I was wondering if it is possible to make formaldehyde (1) from urea (2).

formaldehyde and urea

I noticed that they have a similar structure, but the two hydrogen atoms in formaldehyde are replaced with two amide groups in urea. Would it be possible to remove those groups and replace them with hydrogen?

  • $\begingroup$ Technically yes, but it would require much more than one step. $\endgroup$ – Jan Nov 3 '16 at 18:31
  • $\begingroup$ Do you have any suggestions? $\endgroup$ – Martin Nov 3 '16 at 22:52

This is more a proposition than an answer but after a lot of search on the net, in publications and also with the help of @orthocresol, @Jan and @jerepierre, I propose a reaction that will work. Also the question ask is really unusual, because it is obviously awfull to want to synthetize formaldehyde from urea.

You will find first in this "answer" the best way we found to make it. When I'll have time, I'll add all ideas I had and explain why it was not a good point.

A good question raised by this question is, "is it possible to "cut" the $\ce{C-N}$ bond to replace it by a $\ce{C-H}$ bond?" and if possible in one step. For the moment nobody knows.

The best way we found : synthesis of methanal from urea best way

For the moment I can't explain you why I chose to make the N-alkylation but I know I got it in many of my organic chemistry lessons that this groupement will leave the molecule involving LAH so I wanted to do that. Also we are not at one more step from urea to get formaldehyde.

For the other part formaldehyde is much more reactive than the amide function because on the "diamide" both lone pair of nitrogen atoms are involve in mesomeric forms with the oxygen. Then the carbon is really not electrophilic and LAH will react then one the most reactive function in the reactor which will be the aldehyde.

And then the Formox process because it is use in the industry so I'm sure it will work.

After you will find ideas I had but that won't work too. I'll explain as much as as possible when it will be possible. Sometime it will be only because by experiments nobody have ever succeeded to do it.

This one won't work, one of us, I don't remember who didn't find anything in SciFinder about the possibility to make Eschweiler-Clarke reaction from an amide and especially urea.

This is really awfully awkward because you need formaldehyde itself to make the synthesis of formaldehyde. I was not thinking at that when I start but few minutes later it appears to me that I haven't realize before ^^

synthesis of methanal from urea

At the begining I thought it was great to use $\ce{HCl}$ in excess with $\ce{NaNO_2}$ and then get the carbonic acid $\ce{HO(CO)OH}$, because there is nice ways to reduce this acid and its derivatives but just one time. You can find informations in this publication. But when you have $\ce{H(CO)OH}$ I have really no idea of what to do, even $\ce{LiAlH_4}$ won't work. So at the moment I just have the first possible reaction.

Well also in terms of atoms economy using urea to synthetise formaldehyde is absolutely awkward too.

I hope you find some fun here, I keep thinking about it but it looks to be tricky. Have a good day.

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    $\begingroup$ Eschweiler-Clarke is typically for amines, not amide-type nitrogens. Is there reference for this? How is the formaldehyde not going to be reduced by LAH? $\endgroup$ – jerepierre Nov 10 '16 at 21:19
  • $\begingroup$ @jerepierre This is not an answer as one can understand "answer" this is a proposition. I'm only a chemical engineering student. But I have this reaction in my organic lesson and this is not write anything about "R" in "R-NH2" so I can't answer you. If you use the correct amount of LAH things must work. However I'm note sure if it is possible to reduce formaldehyde with LAH. $\endgroup$ – ParaH2 Nov 10 '16 at 21:27
  • $\begingroup$ @jerepierre what do you think so if I do first a Wittig to "protect" the ketone function, I do my to steps like I did and at this HCl to remove all the LAH and after ozonolisis ? $\endgroup$ – ParaH2 Nov 10 '16 at 21:32
  • $\begingroup$ @jerepierre I am guessing that he is banking on the tetrahedral intermediate being stable enough (a la Weinreb amide) such that aq workup protonates it to form a hemiaminal & destroys the excess LAH. I don't really buy it though. Reaxys has nothing on this transformation. I agree that Eschweiler-Clarke is odd here. Someone I know used to methylate carbamates with NaH/MeI. $\endgroup$ – orthocresol Nov 10 '16 at 21:35
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    $\begingroup$ @9-BBN The Eschweiler-Clarke reference is sufficient to make me believe that part might work. However, the reduction is extremely speculative. Stopping a reduction at the aldehyde oxidation state is not a generally successful process. Simply controlling the stoichiometry does not work for an ester->aldehyde (over reduced to alcohol), and I have no reason to believe it will work here. I understand this is a proposed synthesis. A good proposed synthesis requires careful thought, consideration of possible ways it may fail, and evidence to support its success. $\endgroup$ – jerepierre Nov 11 '16 at 0:27

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