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

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]

4-Phenyl-1,2,4-triazole-3,5-dione
Ball-and-stick model of the PTAD molecule
Names
Preferred IUPAC name
4-Phenyl-3H-1,2,4-triazole-3,5(4H)-dione
Other names
PTAD
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.021.993
UNII
  • InChI=1S/C8H5N3O2/c12-7-9-10-8(13)11(7)6-4-2-1-3-5-6/h1-5H checkY
    Key: ISULLEUFOQSBGY-UHFFFAOYSA-N checkY
  • O=C2/N=N\C(=O)N2c1ccccc1
  • c1ccc(cc1)N2C(=O)N=NC2=O
Properties
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).
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Infobox references

Synthesis

The compound was first synthesized in 1894 by Johannes Thiele and O. Stange. The oxidation of 4-Phenylurazol with lead tetroxide in sulfuric acid yielded small quantities of the substance.[3] It took until 1971 when a practical synthesis was published. The synthesis starts from hydrazine and diethyl carbonate. The product of this step is reacted with phenyl isocyanate and subsequently transformed to the 4-Phenylurazol. Cyclization and subsequent oxidation yields PTAD (6).[4]

Synthesis of PTAD

References
  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.
  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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