom. Assuming Nicodem was wrong, this could potentially prevent rotation, and there would be two stereoisomers (presumably one configuration with the oxygen pointing out 60 degrees away from the methyl group, and the other with the oxygen atom pointing away).

I have never read anything about this before. However, if there were two forms of the compound, I would think that the way to interconvert them would be to use a non-nuceophilic base like N,N-Diisopropylethylamine.

[Edited on 16-6-2013 by AndersHoveland]

watson.fawkes - 15-6-2013 at 18:20

From the end of this page:
Quote:
Thus, the barrier to rotation about the NH2–CHO bond in formamide is over 18 kcal/mol, and the CH3NH–CHO bond in N-methylformamide is more than a kcal/mol greater. Such barriers permit the observation of conformational isomers of amides by room temperature nmr. For simple amides like N-methylacetamide and the formamides noted above, the trans conformer is more stable than cis by more than 1.5 to 2.5 kcal/mol.

organicmadness - 15-6-2013 at 21:19

The only way that makes sense is a nucleophilic attack on the carbon which would drive the double bond back to nitrogen. Would sodium acetate as a strong conjugate base work?

Crowfjord - 16-6-2013 at 17:04

Organicmadness, if you want anyone to take you seriously on a science forum, please provide a reference. Why should anybody just "take your word for it"?

If what you say is true though, I figure the higher boiling variety is merely impure, resulting in boiling point elevation (freshman chemistry). All the formamides have partial double bond character at the C-N bond, giving a planar shape to the molecule and a rotational barrier, just as stated by the reference given above by watson.fawkes.

GreenD - 19-6-2013 at 13:50

Not sure but it would seem to me pure formamide would be the lower bp, while the higher is a solution of formamide/n-methyl formamide.

I can't find that there is an azeotrope, but... maybe.