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

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
ECHA InfoCard	100.021.993
PubChem CID	77913
UNII	V3X3G4TFG6 Y
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 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). Y verify (what is YN ?) Infobox references

Synthesis

The compound was first synthesized in 1894 by Johannes Thiele and Otto Stange. 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]

Synthesis of PTAD