http://nopr.niscpr.res.in/handle/123456789/39829 2026-10-09T11:11:31Z http://nopr.niscpr.res.in/handle/123456789/40217 Title: A case of competitive catalytic cycles in ruthenium(III) cataysed oxidation of dimethyl sulphoxide by cerium(IV) in aqueous sulphuric acid media: A kinetic study Authors: Mohanty, Rajani K; Das, Mahua; Das, Asim K Abstract: The kinetics of oxidation of dimethylsulphoxide (DMSO) by cerium(IV) to dimethylsulphone in the presence of ruthenium(III) (ca. 10^-7 mol dm^-3) has been followed at 30-50&deg;C under the conditions: [DMSO]_T&gt;&gt;[Ce(lV)]_T&gt;&gt;[Ru]_T- The rate of disappearance of [Ce(IV)] has been found to be first order in [Ce(lV)]. The pseudo-first order rate constant (<em>k</em>_o) obtained from -d[Ce(lV)]/dt shows a first order dependence on [Ru]_T- In the reaction, the substrate shows a rate retarding effect. The rate law conforms to: <em>k_o</em>=<em>ka</em>[Ru]_T/{<em>k_b</em>[DMSO]_T+<em>k_c</em>} where <em>k</em>_a, <em>k</em>_b and <em>k</em>_c are the composite rate constants; [Ru]_T and [DMSO]_T represent the total concentrations of ruthenium added as catalyst and substrate respectively. A reaction scheme involving two competitive catalytic cycles, one involving Ru(III)lRu(IV) predominant at higher substrate concentration and the other involving Ru(III)lRu(V) predomtnant at lower concentration of the substrate has been proposed. The cycle, Ru(III)lRu(V) is found to be more efficient. To explain the nonexistence of free radical in the oxidation of the two electron donor substrate (i.e. DMSO), it has been proposed that the two electron transfer occurs at a single step. Page(s): 663-668 1998-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/40216 Title: Acidity/basicity, electron donor properties and catalytic activity of sulphate modified stannic oxide Authors: Sugunan, S; Seena, C R Kumaree Abstract: The surface electron donor properties of sulphate modified stannic oxide have been determined from the adsorption of electron acceptors of various electron affinities on the oxide surface. The acid base properties of stannic oxide have been determined by titration method using Hammett indicators. Catalytic activities of the oxide for esterification of acetic acid using n-butanol, reduction of cyclohexanone in 2-propanol and oxidation of cyclohexanol with benzophenone have been studied. The data have been correlated with the surface electron donor properties of these oxides. The activity for reduction and oxidation decreases and that for esterification reaction increases on modification with sulphate ion. It has been found that electron donating capacity decreased when stannic oxide was modified with sulphate ion. Page(s): 669-673 1998-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/40215 Title: Use of SDS surfactant in the synthesis of highly dispersed BaTiO₃ powders Authors: Potdar, H S; Deshpande, S B; Sainkar, S R; Mitra, A; Date, S K Abstract: The effects of addition of an anionic surfactant sodium dodecyl sulphate (SDS) during precipitation of the molecular precursor, barium titanyl oxalate (BTO) in the preparation of BaTiO3 have been examined. BTO has been synthesized at room temperature using exchange reaction between barium nitrate (BN) and potassium titanyl oxalate (KTO) with various additions of SDS [viz. 0,2 and 20 ml of 1% (wt) soln.]. The resulting three BTO precipitates, after careful washing, are pyrolysed under controlled conditions (700oC, 5h in air). XRD and TEM techniques have been used to identify phase formation, morphology and degree of agglomeration. It is noticed that addition of SDS (20 ml) during synthesis of BTO helps in production of dispersed, spherical cubic barium titanate (BT) powders ( =25 nm) with surface area =123.5 m2/g. Page(s): 674-677 1998-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/40214 Title: Transfer energetics of some tetraalkylammonium ions from water to aqueous alkanols: The solvent effect on hydrophobic hydration and the 3D-structuredness of solvents Authors: Sinha, Rangana; Kundu, Kiron K Abstract: Transfer Gibbs energies (∆<em>G⁰</em>) and entropies (∆<em>S⁰</em>) of tetrapropyl-ammonium ion (Pr₄N⁺) in aqueous mixtures of methanol (MeOH), ethanol (EtOH) and isopropanol (2-PrOH) and also those of tetramethylammonium (Me<span style="text-decoration: line-through;">₄</span>N⁺), tetraethylammonium (Er₄N⁺) and tetrabutylammonium (Bu₄N⁺) ions in aqueous 2-PrOH have been determined by measuring the solubility of tetraphenylborate (Ph₄B^-) salts of Me₄N⁺, Et₄N⁺, Pr4N⁺ and Bu₄N⁺ at five equidistant temperatures by spectrophotometric method. Chemical contribution of solvent effect, i.e., ∆<em>G0_t</em>_ch (Pr₄N⁺) values obtained by subtracting the 'cavity, Born-type electrostatic and ion-dipole interaction effects, are found to increase with co solvent composition in the order: MeOH&lt;EtOH&lt;2-PrOH&lt;t-BuOH. This suggests that destabilization of Pr4N+ ions is dictated by decreased hydrophobic hydration (H_bH) effect overcoming the stabilizing effect of increased dispersion and basicity of alkanols. The observed order of destabilization of R4N+ ions in aqueous 2-PrOH, viz., Me₄N⁺&lt;Et₄N⁺&lt;Pr₄N⁺&lt;Bu₄N⁺ also substantiates the same. The observed T∆<em>S⁰</em>_tch (Pr₄N₊)-composition profiles are, however, found to pass through 'characteristic maxima' at the respective 'magic compositions' of aqueous alkanols and in the same composition in the case of R₄N⁺ ions with their relative order: Bu₄N₊&gt;Pr₄N₊&gt;Et₄N⁺&gt;Me₄N⁺ in aqueous 2-PrOH. These are found to be dictated by H_bH effect resulting from decreased availability of monomeric H₂O molecules as induced by graded 3D-structure promoting propensity of the alkanols and by the hydrophobicity of respective alkylammonium ions. Values of ∆<em>G⁰</em>_tch(-CH₂-) and ∆<em>S⁰_t</em>_ch(-CH2-),as obtained by subtracting those for (Cn,H2D'~1)4N+ from (CnH_2n+1)₄N⁺ where n'=n-I and n=2,3 or 4, are however found to be somewhat non-additive,as in the case of t-BuOH, ACN and NaN03 &nbsp;reported earlier. But when those for R₄N+ ions computed with n=4 and n'=3, are compared with the corresponding values in the latter solvent systems, it is revealed that the solvent effect of hydrophobic hydration (H_bH) that solely dictates the behaviour of -CH2-group, serves as a better indicator of not only the solvent effect of hydrophobic hydration but also the 3D-structuredness of aquo-ionic and non- ionic cosolvents. Page(s): 678-690 1998-08-01T00:00:00Z