Triazenes

Triazenes are organic compounds that contain the functional group −N(R)−N=N− (where R is H, alkyl, aryl).[1] Some anti-cancer medications and dyes are triazenes.[2] Formally, triazenes are related to the unstable triazene, H2N−N=NH. The relationship is more theoretical than practical.

Diphenyl triazene

Production
Dacarbazine is a triazene used in the treatment of melanoma and Hodgkin's lymphoma.[3]
Bis-triazene analogue of Tröger's base

Triazenes are prepared from the N-coupling reaction between diazonium salts and primary or secondary amines.[4] Symmetrical triazenes, for example 1,3-diphenyltriazene (PhN=N−NHPh), are prepared by the partial diazotization of aromatic primary amines, aniline in this example, and the subsequent coupling reaction in the presence of sodium acetate.[5][6] Asymmetrical triazenes, for example (phenyldiazenyl)pyrrolidine (PhN=N−NC4H8), are prepared from the N-coupling reaction between diazonium salts and secondary amines in presence of sodium carbonate[5] or sodium bicarbonate.[4] Bis-triazene carrying analogues of Tröger's base have been obtained similarly.[7]

Production of symmetrical (top) and asymmetrical (bottom) triazenes

Tautomerism
Triazenes derived from primary amines engage in tautomerization.

Triazenes derived from primary amines engage in tautomerism. In the case of 1,3-diphenyltriazine, the tautomers are identical.

Reactions and applications

An important reaction of triazenes is their conversion to diazonium salts.[1] Triazenes decompose in the presence of protonating or alkylating agents into quaternary amines and diazonium salts; as such triazenes have been used as an in situ source of diazonium that reacted with sodium sulfide to give the corresponding thiophenols.[5] A strategy for the protection and deprotection of sensitive secondary amines is based on this principle.[8]

Triazenes used in the synthesis of thiophenols

Polymeric triazenes are applied as conductive and absorbent materials.[9] Triazenes have been used in the synthesis of cinnoline, functionalized lactams, and coumarins.[8][1]

References
  1. Kimball, D. B.; Haley, M. M. (2002). "Triazenes: A Versatile Tool in Organic Synthesis". Angewandte Chemie International Edition. 41 (18): 3338–3351. doi:10.1002/1521-3773(20020916)41:18<3338::AID-ANIE3338>3.0.CO;2-7.
  2. Berneth, Horst (2008). "Methine Dyes and Pigments". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_487.pub2.
  3. "Dacarbazine". The American Society of Health-System Pharmacists. Archived from the original on 11 September 2017. Retrieved 8 December 2016.
  4. Sengupta, Saumitra; Sadhukhan, Subir K. (2002). "Synthesis of Symmetrical trans-Stilbenes by a Double Heck Reaction of (Arylazo)amines with Vinyltriethoxysilane: trans-4,4′-Dibromostilbene". Organic Syntheses. 79: 52. doi:10.15227/orgsyn.079.0052.
  5. Kazem-Rostami, M.; Khazaei, A.; Moosavi-Zare, A. R.; Bayat, M.; Saednia, S. (2012). "Novel One-Pot Synthesis of Thiophenols from Related Triazenes under Mild Conditions". Synlett. 23 (13): 1893–1896. doi:10.1055/s-0032-1316557.
  6. Hartman, W. W.; Dickey, J. B. (1934). "Diazoaminobenzene". Organic Syntheses. 14: 24. doi:10.15227/orgsyn.014.0024.CS1 maint: multiple names: authors list (link)
  7. Kazemostami, Masoud (2017). "Facile preparation of Ʌ-shaped building blocks: Hünlich-base derivatization". Synlett. 28: 1641–1645. doi:10.1055/s-0036-1588180.
  8. Lazny, R.; Poplawski, J.; Köbberling, J.; Enders, D.; Bräse, S. (1999). "Triazenes: A Useful Protecting Strategy for Sensitive Secondary Amines". Synlett. 1999 (8): 1304–1306. doi:10.1055/s-1999-2803.
  9. Khazaei, A.; Zare, A.; Moosavi-Zare, A. R.; Sadeghpour, M.; Afkhami, A. (2013). "Synthesis, characterization, and application of a triazene-based polysulfone as a dye adsorbent". Journal of Applied Polymer Science. 129 (6): 3439–3446. doi:10.1002/app.39069.
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