Chemistry: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 Y
3D model (JSmol)	Interactive image Interactive image
ChemSpider	70304 Y
PubChem CID	77913
UNII	V3X3G4TFG6 Y
InChI InChI=1S/C8H5N3O2/c12-7-9-10-8(13)11(7)6-4-2-1-3-5-6/h1-5H Y Key: ISULLEUFOQSBGY-UHFFFAOYSA-N Y
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).
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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. The most prominent use of PTAD was the first synthesis of prismane in 1973.

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. 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).

Synthesis of PTAD