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Diazald (N-methyl-N-nitroso-p-toluenesulfonamide) is used as a relatively safe and easily handled precursor to diazomethane, which is toxic and unstable.[2] Since its introduction in 1954,[3] Diazald has become the favored commercially available precursor for the synthesis of diazomethane, compared to reagents like N-methyl-N-nitrosourea and N-methyl-N‘-nitro-N-nitrosoguanidine, which are less thermally stable and more toxic and mutagenic, respectively.

Upon the addition of a base such as sodium hydroxide or potassium hydroxide and mild heating (65–70 °C) in a mixture of water, diethyl ether, and a high boiling polar cosolvent (e.g., diethylene glycol monomethyl ether),[4] the N-nitrososulfonamide undergoes successive elimination reactions to produce diazomethane (which is codistilled as an ethereal solution) as well as a p-toluenesulfonate salt as a byproduct, according to the following mechanism:[5][a]

Like other nitroso compounds, it is thermally sensitive, as a result of its weak N–NO bond whose bond dissociation energy was measured to be 33.4 kcal/mol.[8]

Notes

  1. ^ Black (1983) and Brückner (2010) instead suggest a mechanism involving a 1,3-shift to form a toluenesulfonyl diazoate, followed by 1,3-elimination.[6][7]

References

  1. ^ External MSDS, Sigma Aldrich
  2. ^ “Diazald in Chemical Synthesis”. Sigma-Aldrich. Archived from the original on 8 December 2008.
  3. ^ de Boer, Th. J. [at Wikidata]; Backer, H. J. [in Dutch] (January 1954). “A new method for the preparation of diazomethane”. Recueil des Travaux Chimiques des Pays-Bas. 73 (3): 229–234. doi:10.1002/recl.19540730308.
  4. ^ de Boer, Th. J.; Backer, H. J. (1956). “Diazomethane”. Org. Synth. 36: 16. doi:10.15227/orgsyn.036.0016.
  5. ^ de Boer, Th. J. [at Wikidata]; Backer, H. J. [in Dutch] (January 1954). “Mechanism of the alkaline decomposition of sulphonylnitrosamides: (IInd communication on sulphonylnitrosamides)”. Recueil des Travaux Chimiques des Pays-Bas. 73 (7): 582–588. doi:10.1002/recl.19540730711.
  6. ^ Black, T. Howard (1983). “The Preparation and Reactions of Diazomethane” (PDF). Aldrichimica Acta. 16 (1): 3–10.
  7. ^ Brückner, Reinhard [in German] (2010). Harmata, Michael (ed.). Organic Mechanisms: Reactions, Stereochemistry and Synthesis (PDF). Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 677–678. ISBN 9783642036507.
  8. ^ Zhu, Xiao-Qing; Hao, Wei-Fang; Tang, Hui; Wang, Chun-Hua; Cheng, Jin-Pei (March 2005). “Determination of N−NO Bond Dissociation Energies of N-Methyl-N-nitrosobenzenesulfonamides in Acetonitrile and Application in the Mechanism Analyses on NO Transfer”. Journal of the American Chemical Society. 127 (8): 2696–2708. doi:10.1021/ja0443676. ISSN 0002-7863. PMID 15725027.