• Anadi C Dash

      Articles written in Journal of Chemical Sciences

    • Complex formation between 2-imidazoleazobenzene and some divalent metal ions: A kinetic and equilibrium study

      Anadi C Dash Achyuta N Acharya Ramakanta Sahu

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    • Kinetics and mechanism of the reactions of hexaaqua rhodium (III) with sulphur (IV) in aqueous medium

      Suprava Nayak Anadi C Dash

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      An O-bonded sulphito complex, Rh(OH2)5(OSO2H)2+, is reversibly formed in the stoppedflow time scale when Rh(OH2)63+ and SO2/HSO3 buffer (1 <pH< 3) are allowed to react. For Rh(OH2)5OH2++ SO2 □ Rh(OH2)5(OSO2H)2+ (k1/k-1), k1 = (2.2 ±0.2) × 103 dm3 mol−1 s−1, k1 = 0.58 ±0.16 s−1 (25°C,I = 0.5 mol dm−3). The protonated O-sulphito complex is a moderate acid (Kd = 3 × 10−4 mol dm−3, 25°C, I= 0.5 mol dm−3). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10−3 s−1 (31°C) to Rh(OH2)4(O2SO)+ and the chelated sulphito complex takes up another HSO3 in a fast equilibrium step to yield Rh(OH2)3(O2SO)(OSO2H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH2)3(O2SO)(OSO2)- → Rh(OH2)3(O2SO)(SO3) (kiso = 3 × 10−4 s−1, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na4[Rh2(μ-OH)2(OH)2(μ-OS(O)O)(O2SO)(SO3) (OH2)]5H2O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water and most organic solvents and very stable to acid-catalysed decomposition

    • Proximity effect on the general base catalysed hydrolysis of amide linkage: The role of cationic surfactant, CTABr

      Sarat C Dash Anadi C Dash

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      The bis phenoxide forms of (1,2)bis(2-hydroxybenzamido)ethane(I), (1,5)bis(2-hydroxybenzamido) 3-azapentane(II), (1,3)bis(2-hydroxybenzamido)propane(III), and (1,8)bis(2-hydroxybenzamido)3,6-diazaoctane(IV) undergo facile hydrolysis of one of the amide groups (0.02 ≤ [OH]$_T$ (mol dm-3) ≤ 0.5, 10% MeOH (v/v) + H2O medium) without exhibiting [OH] dependence. The reactivity trend follows III > > IIIIV with low activation enthalpy {$25.7\pm 2.8 ≤ \Delta H^{\neq}$(kJ mol-1) $≤ 64.8\pm 7.0$}). The high negative and comparable values of activation entropy {$-234 \pm 8 ≤ \Delta S^{\neq}$(J K-1 mol-1) $≤ −127 \pm 20$} are consistent with closely similar, and ordered transition states which can be assembled by favourably oriented phenoxide groups. The solvent kinetic isotope effect for I, $k^{H2O}/k^{D2O+H2O} \sim 1$ (20 and 50 volume% D2O), indicates that proton transfer is not involved as a part of the rate controlling process. The observed slowing down of the rate of this reaction for I in the micellar pseudo phase of CTABr also supports the proposed mechanism. Under premicellar conditions, however, rate acceleration is observed, a consequence believed to be associated with the capping effect of the hydrophobic tail of the surfactant cation forming the reactive ion-pair, CTA+, (I-2H)2− exclusively in the aqueous pseudo phase.

    • Glyoxylate as a reducing agent for manganese(III) in salen scaffold: A kinetics and mechanistic study

      Akshaya K Kar Achyutananda Acharya Guru C Pradhan Anadi C Dash

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      The kinetics of oxidation of glyoxylic acid (HGl) by MnIII(salen)(OH2)$^+_2$ ((H2salen = N,N'- bis(salicylidene)ethane-1,2-diamine) is investigated at 30.0-45.0°C, 1.83 ≤ pH ≤ 6.10, I = 0.3 mol dm-3(NaClO4). The products are identified as formic acid, CO2 and MnII with the reaction stoichiometry, |𝛥[MnIII]/𝛥[HGl]| = 2. The overall reaction involves fast equilibrium pre-association of MnIII(salen)(OH2)$^+_2$ with HGl and its conjugate base Gl forming the corresponding inner sphere complexes (both HGl and Gl being the monohydrate gem-diol forms) followed by the slow electron transfer steps. In addition, the second order electron transfer reactions involving the inner-sphere complexes and HGl/Gl are also observed. The rate, equilibrium constants and activation parameters for various steps are presented. MnIII(salen)(OH2)(Gl) is virtually inert to intra molecular electron transfer while the process is facile for MnIII(salen)(OH2)(HGl)+ (10$^5k_{et} = 2.8 \pm 0.3$ s-1 at 35.0°C) reflecting the involvement of proton coupled electron transfer mechanism in the latter case. A computational study of the structure optimization of the complexes, trans-MnIII(salen)(OH2)$^+_2$, trans-MnIII(salen)(OH2)(Gl), and trans- MnIII(salen)(OH2)(HGl)+ (all high spin MnIII(d4) systems), reveals strongest axial distortion for the (aqua)(Gl) complex ; HGl bound to MnIII centre by the C=O function of the carboxyl group in the (aqua)(HGl) complex facilitates the formation of a hydrogen bond between the proton of the carboxyl group and the coordinated phenoxide moiety ((O-H…O hydrogen bond distance 1.745 Å) and the gem-diols are not involved in H-bonding in either case. A rate comparison for the second order paths: MnIII(salen)(OH2)(HGl)/Gl)+/0 + HGl/Gl → products, shows that HGl for the (aqua)(HGl) complex is a better reducing agent than Gl for the (aqua)(Gl) complex ($k_{\text{HG}} \tilde 5 k_{\text{Gl}}$). The high values of activation enthalpy (𝛥H$^\neq$ = 93-119 kJ mol-1) are indicative of substantial reorganization of the bonds as expected for inner-sphere ET process.

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