Adsorption of polyacrylic acid and its copolymers with acrylonitrile on zinc oxide particles

Adsorption of polyacrylic acid and its copolymers with acrylonitrile, containing different quantities of carboxyl groups, on the dispersion of zinc oxide was investigated. The kinetics of polymer desorption was investigated based on data concerning the change in concentration of free carboxylic groups of polymer and zinc ions in solution. The concentration of free carboxyl groups decreases and the concentration of zinc ions in the liquid phase above the residue after separation of zinc oxide particles increases with time, reaching a constant value. The dependence of the concentration of free carboxyl groups and zinc ions in the liquid phase on the initial concentration of polymer in the plateau section of the kinetic curve was investigated. Adsorption isotherms of copolymers depend on their solubility in water and can be described by different mathematical models.     

Interaction of hydrogen peroxide and thiourea or its oxides with terephthalic acid

The suitability of thiourea and its oxides for the hydroxylation of terephthalic acid in aqueous solutions was explored. Allsulfur-containing compounds tested were found to favor the formation of hydroxyterephthalic acid. It was shown that thiourea and its di- and trioxides can act as both traps and promoters of hydroxyl radicals in aqueous solutions.     

Kinetics of Iron-catalyzed decomposition of hydrogen peroxide in alkaline solution

The decomposition of alkaline hydrogen peroxide solutions at 20°C has been studied in the presence of both supported iron catalysts and in systems with iron initially in solution. Studies with an iron-alumina supported catalyst showed the decomposition reaction was first order with respect to total peroxide concentration, while studies with alkaline Fe³⁺ produced more complex behavior. This has been attributed to the presence of at least two distinct catalytically active iron species. The first species is highly active and gives rise to high initial rates of reaction. A decrease in concentration of this species is observed together with an increase in concentration of a second, less active, iron species. The catalytic behavior of this “aged” iron species was found to be very similar to that of the supported iron catalyst.     

Kinetics of propylene epoxidation with hydrogen peroxide

The kinetics of propylene oxidation to propylene oxide in the presence of a titanium-containing zeolite in an isopropyl alcohol medium is reported. The influence of the concentrations of the starting substances and reaction products and temperature on the rate of the process is considered. A mathematical model has been derived from the experimental data obtained. The rate constants, adsorption equilibrium constants, and activation energies of the reactions have been calculated.     

Kinetics and equilibria of the copper catalyzed decomposition of hydrogen peroxide activated by pyridine

The catalytic activity of Cu in the decomposition of hydrogen peroxide in presence of pyridine has been investigated at pH-values between 6 and 8 by calorimetry as well as by a CLARK-type electrode. The kinetic data hold the rate law ν_o = k[Cu(py)²⁺]_tot[H₂O₂]_tot/[H⁺] with the rate constant being k = (3.72 ± 0.47)10⁻⁸s⁻¹. From computer simulation of equilibrium concentrations of all species it is shown that the catalytically most active copper pyridine 1:1 complex is always present at concentrations lower than 20% of the total copper concentration. For that reason the efficiency of the labile copper pyridine complex in the hydrogen peroxide decomposition is characterized by an apparent rate constant after rewriting the rate law into equilibrium concentrations: ν_o = k₁[Cu(py)²⁺]_o[HOO⁻]_o. The apparent rate constant k₁ is determined as (3.52 ± 0.32)10⁵ M⁻¹s⁻¹ which can be compared to other catalase-like systems with the same rate law.     

Oxidation of hydrogen chloride with hydrogen peroxide in aqueous solution

Evolution of chlorine into the gas phase upon mixing of aqueous solutions of hydrogen chloride and hydrogen peroxide was studied. The threshold hydrogen chloride concentration corresponding to the onset of the chlorine evolution was determined.     

Kinetics of allyl chloride epoxidation with hydrogen peroxide

The kinetics of allyl chloride oxidation to epichlorohydrin in the presence of titanium-containing zeolite was studied. The influence of the concentrations of the initial substances, reaction products, and temperature on the rate of the process was considered. The mathematical model of the process was constructed on the basis of the experimental data obtained. The rate constants, adsorption equilibrium constants, and activation energies of the reactions were calculated.     

Grafting with acrylonitrile with the redox system cellulose xanthogenate–hydrogen peroxide

The possibility of obtaining modified cellulose products by reacting cellulose xanthogenate in solutions containing oxidizers and acrylonitrile was studied. The ability of the cellulose xanthogenate–hydrogen peroxide redox system to initiate graft copolymerization of acrylonitrile on the cellulose was demonstrated. The influence of various factors on the processes was investigated. An attempt was made to clarify the nature of the reactions involved.     

The kinetics of iodide oxidation by hydrogen peroxide in acid solution

The kinetics of the complex reaction between I⁻ and H₂O₂ in acid media was investigated. The particular attention was focused on the determination of the rate constant of the reaction between HIO and H₂O₂ involved in the investigated complex process. The examination of the whole kinetics was performed by simultaneously monitoring the evolution of O₂ pressure, I₃⁻ and I⁻ concentrations. We modeled the behavior of experimentally followed components based on Liebhafsky’s research. Our preliminary results suggest a significantly higher rate constant (3.5 × 10⁷ M⁻¹ s⁻¹) of the reaction between HIO and H₂O₂ as those proposed in the literature.     

Kinetics and mechanism of the furan peroxide formation in the reaction of furfural with hydrogen peroxide in the presence or absence of sodium molybdate

The kinetics of the initial stage of the furfural reaction with hydrogen peroxide was studied in water in the presence of Na₂MoO₄ and in n-butanol without a catalyst. The mechanisms of furfural conversion in the Na₂MoO₄-H₂O₂ system and oxidation by hydrogen peroxide in the absence of sodium molybdate are discussed. Based on kinetic studies, the mechanism of furan peroxide formation is proposed. Proceedings of X International Conference on Chemistry of Organic and Organoelement Peroxides (Moscow, June 16–18, 1998).     

Kinetics and mechanism of the oxidation of water soluble porphyrin FeIIITPPS with hydrogen peroxide and the peroxomonosulfate ion

The overall six-electron oxidation of water soluble porphyrin Fe(III)TPPS by hydrogen peroxide and peroxomonosulfate ion was studied by the stopped-flow method with UV-vis detection. A three-step consecutive reaction was observed with two intermediates: Fe(III)TPPS --> Int(1)--> Int(2)--> products. The products were identified as the iron(iii) complex of the biliverdin analog formed from TPPS and 4-sulfobenzoic acid. All the rate constants with both oxidizing agents were determined. Intermediate Int(1) is proposed to be the species (TPPS (+))Fe(IV)=O. Although no unambiguous proposal for the structure of Int(2) can be made, it is most probably the product of the four-electron oxidation of the original Fe(III)TPPS, contains an iron-oxo center and has a dissociable proton with a pK of around 3.1. In spite of the protolytic equilibria occuring in the pH region 2-4, the kinetic observations do not show pH dependence.     

Kinetics and mechanism of chromate reduction with hydrogen peroxide in base

[Cr(VI)O(4)](2)(-) is reduced to [Cr(V)(O(2))(4)](3)(-) by hydrogen peroxide in strongly basic media where the acid dissociation of H(2)O(2) (pK(a) = 11.65) is appreciable. The reaction is first order in chromium(VI) and inhibited by hydroxide. The hydrogen peroxide dependence is defined by the form of the effective pseudo-first-order rate constant: k(eff) = [H(2)O(2)](3)/(K(1) + K(2)[H(2)O(2)] + K(3)[HO(2)(-)]) with K(1) = 175(43) s x M(3), K(2) = 403(18) s x M(2), and K(3) = 1422(34) s x M(2). Hydrogen peroxide anion initially attacks chromate, and subsequent equilibrium steps that exchange oxo groups for three peroxo groups precede a rate-determining, one-electron, intramolecular reduction step.     

Chemiluminescence accompanying chitosane destruction in hydrochloric acid solution containing hydrogen peroxide

The chemiluminescence (CL) accompanies the destruction of chitosane (CTS) in the presence of H₂O₂. The CL kinetics has a complex character and can be described as a sum of two exponentials. The photoluminescence monitoring and IR spectra of the reaction mixture indicate the formation of carbonyl groups in the course of CTS destruction. The enhancement of the CL intensity by Fe²⁺ suggests the reaction of Fe²⁺ with hydroperoxides accumulated with CTS decomposition. The macroradicals ROO^· are assumed to be transformed through the cleavage of the glycoside bond via a six-membered cyclic intermediate to form the terminal peroxide radical and ketone.     

High-temperature degradation of polyacrylic acid in aqueous solution

Poly(acrylic acid) (PAA) was decarboxylated in aqueous solution as a function of pH and ionic strength in the temperature range 100–350°C. Degradation kinetics were first order with respect to acid functionality. The rate of decarboxylation at high pH (E_α = 51.1 kcal/mol) was much slower than that at low pH (E_α = 20.3 kcal/mol). At intermediate pH, the reactivity was found to depend on the degree of dissociation of PAA as a functions of ionic strength, pH, and temperature. No monomer was observed in the reaction product. © 1996 John Wiley & Sons, Inc.     

The ferric ion catalyzed decomposition of hydrogen peroxide in perchloric acid solution

Predictions of the “redox” and “complex” schemes for the Fe³⁺ catalyzed decomposition of H₂O₂ have been compared with published and new experimental data by numerical integratior of the appropriate complete sets of differential equations. Apparent discrepancies for the redox scheme at high Fe³⁺/H₂O₂ ratios are shown to disappear in the complete treatment, and inconsistencies of the complex scheme with both kinetic data and spectroscopic measurements are pointed out.     

Investigation of the thermal transformations of acrylonitrile copolymers with methylthiirane in dilute solution in dimethylformamide

The effect of introduction of the comonomer methylthiirane (MT) into the main chain of polyacrylonitrile (PAN) on the thermal transformations of the macromolecules in dilute DMF solution was studied. For this purpose, statistical copolymers of acrylonitrile and MT were synthetized and their pyrolysis in solution was investigated. It was found that introduction of the thioether group into the main chain of PAN results in essential changes in the thermal behaviour of the copolymers as compared to the homopolymer. The results of rheological, thermal and spectral studies on the solutions suggest that the direction of the thermochemical reaction changes on introduction of the thioether group into the PAN molecule. In such copolymers the reaction will preferably proceed by the -C≡N groups forming conjugated cyclic structures.     

Thermal behaviour of copolymers of acrylonitrile with haloalkyl acrylates or methacrylates

Thermal stabilities of copolymers of acrylonitrile with 4–14 mol% of 3-chloro-2-hydroxypropyl acrylate or methacrylate, 2-chloroethyl acrylate or methacrylate and 2-bromoethyl acrylate or methacrylate were studied by TGA in air. A two-step degradation between 300 and 350° and 600 and 650° is observed for both PAN and the copolymers. Initially, the degradation is slow up to 350° for the copolymers (8–23% wt loss) compared with PAN (27% wt loss); the trend reverses after 350°. A mechanism of the degradation has been proposed on the basis of i.r. studies of the residue of the copolymers isothermally heated at 300° for 10 min. The influence of the haloalkyl comonomers on the flammability of acrylic copolymers in terms of limiting oxygen index is also reported.     

Degradation of copolymers of acrylonitrile and styrene in alkaline dimethyl sulphoxide solution

Investigations on the alkaline degradation of copolymers of acrylonitrile and styrene dissolved in dimethyl sulphoxide were carried out by means of viscometry, titrimetry and GPC measurements. The degradation reaction takes place with alkali concentrations higher than 1·3–1·4 × 10^?4 moles of KOH per gram of copolymer. Four to five new macromolecules arise from each starting macromolecule. A consumption of 1·3–1·5 moles of KOH was calculated for each new macromolecule formed.