Oxidimetric determination of methionine and its metal complexes with chloramine-B and dichloramine-B

Simple, rapid, and reproducible methods for the determination of methionine (HMt) and its metal complexes, [NiMt]ClO₄₊ and Na[AgMt₂], in aqueous solutions have been developed, based on their oxidation with chloramine-B and dichloramine-B at room temperature. The direct titration, with a visual or potentiometric endpoint, involves a two-electron change corresponding to the formation of methionine sulfoxide. Several amino acids and common anions and cations do not interfere under these conditions. In the back-titration procedure methionine and its complexes are oxidized by excess CAB in 0.1 N NaOH medium with a four-electron change corresponding to the formation of methionine sulfone. The amino acid and its complexes are, however, oxidized to the respective nitrile, with excess DCB with an eight-electron change.     

Oxidation of isoniazid by N‐haloarenesulfonamidates in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of Isoniazid (INH) by sodium N‐haloarenesulfonamidates, chloramine‐T (CAT), bromamine‐T (BAT), chloramine‐B (CAB), and bromamine‐B (BAB), has been studied in alkaline medium at 303 K. The oxidation reaction follows identical kinetics with a first‐order dependence on each [oxidant] and [INH] and an inverse fractional‐order on [OH^−:]. Addition of the reaction product (p‐toluenesulfonamide or benzenesulfonamide) had no significant effect on the reaction rate. Variation of ionic strength and addition of halide ions have no influence on the rate. There is a negative effect of dielectric constant of the solvent. Studies of solvent isotope effects using D₂O showed a retardation of rate in the heavier medium. The reaction was studied at different temperatures, and activation parameters have been computed from the Arrhenius and Eyring plots. Isonicotinic acid was identified as the oxidation product by GC‐MS. A two‐pathway mechanism is pro‐posed in which RNHX and the anion RNX⁻ interact with the substrate in the rate‐limiting steps. The mechanism proposed and the derived rate laws are consistent with the observed kinetics. The rate of oxidation of INH increases in the order: BAT > BAB > CAT > CAB. This effect is mainly due to electronic factors. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 221–230, 2000     

Oxidation of primary amines by bromamine-B catalyzed by Osmium(VIII) in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB), in the presence of osmium(VIII), has been studied in alkaline medium at 35°C. In the presence of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes the form, rate=k[BAB][OsO₄][OH⁻]^x, which in the absence of the catalyst changes to the form, rate=k[BAB][S][OH⁻]^y, where x and y are less than unity. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and the variation of ionic strength of the solvent medium have no effect on the reaction rate. Activation parameters have been evaluated. The proposed mechanism assumes the formation of a complex intermediate between the active oxidant species, PhSO₂NBr⁻, and the catalyst, OsO₄, in the rate determining step. This complex then interacts with the substrate amine in fast steps to yield the end products. The average value for the deprotonation constant of monobromamine-B, forming PhSO₂NBr⁻, is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as 9.80×10³ at 35°C. The average value for the same constant for the uncatalyzed reactions is 1.02×10⁴ at 35°C. © 1997 John Wiley & Sons, Inc.     

Osmium (VIII) catalyzed kinetics and mechanism of indoles oxidation with Aryl-N-haloamines in alkaline medium

The kinetics of oxidation of the title substrates by sodium N-haloarylsulfonamides (or ary-N-haloamines), chloramine-T (CAT), bromamine-T (BAT), chloramine-B (CAB), and bromamine-B (BAB), catalyzed by osmium(VIII) in alkaline medium has been studied at 30°C. The corresponding oxindoles and arylsulfonamides have been characterized as reaction products. The reaction rate shows a first-order dependence each on |indole|₀ and |oxidant|₀, a fractional-order on |Os(VIII)|, and an inverse first-order on |OH⁻|. Addition of arylsulfon-amide, chloride and bromide, and variation of ionic strength of the medium have no effect on the reaction rate. There is a negative effect of dielectric constant of the solvent. Activation parameters have been calculated from the Arrhenius and Eyring plots. Hammett correlation of substituent effects indicates an LFE relationship with ρ = −1.0, showing the formation of an electron deficient transition state. From enthalpy-entropy relationships and Exner correlations, the isokinetic temperatures (333 K and 326 K) have been determined for the reactions of CAT and BAT, respectively. Proton inventory studies in H₂O-D₂O mixtures have shown the involvement of a single exchangeable proton of OH⁻ ion in the transition state. A mechanism consistent with the observed kinetics has been proposed. © 1996 John Wiley & Sons, Inc.     

Kinetic and mechanistic studies of some aliphatic amines' oxidation by sodium N‐bromo‐p‐toluenesulfonamide in hydrochloric acid medium

Oxidations of n‐propyl, n‐butyl, isobutyl, and isoamyl amines by bromamine‐T (BAT) in HCl medium have been kinetically studied at 30°C. The reaction rate shows a first‐order dependence on [BAT], a fractional‐order dependence on [amine], and an inverse fractional‐order dependence on [HCl]. The additions of halide ions and the reduction product of BAT, p‐toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength of the medium has no influence on the reaction. Activation parameters have been evaluated from the Arrhenius and Eyring plots. Mechanisms consistent with the preceding kinetic data have been proposed. The protonation constant of monobromamine‐T has been evaluated to be 48 ± 1. A Taft linear free‐energy relationship is observed for the reaction with ρ* = −12.6, indicating that the electron‐donating groups enhance the reaction rate. An isokinetic relationship is observed with β = 350 K, indicating that enthalpy factors control the reaction rate. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 776–783, 2000     

Oxidation of metronidazole with sodium N‐bromo‐p‐toluenesulfonamide in acid and alkaline media: A kinetic and mechanistic study

A kinetic study of oxidation of metronidazole (Met) with sodium N‐bromo‐p‐toluenesulfonamide or bromamine‐T (BAT) has been carried out in HClO₄ (30°C) and NaOH (40°C) media. The experimental rate laws obtained are –d[BAT]/dt=k[BAT][Met]^x [H⁺]^y in acid medium and –d[BAT]/dt=k[BAT][Met]^x [OH^?]^y/[PTS]^z in alkaline medium, where x, y, and z are less than unity and PTS is p‐toluenesulfonamide. The reaction was subjected to changes in (a) ionic strength, (b) concentration of added reduction product PTS, (c) concentration of added neutral salts, (d) dielectric permittivity, and (e) solvent isotope effect. In both media, the stoichiometry of the reaction was found to be 1:1, and the oxidation product of metronidazole was identified as its aldehyde. The reaction was studied at different temperatures, and the activation parameters have been evaluated. The reaction constants involved in the proposed schemes were deduced. The reaction was found to be faster in acid medium in comparison with alkaline medium, which is attributed to the involvement of different oxidizing species. Mechanisms proposed and the rate laws derived are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 700–709, 2005     

Synthesis and characterization of iridium chloride complexes: I. Use of N-alkylphenothiazine drugs as ligands

Summary Iridium complexes of N-alkylphenothiazines have been prepared in MeOH. The polynuclear complexes obtained have been characterized by elemental analyses, magnetic susceptibilities, molar conductivities, thermogravimetric analysis and spectral data. The molecular formulae of the new complexes are as follows: [Ir₃(LH)₄Cl₁₀]Cl₂·xMeOH, where L = chlorpromazine (CP), promethazine (PM) or ethopropazine (EP), and x = 1 for CP and 2 for PM or EP; [Ir(TFH₂)₂Cl₄][IrCl₆]·MeOH, where TF = trifluoperazine; and [Ir₂(TRH)₂Cl₁₁(MeOH)]Cl·MeOH and [Ir₄(TRH)₃Cl₁₅], where TR = thioridazine. The complexes are diamagnetic in nature. Tentative structures are proposed for the complexes.     

Ruthenium(III) catalyzed kinetics of chloroacetic acids oxidation by sodium N-bromobenzenesulfonamide in hydrochloric acid medium

Kinetics of uncatalyzed and Ru(III)-catalyzed oxidations of mono-, di-, and tri-chloroacetic acids by the title compound (bromamine-B or BAB) in HCl medium has been studied at 40°C. The uncatalyzed reaction shows a first-order dependence of the rate on [BAB], and fractional and zero orders in [acid] at low and high [HCl] ranges, respectively. The Ru(III)-catalyzed reaction, on the other hand, shows a first-order behavior on each of [BAB] and [substrate], second-order dependence on [Ru(III)], and inverse fractional and inverse first orders in [acid] at low and high [HCl] ranges. Addition of halide ions and the reduction product of BAB, benzenesulfonamide, has no effect on the reaction rate. Variation of ionic strength of the medium has no influence on the reaction. Solvent isotope effect was studied using D₂O. Activation parameters have been evaluated from the Arrhenius plots. Mechanisms consistent with the above kinetic data have been proposed. The protonation constant of monobromamine-B evaluated from the uncatalyzed reaction is 12.4 while that evaluated from Ru(III) catalyzed reaction is 12.7. A Taft linear free-energy relationship is noted for the catalyzed reaction with ρ* = 1.2 and 0.07 indicating that electron withdrawing groups enhance the rate. An isokinetic relation is observed with β = 338 K indicating that enthalpy factors control the reaction rate. © 1993 John Wiley & Sons, Inc.     

Some analytical applications of aromatic sulfonyl haloamines: Determination of thiosemicarbazide alone and in its metal complexes with bromamine-B and dichloramine-B

Simple, rapid, and reproducible back titration methods for the determination of thiosemicarbazide (TSC) in free state and in Zn, Cd, Hg, Ni, Pt, and Pd metal complexes with bromamine-B (BAB) and dichloramine-B (DCB) have been developed. The oxidation reaction involves a 12-electron change per TSC molecule in 0.2–1.0 M NaOH and water-acetic acid media with BAB and DCB, respectively. The proposed analytical procedures for the assay of TSC are also useful for computing the number of TSC ligands present in the respective metal complexes. The two aromatic sulfonyl haloamines used, BAB and DCB, were prepared and then characterized by ¹³C FT-NMR spectral data.     

Sodium N-chlorobenzenesulfonamide as an analytical reagent: Determination of amino acids and their metal complexes

Simple, elegant, and reproducible back-titration methods for the determination of arginine, histidine, threonine, glutamine, alanine, lysine, glycine, and serine in free state and in Zn, Cd, Ni, Cu, Ba, Sr, Mn, and Ag metal complexes with chloramine-B have been developed. The oxidation reaction involves a four-electron change per mole of amino acid, but a six-electron change is noticed with glycine and serine in various solvent and buffer media. The proposed analytical procedures for the assay of amino acids are useful for computing the number of amino acid ligands present in the respective metal complexes. The aromatic sulfonyl haloamine used, CAB, was prepared and then characterized by ¹H and ¹³C FT-NMR spectral data.