Influence of a reaction medium on the oxidation of aromatic nitrogen-containing compounds by peroxyacids

The influence of different solvents on the oxidation reaction rate of pyridine (Py), quinoline (QN), acridine (AN), α-oxyquinoline (OQN) and α-picolinic acid (APA) by peroxydecanoic acid (PDA) was studied. It was found that the oxidation rate grows in the series Py < QN < AN, and the rate of the oxidation reaction of compounds containing a substituent in the α position from a reactive center is significantly lower than for unsubstituted analogues. The effective energies of activation of the oxidation reaction were found. It was shown that in the first stage, the reaction mechanism includes the rapid formation of an intermediate complex nitrogen-containing compound, peroxyacid, which forms products upon decomposing in the second stage. A kinetic equation that describes the studied process is offered. The constants of equilibrium of the intermediate complex formation (K _eq) and its decomposition constant (k ₂) in acetone and benzene were calculated. It was shown that the nature of the solvent influences the numerical values of both K _p and k ₂. It was established that introduction of acetic acid (which is able to form compounds with Py) into the reaction medium slows the rate of the oxidation process drastically. Correlation equations linking the polarity, polarizability, electrophilicity, and basicity of solvents with the constant of the PDA oxidation reaction rate for Py were found. It was concluded that the basicity and polarity of the solvent have a decisive influence on the oxidation reaction rate, while the polarizability and electrophilicity of the reaction medium do not influence the oxidation reaction rate.     

Oxidation of alcohols by chlorine dioxide in organic solvents

The kinetics of oxidation of a series of alcohols (propan-2-ol, 2-methylpropan-1-ol, butan-1-ol, butan-2-ol, 3-methylpentan-1-ol, heptan-4-ol, decan-2-ol, cyclohexanol, borneol) by chlorine dioxide in organic solvents was studied using spectrophotometry. The reaction is described by the second-order rate equation w = k[ROH][ClO₂]. The rate constants were measured in the range of 10–60 °C, and the activation parameters of the processes were calculated. The products were identified, and the yields were determined.     

Kinetics of oxidation of nickel(II) aza macrocycles by peroxydisulphate in aqueous media

The kinetics of the oxidation of nickel (II) hexaaza and nickel (II) pentaaza macrocycles by the peroxydisulphate anion, S₂O₈ ²⁻, were studied in aqueous media. Effect of pH on reaction rate was also studied. The rate increases with increase of S₂O₈ ²⁻ concentration. Rates are almost independent of acid betweenpH 4 and 2, giving overall a relatively simple second-order rate law followed by oxidation within the ion pair solvent shell. Using rate =+1/2 d[Ni(L)³⁺]/dt =k[Ni(L)²⁺][S₂O₈ ²⁻], oxidation rate constants were determined.     

Electron transfer and paramagnetic products of reactions of haloquinones with aliphatic amines

The reactions of chloranil (Cl₄Q) and bromanil (Br₄Q) with aliphatic amines in a DMF : H₂O (5 : 1, vol/vol) mixture were studied. The radical anions of 2,5-didimethylamino-3,6-chloro-p-benzoquinone and 2,5-didimethylamino-3,6-bromo-p-benzoquinone were identified by ESR spectra. The reaction rate constant of the replacement of two chlorine atoms by the amino groups in the radical anion of Cl₄Q at 288 K was estimated.     

Thermal reactions of N,N′ bis(p-nitrophenyl)sulfamide and p-benzoquinone dioxime–acid mixtures

N,N′ Bis(p-nitrophenyl)sulfamide and p-benzoquinone dioxime–acid mixtures were found to undergo an abrupt reaction when heated to give a black polymeric material. These polymeric materials exhibited thermal stability (TGA in N₂) up to 500°C and were insoluble in all solvents including hot concentrated sulfuric acid. From analytical data, structural formulae have been assigned to the polymeric materials that are logically derivable from the starting materials.     

Oxidation of valeraldehyde by chlorine dioxide

The product of the reaction of valeraldehyde with chlorine dioxide was determined, and the solvent effect on the reaction kinetics was studied. The major oxidation product is valeric acid. The reaction rate is described by the second-order equation w = k[RCHO]·[ClO₂]. The rate constants were measured in the 297–328 K interval, and the activation parameters of the reaction were determined.     

Kinetics of oxidation of hydroquinone to <Emphasis Type="Italic">p</Emphasis>-benzoquinone catalyzed by microporous metal-organic frameworks M<Subscript>3</Subscript>(BTC)<Subscript>2</Subscript> [M = copper(II), cobalt(II), or nickel(II); BTC = benzene-1,3,5-tricarboxylate] using molecular oxygen

The kinetics of oxidation of hydroquinone (H₂Q) to p-benzoquinone (Q) catalyzed by microporous metal-organic frameworks (MOFs) using molecular oxygen has been investigated. MOF catalysts with different metals and pore sizes, i.e. M₃(BTC)₂(H₂O) _x (M = Cu^II (1), Co^II (2), or Ni^II (3); BTC = benzene-1,3,5-tricarboxylate; x = 3 for MOF 1 and 12 for 2 and 3), were used to catalyze the oxidation reaction. The apparent first-order reaction rate constant increased with increasing temperature, molar ratio of catalyst/H₂Q, and pH of the medium. A kinetic model for the heterogeneous catalysis is proposed, and the apparent activation energy (E _a), the association constants between the hydroquinone and the catalyst (K _s), and the first-order rate constants for product formation in the MOF channels (k _N) were calculated.     

Oxidation of styrene by 2,3-dichloro-5,6-dicyano-p-benzoquinone

Styrene is oxidized by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), affording hydroquinone mono(2-phenylethyl) ether. Kinetic studies (50°C in CHCl₃) show that the reaction is faster under N₂ than under air and takes placevia intramolecular H-atom transfer within the 1:1 and 1:2 DDQ-styrene charge-transfer complexes. The semiquinone radical intermediate is reoxidized to DDQ by O₂ when the latter is present, therefore, the apparent rate of DDQ reduction is lower. Stability constants of the CT-complexes and kinetic parameters for the oxidation are reported.     

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.     

Inorganic coordination polymers. X. Observations on the formation and nature of poly(di-μ-diphenylphosphinato-hydroxyaquochromium (III)),{Cr(H2O)(OH)-[OP(C6H5)2O]2}x

Under different conditions two products, one green and one brown, were obtained by the air oxidation of chromium(II) diphenylphosphinate. Air oxidation of an aqueous suspension of the phosphinate apparently yields a mixture in which the green form predominates. As initially isolated, the green form is a low molecular weight polymer corresponding to {Cr(H₂O)(OH)[OP(C₆H₅)₂O]₂}_n, with n approximately 11. It spontaneously polymerizes further in organic solvents to high molecular weight polymers of the same composition, with n in the range 150–200. This polymerization reaction in volves the elimination of water and is probably a reaction between endgroups resulting in a basically linear polymer. The brown product, corresponding to low molecular weight {Cr₂(H₂O)(OH)₂[OP(C₆H₅)₂O]₄}_p, also polymerizes spontaneously but at a faster rate and to a gel. The polymer so produced is less soluble than that produced from the low molecular weight green product and is probably crosslinked.     

Oxidation of phenols with chlorine dioxide

The oxidation of different phenols, viz., phenol, 3-methylphenol, 4-methylphenol, 4-tert-butylphenol, 2-cyclohexylphenol, 2,6-di-tert-butyl-4-methylphenol, and 2,4-dichlorophenol, with chlorine dioxide in acetonitrile was studied spectrophotometrically. The reaction rate is described by a second-order equation w = k[PhOH]· [ClO₂]. The rate constants were measured and activation parameters of oxidation were determined in a temperature interval of 10–60°C. A dependence of the reaction rate constant on the phenol structure was found. The oxidation products were identified, and their yields were established.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2184–2187, October, 2004.     

Some observations on the spectrophotometric determination of amino acids via interaction with p-benzoquinone

Spectrophotometric quantitative determination of amines and sulfa drugs via interaction with p-benzoquinone was extended to determination of amino acids, whereby the colored products obtained display maximum absorption at λ = 490–500 nm, E₁ cm^1% in the range 160–480, and a concentration range of 1.5–34.0 μg/ml. The effects of time, concentration, temperature, and cooling on the nature of the reaction product were investigated. The reaction proved to be irreversible. A monosubstituent compound is more easily formed in the presence of excess p-benzoquinone. A linear relation between the formation constant (K_f) and pK_α for the tested amino acids has been observed. Determination of adrenaline by this method is considered to offer an indirect means of determination of tyrosine.     

Investigation of cationic copolymerization of styrene with p-benzoquinone

The kinetics of copolymerization of styrene with p-benzoquinone in the presence of BF₃OEt₂ is investigated. The rate constants and activation energy of the copolymerization process are determined. The reaction orders for monomer and catalyst are estimated. It is found that the rate of styrene and quinone copolymerization increase and the induction period decreases owing to addition of the latter. It is shown that the copolymerization rate achieves its maximum at an equimolal ratio of monomers. This phenomenon is explained by formation of active molecular complex between styrene and p-benzoquinone. On the basis of obtained data the course of copolymerization is interpreted and the cationic mechanism of copolymerization process is proposed.     

Electrochemical determination of <Emphasis Type="Italic">p</Emphasis>-cresol using mesoporous TiO<Subscript>2</Subscript>-modified carbon paste electrode

A mesoporous TiO₂ (meso-TiO₂) was synthesized, and used to prepare modified carbon paste electrode (CPE). The electrochemical sensing properties were characterized using K₃[Fe(CN)₆], showing that meso-TiO₂ modified CPE possesses larger surface area and higher electron transfer rate. The electrochemical behavior of p-cresol was investigated. At the meso-TiO₂ modified CPE, the oxidation peak current of p-cresol remarkably increases, and the oxidation peak potential shifts negatively, suggesting that meso- TiO₂ exhibits highly efficient catalytic activity to the oxidation of p-cresol. Based on this, a sensitive, rapid and convenient electrochemical method was developed for the detection of p-cresol. The linear range is from 1.5 × 10⁻⁷ and 2.0 × 10⁻⁵ mol l⁻¹, and the limit of detection is as low as 8.0 × 10⁻⁸ mol l⁻¹. Finally, the new method was successfully used to determine p-cresol in water samples.     

Ruthenium(III) – catalyzed oxidative cleavage of <Emphasis Type="Italic">p</Emphasis>-aminoazobenzene by chloramine-B in alkaline medium and uncatalyzed reaction in acid medium: spectrophotometric kinetic and mechanistic study

p-Aminoazobenzene (PAAB) is one of the important monoazo dyes and its oxidation kinetic study is of much use in understanding the mechanistic profile of PAAB in redox reactions. Consequently, the kinetics of oxidation of PAAB by sodium N-chlorobenzenesulfonamide or chloramine-B (CAB) in HClO₄ medium and in NaOH medium catalyzed by ruthenium(III) chloride (Ru^III) have been investigated at 298 K. U.v.–vis spectrophotometry was used as a basic analytical approach in this study. Under an identical set of experimental conditions, the reactions of PAAB–CAB in HClO₄ medium were facile, but the reactions became too slow to be studied in alkaline medium and hence ruthenium(III) chloride has been used as a catalyst in alkaline medium. The stoichiometry (1:2) and oxidation products (nitrosobenzene and p-nitrosoaniline) are the same in both media, but the kinetic and mechanistic patterns were found to be different. The experimental rate laws obtained are: − d[CAB]/dt = k [CAB]₀ [PAAB]₀ [H⁺] in acid medium and − d[CAB]₀/dt = k [CAB]₀ [PAAB]₀[OH⁻] ^x [Ru^III] ^y in alkaline medium, where x and y are less than unity. The reaction was examined with reference to changes in (a) concentration of benzenesulfonamide, (b) concentration of added neutral salts, (c) ionic strength, (d) dielectric permitivity and (e) solvent isotope effect. The reaction was also studied at different temperatures and the overall activation parameters have been evaluated. The oxidation reaction fails to induce the polymerization of added acrylonitrile. C₆H₄SO₂NHCl and C₆H₄SO₂NCl⁻ have been postulated as the reactive oxidizing species in acidic and alkaline media, respectively. It was found that the reactions are nearly 20 times faster in acid medium in comparison with alkaline medium. It was also observed that ruthenium(III) was an efficient catalyst for the facile oxidation of PAAB by CAB in alkaline medium by making the reaction go twelve-fold faster than the uncatalyzed reactions. The catalytic constant (K _C) has been calculated at different temperatures and the values of activation parameters with respect to ruthenium(III) have also been evaluated in alkaline medium. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced.     

Synthesis of aromatic polyesters and polyamides by alternating copolymerizations of 1,4-dicarbonyl-1,4-dihydronaphthalene with bezoquinones and benzoquinone diimines

1,4-Dicarbonyl-1,4-dihydronaphthalene ( 1 ) was synthesized by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride with triethylamine and obtained as its very dilute solution, but it easily polymerized in the concentration as high as 0.1 mol/L to give its polymer. 1 generated in situ by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride in a deoxygenated toluene polymerized alternatingly with benzoquinones such as 2-dodecylthio-p-benzoquinone, 2,5-di(tert-butyl)-p-benzoquinone, p-benzoquinone, and 2,3-dichloro-5,6-dicyano-p-benzoquinone, and with benzoquinone diimines such as N,N′-diethoxycarbonyl-p-benzoquinone diimine, N,N′-dibenzoyl-p-benzoquinone diimine, and N,N′-diphenyl-p-benzoquinone diimine to give aromatic polyesters and polyamides, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1929–1936, 1998     

Potentiostatic preparation of poly-1,3-dimethoxybenzene films. Kinetics and bilayer structure

The anodic oxidation of 1,3-dimethoxybenzene (MDMB) on a platinum electrode in non-aqueous tetrabutylammonium perchlorate (TBAP) + acetonitrile solutions begins at 1100 mV. Under polarization at constant potential a polymer film is formed at potentials above than 1700 mV. The empirical kinetics of the formation and growth of this film were investigated using microgravimetry and coulometry. Under all experimental conditions the polymerization rate R_p changes after 10 s of polarization, and this behavior can be described by the empirical equationsR_p = k[MDMB]^0.3[TBAP]^0.4t_pol <10sR′_p = k′[MDMB]^0.9[TBAP]^0.5t_pol 10 s The apparent activation energy is 25 ± 1 kJ mol⁻¹ in both cases. The electrogenerated polymer film has a bilayer structure: a inner compact adherent golden layer, and an outer powdery brown layer.     

Synthesis of magnesium catecholate and <Emphasis Type="Italic">o</Emphasis>-semiquinone complexes by oxidation of the metal with 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

Oxidation of amalgamated magnesium metal with 3,6-di-tert-butyl-o-benzoquinone (1) in different aprotic organic solvents afforded magnesium catecholate and bis-o-semiquinolate complexes. The catecholate derivatives of magnesium CatMgL₂ (Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, L = THF or Py) were synthesized in high yields in pyridine and tetrahydrofuran, respectively. The reactions in diethyl ether or dimethoxyethane produced hexacoordinated metal bis-o-semiquinolates SQ₂MgL_n (SQ is the 3,6-di-tert-butyl-o-benzoquinone radical anion, L = Et₂O, n = 2; L = DME, n = 1). The reaction with the use of toluene as the solvent gave a magnesium bis-o-semiquinolate complex containing the coordinated unreduced o-quinone molecule. The molecular structures of the [CatMgPy₂]₂ and SQ₂Mg·DME complexes were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–98, January, 2007.     

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: k_obs =a +b[H⁺]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.