Polarographic study of the 1-(2,4-dimethylphenylazo)-2-naphthol (sudan II) in hydroalcoholic medium

Abstract

The polarographic behaviour of the Sudan II azo-dye in a 60% hdyroalcoholic medium has been studied using different polarographic techniques. The electrochemical reaction involves a four-electron exchange in both acid and basic media, yielding the formation of 1-amino-2-naphthol and 2,4-dimethyl-aniline. The reduction process is irreversible and the limiting current is diffusion-controlled. The E 1 2 is strongly dependent on pH, involving mechanism changes, passing from acid catalysis, up to pH 5, to basic catalysis, between pH 6.3 and 10.4, and finally above pH 12 to the direct reduction of Sudan II without a previous protonation reaction. The proportionality between diffusion current and Sudan II concentration allows its polarographic determination over a wide concentration range. The determination limit using differential pulse polarography is 3.0 × 10 −7 M, with a variation coefficient of about 4% at a 6.50 × 10 −7 M concentration level.