ROLE OF MIXED SURFACTANTS ON THE OXIDATION OF MALACHITE GREEN BY NITRITE IONS

Abstract

The oxidation of malachite green (MG)⁺ with nitrite ions in aqueous solutions of sodium dodecyl sulphate (SDS), Triton X-100 (TX-100), and their mixtures at 25oC has been used as a probe for investigating the catalytic/inhibitive property of SDS/TX-100 mixed systems. The results showed that the composition of the mixed surfactants has quite significant influence on the rate constant of the oxidation
reaction when compared with the reaction in the single surfactant system and the effect of SDS was found crucial. The results indicated 62-85% lower reactivity as the mole fraction increased and a higher pseudofirst order rate constant in aqueous solution than in the surfactants or their mixtures were also observed with a rapid decrease until saturation was reached in pure SDS indicating an overall inhibition. The kinetic mechanism of the micellar effects was probed and rationalized using existing Clint’s, Menger and Portnoy,
Rubingh’s and Maeda’s theories for mixed micellar systems. Strong electrostatic attraction between the protonated species and the anionic surfactant aggregates was important in the reaction process.