Author Topic: Aliphatic Diazotization  (Read 548 times)

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halfapint

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Aliphatic Diazotization
« on: May 09, 2002, 07:57:00 AM »
PrimoPyro

Post 306222

(PrimoPyro: "Ever Heard Of The Schlotterbeck reaction? ;-)", Chemistry Discourse)
thinks for some obscure reason he'd like to have the use of some diazotoluene, within the milieu of a trivial gedankenexperiment, to further our pursuit of pure knowledge, free of any contamination by secular applications in the carnal mercantile world like making P2P. It isn't quite clear to me whether his proposal, C6H5-CHN2 diazotoluene + CH3CHO acetaldehyde --> C6H5-CH2-CO-CH3 phenylacetone + N2 nitrogen, will work to the exclusion of its inverse, C6H5-CHO benzaldehyde + CH3-CHN2 diazoethane --> C6H5-CH2-CO-CH3 phenylacetone + N2 nitrogen.

Either way, a diazotized aliphatic compound is required heavier than diazomethane, which makes up 99.6% of the diazoalkyl compounds present in the world, as well as 87.2% by weight of the chemical literature concerned with diazo aliphatic compounds. One consideration is that diazo things blow up sometimes. Explosives with nitrogen have chemical potential proportional to their relative nitrogen content, so small molecules with lots of nitrogen are more hazardous than larger molecules containing the same amount of nitrogen, as a rough rule of thumb. So diazotoluene should turn out slightly less hazardous than diazoethane, which in turn might be slightly safer than diazomethane. This consideration is just a side issue, for water, alcohol or formamide solvent in the Buchner-Curtius-Schlotterbeck reaction should keep things safe.

With that background in place, let's see what Jerry March says in Advanced Organic Chemistry:

Reactions in Which N=N Bonds Are Formed
7-48
Eliminations to Give Diazoalkanes
Various N-nitroso-N-alkyl compounds undergo elimination to give diazoalkanes.436 One of the most convenient methods for the preparation of diazomethane involves base treatment (This means strong base, the ethoxide ion is shown) of N-nitroso-N-methyl-p-toluenesulfonamide.437
CH3C6H4SOON(CH3)NO + OEt- ---> CH2N2 + CH3C6H4SOOEt + OH-
So for diazoethane:
CH3C6H4SOON(C2H5)NO + NaOEt ---> CH3CHN2 + CH3C6H4SOOEt + NaOH
And for diazotoluene:
CH3C6H4SOON(C6H5CH2)NO + NaOEt ---> C6H5CHN2 + CH3C6H4SOOEt + NaOH

However, other compounds commonly used are (base treatment is required in all cases):
N-nitroso-N-alkylureas
N-nitroso-N-alkylcarbamates
N-nitroso-N-alkylamides
N-nitroso-N-alkyl-4-amino-4-methyl-2-pentanones

All these compounds can be used to prepare diazomethane, though the sulfonamide, which is commercially available, is most satifactory. (N-nitroso-N-methyl carbamate and N-nitroso-N-methylurea give good yields, but are highly irritating and carcinogenic.438) For higher diazoalkanes the preferred substrates are nitrosoalkylcarbamates.

436 Black, Aldrichimica Acta 16, 3-10 (1983)
     Cowell and Ledwith, Q. Rev. Chem. Soc. 24, 119-167 (1970), pp. 126-131
     Sandler and Karo, "Organic Functional Group Preparations," vol. 1, pp. 389-397 (1968), Academic Press, New York, 1972
     Smith, "Open-Chain Nitrogen Compounds,", vol. 2, especially pp. 257-258, 474-475, W. A. Benjamin, New York, 1966
437  de Boer and Backer, Org. Synth. IV, 225, 250
     Hudlicky, J. Org. Chem. 45, 5377 (1980)
438  Searle, Chem. Br. 6, 5-10 (1970)




so this boils down to 2 things we might want:
CH3CH2-N(NO)-COOC2H5 N-nitroso-N-ethyl carbamate, which on treatment with sodium ethoxide gives diazoethane, or
C6H5CH2-N(NO)-COOC2H5 N-nitroso-N-benzyl carbamate which gives diazotoluene with strong base.

Tentatively, let's plan on producing the diazoethane or diazotoluene in ethanol, then reacting with benzaldehyde or acetaldehyde in the same pot, without isolation of the diazotized compound. If this is at all chemically acceptable, in the presence of the byproduct of the diazotization reaction and basic conditions, it should totally mitigate any hazard associated with isolated diazo compounds. If the basic conditions are not appropriate for the Buchner-Curtius-Schlotterbeck reaction, (once we learn what the conditions of this reaction actually are), we should consider simply titrating the diazotization solution to neutrality with mineral acid, and then proceeding as above, again avoiding isolation of the diazo compound in the interests of safety. Or maybee this is just a nervous Nellie approach, what you think?


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