Inner-sphere oxidation of ethylenediaminetetraacetatocobaltate(II) by N-bromosuccinimide

Summary The kinetics of oxidation of [Co^II(EDTA)]^2- (EDTA = ethylenediaminetetraacetate) by N-bromosuccinimide (NBS) in aqueous solution obey the equation: Rate = k ₂ K ₃[Co^II]_T[NBS]/{1 + [H⁺]/K ₂ + K ₃[NBS]} where k ₂ is the rate constant for the electron-transfer process, K ₂ the equilibrium constant for the dissociation of [Co^II(EDTAH)(H₂O)]^– to [Co^II(EDTA)(OH)]^3– and K ₃ the pre-equilibrium formation constant. The activation parameters are reported. It is proposed that electron transfer proceeds via an inner-sphere mechanism with the formation of an intermediate which slowly generates hexadentate[Co^III(EDTA)]^–.Abstracted from the M.Sc. thesis of Eman S. H. Khaled.     

Inner-sphere oxidation of iron(II) by tris(malonato)cobaltate(III)

The kinetics of oxidation of Fe²⁺ by [Co(C₃H₂O₄)₃]^3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H⁺] is in accordance with eqn (i) k₂ = k′₂ + k₃[H⁺] (i) where k′₂ and k₃ have values of 73.4 ± 14.0 M ^?1 s^?1 and 353 ± 41 M^?2 s^?1, respectively, at 1.0 M ionic strength (NaClO₄) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC₃H₂O₄]⁺, was observed. The increase in the rate of oxidation with increasing [H⁺] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe₂₊ by the carbonyl oxygens of malonate in the transition state.     

Inner-sphere oxidation of ternary nitrilotriacetatocobalt(II) complexes involving oxalate and phthalate by periodate

The oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ and [Co^II(nta)(ph)(H₂O)₂]³⁻ (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ by periodate, obeys the following equation: d[Co^III]/dt = [Co^II(nta)(ox)(H₂O)₂³⁻][H₅IO₆] {k ₄ K ₅ + (k ₅ K ₆ K ₂/[H⁺]} while the reaction of [Co^II(nta)(ph)(H₂O)₂]³⁻ with periodate in aqueous acidic medium obeys the following rate law: d[Co^III]/dt = k ₆ K ₈[Co^II]_T [I^VII]_T/{1 + [H⁺]/K ₇ + K ₈[I^VII] _T }. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.     

Kinetics and mechanism of the oxidation of a ternary complex involving nitrilotriacetatocobaltate(II) and malonic acid by N-bromosuccinimide

The kinetics of oxidation of [Co^IINM(H₂O)]^3– (N = nitrilotriacetate, M = malonate) by N-bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: d[Co^III]/dt = k ₁ K ₂[NBS][Co^II]_T/{1 + K₂[NBS] + (H⁺/K₁)} where k ₁ is the rate constant for the electron transfer process, K ₁ the equilibrium constant for dissociation of [Co^IINM(H₂O)]^3– to [Co^IINM(OH)]^4– + H⁺, and K ₂ the pre-equilibrium formation constant. Values of k ₁ = 1.07 × 10^–3 s^–1, K ₁ = 4.74 × 10^–8 mol dm^–3 and K ₂ = 472 dm³ mol^–1 have been obtained at 30 °C and I = 0.2 mol dm^–3. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Co^IINM(OH)]^4– is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism.     

Kinetics and mechanism of the oxidation of a ternary complex involving nitrilotriacetatocobaltate(II) and succinic acid by N-bromosuccinimide

The kinetics of oxidation of [Co^IINS(H₂O)₂]^3– by N-bromosuccinimide (NBS) in aqueous solution has been studied spectrophotometrically in the 20–40 °C range. The reaction is first order each in [NBS] and [Co^IINS(H₂O)₂]^3–, and the rate of reaction increases with increasing pH between 6.64 and 7.73. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Co^IINS(H₂O)(OH)]^4– is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism.     

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).     

Kinetics and mechanism of the oxidation of diaqua(nitrilotri- acetato)chromium(III) complex by N-bromosuccinimide

The kinetics of oxidation of the diaqua(nitrilotriacetato)chromium(III) complex [CrIIInta(H2O)2], by N-bromosuccinimide (NBS) to chromium(VI) in aqueous solution obeys the equation: where k1 is the rate constant for the electron-transfer process, K1 the equilibrium constant for the dissociation of [CrIIInta(H2O)2] to [CrIIInta(H2O)(OH)]−, and K2 is the pre-equilibrium formation constant for the precursor complex [CrIIInta(OH)(NBS)]−. The thermodynamic activation parameters were calculated and it is proposed that electron transfer proceeds via an inner-sphere mechanism. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetics and mechanism of the oxidation of chromium(III)–dipicolinic acid complex by N-bromosuccinimide

The kinetics of oxidation of the chromium(III)–dipicolinic acid complex [Cr^III(DPA)₂(H₂O)₂]^– by N-bromosuccinimide (NBS) in aqueous solution to Cr^VI have been studied spectrophotometrically over the 20–40 °C range. The reaction is first order with respect to both [NBS] and [Cr^III], and increases with pH over the 5.92–6.93 range. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of [NBS] to chromium(III).     

Kinetics and mechanism of oxidation of (aqua-2-aminomethyl-pyridine) chromium(III) by N-bromosuccinimide

Summary The kinetics of oxidation of (aqua-2-aminomethyl-pyridine) Cr^III by N-bromosuccinimide (NBS) in aqueous solution to yield chromium(VI) has been studied spectrophotometrically over the 25–40 °C range. The reaction rate is first order with respect to both [NBS] and [Cr^III], and increases with increasing pH between 7.6 and 8.6. The thermodynamic activation parameters were calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Cr(L)₂(OH)]²⁺ was considered to be the most reactive form compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism.     

Kinetic studies of the oxidation of chromium(III) by N-bromosuccinimide

Summary A kinetic study of the oxidation of chromium(III) by N-bromosuccinimide (NBS) in aqueous solutions and H₂O-MeOH solvent mixtures were performed. The kinetics in aqueous solutions obeyed the rate law: d[Cr^VI]/dt = {k ₄ K _h K ₂[NBS][Cr^III]_T}/[₊]{1 + K _h/[H⁺] + (K ₁ + K _h K ₂/[H⁺][NBS])} where K _h, K ₁ and K ₂ are the hydrolysis constant of [Cr^III(H₂O)₆]³⁺, and pre-equilibrium formation constants for the protonated and deprotonated precursor complexes, respectively. An innersphere mechanism is proposed. An argument based on isokinetic correlations among activation parameters for the oxidation of a series of cobalt(II) and chromium(III) complexes including [Cr(H₂O)₆]³⁺ is presented in support of a common mechanism for these reactions. Abstracted from the Ph.D. Thesis (Ain Shams University) of A. E.-D. M. Abdel-Hady.     

Kinetics and mechanism of oxidation of (ethylenediaminediacetato)chromium(III) by N-bromosuccinimide

The kinetics of oxidation of (ethylenediaminediacetato)-chromium(III), [Cr(EDDA)(OH2)2]+, by N-bromosuccinimide (NBS) in aqueous solution to yield CrVI have been studied spectrophotometrically over the 20–40°C range. The reaction rate is first order with respect to both [NBS] and [CrIII], and increases with pH over the range 4.8–5.8. The activation parameters were calculated. A mechanism in which deprotonated [CrIII(EDDA)(OH2)(OH)] is the reactive species is suggested. The electron transfer may proceed via an inner sphere mechanism through bridging of the two reactants by the hydroxo ligand.     

Inner-sphere oxidation of cis-diaquabis(oxalato)chromate(III) by periodate in aqueous weakly acidic solutions

The kinetics of oxidation of cis-[Cr^III(ox)₂(H₂O)₂]^– (ox = C₂O₄ ^2–) by IO₄ ^– showed a first-order dependence on the initial Cr^III complex concentration in the presence of a vast excess of [IO₄ ^–]. The dependence of the pseudo-first-order rate constant on [IO₄ ^–] is complex and is consistent with the formation of a precursor complex. It is proposed that this complex is formed through the coordination of the two carbonyl oxygens of the ox ligand with the IO₄ ^– ion, forming a cyclic intermediate. The kinetics are consistent with the hydroxo form of the Cr^III complex being the reactive species, whereas the aqua species forms an unreactive complex.     

Kinetics and mechanism of oxidation of tris(ethylenediamine)-chromium(III) by N-bromosuccinimide

Summary In aqueous solutions, [Cr(en)₃]³⁺ aquates to [Cr(en)₂-(H₂O) ₂]³⁺. A kinetic study of the oxidation of [Cr(en)₃]³⁺ by N-bromosuccinimide (NBS) in aqueous solutions and water-alcohol solvent mixtures was performed. The reaction is first order with respect to both total [Cr^III] and [NBS]. The rate is inversely dependent upon [H⁺] in the 7.0–7.9 pH range, and varies with the co-solvent according to the order: MeOH > EtOH > PrOH. An appropriate mechanism, in which the deprotonated [Cr(en)₂(OH)(H₂O)]²⁺ is the reactive species, is suggested. Thermodynamic activation parameters have been calculated.Abstracted from the PhD thesis (Ain Shams University) of A. E.- D. M. Abdel-Hady.     

Kinetics and mechanism of palladium(II) catalysed oxidation of amines and aminoalcohols by N-bromosuccinimide in perchloric acid

Summary The kinetics of oxidation of amines (EtNH₂, Et₂NH, Et₃N) and aminoalcohols [H₂NCH₂CH₂OH, H₂N(CH₂)₃OH, (CH₂CH₂OH)₂NH, (CH₂CH₂OH)₃N] by N-bromosuccinimide (NBS) have been studied in aqueous HClO₄ with PdCl₂ as catalyst, and in the presence of Hg(OAc)₂ to ensure oxidation by pure NBS. The order of reaction with respect to NBS was unity, however, an increase in [NBS]₀ resulted in a decrease in the rate constant. The rate was directly proportional to [Pd^II] for the aminoalcohols while for EtNH₂ the rate was proportional to k + k[Pd^II] (where k and k are rate constants for the uncatalysed and catalysed paths, respectively). Retarding effects for HClO₄, succinimide, Cl^– and AcOH on the rate of oxidation were observed. The kinetic data support the formation of [Pd^II-A] and [Pd^II-(A)₂] complexes (where A represents amine or aminoalcohol). A mechanism, consistent with the observed kinetic data, is proposed.     

Kinetics and mechanism of oxidation in the diaqua(nitrilotriacetato)cobaltate(II)/N-bromosuccinimide reaction: evidence for iron(II) catalysis

Summary Oxidation of the diaqua(nitrilotriacetato)cobaltate(II) complex, [CoIInta(H2O)2]-, by NBS has been studied in aqueous medium. The kinetics of the reaction in the presence of an iron(II) catalyst obey the rate law: Catalysis by iron(II) is believed to be due to the oxidation of iron(II) to iron(III), which acts as the oxidizing agent. The thermodynamic activation parameters were calculated and we propose that electron transfer proceeds through an inner-sphere mechanism. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetics and mechanism of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) by N-bromosuccinimide in aqueous acidic medium

The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H₂O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm^?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H₂O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed.     

Reactions of some diorganonickel(II) complexes with N-bromosuccinimide

The reactions of some diorganonickel(II) complexes with N-bromosuccinimide (NBS) resulted in facile bromine for hydrogen substitution in aromatic, alkynyl or alkenyl substituents, or in the addition of NBS to CC bonds.     

Continuous-flow chemiluminescence determination of isoniazid by oxidation with N-bromosuccinimide

A rapid and precise continuous-flow method is described for the determination of isoniazid (0.050-20.0 micrograms ml(-1)) based on the chemiluminescence produced during its reaction with N-bromosuccinimide in alkaline medium. The emission intensity is greatly enhanced by the presence of ammonia. The procedure is automated and samples can be analysed at a rate of 112 solutions per hour with a relative error of about 2%. When applied to tablets, the method is relatively free from interferences from common excipients and co-existing compounds. The results obtained for the assay of commercial preparations compared well with those obtained by an official chemical method and demonstrated good accuracy and precision.     

Ru(III) catalyzed oxidation of some aliphatic alcohols by N-bromosuccinimide (NBS). A kinetic study

Kinetics of Ru(III) catalyzed oxidation of methanol, ethanol, n-propanol, n-butanol, isopropanol and iso-butanol by N-bromosuccinimide (NBS) in the presence of Hg(II) acetate have been studied in acid medium. The oxidation exhibits a fractional order in [alcohol] and first order in [NBS]. The applicability of Taft's equation was tested. The probable mechanism is discussed.

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, , -, -, - () Hg(II), Ru(III), . . . .

     

Determination of nitric oxide by bromate oxidation of the nitrosyl ethylenediaminetetra-acetatoiron(II) complex

A new spectrophotometric method for nitric oxide is proposed, based on formation of the nitrosyl-ethylenediaminetetra-acetatoiron(II) complex [Fe(II)NO-edta] by absorption of NO in Fe(II)edta solution and spectrophotometric determination of the NO(-)(2) produced by oxidation of the Fe(II)NO-edta complex by potassium bromate. The oxidation is easily performed completely and the absorption efficiency for 10.1-102.0 ppm NO (flow-rate, 100 ml/min) is nearly 100%. The detection limit is about 3 ppm for a sampling absorption time of 30 min.