Oxidation of 2‐Phenylethylamine with N‐Bromosuccinimide in Acid and Alkaline Media: A Kinetic and Mechanistic Study

A kinetic study of oxidation of 2‐phenylethylamine (PEA), a bioactive compound, with potent oxidant, N‐bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimental rate laws obtained are: ‐d [NBS] /dt = k[NBS][PEA][H⁺] in hydrochloric acid medium and ‐d [NBS]/dt = k[NBS][PEA]^x[OH^?]^y in alkaline medium where x and y are less than unity. Accelerating effect of [Cl^?], and retardation of the added succinimide on the reaction rate have been observed in acid medium. Variation of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The reactions were studied at different temperatures and the activation parameters have been evaluated. The reaction constants involved in the proposed mechanisms were computed. The reaction was found to be faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the observed experimental results.     

Electron transfer at tetrahedral cobalt(II). Part 1. Kinetics of bromate ion reduction

Summary The bromate ion reduction by 12-tungstocobaltate(II) anion has been investigated. The reaction obeys the empirical rate law:-d[reductant]/dt=5(a+b[H⁺]²)[BrO ₃ ^– ][reductant]: where a=(2.49±0.18)×10^–4M^–1 s^–1, b=(4.65±0.20)×10^–5M^–3s^–1 at 24.5±0.1°C [H⁺]=0.05–1.50M and I=2.0M (NaClO₄). This rate law is interpreted in terms of parallel reactions of BrO ₃ ^– and H₂BrO ₃ ⁺ . On the basis of the observed anion catalysis, substitution intertness of the reductant and Marcus type linear free energy relations, the outer sphere mechanism is proposed for both pathways.     

Inner-sphere oxidation of 2-aminomethylpyridinecobalt(II) complex by N-bromosuccinimide

The kinetics of the oxidation of the 2-aminomethylpyridineCo^II complex by N-bromosuccinimide (NBS), have been studied in aqueous solutions under various conditions, and obey the following rate law:Rate = [NBS][Co(L)(H₂O)₂]²⁺[k₂₊k₃/[H⁺]]An inner-sphere mechanism is proposed for the oxidation pathway for both protonated and deprotonated complex species, with the formation of an intermediate, which is slowly converted into the final oxidation products. The reaction rate is increased by increasing the pH, T, [complex], and decreased by increasing ionic strength over the range studied.     

Oxidations of hypophosphorus and arsenious acids by 12-tungstocobaltate(III) anion in aqueous solution

Summary The kinetics of oxidation of hypophosphorus and arsenious acids by 12-tungstocobaltate(III) anion have been studied in aqueous hydrochloric acid at constant ionic strength (I=2.0 M NaCl). The reactions obey the second-order rate law d[oxidant]/dt=2k [oxidant] [reductant]. Variation of [H⁺] in the range 0.10–1.50 M has no effect on the rates. Possible mechanistic interpretations of these observations are suggested.     

Osmium(VIII) oxidation of arsenic(III) in aqueous sulphuric acid

The oxidation of As^III by Os^VIII or Os^VI in aqueous H₂SO₄ follows the rate law:

Nd（OprI）2Cl－AlEt_3均相二元催化剂异戊二烯聚合动力学Ⅰ．一般动力学研究

用膨胀计研究了Ｎｄ（ＯＰｒ＾ｉ）２Ｃｌ－ＡｌＥｔ３均相稀土催化剂异戊二烯聚合动力学。在实验条件下，本体系显示稳态聚合特征；聚合速度对单体浓度和催化剂浓度均为一级关系，即聚合速度方程为Ｒｐ－Ｋｐ［Ｎｄ］［Ｍ］；本体系总的活化能Ｅａ为５７．４ｋＪ／ｍｏｌ。     

Kinetics and mechanism of silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate in acetate buffers

Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k ₁ K _inf2 ^sup-1 [H⁺]² + k ₂[H⁺] + k ₃ K ₃)/ ([H⁺]²/K ₂ + [H⁺] + K ₃)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made.     

Base hydrolysis ofcis-dichlorobis(1,2-diaminoethane),cis-α-dichloro(1,8-diamino-3,6-diazaoctane) andcis-α-chlorohydroxo-(1,8-diamino-3,6-diazaoctane) ruthenium(III) complexes

The kinetics of base hydrolysis ofcis-[RuCl₂(en)₂]⁺ (en=1,2-diaminoethane),cis-α-[RuCl₂(trien)]⁺ andcis-α-[RuCl(OH)(trien)]²⁺ (trien=1,8-diamino-3,6-diazaoctane) have been studied. All the reactions are fast and obey the second-order rate law,-d[complex]/dt=k[OH⁻][complex], with complete retention of configuration. A conjugate base mechanism involving a squarepyramidal intermediate is suggested. The Arrhenius parameters and rate constants found are respectively: ΔH^≠ 14.2±0.5, 7.2±0.1, 10.9±0.1 M cal mol⁻¹; ΔS^≠ 1.3, 29, 22 cal deg⁻¹ mol; log A 13.5, 6.9, 8.6 k_OH 533 (27.2°C) 14.5 (24.4° C) 1.65 (25°C) M⁻¹s⁻¹.     

DPPH-initiated oxygenation of 3-hydroxyflavone to O-benzoylsalicylic acid

Summary The oxidation of 3-hydroxyflavone (flaH) to O-benzoylsalicylic acid (O-bs) initiated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) has been investigated in acetonitrile at ambient temperature. The kinetics was followed by monitoring the disappearance of DPPH spectrophotometrically at 520 nm and the rate constants were determined according to the rate law -d[DPPH]/dt = k [DPPH][Substrate]. The mean value of the rate constant k at 295 K is 1.21 ± 0.03 dm³ mol^-1 s^-1.     

Kinetics and mechanism of oxidation of dimethyl sulfoxide by chloramine-T in aqueous solution

The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine-T (CAT) is studied in HClO₄ and NaOH media with OsO₄ as a catalyst in the latter medium. In acid medium, the rate law is -d [CAT]/dt = k [CAT][DMSO][H⁺]. Alkali retards the reaction and the rate law takes the form -d [CAT]/dt = k [CAT][DMSO][OsO₄]/[NaOH], but is reduced to -d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied. The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO₄ which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine-T and the substrate.     

Oxidation of glutathione by diaquatetrakis(2,2′-bipyridine)-μ-oxo diruthenium(III) ion in aqueous acidic solutions

Summary The kinetics of the oxidation of glutathione by diaquatetrakis(2,2-bipyridine)--oxo diruthenium(III) ion in aqueous HClO₄ have been investigated. The reaction obeys the empirical rate law:-2d[oxidant]/dt = k[oxidant][reductant]/[H⁺] where k = 7.42 ± 0.40 × 10^-3 s^-1 at 25.5 °C, [H⁺] = 0.005–0.05 M and I = 1.0 M (LiClO₄). Free radicals are important in the reaction and a mechanism consistent with the experimental results has been postulated.     

Kinetische Untersuchungen zur Bildung von N-Nitrosoverbindungen II. Entstehung von N-Nitroso-N-methylharnstoff in wäßriger Perchlorsäurelösung

The kinetics of nitrosation of Methylurea (MU) in aqueous perchloric solution has been studied using two techniques: a dynamic spectrophotometric and a stopped-flow technique. The rate law obtained, whenpH was varied in the range 0.27–3.22, is $$---d[nitrite]/dt = f[MU][nitrite][H^ + ]/(1 + g/[H^ + ])$$ where [MU] and [nitrite] represent stoichiometric concentrations. At 288.0 K and μ=1.0M,f=(15.6±0.5)M ^?2s^?1 andg=(1.06±0.08) 10^?3 M. This rate law becomes independent of the acidity of the solution when this is increased ([ClO₄H])>1.00M). These results together with the activation of the nitrosation rate by the ionic strength and the negative value of the activation entropy shown that only the NO₂H₂ ⁺ or NO⁺ is the effective carrier for the nitrosation. Comparisons with the nitrosation of dimethylamine were also made leading to the conclusion that there is no simple explanation for the fact that the nitrosation via NO₂H₂ ⁺/NO⁺ disappears when the nitrosable compound is of increased basicity.     

Electrochemical oxidation of 4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d] pyrimidine-4,6-dione (oxipurinol) at the pyrolytic graphite electrode

The electrochemical oxidation of 4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d] pyrimidine-4,6-dione (oxipurinol) at the pyrolytic graphite electrode (PGE) has been studied. Oxipurinol exhibits up to three voltammetric oxidation peaks at the PGE between pH 1–12. The first pH-dependent peak (peak I_a) is proposed to be an initial, irreversible 2e-2H⁺ reaction to give 5,6-dihydro-4H-pyrazolo[3,4-d] pyrimidine-4,6-dione. This primary product further reacts by two routes. The major route, accounting for ca. 90% of the latter compound, involves a Michael addition of water followed by further electrochemical oxidation and hydrolysis to give 5,6-dihydro-5,6-dihydroxy-5-carboxy-6-diazenouracil. The minor route involves further electrochemical oxidation of 5,6-dihydro-4H-pyrazolo[3,4-d]-pyrimidine-4,6-dione in a 2e-2H⁺ reaction to give 4,5,6,7-tetrahydro-3H-pyrazolo[3,4-d]-pyrimidine-3,4,6-trione.Decomposition and, generally, additional electrochemical reactions of 5,6-dihydro-5,6-dihydroxy-5-carboxy-6-diazenouracil result in the formation of alloxan, parabanic acid, 6-diazo-isobarbituric acid and 5′-hydroxy-5-carboxy-6,6′-azouracil. The two latter compounds have never previously been reported. Decomposition of 4,5,6,7-tetrahydro-3H-pyrazolo[3,4-d]pyrimidine-3,4,6-trione results in formation of uracil-5-carboxylic acid.Detailed reaction schemes have been proposed to explain the observed electrochemistry and the formation of the observed products.     

Kinetics and mechanism of oxidation of secondary alcohols by potassium bromate

The oxidation by Br(V) of propan-2-ol follows the rate law (?d[Br(V)]/dt) = k₄ [alcohol][Br(V)][H⁺]². The initial reaction is complicated by the presence of the product bromide ion. The reaction is composed of two second order reactions—the first, a comparatively slow one and the second stage, a faster reaction which is mainly bromine oxidation. The pure bromate oxidation can be followed by the initial addition of mercuric acetate which prevents the accumulation of bromine in the system under these conditions. The reaction rate does not depend on the nature and structure of the alcohol. A mechanism involving a slow rate-determining formation of an alkyl-bromate ester followed by a fast decomposition to the products is in accord with the observed results.     

N,N-二甲基羟胺与HNO2的反应动力学

分别在高氯酸和硝酸介质中研究了N,N-二甲基羟胺(DMHAN)与HNO₂的反应动力学,通过考察溶液酸度、还原剂浓度、离子强度和温度等因素对反应过程的影响,获得高氯酸介质中反应动力学速率方程为-d[HNO₂]/dt=k[DMHAN][HNO₂],在18.5 ℃,离子强度μ=0.73 mol/L时,反应速率常数k=(12.8±1.0) mol/(L·min),反应活化能Ea=41.5 kJ/mol。 在硝酸介质中DMHAN与HNO₂的反应比较复杂,硝酸浓度较高时,硝酸将参与反应重新生成HNO₂,且硝酸浓度越大,HNO₂的生成速度越快,HNO₂与DMHAN的反应是自催化氧化的。 对DMHAN与HNO₂的反应产物进行了分析,并推导了硝酸体系中DMHAN与HNO₂的反应机理。     

Kinetic study of the oxidation of L-threonine by MnO4? ions

A self-catalytic effect attributed to Mn²⁺ ions was observed when studying the oxidation of L-threonine by permanganate ions. The process obeys the rate equation:

Kinetics and mechanism of oxidation of uric acid with thallium(III) in acetate buffers

The kinetics of oxidation of uric acid by thallium(III) has been studied in acetate buffers; the oxidation products are alloxan and urea. Deprotonated uric acid, UaH⁻, and T1(OAc)₃ are the reacting species. A probable reaction mechanism has been proposed conforming with rate law (1)-d[T1^III]/dt=(k′₁K′₁+k′₂K′₂K₁/[H⁺]) [T1^III][UaH₂]/1+K₄[OAc⁻] A comparative analysis with other soft acids Hg^II and Pb^IV has been attempted.     

Kinetics and mechanism of oxidation of ferrocyanide by N-bromosuccinimide in aqueous acidic solution

The kinetics of oxidation of ferrocyanide by N-bromosuccinimide (NBS) has been studied spectrophotometrically in aqueous acidic medium over temperature range 20–35 °C, pH = 2.8–4.3, and ionic strength = 0.10–0.50 mol dm⁻³ over a range of [Fe²⁺] and [NBS]. The reaction exhibited first order dependence on both reactants and increased with increasing pH, [NBS], and [Fe²⁺]. The rate of oxidation obeys the rate law: d[Fe³⁺]/dt = [Fe(CN)₆]^4–[HNBS⁺]/(k ₂ + k ₃/[H⁺]). An outer-sphere mechanism has been proposed for the oxidation pathway of both protonated and deprotonated ferrocyanide species. Addition of both succinimide and mercuric acetate to the reaction mixture has no effect on the reaction rate under the experimental conditions. Mercuric acetate was added to the reaction mixture to act as scavenger for any bromide formed to ensure that the oxidation is entirely due to NBS oxidation.     

Kinetic Studies of Chromic Acid Oxidation of Glyoxal

The kinetics of chromic acid oxidation of glyoxal is reported. The reaction is first-order in glyoxal and indicates a gradual change from a first-order to a zero-order dependence on acidity. The kinetic nature of this reaction has been studied and the rate law is consistent with a proposed mechanism as follows; rate = kK_b, K[Cr⁺⁶][Gx][H⁺]/(l+0.238[H⁺]) at 25°C. The product analysis indicates that formic acid is the oxidation product under similar kinetic condition.     

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.