Free-radical chain oxidation of 1,4-dioxane inhibited by 2-thio-6-aminouracil

The effect of 2-thio-6-aminouracil on the oxygen uptake kinetics has been studied in 1,4-dioxane free-radical chain oxidation as a model system. The presence of a thiocarbonyl group in the 2-position of the uracil ring makes 6-aminouracil highly reactive towards 1,4-dioxane peroxy radicals. The rate constant of the 1,4-dioxane peroxy radical interaction with 2-thio-6-aminouracil has been measured to be k₇ = (3.0 ± 0.5) × 10⁵ L mol^–1 s^–1 (333 K). The stoichiometric inhibition factor f = 1.1 ± 0.1 has been determined.     

Comparative study of the antioxidant properties of selected flavonols and flavanones

The antioxidant properties of morin, myricetin, fisetin, naringenin, and naringin were studied using the initiated oxidation of 1,4-dioxane as the model reaction. The antioxidant activity of these compounds was quantitatively characterized by the apparent rate constant of inhibition, fk _in. Morin, myricetin, and fisetin are comparable with ionol in antioxidant efficiency.     

Antioxidant properties of conjugates of 20-hydroxyecdysone derivatives with a polysubstituted chromanylaldehyde

The antioxidant properties of 20-hydroxyecdysone and its conjugates with (6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)acetaldehyde are reported for initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of these compounds is characterized in terms of the effective rate constant of inhibition, fk _In.     

Antioxidant properties of conjugates of triterpenic acids with amido derivatives of Trolox

The antioxidant properties of conjugates of betulonic and betulinic acids with amido derivatives of the acid Trolox were studied for initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the compounds was characterized in terms of the apparent inhibition rate constant fk _In.     

Antioxidant activity of uracil derivatives

The antiradical properties of a number of uracil derivatives are studied in initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the uracil derivatives as inhibitors is estimated. The antiradical activity of the compounds is quantitatively characterized in terms of the effective rate constant of inhibition, fk _In.     

Antioxidant properties of some 7,8-benzo-5,6-dihydro(4H)selenochromene derivatives

The antioxidant properties of 2,4-diphenyl-7,8-benzo-5,6-dihydro(4H)selenochromene, some of its chlorine-containing derivatives, and selected chromilium salts based on these derivatives have been investigated using the initiated oxidation of 1,4-dioxane as a model reaction. The antioxidant activity of these compounds is quantitatively characterized by the apparent inhibition rate constant fk ₇.     

Characterization of two linear chain compounds: Ferromagnet NiCl2(CH3OH)2(1,4-dioxane)0.5 (1) and paramagnet [NiCl2(H2O)2(1,4-dioxane)](1,4-dioxane) (2)

The solvent-mediated crystal-to-crystal transformation was observed from yellow crystal of NiCl₂(CH₃OH)₂(1,4-dioxane)_0.5 (1) to green crystal of [NiCl₂(H₂O)₂(1,4-dioxane)](1,4-dioxane) (2) under high humidity or adding of H₂O in CH₃OH/1,4-dioxane solution. The μ-Cl₂ bridge in 1 replaced by 1,4-dioxane bridge in 2. In 1, the chlorine-bridged linear chains of NiCl₂(CH₃OH)₂ and 1,4-dioxane molecules stack along the b- and c-axis alternatively with hydrogen bonds intrachain, interchain, between chain and solvent. These hydrogen bonds and dipolar interaction between ferromagnetic coupling chlorine-bridged chains result in long-range ferromagnetic ordering at 3.1 K and a strong frequency dependence of the ac-susceptibilities associated to domain structures with very large shape anisotropy was observed below 3.1 K. In 2, layers of 1,4-dioxane-bridged linear chains of NiCl₂(H₂O)₂(1,4-dioxane) are intercalated by layer of 1,4-dioxane molecules with hydrogen bonds between chain and solvent. Compound 2 is paramagnet to 2 K.     

Inhibiting effect of 5-amino-5-methyluracil and its derivatives on the free-radical oxidation of 1,4-dioxane

The antiradical activity of 5-amino-6-methyluracil in the initiated radical-chain oxidation of 1,4-dioxane as a model system was studied quantitatively. The rate constant k ₇ of its reaction with the peroxyl radical of 1,4-dioxane was measured to be (5.6 ± 1.8) × 10⁵ L mol^?1 s^?1 at 333 K. The effect of the methyl substituents in the 1- and 3-positions of the uracil ring and in the amino group on the rate constant of inhibition was studied. The strengths of all N-H bonds in the 5-amino-6-methyluracil and its derivatives were calculated in the G3MP2B3 approximation and were compared with the measured rate constants of inhibition. By the example of the reaction of 5-amino-6-uracil with i-PrO ₂ ^?? , different attack pathways of the peroxyl radical at the N-H bonds of uracil were analyzed in the UB3LYP/6-311+G(d,p) approximation. The lowest activation barrier (5.8 kJ/mol) was observed for peroxyl radical attack on the (C⁵)N-H bonds. The site responsible for the inhibition activity of the compound is the amino group.     

Gas-phase oxidation of 1,4-dioxane

An experimental investigation in a conventional static apparatus of the oxidation of equimolecular mixtures 1,4-dioxane-O₂ has shown that 1,4-dioxane reacts with oxygen more readily than most hydrocarbons. Cool flames and ignitions were observed above 200°C in a pressure range up to 300 torr. The products of the slow reaction and cool flame were analyzed by gas chromatography and GC-MS; the slow reaction gives only CO, CO₂, H₂CO, H₂, C₂H₄, and H₂O. A radical chain mechanism is suggested and discussed by using an evaluation of the rate constants of the possible elementary steps by the methods of thermochemical kinetics.     

Free-radical chain oxidation of 1,4-dioxane and styrene in the presence of fullerene C60

The antiradical activity of fullerene C₆₀ was studied for the oxidation of 1,4-dioxane and styrene initiated by azobisisobutyronitrile and benzoyl peroxide as model reactions. The effective rate constants of the reaction of peroxyl radicals with fullerene C₆₀ (k ₇) and the stoichiometric inhibition factor (f _eff) were determined in air ( $P_{O_2 }$ = 0.21 atm) and oxygen ( $P_{O_2 }$ = 1.0 atm). The rate of the liquid-phase oxidation of 1,4-dioxane does not depend on $P_{O_2 }$ , and the effective rate constant of inhibition is k ₇ = (2.4 ± 0.2) × 10⁴ L mol^?1 s^?1. Chain termination in the oxidation of styrene occurs when C₆₀ reacts with both the peroxyl radicals (k ₇ = (1.2 ± 0.1) × 10³ L mol^?1 s^?1) and alkyl (k ₈ = 1.07 × 10⁷ L mol^?1 s^?1) radicals.     

Quantitative study of antioxidant properties of phenolcarboxylic acids from <Emphasis Type="Italic">Larix sibirica</Emphasis> bark

Antioxidant properties of caffeic, ferulic, vanillic, and 4-hydroxybenzoic acids isolated from Larix sibirica Ledeb. bark were studied using model radical-chain reactions for oxidation of propan-2-ol and 1,4-dioxane under kinetic control. Quantitative characteristics of the antioxidant activities were determined as effective rate constants fk_In for oxidation chain termination of the phenolcarboxylic acids. It was found that caffeic acid had the highest antioxidant activity among the investigated natural compounds. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 124–127, March–April, 2008.     

Inhibiting effect of 6-methyluracil derivatives on the free -radical oxidation of 1,4-dioxane

The antioxidation activity of 5-substituted 6-methyluracils was quantitatively estimated in the model system of initiated radical-chain oxidation of 1,4-dioxane. The rate constants of the reactions of 1,4-dioxane peroxide radicals with 6-methyluracil (1), 6-methyl-5-piperidinouracil (2), 6-methyl-5-morpholinomethyluracil (3), 6-methyl-5-morpholinouracil (4), 6-methyl-5-methylaminouracil (5), 5-ethylamino-6-methyluracil (6), and 5-hydroxy-6-methyluracil (7) were measured. Among compounds 1–7, derivative 7 is most efficient with an inhibition rate constant of (5.2±0.1) · 10⁴ L mol^-1 s^-1 (60 °C).     

“LIVING-LIKE” CATIONIC POLYMERIZATION OF ISOBUTYL VINYL ETHER INITIATED BY CARBOXYL GROUPS ON CARBON BLACK SURFACE/ETHYLALUMINUM DICHLORIDE SYSTEM IN THE PRESENCE OF 1,4-DIOXANE

The effect of 1,4-dioxane as an added base on the cationic polymerization of isobutyl vinyl ether (IBVE) initiated by carboxyl groups on carbon black surface/ethylaluminum dichloride (EtAlCl₂) system was investigated. Although the cationic polymerization of IBVE by carbon black/EtAlCl₂ system the absence of 1,4-dioxane instaneously proceeded and the monomer conversion achieved 100% within a minute. The molecular weight distribution (MWD) of polyIBVE obtained was very broad. On the contrary, the MWD of polyIBVE obtained was very narrow and narrower than that obtained from the carbon black/ZnCl₂ initiating system by the addition of 1,4-dioxane. The number-average molecular weight (Mn) of polyIBVE obtained was directly proportional to monomer conversion in the cationic polymerization. However, the Mn of polyIBVE obtained from the polymerization by the initiating system in the the presence of 1,4-dioxane was smaller than that of the calculated value, assuming that polyl(IBVE) chain forms per unit carboxyl group on carbon black surface. It was concluded that carbon black/EtAlCl₂ initiating systems in the presence of 1,4-dioxane has an ability to initiate “living-like” cationic polymerization of IBVE based on the above results. PolyIBVE was grafted onto a carbon black surface after quenching the above “living-like” cationic polymerization systems with methanol.     

Reactivity and mechanism of the action of C<Subscript>60</Subscript> fullerene used as an inhibitor for the radical chain oxidation of 1,4-dioxane

The kinetics and mechanism of the antioxidative action of С₆₀ fullerene are studied via highly sensitive manometry and kinetic spectrophotometry, based on the example of a model reaction of the initiated oxidation of 1,4-dioxane. The adequacy of the proposed mechanism according to the experimental data is analyzed by means of mathematical modeling. The mechanism behind the inhibiting process is found to be a multi-center radical reaction. The rate constants of the elementary stages are determined.     

Coupled processes in carbon monoxide oxidation: Kinetics and mechanism of CO oxidation by oxygen in PdX<Subscript>2</Subscript>-organic solvent-water systems

PdX₂-organic solvent-water solutions, where X = halide (preferably bromide or iodide) and the organic solvent is 1,4-dioxane or tetrahydrofuran, are suggested as catalytic systems for CO oxidation. A number of coupled processes take place in these systems. The kinetics and mechanism of CO oxidation by oxygen in the PdI₂-LiI-1,4-dioxane-water system are reported. Cyclohexene hydrocarboxylation into cyclohexanecarboxylic acid can be carried out as part of the coupled process occurring in the PdBr₂-tetrahydrofuran-water system.     

Reaction of chlorine dioxide with phenol

The kinetics of phenol oxidation with chlorine dioxide in different solvents (2-methylpropan-1-ol, ethanol, 1,4-dioxane, acetone, acetonitrile, ethyl acetate, dichloromethane, heptane, tetrachloromethane, water) was studied by spectrophotometry. In all solvents indicated, the reaction rate is described by an equation of the second order w = k[PhOH]·[ClO₂]. The rate constants were measured (at 10—60 °C), and the activation parameters of oxidation were determined. The reaction rate constant depends on the solvent nature. The oxidation products are a mixture of p-benzoquinone, 2-chloro-p-benzoquinone, and diphenoquinone.     

UV-VIS spectroscopic study of the solvatochromism and chelating reaction of a benzothiazoline merocyanine in mixed solvents

Solvatochromism and chelating reaction of a benzothiazoline merocyanine are studied by UV-VIS spectra in DMF-H₂O, DMF-1,4-dioxane and DMSO-1,4-dioxane. The effect of solvent polarity on UV-VIS absorption maxima and on equlibrium constant K of the chelating reaction is discussed. A linear correlation is obtained between lnK and E_T.     

On the structure of the radical addition product of 2-benzoxypentafluoropropene with 1,4-dioxane

The structure of the addition reaction product of 2-benzoxypentafluoropropene [CF₂ = C(CF₃)OCOC₆H₅] with 1,4-dioxane was investigated by the crystallographic analysis of the single crystal to conclude that the 2,6-disubstitution of 1,4-dioxane took place, on the contrary to the assumption that the reaction would take place at the 2- and 5-positions based on the product structure of 2-benzoxypentafluoropropene with tetrahydrofuran. Modified polyaddition reaction mechanism of bis(α-trifluoromethyl-β,β-difluorovinyl) terephthalate [CF₂ = C(CF₃)OCO-C₆H₄-COOC(CF₃) = CF₂] with 1,4-dioxane including 1,5-radical shift mechanism is proposed.     

Kinetics and mechanism of the reactions of diethylzinc with phenols in cyclic ethers

Reactions of diethylzinc and phenols (phenol, 2-ethylphenol, 2-chlorophenol, 3-ethylphenol, 3-chlorophenol, 4-ethylphenol and 4-chlorophenol) have been carried out in tetrahydrofuran and 1,4-dioxane as solvents. Monomeric ethylzinc phenoxide has been found to be a product of the diethylzinc and phenol (1:1) reaction in 1,4-dioxane solution. Kinetic studies on the ethylzinc phenoxides and phenols reaction in tetrahydrofuran solution established the rate constants and the S_Ei mechanism of the reaction.     

Preferential solvation of indomethacin in 1,4-dioxane + water mixtures according to the inverse Kirkwood–Buff integrals method

The preferential solvation parameters (δx_1,3) of indomethacin (IMC) in 1,4-dioxane + water binary mixtures were derived from their thermodynamic properties by means of the inverse Kirkwood–Buff integrals method. δx_1,3 is negative in water-rich and 1,4-dioxane-rich mixtures but positive in cosolvent compositions from 0.17 to 0.69 in mole fraction of 1,4-dioxane at 298.15 K. It is conjecturable that in water-rich mixtures, the hydrophobic hydration around the aromatic and methyl groups of the drug plays a relevant role in the solvation. The higher solvation by 1,4-dioxane in mixtures of similar cosolvent compositions could be mainly due to polarity effects. Finally, the preference of this drug for water in 1,4-dioxane-rich mixtures could be explained in terms of the higher acidic behavior of water molecules interacting with the hydrogen-acceptor groups present in IMC.