Diphenyl thiocarbazide

The precipitate is almost pure white. More diphenyl-thiocarbazide crystallizes from the red alcoholic filtrate and washings, if they are allowed to evaporate slowly. When the mixture is allowed to stand for some time before it is filtered, the amount of precipitate is increased and that of the material left in the filtrate is decreased. 

Tellurium(IV) reacts with thiourea, S=C(NH2)2, (whose concentration in the final solution should be -10%) in 1 M H2SO4, HNO3, or H3PO4 to form a yellow cationic complex suitable for spectrophotometry [36]. The absorption maximum of the complex occurs at 320 nm. The cationic complex of tellurium with thiourea can be extracted with TBP as the ion-associate with thiocyanate ions. The following thiourea derivatives have been proposed for the spectrophotometric determination of tellurium l,4diphenylthiosemicarbazide [37], diphenyl-thiocarbazide, dinaphthylthiourea, and tetramethylthiourea [38]. 

Dithiadiazines. (1) Oxidative cyclization of l,6-diphenyl-2,5-dithiobiurea (Equation 14) (2) oxidative cyclization of A, A -dicarbethoxy-A, A -bis(mercaptomethyl)hydrazine (Scheme 32) (3) condensation of an oxamic acid thiocarbazide with chlorocarbonylsulfenyl chloride (Equation 21) (4) condensation of thiosemicarbazide derivatives with A -phenyl-3 -chloroisothiocarbamoyl chloride (Equation 22). Method (4) is the most general of these, provides good yields, and precursors are reasonably accessible. 

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