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

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 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]

Notes and References

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