Theoretic
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Diazomethane
Interesting compound diazomethane... is very much structurally like methyl azide. Despite its huge polarity, is a gas. Its protonated form, the methyl
diazonium ion, is formed from methylamine and nitrous acid, the commonest of chemicals, yet desintegrates immediately and so far as I know can't
be deprotonated without shattering. Has to be prepared from obscure chemicals like hydrazine or methylnitroso derivatives, yet has a very simple
structure. Can easily split off a very stable and unreactive N2 molecule and become a methylene radical with two unpaired electrons, thus invaluable
in organic syntheses.
I know of three ways of preparong it: chloroform plus hydrazine, methylnitroso derivatives plus alcohol and alkali in ether, and (in theory)
deprotonation of the nethyl diazonium cation formed from methylamine and nitrous acid. Also, methylammonium nitrate can be dehydrated to give
CH3NHNO2, this could be reduced to CH3NHNO and this dehydrated to CH2N2 (diazomethane). Or, reduced to CH3NHN.
Is there a way of deprotonating CH3N2+? Do you know of another way of preparing it or improving an existing one? Share your ideas.
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Marvin
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Diazomethane is very toxic (You knew I was going to say this), its also carcinogenic/mutagenic, like a lot of its precursors (nitrosamines). People
on a small exposure can also become hypersensitive to diazomethane.
The description is neerly right about treating methylamine with nitrous acid, however its not the removal of the proton that causes it to
disintegrate, rather that a proton cannot be removed fast enough to prevent it falling apart (if you do it in base, the nitrous acid isnt around for
it to diazotize). It is possible to force this by freezing the methyl nitrosoamine with dry ice (by diazotising cold with nitrosyl chloride) and then
treat that with a conc solution of KOH, but not easy outside a lab.
Chloroform + hydrazine in base works but I understand the product decomposes the hydrazine limiting the yeild.
I was toying with the idea of trying to make N-methyl urea from methylamine and a cyanate, but it looks like the nitroso compound we want has to be
made by reducing the nitro with zinc. N-nitroso-N-methyl urea does have the advantage you dont have to distil in order to make an ether solution.
A fairly feasable method seems to be to make mesityl oxide from acetone (saturate with dry HCl leave a day or so and then fractionate for acetone,
mesityl oxide and phorone after neutralisation) and react this with methylamine (from hexamine hydrolysis or whatever) and then nitrosate. The only
example of this liberating diazomethane I have though uses sodium ethoxide as the base, and I'm unsure if a simple hydroxide will work properly
as it does with other N-methyl-N-nitroso precursors. Theres always the entraining method of making the ethoxide but by the time you get to this point
its a lot of effort to make a very unsubtle reagent and you then have to distill the explosive gas to get an uncontaminated ether solution.
[Edited on 9-7-2004 by Marvin]
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Theoretic
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"The description is neerly right about treating methylamine with nitrous acid, however its not the removal of the proton that causes it to
disintegrate, rather that a proton cannot be removed fast enough to prevent it falling apart (if you do it in base, the nitrous acid isnt around for
it to diazotize)."
Well I did want to say that it can't be deprotonated fast enough, I couldn't say it properly.
"It is possible to force this by freezing the methyl nitrosoamine with dry ice (by diazotising cold with nitrosyl chloride) and then treat that
with a conc solution of KOH, but not easy outside a lab."
*puppy-like* Yip, yip!
Gas phase!
Methylamine, nitrosyl chloride, hydrogen chloride and diazomethane are all gases, esaily condensable as desired! 
So what?
So our precious product CH3N2Cl doesn't bump into nearly as many molecules and is so much less likely to shatter. I think it does the product as
much increase in life expectancy as dry-ice freezing. And in gas phase you can use ammonia to deprotonate!
Great idea about NOCl there... what about RONO? As nitrosylator? An intermediate would form like so:
RONO + CH3NH2 => RONNCH3 + H2O. That Would then rearrange and split into RON and CH2N2.
This would too (like NOCl) circumvent the unstable protonated form and give high yield.
Oh, and what about the dehydration of methylammonium nitrate? The usual methylnitroso organic derivative route is mechanistically similar, could this
work:
CH3NH3NO3 => CH2N2 + 2H2O (with a dehydrating agent of course)?
Then there is CH4 + N2O, but that's just not feasible except with a VERY effective catalyst... 
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Marvin
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Since its not been explicitly mentioned, Diazomethane can detonate on contact with ground glassware. Special glassware must be used.
If you try making it in the gas phase so it bumps into less molecules then logically this could extend the life, but then it would also increase the
time taken to deprotonate, so I'm not convinced. I am unsure how nitrous esters act as nitrosating agents so I have no idea if that would work.
I'm not optimistic of the whole method.
Dehydration of methylamine nitrate is not balenced, check the oxygens, this of course will get you back to methylamine and nitrous acid and so nothing
new.
A possibility that has occured to me is that NH2CH2COOCH2CH3, which can be presumably be made from chloracetic acid, ammonia and ethanol can be
diazotised. If the compound following treatment with the diazoalkyl can be made to decarboxylate following hydrolysis then this would be functionally
equivalent to diazomethane.
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Theoretic
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"Dehydration of methylamine nitrate is not balenced, check the oxygens, this of course will get you back to methylamine and nitrous acid and so
nothing new."
Realised that a few days ago, couldn't get around to editing.
True, not diazomethane but methyleneiminenitrosyl CH2N2O will be formed. This could in theory be reduced to diazomethane by ammonium sulfide. If
that's too strong and will reduce CH2N2 also, then sulfite should work.
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JohnWW
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Re: Diazomethane
Diazomethane, CH2N2, can be used to obtain methyl esters of carboxylic acids, including fatty acids, in a solution in ether (bright yellow):
CH2N2 + R-COOH -> R-COOCH3 + N2
I once used it for this purpose, for GC/HPLC chromatographic analysis of the resulting esters, in the late 1960s as a student. However, it is now in
disfavor for this purpose, because of its being toxic and explosive.
Its structure is CH2=N(+)=N(-), with one pentavalent and one trivalent N, bearing positive and negative charges. There may be some
resonance-stabilization through the alternative electronic arrangement CH2(-)-N(+)(triple-bond)N, in which the negative charge is on the C.
See http://www.cem.msu.edu/~reusch/VirtualText/crbacid1.htm ,
http://www.ebiotrade.com/buyf/productsf/Molecular%20Probes/s... ,
http://www.crab.rutgers.edu/~alroche/Ch20.doc ,
obtained using the search string: diazomethane esterification carboxylic
John W.
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AndersHoveland
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heating a mixture of potassium hydroxide, chloroform, and hydrazine hydrate together (using pure alcohol as the solvent) forms a solution of
diazomethane. This has, of course, extremely deadly vapors. Diazomethane gas is also extremely unstable, and can explode simply from contact with
sharp edges or even scratches in glassware!
[Edited on 5-3-2012 by AndersHoveland]
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ScienceSquirrel
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Thread Pruned
13-3-2012 at 05:30 |
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