Prepare 4-phenylurazole from ethyl carbazate and then oxidize the urazole with gaseous dinitrogen tetroxide to yield 4-phenyl-1,2,4-tri- azoline-3,5-dione la. Modification of the ethyl carbazate procedure in which analytically pure monoalkylhydrazine hydrochlorides were isolated in greater than 90% yield, starting from a ketone or aldehyde. Treatment of primary amines is with chloroamine or hydroxylamine-0-sulfonic acid and the condensation of a carbonyl compound with ethyl carbazate. The FeCl 3 -catalyzed reaction of ethyl carbazate (2 b) proceeded readily to give β-hydroxyester 3 b in better yield. A new one-pot neat synthesis of some 5-aryl-2,4-dihydro-3H-1,2,4-triazol-3-ones through cyclocondensation of ethyl carbazate with aryl nitriles catalyzed by DMAP as an efficient and basic nucleophilic catalyst is described.
Fractionate the carbazate using a Vigreux column (p 11) until the distillate crystallises [Allen & Bell Org Synth Coll Vol III 404 1955, Beilstein 3 IV 174].