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

diene In organic chemistry, a diene ( ); also diolefin, ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nome ...

s in Diels-Alder reactions. The most prominent use of PTAD was the first synthesis of

prismane Prismane or Ladenburg benzene is a polycyclic hydrocarbon with the formula C6H6. It is an isomer of benzene, specifically a valence isomer. Prismane is far less stable than benzene. The carbon (and hydrogen) atoms of the prismane molecule are ar ...

in 1973.

Synthesis

The compound was first synthesized in 1894 by

Johannes Thiele Johannes Thiele may refer to: *Johannes Thiele (zoologist) *Johannes Thiele (chemist) {{hndis, Thiele, Johannes ...

and . The oxidation of 4-Phenylurazole with

lead tetroxide Lead(II,IV) oxide, also called red lead or minium, is the inorganic compound with the formula . A bright red or orange solid, it is used as pigment, in the manufacture of batteries, and rustproof primer paints. It is an example of a mixed va ...

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

yielded small quantities of the substance. It took until 1971 until a practical synthesis was published. The synthesis starts by combining

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...

and

diethyl carbonate Diethyl carbonate (sometimes abbreviated DEC) is an ester of carbonic acid and ethanol with the formula OC(OCH2CH3)2. At room temperature (25 °C) diethyl carbonate is a colorless liquid with a low flash point. Diethyl carbonate is used as ...

. The product of this step is reacted with

phenyl isocyanate Phenyl isocyanate is an organic compound typically abbreviated PhNCO. The molecule consists of a phenyl ring attached to the isocyanate functional group. It is a colourless liquid that reacts with water. Phenyl isocyanate has a strong odor and te ...

to form 4-Phenyl-1-carbethoxysemicarbazide (4), which is cyclized with base to form 4-Phenylurazole (5). Oxidation with

tert-Butyl hypochlorite ''tert''-Butyl hypochlorite is the organic compound with the formula (CH3)3COCl. A yellow liquid, it is a rare example of an organic hypochlorite, i.e. a compound with an O-Cl bond. It is a reactive material that is useful for chlorinations. It ...

then yields PTAD (6). Also ''Organic Syntheses, Coll.'' Vol. 6, p.936 (1988) Synthesis PTAD

References

{{DEFAULTSORT:Phenyl-1,2,4-triazole-3,5-dione, 4- Triazoles Phenyl compounds