Inner-sphere oxidation of a ternary dipicolinatochromium(III) complex involving a malonic acid co-ligand

The oxidation of a ternary complex of chromium(III), [Cr^III(DPA)(Mal)(H₂O)₂]^?, involving dipicolinic acid (DPA) as primary ligand and malonic acid (Mal) as co-ligand, was investigated in aqueous acidic medium. The periodate oxidation kinetics of [Cr^III(DPA)(Mal)(H₂O)₂]^? to give Cr(VI) under pseudo-first-order conditions were studied at various pH, ionic strength and temperature values. The kinetic equation was found to be as follows: \( {\text{Rate}} = {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} \mathord{\left/ {\vphantom {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}}} \right. \kern-0pt} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}} \) where k ₆ (3.65 × 10^?3 s^?1) represents the electron transfer reaction rate constant and K ₄ (4.60 × 10^?4 mol dm^?3) represents the dissociation constant for the reaction \( \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)_{2} } \right]^{ - } \rightleftharpoons \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)\left( {\text{OH}} \right)} \right]^{2 - } + {\text{H}}^{ + } \) and K ₅ (1.87 mol^?1 dm³) and K ₆ (22.83 mol^?1 dm³) represent the pre-equilibrium formation constants at 30 °C and I = 0.2 mol dm^?3. Hexadecyltrimethylammonium bromide (CTAB) was found to enhance the reaction rate, whereas sodium dodecyl sulfate (SDS) had no effect. The thermodynamic activation parameters were estimated, and the oxidation is proposed to proceed via an inner-sphere mechanism involving the coordination of IO₄ ^? to Cr(III).     

Determination of thermodynamic properties of YRhO3(s) by solid-state electrochemical cell and differential scanning calorimeter

The standard molar Gibbs free energy of formation of YRhO₃(s) has been determined using a solid-state electrochemical cell wherein calcia-stabilized zirconia was used as an electrolyte. The cell can be represented by: ( - )\textPt - Rh/{ \textY₂\textO_\text3( \texts ) + \textYRh\textO₃( \texts ) + \textRh( \texts ) }//\textCSZ//\textO₂( p( \textO₂ ) = 21.21  \textkPa )/\textPt - Rh( + ) \left( - \right){\text{Pt - Rh/}}\left\{ {{{\text{Y}}_2}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right) + {\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right) + {\text{Rh}}\left( {\text{s}} \right)} \right\}//{\text{CSZ//}}{{\text{O}}_2}\left( {p\left( {{{\text{O}}_2}} \right) = 21.21\;{\text{kPa}}} \right)/{\text{Pt - Rh}}\left( + \right) . The electromotive force was measured in the temperature range from 920.0 to 1,197.3 K. The standard molar Gibbs energy of the formation of YRhO₃(s) from elements in their standard state using this electrochemical cell has been calculated and can be represented by: D_\textfG^\texto{ \textYRh\textO₃( \texts ) }/\textkJ  \textmo\textl ^{- 1}( ±1.61 ) = - 1,147.4 + 0.2815  T  ( \textK ) {\Delta_{\text{f}}}{G^{\text{o}}}\left\{ {{\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right)} \right\}/{\text{kJ}}\;{\text{mo}}{{\text{l}}^{ - 1}}\left( {\pm 1.61} \right) = - 1,147.4 + 0.2815\;T\;\left( {\text{K}} \right) . Standard molar heat capacity C^o_p,m C^{o}_{{p,m}} (T) of YRhO₃(s) was measured using a heat flux-type differential scanning calorimeter in two different temperature ranges from 127 to 299 K and 305 to 646 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: $ {*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ $ \begin{array}{*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ \end{array} The heat capacity of YRhO₃(s) was used along with the data obtained from the electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.     

Studies on electron transfer reactions: reduction of heteropoly 10-tungstodivanadophosphate by <Emphasis Type="SmallCaps">l</Emphasis>-cysteine in aqueous acid medium

l-cysteine undergoes facile electron transfer with heteropoly 10-tungstodivanadophosphate, [ \textPV^\textV \textV^\textV \textW _{1 0} \textO _{4 0} ]^{5 -} , \left[ {{\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} } \right]^{5 - } , at ambient temperature in aqueous acid medium. The stoichiometric ratio of [cysteine]/[oxidant] is 2.0. The products of the reaction are cystine and two electron-reduced heteropoly blue, [PV^IVV^IVW₁₀O₄₀]⁷⁻. The rates of the electron transfer reaction were measured spectrophotometrically in acetate–acetic acid buffers at 25 °C. The orders of the reaction with respect to both [cysteine] and [oxidant] are unity, and the reaction exhibits simple second-order kinetics at constant pH. The pH-rate profile indicates the participation of deprotonated cysteine in the reaction. The reaction proceeds through an outer-sphere mechanism. For the dianion ⁻SCH₂CH(NH₃ ⁺)COO⁻, the rate constant for the cross electron transfer reaction is 96 M⁻¹s⁻¹ at 25 °C. The self-exchange rate constant for the ^- \textSCH₂ \textCH( \textNH₃ ⁺ )\textCOO ^- \mathord

Thermochemistry of paracetamol

Combustion calorimetry, Calvet-drop sublimation calorimetry, and the Knudsen effusion method were used to determine the standard (p ^o = 0.1 MPa) molar enthalpies of formation of monoclinic (form I) and gaseous paracetamol, at T = 298.15 K: \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text cr I ) = - ( 4 10.4 ±1. 3)\text kJ  \textmol ^{- 1} \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) = - ( 4 10.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text g ) = - ( 2 80.5 ±1. 9)\text kJ  \textmol ^{- 1} . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) = - ( 2 80.5 \pm 1. 9){\text{ kJ}}\;{\text{mol}}^{ - 1} . From the obtained \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text cr I ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) value and published data, it was also possible to derive the standard molar enthalpies of formation of the two other known polymorphs of paracetamol (forms II and III), at 298.15 K: \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text crII ) = - ( 40 8.4 ±1. 3)\text kJ  \textmol ^{- 1} \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crII}}} \right) = - ( 40 8.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text crIII ) = - ( 40 7.4 ±1. 3)\text kJ  \textmol ^{- 1} . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crIII}}} \right) = - ( 40 7.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} . The proposed \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text g ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) value, together with the experimental enthalpies of formation of acetophenone and 4′-hydroxyacetophenone, taken from the literature, and a re-evaluated enthalpy of formation of acetanilide, \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textON,\text g ) = - ( 10 9. 2 ± 2. 2)\text kJ  \textmol ^{- 1} , \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{ON}},{\text{ g}}} \right) = - ( 10 9. 2\,\pm\,2. 2){\text{ kJ}}\;{\text{mol}}^{ - 1} , were used to assess the predictions of the B3LYP/cc-pVTZ and CBS-QB3 methods for the enthalpy of a isodesmic and isogyric reaction involving those species. This test supported the reliability of the theoretical methods, and indicated a good thermodynamic consistency between the \Updelta_\textf H_\textm^\texto \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} (C₈H₉O₂N, g) value obtained in this study and the remaining experimental data used in the \Updelta_\textr H_\textm^\texto \Updelta_{\text{r}} H_{\text{m}}^{\text{o}} calculation. It also led to the conclusion that the presently recommended enthalpy of formation of gaseous acetanilide in Cox and Pilcher and Pedley’s compilations should be corrected by ~20 kJ mol⁻¹.     

Kinetics and mechanism of oxidation of the chromium(III)-DL-aspartic acid complex/periodate reaction. Evidence for iron(II) catalysis

The kinetics of oxidation of the chromium(III)-DL- aspartic acid complex, [CrIIIHL]+ by periodate have been investigated in aqueous medium. In the presence of Fe^II as a catalyst, the following rate law is obeyed:

Solvent extraction of microamounts of cesium into nitrobenzene using ammonium and thallium dicarbollylcobaltates in the presence of 2,3-naphtho-15-crown-5

Extraction of microamounts of cesium by a nitrobenzene solution of ammonium dicarbollylcobaltate ( \textNH ₄ ⁺ \textB ^- ) ( {{\text{NH}}_{ 4}^{ + } {\text{B}}^{ - } }) and thallium dicarbollylcobaltate ( \textTl ⁺ \textB ^- ) ( {{\text{Tl}}^{ + } {\text{B}}^{ - } }) in the presence of 2,3-naphtho-15-crown-5 (N15C5, L) has been investigated. The equilibrium data have been explained assuming that the complexes \textML ⁺ {\text{ML}}^{ + } and \textML ₂ ⁺ {\text{ML}}_{ 2}^{ + } ( \textM ⁺ = \textNH₄ ⁺ ,\textTl ⁺ ,\textCs ⁺ ) ( {{\text{M}}^{ + } = {\text{NH}}_{4}^{ + } ,{\text{Tl}}^{ + } ,{\text{Cs}}^{ + } } ) are present in the organic phase. The stability constants of the \textML ⁺ {\text{ML}}^{ + } and \textML₂ ⁺ {\text{ML}}_{2}^{ + } species ( \textM ⁺ = \textNH₄ ⁺ ,\textTl ⁺ ) ( {{\text{M}}^{ + } = {\text{NH}}_{4}^{ + } ,{\text{Tl}}^{ + } }) in nitrobenzene saturated with water have been determined. It was found that the stability of the complex cations \textML ⁺ {\text{ML}}^{ + } and \textML₂ ⁺ {\text{ML}}_{2}^{ + } (\textM ⁺ = \textNH₄ ⁺ ,\textTl ⁺ ,\textCs ⁺ ;  \textL = \textN15\textC5) ({{\text{M}}^{ + } = {\text{NH}}_{4}^{ + } ,{\text{Tl}}^{ + } ,{\text{Cs}}^{ + } ;\;{\text{L}} = {\text{N}}15{\text{C}}5}) in the mentioned medium increases in the \textCs ⁺   <  \textNH₄ ⁺   <  \textTl ⁺ {\text{Cs}}^{ + }\,<\, {\text{NH}}_{4}^{ + }\,<\,{\text{Tl}}^{ + } order.     

Extraction of strontium and barium into nitrobenzene by using synergistic mixture of hydrogen dicarbollylcobaltate and polyethylene glycol PEG 1000

Extraction of microamounts of strontium and barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of polyethylene glycol PEG 1000 (L) has been investigated. The equilibrium data have been explained assuming that the complexes \textH ₂ \textL^{2 +} {\text{H}}_{ 2} {\text{L}}^{2 + } , \textML ²⁺ {\text{ML}}^{ 2+ } and \textMHL ³⁺ {\text{MHL}}^{ 3+ } ( \textM ²⁺ = \textSr ²⁺ ,  \textBa ²⁺ ) \left( {{\text{M}}^{ 2+ } = {\text{Sr}}^{ 2+ } ,\,\,{\text{Ba}}^{ 2+ } } \right) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. It was found that in water-saturated nitrobenzene the stability constant of the \textBaL ²⁺ {\text{BaL}}^{ 2+ } cationic complex species is somewhat higher than that of the complex \textSrL ²⁺ {\text{SrL}}^{ 2+ } .     

Catenated Gallium Compounds Supported by a<Emphasis Type="Italic"> Tris</Emphasis>(pyrazolyl)hydroborato Ligand

[ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]M (M = K, Tl) reacts with “GaI” to give a series of compounds that feature Ga–Ga bonds, namely [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→GaI₃, [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]GaGaI₂GaI₂( \textHpz^\textMe₂ {\text{Hpz}}^{{{\text{Me}}_{2} }} ) and [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga(GaI₂)₂Ga[ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ], in addition to the cationic, mononuclear Ga(III) complex {[ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]₂Ga}⁺. Likewise, [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]M (M = K, Tl) reacts with (HGaCl₂) ₂ and Ga[GaCl₄] to give [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→GaCl₃, {[ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]₂Ga}[GaCl₄], and {[ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]GaGa[ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]}[GaCl₄]₂. The adduct [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→B(C₆F₅)₃ may be obtained via treatment of [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]K with “GaI” followed by addition of B(C₆F₅)₃. Comparison of the deviation from planarity of the GaY₃ ligands in [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→GaY₃ (Y = Cl, I) and [ \textTm^{\textBu\textt} {\text{Tm}}^{{{\text{Bu}}^{\text{t}} }} ]Ga→GaY₃, as evaluated by the sum of the Y–Ga–Y bond angles, Σ(Y–Ga–Y), indicates that the [ \textTm^{\textBu\textt} {\text{Tm}}^{{{\text{Bu}}^{\text{t}} }} ]Ga moiety is a marginally better donor than [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga. In contrast, the displacement from planarity for the B(C₆F₅)₃ ligand of [ \textTp^\textMe₂ {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→B(C₆F₅)₃ is greater than that of [ \textTm^{\textBu\textt} {\text{Tm}}^{{{\text{Bu}}^{\text{t}} }} ]Ga→B(C₆F₅)₃, an observation that is interpreted in terms of interligand steric interactions in the former complex compressing the C–B–C bond angles.     

Vanadium(V)-substituted Keggin-type heteropolyoxotungstophosphates as electron transfer and antimicrobial agents: oxidation of glutathione and sensitization of MRSA towards β-lactam antibiotics

Glutathione (GSH) undergoes facile electron transfer with vanadium(V)-substituted Keggin-type heteropolyoxometalates, [ \textPV^\textV \textW _{1 1} \textO _{4 0} ] ^{4 -} [ {\text{PV}}^{\text{V}} {\text{W}}_{ 1 1} {\text{O}}_{ 4 0} ]^{{ 4 { - }}} (HPA1) and [ \textPV^\textV \textV^\textV \textW _{1 0} \textO _{4 0} ] ^{5 -} [ {\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} ]^{{ 5 { - }}} (HPA2). The kinetics of these reactions have been investigated in phthalate buffers spectrophotometrically at 25 °C in aqueous medium. One mole of HPA1 consumes one mole of GSH and the product is the one-electron reduced heteropoly blue, [ \textPV^\textIV \textW _{1 1} \textO ₄₀ ] ^5- [ {\text{PV}}^{\text{IV}} {\text{W}}_{ 1 1} {\text{O}}_{ 40} ]^{ 5- } . But in the GSH-HPA2 reaction, one mole of HPA2 consumes two moles of GSH and gives the two-electron reduced heteropoly blue [ \textPV^\textIV \textV^\textIV \textW ₁₀ \textO ₄₀ ] ^7- [ {\text{PV}}^{\text{IV}} {\text{V}}^{\text{IV}} {\text{W}}_{ 10} {\text{O}}_{ 40} ]^{ 7- } . Both reactions show overall third-order kinetics. At constant pH, the order with respect to both [HPA] species is one and order with respect to [GSH] is two. At constant [GSH], the rate shows inverse dependence on [H⁺], suggesting participation of the deprotonated thiol group of GSH in the reaction. A suitable mechanism has been proposed and a rate law for the title reaction is derived. The antimicrobial activities of HPA1, HPA2 and [ \textPV^\textV \textV^\textV \textV^\textV \textW ₉ \textO _{4 0} ] ^{6 -} [ {\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 9} {\text{O}}_{ 4 0} ]^{{ 6 { - }}} (HPA3) against MRSA were tested in vitro in combination with vancomycin and penicillin G. The HPAs sensitize MRSA towards penicillin G.     

Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol by bis(hydrogen periodato)argentate(III) complex anion: a kinetic study

Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol (MPPD) by bis(hydrogenperiodato) argentate(III) complex anion, [Ag(HIO₆)₂]⁵⁻ has been studied in aqueous alkaline medium by use of conventional spectrophotometry. The major oxidation product of MPPD has been identified as 3-(4-methoxyphenoxy)-2-ketone-1-propanol by mass spectrometry. The reaction shows overall second-order kinetics, being first-order in both [Ag(III)] and [MPPD]. The effects of [OH⁻] and periodate concentration on the observed second-order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced:

Kinetics and mechanism of the oxidation of hydrogen peroxide by the octacyanotungstate(V) ion in alkaline aqueous media

Summary The oxidation of H₂O₂ by [W(CN)₈]^3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law, , strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k _s, given by , involves the formation of [W(CN)₈· H₂O₂]^3–, [W(CN)₈· H₂O₂·W(CN)₈]^6– and [W(CN)₈· HO]^3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)₈·HO]^3– (k _a) and its conjugate base [W(CN)₈·O]^4– (k _b). At 25 °C, I = 0.20 m (NaCl), the rate constant with H _a =40±6kJmol^–1 and S _a =–151±22JK^–1mol^–1; the rate constant with H _b =36±1kJmol^–1 and S _b =–136±2JK^–1mol^–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)₈·HO]^3–, K ₅ =(5.9±1.7)×10^–10 m, with and is the first acid dissociation constant of H₂O₂. The second pathway, with rate constant, k _f, involves the formation of [W(CN)₈· HO₂]^4– and is followed by a formal two-electron redox process with [W(CN)₈]^3–. The pH-dependent rate constant, k _f, is given by . The rate constant k ₇ =23±6m ^–1 s ^–1 with and at 25°C, I = 0.20 m (NaCl).     

Kinetics and mechanism of oxidation of cis-diaquabis(glycinato)chromium(III) by periodate ion in aqueous solutions

The kinetics of oxidation of cis-[Cr^III(gly)₂(H₂O)₂]⁺ (gly = glycinate) by $ {\text{IO}}_{ 4}^{ - } $ has been studied in aqueous solutions. The reaction is first order in the chromium(III) complex concentration. The pseudo-first-order rate constant, k _obs, showed a small change with increasing $ \left[ {{\text{IO}}_{ 4}^{ - } } \right] $ . The pseudo-first-order rate constant, k _obs, increased with increasing pH, indicating that the hydroxo form of the chromium(III) complex is the reactive species. The reaction has been found to obey the following rate law: $ {\text{Rate}} = 2k^{\text{et}} K_{ 3} K_{ 4} \left[ {{\text{Cr}}\left( {\text{III}} \right)} \right]_{t} \left[ {{\text{IO}}_{ 4}^{ - } } \right]/\left\{ {\left[ {{\text{H}}^{ + } } \right] + K_{ 3} + K_{ 3} K_{ 4} \left[ {{\text{IO}}_{ 4}^{ - } } \right]} \right\} $ . Values of the intramolecular electron transfer constant, k ^et, the first deprotonation constant of cis-[Cr^III(gly)₂(H₂O)₂]⁺, K ₃ and the equilibrium formation constant between cis-[Cr^III(gly)₂(H₂O)(OH)] and $ {\text{IO}}_{ 4}^{ - } $ , K ₄, have been determined. An inner-sphere mechanism has been proposed for the oxidation process. The thermodynamic activation parameters of the processes involved are reported.     

Kinetics of heterogeneous decomposition of hydrogen peroxide

The kinetics of the decomposition of hydrogen peroxide was studied in aqueous medium in the temperature range 25–40°C in the presence of Wofatit KPS-resin in the form of Cu(II)-ammine complex ions. The rate constant was deduced at various degrees of resin cross-linkage and different concentrations of hydrogen peroxide. The order of the decomposition reaction varied from first order to half order, i.e., the order of the reaction decreased with increasing the concentration of H₂O₂. The decomposition process was found to be a catalytic reaction which was controlled by the chemical reaction of H₂O₂ molecules with the active species inside the resin particles. The mechanism of the reaction can be summarized by the equation in which the subsequent reactions of the probable active complex are discussed.     

Kinetics and Mechanism of the Reduction of Enneamolybdonickelate(IV) by Arsenite

The kinetics and mechanism of the reduction of enneamolybdonickelate(IV) by arsenite in aqueous acid solution was studied by spectrophotometry. The reaction rate increases with increasing concentrations of H⁺ and with temperature. The associated rate law is: . The rate constants and activation parameters of the rate-determining step were evaluated. A mechanism related to this reaction was proposed.     

Kinetics of the uninhibited and ethanol-inhibited CoO,Co<Subscript>2</Subscript>O<Subscript>3</Subscript> and Ni<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyzed autoxidation of sulfur(IV) in alkaline medium

For getting an insight into the mechanism of atmospheric autoxidation of sulfur(IV), the kinetics of this autoxidation reaction catalyzed by CoO, Co₂O₃ and Ni₂O₃ in buffered alkaline medium has been studied, and found to be defined by Eqs. I and II for catalysis by cobalt oxides and Ni₂O₃, respectively.

Stability constants of some metal cation complexes of tetraphenyl p - tert -butylcalix[4]arene tetraketone in nitrobenzene saturated with water

Abstract  

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium \textM^{2 +} ( \textaq ) + 1 ·\textSr^{2 +} ( \textnb ) \rightleftarrows 1 ·\textM^{2 +} ( \textnb ) + \textSr^{2 +} ( \textaq ) {\text{M}}^{2 + } \left( {\text{aq}} \right) + {\mathbf{1}} \cdot {\text{Sr}}^{2 + } \left( {\text{nb}} \right) \rightleftarrows {\mathbf{1}} \cdot {\text{M}}^{2 + } \left( {\text{nb}} \right) + {\text{Sr}}^{2 + } \left( {\text{aq}} \right) taking place in the two-phase water–nitrobenzene system (M²⁺ = Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, UO₂ ²⁺, Mn²⁺, Co²⁺, Ni²⁺; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the 1 · M²⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Ba²⁺, Mn²⁺ < Co²⁺ < Cu²⁺, Ni²⁺ < Zn²⁺, Cd²⁺, UO₂ ²⁺ < Ca²⁺ < Pb²⁺.     

Kinetics and mechanism of oxidation of hydroxylamine by tetrachloroaurate(III) ion

The oxidation of H₂NOH is first-order both in [NH₃OH⁺] and [AuCl₄ ^–]. The rate is increased by the increase in [Cl^–] and decreased with increase in [H⁺]. The stoichiometry ratio, [NH₃OH⁺]/[AuCl₄ ^–], is 1. The mechanism consists of the following reactions.

Thermochemical properties of two nitrothiophene derivatives

This article reports the values of the standard (p ^o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, \Updelta_\textf H_\textm^\texto ( \textg ), {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right), at T = 298.15 K, of 2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde as −(48.8 ± 1.6) and (4.4 ± 1.3) kJ mol⁻¹, respectively. These values were derived from experimental thermodynamic parameters, namely, the standard (p ^o = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, \Updelta_\textf H_\textm^\texto ( \textcr ) , {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{cr}} \right) , at T = 298.15 K, obtained from the standard molar enthalpies of combustion, \Updelta_\textc H_\textm^\texto , {{\Updelta}}_{\text{c}} H_{\text{m}}^{\text{o}} , measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method. The results are interpreted in terms of enthalpic increments and the enthalpic contribution of the nitro group in the substituted thiophene ring is compared with the same contribution in other structurally similar compounds.     

Iodine Hydrolysis Equilibrium

The equilibrium constant for the hydrolytic disproportionation of I₂

Extraction and DFT study on the complexation of the cesium cation with dibenzo-21-crown-7

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium \textCs ⁺ ( \textaq ) + \textA ^- ( \textaq ) + 1( \textnb )\underset \rightleftharpoons 1·\textCs ⁺ ( \textnb ) + \textA ^- ( \textnb ) {\text{Cs}}^{ + } \left( {\text{aq}} \right) + {\text{A}}^{ - } \left( {\text{aq}} \right) + {\mathbf{1}}\left( {\text{nb}} \right)\underset {} \rightleftharpoons {\mathbf{1}}\cdot{\text{Cs}}^{ + } \left( {\text{nb}} \right) + {\text{A}}^{ - } \left( {\text{nb}} \right) taking place in the two-phase water-nitrobenzene system (A⁻ = picrate, 1 = dibenzo-21-crown-7; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, A⁻) = 4.4 ± 0.1. Further, the stability constant of the 1·Cs⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β_nb (1·Cs⁺) = 6.3 ± 0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the resulting cationic complex species 1·Cs⁺ was solved.