REACTION BETWEEN THE DPPH FREE-RADICAL AND POTASSIUM CYANIDE IN THE PRESENCE OF CROWN-ETHER 18C6

Reaction of the stable free radical N,N-diphenyl-N'-picrylhydrazyl (DP PH) with potassium cyanide and crown ether [18C6] in methylene chlorid e yielded diphenyl-N'(3-cyano-2,4,6-trinitrophenyl)hydrazine (1) and N -diphenyl-N'-(2-cyano-4,6-dinitrophenyl)hydrazine (2). The new compoun ds 1 and 2 were characterized by H-1 NMR, C-13 NMR, IR, and UV-vis see ctroscopies, as well as elemental analysis. Oxidation generated the co rresponding free radicals 3 and 4, which were characterized by their E PR spectra. In the first stage, potassium cyanide is dissolved as a hy drophobic supramolecular complex (18C6...K)+CN- and then the activated cyanide anion reacts with DPPH to yield compounds 1 and 2. Compound 1 is formed by direct nucleophilic attack of CN- on the picryl ring. Th e formation of compound 2 could have two explanations: (a) an ipso att ack of the cyanide radical on the ortho-nitro group with release of NO 2 (this nitro radical then reacts with DPPH to give the N-phenyl-N-(p- nitrophenyl)-N'-picrylhydrazine (NO2DPPH2) as a confirmed byproduct) o r (b) a cyanide anion attacks the ortho-nitro group with sigma-complex (Meisenheimer) formation and release of a nitrite anion, which in the presence of DPPH gives a nitro free radical and the above mentioned ( NO2DPPH2). On replacing DPPH by the stronger oxidant N,N-di-(p-nitroph enyl)-N'-picrylhydrazyl ((NO2)(2)DPPH) the cyano free radical was trap ped by phenyl-t-butylnitrone and characterized by EPR spectroscopy.