Kinetics and mechanism of the reaction of dimethyldioxirane with cumene

The reaction of dimethyldioxirane with cumene (22–52°C) follows a chain-radical mechanism. The kinetic regularities of this reaction were studied by the chemiluminescence and kinetic UV spectrophotometry methods by monitoring the consumption of dioxirane. The process is inhibited by oxygen. In the absence of O₂, the process is accelerated due to the decomposition of dimethyldioxirane induced by alkyl radicals. In this case, the reaction occurs according to a complicated kinetic law including the first and second orders with respect to dioxirane. Based on the kinetics and reaction products, the scheme of the process was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 694–702, April, 1997.     

Kinetics of dimethyldioxirane decomposition in the presence of cumene

Dimethyldioxirane consumption increases considerably in the presence of cumene. The product composition (cumic alcohol, acetophenone, α-methylstyrene) and the inhibiting effect of oxygen prove a radical reaction mechanism. The kinetic order for dimethyldioxirane increases with the conversion from 1.5 to 2.     

Kinetics of cumene hydroperoxide-dependent aniline hydroxylation with hemoglobin participation

The kinetics of cumene hydroperoxide-dependent aniline hydroxylation to p-aminophenol with hemoglobin (Hb³⁺) participation has been studied in a phosphate buffer at pH 7.4 and 37°C. The data obtained point to hemoglobin complexing with aniline and cumene hydroperoxide (CHP). The character of aniline hydroxylation by the CHP-Hb³⁺ system is discussed.

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37°C pH 7,4 - (Ho³⁺). Hb³⁺ . -Hb³⁺.

     

Catalytic thermal reactions of cumene over sepiolite and palygorskite

The catalytic activity of sepiolite and palygorskite in cracking and disproportionation reactions of cumene was studied. The formation of benzene, diisopropylbenzene and propylene characterizes Brönsted acid sites whereas that of ethylbenzene characterizes Lewis acid sites. At 150 and 250°C the reactions are determined mainly by the presence of acid sites in the channels of these clays. The yields are significantly higher in sepiolite as compared to palygorskite. The concentration of acid sites and their strength increase with the thermal loss of zeolitic and part of the bound water. At 350°C the reactions are determined by the acidity of the external surface of both minerals and yields are only slightly higher in sepiolite. At 150°C most acid sites are of the Brönsted type. With the rise in temperature the relative concentration of Lewis acid sites increases.

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Zusammenfassung Es wurde die katalytische Aktivität von Sepiolith und Palygorskit in Krack- und Disproportionierungsreaktionen von Kumol untersucht. Die Bildung von Benzol, Diisopropyl-benzol und Propylen charakterisieren Aziditätsstellen nach Bronsted, während die Bildung von Ethylbenzol Aziditätsstellen nach Lewis charakterisiert. Bei 150°C und 250°C werden die Reaktionen hauptsächlich durch die Gegenwart von Aziditätsstellen in den Tunnelgebilden dieser Tonerden bestimmt. Bezogen auf Palygorskit sind die Ausbeuten bei Sepiolith eindeutig höher. Die Konzentration der Aziditätsstellen und ihre Stärke nehmen mit der thermischen Abgabe von zeolithischem und eines Teiles des gebundenen Wassers zu. Bei 350°C werden die Reaktionen durch die Azidität der externen Oberfläche beider Mineralien bestimmt und die Ausbeuten sind in Sepiolith kaum höher. Bei 150°C sind die meisten Aziditätsstellen vom Brönsted-Typ. Mit ansteigender Temperatur nimmt auch die relative Anzahl von Lewis-Aziditätsstellen zu.

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Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60^th birthday     

Phosphorescence of carbonyl compounds produced by thermal and photo-oxidation of polybutadiene

Using phosphorescence analysis, the energy levels of the triplet states of some of the macrocarbonyl molecules formed in the photo-oxidation of commercial polybutadiene (48% trans, 42% cis and 10% vinyl) have been determined. The triplet energy levels of 26 additives were also determined so that predictions could be made regarding the probable efficiencies of these additives for quenching the excited states of the carbonyl species. These predictions have been substantiated by the observation of triplet-triplet quenching of a model α,β-unsaturated ketone in the solid state by one of the commercial u.v. stabilizers with a low-lying triplet energy level.     

Kinetics and mechanism of aniline hydroxylation by cumene hydroperoxide in the presence of catalase

In a phosphate buffer with pH=7.4 at 20°C the kinetics of aniline hydroxylation to p-aminophenol by the catalase-cumene hydroperoxide system has been studied. The reaction mechanism of this system is discussed.

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20°C pH 7,4 - . .

     

Effect of the thermal history of polymer and temperature on photo-oxidation of branched polyethylene

Photo-oxidation of branched polyethylenes (35 and 10 methyl groups per 1000 carbon atoms) was carried out in oxygen using light with maximum intensity at 254 nm. Two steps of the photo-oxidation were observed; both are influenced by the thermal history of the polymer. The results are discussed in connection with reorganization in the crystalline phase. It is suggested that transfer of some chemical defects (precursors of oxidation) to the amorphous phase occurs during slow cooling and annealing of the crystalline material.     

Kinetics of the initial stage of catalytic radical chain oxidation of cumene with catalyst deactivation

We have developed a method for estimating the rate constant for the reaction of catalyst deactivation in a radical chain process in the presence of catalysts with low stability. Its applicability is demonstrated in the reaction of oxidation of cumene in the presence of alkylammonium halides.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 2, pp. 69–74, March–April, 1994.     

Kinetics of the reactions of 2,4,6-tri-t-butylphenoxyl with cumene hydroperoxide,cumylperoxyl radicals,and molecular oxygen

Reactions of 2,4,6-tri-t-butylphenoxyl (TBP) with cumene hydroperoxide (ROOH), cumylperoxyl radicals (RO₂), and molecular oxygen in benzene solution have been investigated kinetically by the ESR method. The rate constant of the reaction TBP + ROOH has been estimated in the temperature range 27°-75°C: log₁₀(k_?7/M^?1sec^?1) = (7.1 ± 0.4) - (10.9 ± 0.6 kcal mole^?1)/θ The ratio of the rate constants of reactions TBPH + RO₂ products has been determined from the experimental dependence of the rate constant of reaction TBP with ROOH on [TBPH]₀/[TBP]₀. Putting k₇ = 4.0 × 10³M^?1sec^?1, we obtain k₈ = (2.0 ± 0.2) × 10⁸M^?1sec^?1 at 30°C. The reaction of TBP with O₂ obeys the kinetic law ?d[TBP]/dt = k′[O₂][TBP]². This is in accordance with scheme TBP + O₂ ← TBP ?O₂ [I]; TBP ?O₂ + TBP · products, log₁₀ (k′/M^?2sec^?1) = (?14.5 ± 0.9) + (27.2 ± 1.4)/θ at 66°?78°C, where ° = 2.303RT.     

Kinetics of devitrification and differential thermal analysis

A quantitative relationship between kinetic parameters and DTA curves has been derived for devitrification reactions which are described by a Johnson—Mehl—Avrami equation.Both activation energy, E, and reaction order, n, can be derived from DTA curves and related to the probable reaction mechanism.Experimental results and isothermal literature data are consistent.     

Kinetics of thermal decomposition of hexanitrohexaazaisowurtzitane

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry, manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and solution were determined. The content of N₂ amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed, and one NO₂ group remains in the residue, which contains amino groups and no C−H bonds. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 815–821, May, 2000.     

Aerobic oxidation of cumene to cumene hydroperoxide catalyzed by metalloporphyrins

A protocol for the aerobic oxidation of cumene to cumene hydroperoxide (CHP) catalyzed by metalloporphyrins is reported herein. Typically, the reaction was performed in an intermittent mode under an atmospheric pressure of air and below 130°C. Several important reaction parameters, such as the structure and concentration of metalloporphyrin, the air flow rate, and the temperature, were carefully studied. Analysis of the data obtained showed that the reaction was remarkably improved by the addition of metalloporphyrins, in terms of both the yield and formation rate of CHP while high selectivity was maintained. It was discovered that 4 or 5 h was the optimal reaction time when the reaction was catalyzed by monomanganese-porphyrin ((p-Cl)TPPMnCl) (7.20 × 10^?5 mol/l) at 120°C with the air flow rate being 600 ml/min. From the results, we also found that higher concentration of (p-Cl)TPPMnCl, longer reaction time and higher reaction temperature were all detrimental to the production of CHP from cumene. Studies of the reaction kinetics revealed that the activation energy of the reaction (E) is around 38.9 × 10⁴ kJ mol^?1. The low apparent activation energy of the reaction could explain why the rate of cumene oxidation to CHP in the presence of metalloporphyrins was much faster than that of the non-catalyzed oxidation.     

Kinetics of thermal decomposition of dinitramide

Kinetic regularities of thermal decomposition of dinitramide in aqueous and sulfuric acid solutions were studied in a wide temperature range. The rate of the thermal decomposition of dinitramide was established to be determined by the rates of decomposition of different forms of dinitramide as the acidity of the medium increases: first, N(NO₂)⁻ anions, then HN(NO₂)₂ molecules, and finally, protonated H₂N(NO₂)₂ ⁺ cations. The temperature dependences of the rate constants of the decomposition of N(NO₂)⁻ (k _an) and HN(NO₂)₂ (k′_ac) and the equilibrium constant of dissociation of HN(NO₂)₂ (K _a) were determined:k _an=1.7·10¹⁷ exp(−20.5·10³/T), s⁻¹,k′_ac=7.9·10¹⁶ exp(−16.1·10³/T), s⁻¹, andK _a=1.4·10 exp(−2.6·10³/T). The temperature dependences of the decomposition rate constant of H₂N(NO₂)₂ ⁺ (k _d) and the equilibrium constant of the dissociation of H₂N(NO₂)₂ ⁺ (K _d) were estimated:k _d=10¹² exp(−7.9·10³/T), s⁻¹ andK _d=1.1 exp(6.4·10³/T). The kinetic and thermodynamic constants obtained make it possible to calculate the decomposition rate of dinitramide solutions in a wide range of temperatures and acidities of the medium. In this series of articles, we report the results of studies of the thermal decomposition of dinitramide performed in 1974–1978 and not published previously. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2129–2133, December, 1997.     

Kinetics of thermal decomposition of ammonium persulfate

Kinetics of thermal decomposition of ammonium persulfate was studied by calorimetry and Raman spectroscopy. The values of activation energies of the overall reaction and its individual stages were estimated.     

Kinetics of thermal dehydroxylation of aluminous goethite

The kinetics of dehydroxylation of synthetic aluminous goethite was studied using isothermal and non-isothermal thermogravimetry. The complete isothermal dehydroxylation can be described by the Johnson-Mehl equation with up to three linear regions in plots of lnln [1/(1–y)]vs. Int Kinetics for the initial stage of dehydroxylation changed from diffusion to first-order through the temperature range 190 to 260°C. The rate of dehydroxylation was reduced by Al-substitution and increased with temperature. Activation energy for dehydroxylation, calculated from the time to achieve a given dehydroxylation extent, varied depending on the extent of dehydroxylation and Al-substitution. Non-stoichiometric OH existed in goethite and some remained in hematite after the complete crystallographic transition.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.