4-Phenyl-1,2,4-triazole-3,5-dione

4-Phenyl-1,2,4-triazole-3,5-dione
Names
	Preferred IUPAC name 4-Phenyl-3H-1,2,4-triazole-3,5(4H)-dione
	Other names PTAD
Identifiers
CAS Number	4233-33-4 ;
3D model (JSmol)	Interactive image; Interactive image;
ChemSpider	70304 ;
ECHA InfoCard	100.021.993
PubChem CID	77913;
UNII	V3X3G4TFG6 ;
CompTox Dashboard (EPA)	DTXSID00195142 ;
	InChI InChI=1S/C8H5N3O2/c12-7-9-10-8(13)11(7)6-4-2-1-3-5-6/h1-5H Key: ISULLEUFOQSBGY-UHFFFAOYSA-N ;
	SMILES O=C2/N=N\C(=O)N2c1ccccc1; c1ccc(cc1)N2C(=O)N=NC2=O;
Properties
Chemical formula	C8H5N3O2
Molar mass	175.15
Appearance	red solid
Melting point	165 °C (329 °F; 438 K)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

4-Phenyl-1,2,4-triazoline-3,5-dione (PTAD) is an azodicarbonyl compound. PTAD is one of the strongest dienophiles and reacts rapidly with dienes in Diels-Alder reactions.^[1] The most prominent use of PTAD was the first synthesis of prismane in 1973.^[2]

Synthesis

The compound was first synthesized in 1894 by Johannes Thiele and Otto Stange [de]. The oxidation of 4-Phenylurazole with lead tetroxide in sulfuric acid yielded small quantities of the substance.^[3] It took until 1971 until a practical synthesis was published. The synthesis starts by combining hydrazine and diethyl carbonate. The product of this step is reacted with phenyl isocyanate to form 4-Phenyl-1-carbethoxysemicarbazide (4), which is cyclized with base to form 4-Phenylurazole (5). Oxidation with tert-Butyl hypochlorite then yields PTAD (6).^[4]

References

^ Korobitsyna, I. K.; Khalikova, A. V.; Rodina, L. L.; Shusherina, N. P. (1983). "4-Phenyl-1,2,4-triazoline-3,5-dione in organic synthesis (review)". Chemistry of Heterocyclic Compounds. 19 (2): 117–136. doi:10.1007/BF00506417. S2CID 98081187.
^ Katz T. J., Acton N. (1973). "Synthesis of Prismane". Journal of the American Chemical Society. 95 (8): 2738–2739. doi:10.1021/ja00789a084.
^ Thiele, J.; Stange, O. (1894). "Ueber Semicarbazid". Justus Liebigs Annalen der Chemie. 283 (1–2): 1–43. doi:10.1002/jlac.18942830102.
^ Cookson, R. C. (1971). "4-Phenyl-1,2,4-triazole-3,5-dione" (PDF). Organic Syntheses: 121. doi:10.1002/0471264180.os051.30. ISBN 0471264229. Also Organic Syntheses, Coll. Vol. 6, p.936 (1988)

[1] Korobitsyna, I. K.; Khalikova, A. V.; Rodina, L. L.; Shusherina, N. P. (1983). "4-Phenyl-1,2,4-triazoline-3,5-dione in organic synthesis (review)". Chemistry of Heterocyclic Compounds. 19 (2): 117–136. doi:10.1007/BF00506417. S2CID 98081187.

[2] Katz T. J., Acton N. (1973). "Synthesis of Prismane". Journal of the American Chemical Society. 95 (8): 2738–2739. doi:10.1021/ja00789a084.

[3] Thiele, J.; Stange, O. (1894). "Ueber Semicarbazid". Justus Liebigs Annalen der Chemie. 283 (1–2): 1–43. doi:10.1002/jlac.18942830102.

[Organic_Syntheses-4] Cookson, R. C. (1971). "4-Phenyl-1,2,4-triazole-3,5-dione" (PDF). Organic Syntheses: 121. doi:10.1002/0471264180.os051.30. ISBN 0471264229. Also Organic Syntheses, Coll. Vol. 6, p.936 (1988)

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