Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The structure of products of coupling of (α-ethoxycarbonyl-β-amino)ethylidene malononitrile (Ia) and (α-cyano-β-amino)ethylidene malononitrile (Ib) with aromatic diazonium salts could be established to be the corresponding hydrazone IIa (α-ethoxycarbonyl-α-phenylhydrazono-β-amino)ethylidene malononitrile and IIb (α-cyano-α-p-bromophenylhydrazono-β-amino)ethylidene malononitrile, via inspection of acid dissociation constants and the electrochemical behaviour of these products. IIa and IIb showed pK_a ≈ 6 which is comparable to that of 2-phenylhydrazono-3-iminobutyronitrile (IV). The polarograms were found to be similar and consisted mainly of 4e reduction wave characteristic for hydrazones; also similar to the model hydrazone IV. The behaviour of 1-(p-methoxyphenyl)-3,5-dicyano-4-amino-6-iminopyridazine (IIIb) was found to be totally different. It did not reveal any potentiometrically traceable ionization step in aqueous media. Moreover its polarograms were totally different and consisted of two 2e waves. The more positive was E_1/2-pH dependent and the more negative was E_1/2-pH independent. Both waves were assigned for saturation of exocyclic and endocyclic C=N linkage. The mechanism of the electrode processes is also discussed.