Nageswara Rao Anipindi

Kinetics and mechanism of substitution of bis(tptz)iron(II) by 2,2′-bipyridine and 1,10-phenanthroline

The kinetics of substitution of Fe(tptz)2+2 by 2,2′-bipyridine and 1,10-phenanthroline have been investigated in acetate buffers in the 3.6–5.6 pH range employing stopped-flow spectrophotometry. These reactions are very fast and complete within 5 s. The rate of substitution is linearly dependent on [phen] and [bpy]2, and increases with the increase in pH. Suitable mechanisms have been proposed involving the unprotonated form of the entering ligand, viz. bipyridine/phenanthroline as the reactive species. The pKa values of bipyridine and phenanthroline, determined from the kinetic data, are in agreement with the literature values. It is concluded that the substitutions of iron(II)-diimine complexes also occur by an associative mechanism.

Synthesis and characterization of Cs-exchanged heteropolyacid catalysts functionalized with Sn for carbonolysis of glycerol to glycerol carbonate

Cs exchanged heteropolyacid catalysts functionalized with various Sn contents were prepared by wet impregnation method. These catalysts were characterized by X-ray diffraction, FT-IR, Raman spectroscopy, temperature programmed desorption of ammonia and BET surface area measurements. The catalytic properties of Sn–CsPW catalysts were evaluated for the synthesis of glycerol carbonate and they exhibit an unprecedented activity for the higher glycerol conversion and selectivity towards glycerol carbonate under vacuum conditions. Sn-functionalized Cs exchanged heteropolyacid catalysts (CsPW) play a significant role in the enhancement of acidity, catalytic activity and stability. The glycerol conversion and the selectivity of carbonate formation mainly depend on the Sn content and acidity of the catalysts. Different reaction parameters such as Sn molar ratio, glycerol to urea molar ratio, reaction temperature were investigated and also optimum conditions were established. The catalyst containing molar ratio of 3:1 Sn–CsPW has shown highest conversion and glycerol carbonate selectivity.

The oxalic acid catalysed oxidation of bis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II) by chromium(VI) in acetate buffer

SummaryThe reaction between bis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II), Fe(TPTZ)inf2sup2+and chromium(VI) in acetate buffers is very slow. However, in the presence of oxalic acid (catalyst) it is very fast and is completed within 10s. The reaction was studied in the 3.6–5.6 pH range using stopped-flow spectrophotometry. The reaction is first order in the substrate and zero order in the oxidant. The rate of the reaction increases with the increase in pH. Kinetic evidence for complexation between the substrate and the catalyst was obtained and a mechanism involving the formation of an ion-pair between Fe(TPTZ)inf2sup2+and the oxalate ion is proposed.

Kinetic and mechanistic studies on the oxidation of hydroxylamine, semicarbazide, and thiosemicarbazide by iron(III) in the presence of triazines

In the presence of 3-(2-pyridyl)-5,6-bis(4-phenyl-sulphonicacid)-1,2,4-triazine disodium salt (PDTS), 3-(4-(4-phenylsulphonic-acid)-2-pyridyl)-5,6-bis(4-phenylsulphonic-acid)-1,2,4-triazine trisodium salt (PPDTS), or 2,4-bis(5,6-bis(4-phenylsulphonic-acid)-1,2,4-triazin-3-yl)pyridine tetra sodium salt (BDTPS), iron(III) oxidizes hydroxylamine to nitrogen gas, semicarbazide to CO2 and NH3 and thiosemicarbazide to a disulfide. The corresponding iron product is the 1:3 complex of iron(II) and PDTS, PPDTS, or BDTPS. The kinetics of these reactions was studied by monitoring the iron(II) product by conventional spectrophotometry. The reaction is first order in iron(III). Kinetic evidence was obtained for the formation of 1:1:2 ternary complexes of iron(III), substrate, and sulfonated triazine. Evidence for the ternary intermediate complexes was obtained by ion-exchange studies using 59Fe-labeled iron(III) solutions. The dissociation of the ternary complex is identified as the rate-determining step.

Kinetics and mechanism of the oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)iron(II) bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III) in acetate buffer

SummaryThe rapid oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II), [Fe(TPTZ)2]2+, bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III), [MnIII(Y)]−, in acetate buffers was monitored using stopped-flow spectrophotometry. The reaction is first order in the substrate and evidence was obtained for pre-complexation between the oxidant and the substrate. The reaction rate increases as the pH increases. Characterisation of the products using the radiotracers54Mn and59Fe indicated that [MnII(Y)]2− and [Fe(TPTZ)2]3+ are the final products. The reaction obeys the rate law:

KINETICS AND MECHANISM OF COBALT(III) OXIDATION OF BIS(2,2',6',2 -TERPYRIDINE) IRON(II) IN SULFURIC ACID SOLUTIONS

k_{obs} = \frac{{k_3 K_2 [Mn^{III} (Y)^ - ]_t }}{{\{ 1 + K_1 [H^ + ] + K_2 [Mn^{III} (Y)^ - ]_t \} }}

A spectrophotometric kinetic investigation of the catalyzed vanadium(V)-iodide reaction

SummaryKinetic studies have been carried out on the reaction betweenbis(2,2′,6′,2″-terpyridine)iron(II), [Fe(tpy)2]2+, and MnIII in H2SO4 medium using stopped-flow spectrophotometry. The reaction is first order with respect to both [Fe(tpy)22+] and [MnIII]; second order overall, and the rate increases with increasing [H+]. The MnII and [Fe(tpy)2]3+ products have negligible effect on the reaction. A scheme featuring aquomanganese(III) as the reactive oxidising species is proposed.