Kinetics and mechanism of the reduction of dichromate ion by 2-methyl pentane-2,4-diol in aqueous hydrochloric acidic medium

Abstract

INTRODUCTION Oxidative properties of Cr(VI) are of considerable importance in both analysis and oxidation of organic and inorganic substrates . Cr (VI) in water exists as CrO4, HCr2O7 and H2Cr2O7 . Of all these species, HCrO4 has been identified as the only active oxidizing species in aqueous acidic solution . Although some kinetic information has been published on the oxidation of secondary alcohol by Cr(VI) 1,2, 8-16 complementary studies on its possible reaction pathways are scanty. It is in the light of this that the present work was undertaken with the aim of providing relevant information on the plausible mechanism for the electron transfer reaction of 2-methylpentane-2,4-diol . EXPERIMENTAL Materials 2-methylpentane-2,4-diol (BDH) hereafter referred to as diol was used as supplied in making its standard solution. Sodium dichromate solution in distilled water was then standardized using titrimetric method. A stock solution of HCl was prepared by diluting the commercial acid (M&B) and the solution was standardized titrimetrically using sodium carbonate. Stock solutions of sodium methanoate, sodium chloride and sodium ethanoate were prepared from Analar grade salts. The stoichiometry and kinetics of the reduction of dichromate ion by 2-methylpentane-2,4-diol have been investigated in aqueous hydrochloric acid medium at 27 ±1°C. The reaction is first order with respect to oxidant and reductant concentrations and also acid dependent. The empirical rate law conforms to the rate equation: )] ( ][ tan ][ [ ] [