A shock tube study of the pyrolysis of NO2

NO₂ concentration profiles in shock-heated NO₂/Ar mixtures were measured in the temperature range of 1350–2100 K and pressures up to 380 atm using Ar⁺ laser absorption at 472.7 nm, IR emission at 6.25±0.25 μm, and visible emission at 300–600 nm. In the course of this study, the absorption coefficient of NO₂ at 472.7 nm was measured at temperatures from 300 K to 2100 K and pressures up to 75 atm. Rate coefficients for the reactions NO₂+M→NO+O+M (1), NO₂+NO₂→2NO+O₂ (2a), and NO₂+NO₂→NO₃+NO (2b) were derived by comparing the measured and calculated NO₂ profiles. For reaction (1), the following low- and high-pressure limiting rate coefficients were inferred which describe the measured fall-off curves in Lindemann form within 15% [FORMULA] The inferred rate coefficient at the low- pressure limit, k_1o, is in good agreement with previous work at higher temperatures, but the energy of activation is lower by 20 kJ/mol than reported previously. The pressure dependence of k₁ observed in the earlier work of Troe [1] was confirmed. The rate coefficient inferred for the high pressure limit, k_1∞, is higher by a factor of two than Troe's value, but in agreement with data obtained by measuring specific energy-dependent rate coefficients. For the reactions (2a) and (2b), least-squares fits of the present data lead to the following Arrhenius expressions: [FORMULA] For reaction (2), the new data agree with previously recommended values of k_2a and k_2b, although the present study suggests a slightly higher preexponential factor for k_2a. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 483–493, 1997.     

Experimental and theoretical study of vibrational spectra and structure of dihalogermylene and dihalostannylene complexes with 1,4-dioxane and triphenylphosphine

Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh₃ have been reported, the structures of the complexes Cl₂Ge·C₄H₈O₂ and Cl₂Ge·PPh₃ updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X₂M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh₃ are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X₂M^II particles, still persists, suggesting that the X₂M moieties preserve their specifity as carbene analogues also in the complexes.     

Experimental and theoretical investigation of the kinetics of the reaction of atomic chlorine with 1,4-dioxane

The rate coefficients for the reaction of 1,4-dioxane with atomic chlorine were measured from T = 292-360 K using the relative rate method. The reference reactant was isobutane and the experiments were made in argon with atomic chlorine produced by photolysis of small concentrations of Cl2. The rate coefficients were put on an absolute basis by using the published temperature dependence of the absolute rate coefficients for the reference reaction. The rate coefficients for the reaction of Cl with 1,4-dioxane were found to be independent of total pressure from p = 290 to 782 Torr. The experimentally measured rate coefficients showed a weak temperature dependence, given by k(exp)(T) = (8.4(-2.3)(+3.1)) × 10(-10) exp(-(470 ± 110)/(T/K)) cm3 molecule (-1) s(-1). The experimental results are rationalized in terms of statistical rate theory on the basis of molecular data obtained from quantum-chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, while single-point energies of the stationary points were computed at CCSD(T) level of theory. The calculations indicate that the reaction proceeds by an overall exothermic addition-elimination mechanism via two intermediates, where the rate-determining step is the initial barrier-less association reaction between the chlorine atom and the chair conformer of 1,4-dioxane. This is in contrast to the Br plus 1,4-dioxane reaction studied earlier, where the rate-determining step is a chair-to-boat conformational change of the bromine-dioxane adduct, which is necessary for this reaction to proceed. The remarkable difference in the kinetic behavior of the reactions of 1,4-dioxane with these two halogen atoms can be consistently explained by this change in the reaction mechanism.     

Experimental and theoretical study of the pyrolysis of trichlorosilane

Pyrolysis of trichlorosilane (TCS) and copyrolysis of TCS with 1,3-butadiene were studied. The enthalpies and activation energies for the reactions of the products of TCS pyrolysis were found by quantum-chemical calculations. A direct study of the pyrolysis of TCS by mass spectrometry was carried out. Based on the thermochemical parameters found by quantum-chemical calculations and on the results of GLC and mass spectrometry concerning the composition of the pyrolysis products, it was concluded that the pyrolysis of TCS follows a scheme that includes formation of radicals and silylenes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1659–1662, September, 1997.     

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.     

Reaction kinetics of NH in the shock tube pyrolysis of HNCO

The high temperature kinetics of NH in the pyrolysis of isocyanic acid (HNCO) have been studied in reflected shock wave experiments. Time histories of the NH(X³Σ^?) radical were measured using a cw, narrow-linewidth laser absorption diagnostic at 336 nm. The second-order rate coefficients of the reactions: (1) were determined to be: cm³?mol^?1?s^?1, where f and F define the lower and upper uncertainty limits, respectively. The data for k_1a are somewhat better fit by:      

Nitration of phenol in 1,4-dioxane

The nitration of phenol with excess nitric acid in aqueous dioxane, in contrast to the nitration in aqueous ethanol, yields exclusively 2,4-dintrophenol, whereas at equimolar ratio of phenol and nitric acid the major reaction products are mononitrophenols (99%), among which the p-isomer prevails.     

Shock tube and modeling study of propene pyrolysis

The thermal decomposition of propene behind reflected shock waves with 1200 < T₅ < 1800 K and 1.6 × 10^?5 < ρ₅ < 2.7 × 10^?5 mol/cm³ was studied by IR laser kinetic absorption spectroscopy and gas-chromatographic analysis of reaction products. The present data together with earlier shock tube data were satisfactorily modeled with a 51-reaction mechanism. As the initial step of the reaction, three channels, C₃H₆ = CH₃ + C₂H₃ (1), C₃H₆ = H + AC₃H₅ (2), and C₃H₆ = CH₄ + C₂H₂ (3), were necessary to interpret all the experimental data. © John Wiley & Sons, Inc.     

Homolytic amination of benzo-1,4-dioxane

When 5,6-benzo-1,4-dioxane was reacted with N,N-dialkylchloramines in the presence of FeSO₄ at 10–20C in a solution of acetic and sulfuric acids, 6-(N,N-dialkylamino)benzo-1,4-dioxanes and 6-chloro- and 6,7-dichloro-benzo-1,4-dioxanes were obtained. Under the conditions used in the study mainly chlorination products were synthesized. Reaction of 5,6-benzo-1,4-dipxane with the system (NH₃OH)₂SO₄-TiCl₃ resulted in the formation of 6-aminobenzo-1,4-dioxane.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 316–318, March, 1989.     

Synthesis of acetylenic derivatives of 1,4-dioxane

Cyclic ketals — 2,5-dimethyl-2,5-bis(4-penten-2-ynyloxy)-1,4-dioxane and 2,5-dimethyl-2,5-bis(3-phenyl-2-propynyloxy)-1,4-dioxane — were isolated in the reaction of propargyl alcohol with vinyl- and phenylethynylcarbinols in the presence of HgO-BF₃.O(C₂H₅)₂ catalytic system.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1029–1030, August, 1986.     

Synthesis of nucleoside analogs of 1,4-oxathiane, 1,4-dithiane,and 1,4-dioxane

The two regioisomers 6-chloro-9-(1, 4-oxathian-3-yl)-9H-purine ( 5 ) and 6-chloro-9-(1,4-oxathian-2-yl)-9H-purine ( 6 ) were obtained when 3-acetoxy-1,4-oxathiane ( 3 ) was subjected to the acid-catalyzed fusion procedure; compound 3 was prepared by a Pummerer reaction with 1,4-oxathiane 4-oxide ( 2 ). The nucleoside analog 6 could he converted into the adenine derivative 7 and 9-(1,4-oxathian-2-yl)-9H-purine-6(1H)thione ( 8 ). The following nucleoside analogs have also been synthesized: 6-chloro-9-(1,4-dithian-2-yl)-9H-purine ( 13 ), 9-(1,4-dithian-2-yl)adenine ( 14 ), 9-(1,4-dithian-2-yl)-9H-purine-6(1H)thione ( 15 ), and 6-chloro-9-(1,4-dioxan-2-yl)-9H-purine ( 18 ).     

Adsorption and photocatalytic degradation of 1,4-dioxane on TiO2

1,4-Dioxane in hexane as a solvent was adsorbed on TiO₂ due to an electrostatic interaction. The porous TiO₂ pellets (SG) prepared by sol–gel method were superior adsorbent to ST-B21 and Degussa P-25. Effects of firing temperature of the pellets and the initial concentrations of 1,4-dioxane on the adsorption percents were examined. Photocatalytic degradation of aqueous 1,4-dioxane gave 1,2-ethanediol diformate and formic acid as intermediates. Analysis of total organic carbon indicated that 1,4-dioxane was mineralized effectively in the following order: P-25 > ST-B21 > SG. The photocatalytic degradation of 1,4-dioxane adsorbed on the TiO₂ pellets in air showed that ST-B21 had a higher activity than SG. These facts indicate that SG pellet acts as a good adsorbent because of its high specific surface area but the internal region of the pores is not illuminated and acts only as a support.     

Kinetics of chloromethylation of benzo-1,4-dioxane

The chloromethylation of benzo-1,4-dioxane in acetic acid in presence of SnCl₄, SbCl₃, ZnCl₂, and SbCl₅ catalysts was investigated. The activation energy of the process was found to be 19.6 kcal/mole. The reaction is zero order in chloride ion and first order in the Hammett acidity function. In excess HCl the reaction is described by a second-order equation. The relative activities of the methyl chlorides in the chloromethylation of benzo-1,4-dioxane were determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 459–462, April, 1981.     

Shock tube and modeling study of 1,3-butadiene pyrolysis

1,3-Butadiene (1,3-C₄H₆) was heated behind reflected shock waves over the temperature range of 1200–1700 K and the total density range of 1.3 × 10⁻⁵ −2.9 × 10⁻⁵ mol/cm³. Reaction products were analyzed by gas-chromatography. The concentration change of 1,3-butadiene was followed by UV kinetic absorption spectroscopy at 230 nm and by quadrupole mass spectrometry. The major products were C₂H₂, C₂H_4, C₄H₄, and CH₄. The yield of CH₄ for a 0.5% 1,3-C₄H₆ in Ar mixture was more than 10% of the initial 1.3-C₄H₆ concentration above 1500 K. In order to interpret the formation of CH₄ successfully, it was necessary to include the isomerization of 1,3-C₄H₆ to 1,2-butadiene (1,2-C₄H₆) and to include subsequent decomposition of the 1,2-C₄H₆ to C₃H₃ and CH₃. The present data and other shock tube data reported over a wide pressure range were qualitatively modeled with a 89 reaction mechanism, which included the isomerizations of 1,3-C₄H₆ to 1,2-C₄H₆ and 2-butyne (2-C₄H₆). © 1996 John Wiley & Sons, Inc.     

Thermal polymerization of N-tert-butylacrylamide in 1,4-dioxane

The kinetics of the thermal polymerization of N-tert-butylacrylamide were investigated in 1,4-dioxane as solvent, in the 65–80°C temperature range. It was found that the overall rate of polymerization which was determined by a gravimetric method is proportional to the 1.9 power of monomer concentration at 70°C. The rate of initiation was determined by ESR spectroscopy using DPPH as an inhibitor, and it was found that the order of initiation rate is 1.8 with respect to monomer concentration at 70°C. The overall activation energy for the thermal polymerization of N-tert-butylacrylamide was found to be 64 ± 9 kJ mol^?1 in the 65–80°C temperature range. The activation energy for the rate of initiation was also determined and it was found to be 90 ± 23 kJ mol^-1.     

Homolytic alkylation of benzimidazole by 1,4-dioxane

The homolytic alkylation of benzimidazoles by 1,4-dioxane has been studied. Introduction of an ethyl group at position 1 and a sulfonic group at position 2 of the heterocycle lowers the yield of products of substitution of hydrogen or the sulfonic group at position 2 by a dioxanyl radical.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 791–792, June, 1988.     

A shock tube study of the reaction S + H2 ⇌ SH + H in pyrolysis and photolysis systems

Atomic resonance absorption spectroscopy (ARAS) was applied to measure S atoms, behind shock waves in COS/H₂ pyrolysis or CS₂/H₂ photolysis systems. Both the pyrolysis of COS and the photolysis CS₂ was used to generate the S atoms, which subsequently reacts with H₂ via the reaction: The photolysis experiments were designed to provide clear first-order conditions for reaction (R3); i.e., the H₂ concentration exceeds that of S by at least a factor of 100. The S atom profiles obtained during pyrolysis of highly diluted COS/H₂/Ar mixtures were analyzed by computer simulations based on a simplified reaction mechanism using the rate coefficient k₃ as a fitting parameter. Both groups of experiments covered the temperature range of 1257 K ? T ? 3137 K and lead to a rate coefficient of: . © 1995 John Wiley & Sons, Inc.     

A theoretical study on the pyrolysis of perfluorobutanoic acid as a model compound for perfluoroalkyl acids

The potential energy surface is mapped out for all plausible reactions in the self-decomposition of perfluorobutanoic acid (CF₃CF₂CF₂COOH) as a model compound for the notoriously toxic and bio-accumulative perfluoroalkyl acids. Initial decomposition of perfluorobutanoic acid is found to be controlled by HF elimination and the formation of an α-lactone intermediate. The fate of this intermediate is predicted to be dominated by two competing channels, namely formation of pentafluoropropanoyl fluoride (CF₃CF₂COF) and the closed-shell singlet CF₃CF₂CF:. Direct elimination of CO₂ through decarboxylation is found to be retarded by strong hyperconjugation effects induced by fluorine atoms on the carbon chain. The results presented herein provide insightful information towards a comprehensive understanding of the decomposition of perfluoroalkyl acids in thermal systems.     

Determination of 1,4-dioxane in household detergents and cleaners

A possible human carcinogen, 1,4-dioxane, was investigated as to its concentration levels in household detergents and cleaners currently sold in Japan. A solid-phase extraction combined with stable isotope dilution and gas chromatographic/mass spectrometric determination was evaluated for the determination of 1,4-dioxane in household products. The evaluation of the method was performed using a recovery study of 1,4-dioxane-d8 from detergent and cleaner samples. The mean overall recovery and relative standard deviation were 78 and 15%, respectively. The limit of quantitation was 0.05 mg/kg. This method was satisfactorily applied to the determination of 1,4-dioxane in household products. 1,4-Dioxane was detected in 40 out of the 51 investigated samples. The concentrations ranged from 0.05 to 33 mg/kg, and the mean was 2.7 mg/kg. The mean of the products that included anionic surfactants, i.e., alkylpoly(oxyethylene)sulfates, was 7.2 mg/kg, which was higher than the 0.39 mg/kg mean for the other surfactants. Moreover, the 1,4-dioxane load/person was estimated to be 0.061 mg/day/person in Japan, which was 27% of the load from the domestic effluent.