Kinetics and mechanism of the picolinic acid catalysed chromium(VI) oxidation of ethane-1,2-diol in the presence and absence of surfactants

摘要: The kinetics and mechanism of the CrVI oxidation ethane-1,2-diol in presence absence picolinic acid (PA) aqueous media have been carried out under conditions: [ethane-1,2-diol]T ≫ [CrVI]T [PA]T at different temperatures. micellar effect on title reactions has studied order to substantiate suggested mechanism. Under experimental conditions, is predominantly oxidised hydroxyethanal kinetic contribution from glycol splitting path negligible. In PA, simple alcohol mechanism, involving one —OH group, operates. PA-catalysed path, a CrVI–PA cyclic complex proposed as active oxidant. subject nucleophilic attack by substrate form ternary which subsequently experiences redox decomposition (through 2e transfer) leading CrIV–PA complex. then participates further organic ultimately converted into inert CrIII–PA It striking note that uncatalysed shows second-order dependence [H+], while zeroth-order [H+]. Both paths show first-order [CrVI]T. [PA]T. All these observations (i.e. patterns reactants) remain unaltered externally added surfactants. cationic surfactant cetylpyridinium chloride, CPC) anionic sodium dodecyl sulfate, SDS) both PA. CPC acts an inhibitor restricts reaction phase, SDS catalyst proceed simultaneously with enhanced rate phase. observed effects explained considering preferential partitioning reactants between applicability models, e.g. Menger–Portnoy model, Piszkiewicz cooperative pseudo-phase ion exchange (PIE) tested explain effects.