Org Prep Daily

September 4, 2007

Soliciting advice on diazomethane

Filed under: questions — milkshake @ 9:49 pm

diazo.jpg Credit: Jiri Sliva

I have been doing Arndt-Eistert homologation (example: OrgSyn 79, p.154, 2002) so I needed pure anhydrous diazomethane solution. I made diazomethane from nitrosomethyl urea (NMU) and to avoid the distillation, I transfered diazomethane from my KOH-dried diazomethane solution in toluene by passing a stream of Ar through it (at R.T. for 30 min) and condensing the liberated dry Ar-diluted diazomethane gas directly into the reaction mixture cooled to -78C. (I heard of this alternative of diazomethane solution distillation from Rapoport group – and it worked, though I cannot recomend doing this kind of gas transfer on large scale because diazomethane is so nasty and toxic.)

I have only a limited experimental experience with diazomethane. There is plenty literature on the subject. But I would like to ask you about your personal perspective: What is you favorite method of making high-purity dry diazomethane solutions (that can be used for sensitive applications such as Arndt-Eistert)? 

One reason why I am asking this is that it apears to me that all the commonly used precursors of diazomethane have some problems associated with their use: Diazald needs a presence of alcohol (preferably a high-boiling one) or a phase-transfer catalyst to work with aqueous hydroxide and the produced diazomethane solution should be distilled to remove the sideproducts. MNNG is highly toxic and difficult to buy nowadays. NMU is expensive, explosive, very carcinogenic and the NMU-produced diazomethane solution contains trace of methylamine. So I would be delighted to learn what you have tried and liked.

The other reason is that I have one rather simple-minded idea – that I would like to try, to see if it works –  for a method of preparing contaminant-free anhydrous diazomethane solution without the risky distillation step. I would like to know if you think it is a worthwhile use of lab time, if you think a new method is even needed – a method that would be convenient and work with benign commercial reagents. 

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