Cookson’s reagent

Phenyl-l,2,4-triazoline-3,5-dione (often PTAD or Cookson s reagent ) is a highly reactive dieno-phile it has often been used to trap nnstable dienes or characterize dienes as adducts. Two examples of its reactivity are shown below. 

The isolation of PBG by Westall (7) and the determination of its structure by Cookson and Rimington (77, 78) were crucial steps in the detailed description of the biosynthesis of porph3rrin. PBG (Fig. 11) was first detected by Sachs 88) in the urine of patients with acute porphyria, since the urine turned red with Ehrlich s reagent (p-dimethylaminobenzaldehyde in acid solution). This red compound was insoluble in CHClj thus differentiating it from urobilinogen. Waldenstrom (83) recognized PBG as a distinct entity. It has been also found in the liver and feces 84,85) of these patients. 

Diethyl azodicarboxylate reacts smoothly with a wide variety of alcohols, mercaptans, anilines, and hydrazobenzenes to form 0x0 compounds, disulfides, and azobenzenes. The reaction does not proceed further after abstraction of hydrogen because the reagent has no oxygen atoms available for oxidation. F. e. and procedures s. F. Yoneda, K. Suzuki, and Y. Nitta, Am. Soc. 88, 2328 (1966) improved yields of ketones with A-phenyl ly2,A-triazoline 3,5-dione s. R. C. Cookson I. D. R. Stevens, and C. T. Watts, Chem. Gommun. 1966, 744. 

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