Kinetics and mechanism of reduction of 2-(p-dimethylaminopheny1)azamethine-l-ethylpy dinium iodide and its analogues by hydrazine hydrate in aqueous ethanolic medium

Abstract

The kinetics of reduction of 2-(<em>p</em>-dimethylaminophenyl)azamethine-l-ethylpyridinium iodide (1) by hydrazine hydrate has been studied spe trophotometrically in the temperature range of 200-4SOC.The reaction order has been found to be 0 e in [dye], zero in [hydrazine]and -0.3 in [OH^-]. Reduction rates decrease with increase in ethanol ontent of the medium as well as [OH^-]. The rates depend on organic co-solvent used and follow the rder: MeOH > EtOH > <em>n</em>-propanoL A comparative study of the reduction rates of dye (I), 4-(<em>p</em>-dimethylminophenyl)azamethine-l-ethylpyridinium iodide (II) and 2-(<em>p</em>-dimethylaminophenyl)azamethine-l-ethylquinolinium iodide (III) indicates that the rates depend on the structure of the azacyanine dye used a follow the order: dye (III) > dye (I) > dye (II). Activation parameters have been evaluated and a mechanism consistent with the experimental results has been suggested.