A theoretical investigation on the kinetics and reactivity of the gas-phase reactions of ethyl chlorodifluoroacetate with OH radical and Cl atom at 298 K

The mechanism, kinetics, and thermochemistry of the gas-phase reactions of CF₂ClC(O)OCH₂CH₃,ethyl chlorodifluoroacetate (ECDFA) with the OH radical and Cl atom are investigated. Geometry optimization and frequency calculations have been performed at the MPWB1K/6-31+G(d,p) level of theory and energetic information is refined by using G2(MP2) theory. Transition states are searched on the potential energy surface of reaction channels and each of the transition states is characterized by the presence of only one imaginary frequency. Connections of the transition states between designated local minima are confirmed by intrinsic reaction coordinate calculation. Theoretically calculated rate constants at 298 K using the Canonical Transition State Theory are found to be in good agreement with the experimentally measured ones. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF₂ClC(O)OCH₂CH₃, CF₂ClC(O)OCH₂CH₂, and CF₃C(O)OCHCH₃ are also reported for the first time. The hydrogen abstraction occurs mainly from –CH₂ group. The T1 diagnostic calculation suggests that the multi-reference character is not an issue for such systems. The estimated atmospheric life time of ECDFA is expected to be around 24 days.     

Measuring the rate constant of the reaction between carbon monoxide and iodine oxide at 298–363 K by the resonance fluorescence method

The rate constant of the reaction between the IO radical and carbon monoxide has been measured by the iodine atom resonance fluorescence method in the temperature range from 298 to 363 K. The reaction mainly takes place on the wall of the reactor.     

Measurement of the rate constants for the reactions of the IO• radical with sulfur-containing compounds H2S, (CH3)2S, and SO2

The reactions of iodine monoxide (IO^•) with sulfur-containing compounds, which are important for the atmospheric chemistry, are studied. An attempt is made to distinguish between the heterogeneous and homogeneous reaction pathways. It is shown that, under the experimental conditions, the reactions proceed on the wall and generate iodine atoms into the gas phase. It is found that, at room temperature, the rate constants for the gas-phase reactions of IO^• with (CH₃)₂S and H₂S are lower than 2.5 × 10⁻¹⁴ and 8.0 × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, respectively; the rate constant for the gas-phase reaction of iodine monoxide with SO₂ ≤ 5.6 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹.     

Fluorescence quenching of para-substitutedstyrenes by tetramethylethylene. Correlationanalysis of the quenching coefficient KSV and thequenching rate constant k_q by the dual-parameter equation with polar and spin-delocalization substituent constants

The fluorescence quenching coefficient (Ksv) and the quenching rate constant kq of ten para-substituted styrenes (1-Ys) have been measured and correlation-analyzed by both the dual-parameter equation (Eq. 1) with (ρxσx+ρ'σ') and the single-parameter equation (Eq. 2) with ρxσx. Ex-cellent results have been obtained for the correlation of KSV against (ρxσmb+ρ'σ'JJ) or (ρxσ+ +ρ'σ'JJ). Our results suggest that, possibly, there might be no need to use excited-state substituent constant for the fluorecence quenching process of excited states of styrenes.     

Rate constants for the gas-phase reactions of OH and O3 with β-ocimene, β-myrcene, and α- and β-farnesene as a function of temperature

The rate constants for the gas-phase reactions of hydroxyl radicals and ozone with the biogenic hydrocarbons β-ocimene, β-myrcene, and α- and β-farnesene were measured using the relative rate technique over the temperature ranges 313-423 (for OH) and 298-318 K (for O?) at about 1 atm total pressure. The OH radicals were generated by photolysis of H?O?, and O? was produced from the electrolysis of O?. Helium was used as the diluent gas. The reactants were detected by online mass spectrometry, which resulted in high time resolution, allowing large amounts of data to be collected and used in the determination of the Arrhenius parameters. The following Arrhenius expressions have been determined for these reactions (in units of cm3 molecules?1 s?1): for β-ocimene + OH, k = (4.35(-0.66)(+0.78)) × 10?11 exp[(579 ± 59)/T]; for β-ocimene + O?, k = (3.15(-0.95)(+1.36)) × 10?1? exp[-(626 ± 110)/T]; for β-myrcene + O?, k = (2.21(-0.66)(+0.94)) × 10?1? exp[-(520 ± 109)/T]; for α-farnesene + OH, k(OH) = (2.19 ± 0.11) × 10?1? for 23-413 K; for α-farnesene + O?, k = (3.52(-2.54)(+9.09)) × 10?12 exp[-(2589 ± 393)/T]; for β-farnesene + OH, k(OH) = (2.88 ± 0.15) × 10?1? for 323-423 K; for β-farnesene + O?, k = (1.81(-1.19)(+3.46)) × 10?12 exp[-(2347 ± 329)/T]. The Arrhenius parameters here are the first to be reported. The reactions of α- and β-farnesene with OH showed no significant temperature dependence. Atmospheric residence times due to reactions with OH and O? were also presented.     

Relative rate study of the kinetics, mechanism, and thermodynamics of the reaction of chlorine atoms with CF3CF═CH2 (HFO-1234yf) in 650-950 Torr of N2 or N2/O2 diluent at 296-462 K

The rate constant of the reaction Cl + CF(3)CF═CH(2) (k(1)) has been measured relative to several reference species using the relative rate technique with either gas chromatographic analysis with flame-ionization detection (GC/FID) or Fourier transform infrared (FTIR) analysis. Cl atoms were generated by UV irradiation of Cl(2)/CF(3)CF═CH(2)/reference/N(2)/O(2) mixtures. At 300-400 K in the presence of >20 Torr O(2), k(1) = 1.2 × 10(-11) e((+1100/RT)) cm(3) molecule(-1) s(-1). In N(2) diluent, k(1) has a sharp negative temperature coefficient resulting from the relatively small exothermicity of the following reactions: (1a) Cl + CF(3)CF═CH(2) ? CF(3)CFClCH(2)(?); (1b) Cl + CF(3)CF═CH(2) ? CF(3)CF(?)CH(2)Cl (reaction 1), which were determined in these experiments to be ～16.5 (±2.0) kcal mol(-1). This low exothermicity causes reaction 1 to become significantly reversible even at ambient temperature. The rate constant ratio for the reaction of the chloroalkyl radicals formed in reaction 1 with Cl(2) (k(2)) or O(2) (k(3)) was measured to be k(2)/k(3) = 0.4 e(-(3000/RT)) for 300-400 K. At 300 K, k(2)/k(3) = 0.0026. The reversibility of reaction 1 combined with the small value of k(2)/k(3) leads to a sensitive dependence of k(1) on the O(2) concentration. Products measured by GC/FID as a function of temperature are CF(3)CFClCH(2)Cl, CF(3)COF, and CH(2)Cl(2). The mechanism leading to these products is discussed. The rate constant for the reaction Cl + CF(3)CFClCH(2)Cl (k(11)) was measured as a function of temperature (300-462 K) at 760 Torr to be k(11) = 8.2 × 10(-12) e(-(4065/RT)) cm(3) molecule(-1) s(-1). Rate constants relative to CH(4) for the reactions of Cl with the reference compounds CH(3)Cl, CH(2)Cl(2), and CHCl(3) were measured at 470 K to resolve a literature discrepancy. (R = 1.986 cal K(-1) mol(-1)).     

Rate constants for the gas‐phase reactions of a series of C3?C6 aldehydes with OH and NO3 radicals

By using relative rate methods, rate constants for the gas‐phase reactions of OH and NO₃ radicals with propanal, butanal, pentanal, and hexanal have been measured at 296 ± 2 K and atmospheric pressure of air. By using methyl vinyl ketone as the reference compound, the rate constants obtained for the OH radical reactions (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹) were propanal, 20.2 ± 1.4; butanal, 24.7 ± 1.5; pentanal, 29.9 ± 1.9; and hexanal, 31.7 ± 1.5. By using methacrolein and 1‐butene as the reference compounds, the rate constants obtained for the NO₃ radical reactions (in units of 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹) were propanal, 7.1 ± 0.4; butanal, 11.2 ± 1.5; pentanal, 14.1 ± 1.6; and hexanal, 14.9 ± 1.3. The dominant tropospheric loss process for the aldehydes studied here is calculated to be by reaction with the OH radical, with calculated lifetimes of a few hours during daytime. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 79–84, 2000     

Synthesis of pyrazolines by the reactions ofα,β-enones with diazomethane and hydrazines (review)

The first representatives of pyrazolines were synthesized in the last century. These nitrogen-containing heterocyclic compounds became important in the development of different bioactive substances. For this reason, various procedures have been worked out for their synthesis. In the present article we summarize those synthetic methods providing 1- or 2-pyrazolines by the reactions of ,-unsaturated ketones with diazomethane or hydrazine derivatives.Department of Organic Chemistry, Kossuth Lajos University, Egyetem ter I, H 4010 Debrecen, Hungary. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 747–759, June, 1997.     

Kinetic studies of reactions of the nitrate radical (NO3) with peroxy radicals (RO2): an indirect source of OH at night?

A discharge-flow system, coupled to cavity-enhanced absorption spectroscopy (CEAS) detection systems for NO3 at lambda=662 nm and NO2 at lambda=404 nm, was used to investigate the kinetics of the reactions of NO3 with eight peroxy radicals at P approximately 5 Torr and T approximately 295 K. Values of the rate constants obtained were (k/10(-12) cm3 molecule-1 s-1): CH3O2 (1.1+/-0.5), C2H5O2 (2.3+/-0.7), CH2FO2 (1.4+/-0.9), CH2ClO2 (3.8(+1.4)(-2.6)), c-C5H9O2 (1.2(+1.1)(-0.5)), c-C6H11O2 (1.9+/-0.7), CF3O2 (0.62+/-0.17) and CF3CFO2CF3 (0.24+/-0.13). We explore possible relationships between k and the orbital energies of the reactants. We also provide a brief discussion of the potential impact of the reactions of NO3 with RO2 on the chemistry of the night-time atmosphere.     

Formation of the pyrroline N-oxide ring by interaction of α-isonitrosoketones — derivatives of tetrahydrobenzofurazan and -furoxan with aldehydes and morpholine and some of the reactions of these compounds

-Isonitroso ketones, derivatives of tetrahydrobenzofurazan and furoxan, react with aldehydes (acetaldehyde and propionaldehyde) and morpholine to form derivatives of tetrahydropyrrolo[2,3-e]-2,1,3-benzoxadiazole 6-oxide. Treatment of the latter with hydrazine hydrate gave derivatives of 4,5-dihydro-1,2,5-oxadiazolo[3,4-f]cinnoline which are readily dehydrogenated with tetrachloro-benzoquinone to derivatives of 1,2,5-oxadiazolo[3,4-f]cinnoline. Reduction of tetrahydropyrrolo[2,3-e]-2,1,3-benzoxadiazole 6-oxides with sodium borohydride gave derivatives of N-hydroxyhexahydro-pyrrolo[2,3-e]-2,1,3-benzoxazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1558–1563. October, 2004.     

Efficient synthetic method for the preparation of allyl- and propargyl-epoxides by allylation and propargylation of α-haloketones with organozinc reagents

A simple, efficient, and non-metal catalyzed synthetic method for the preparation of substituted allyl- and propargyl-epoxides by allylation and propargylation of α-halo ketones with organozinc reagents in mild conditions is reported in this paper. The present method complements the existing synthetic methods due to some advantageous properties of the organozinc reagents such as availability, selectivity, operational simplicity and low toxicity.     

Ultrasonic velocities and isentropic compressibilities of N-methyl-2-pyrrolidone with ketones and branched alcohols at 303.15 K

The ultrasonic sound velocities and densities are measured for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with ketones and branched alcohols at 303.15?K. The ketones include methyl ethyl ketone, methyl propyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone. The branched alcohols include 2-propanol, 2-methyl-1-propanol, 3-methyl-1-butanol, 2-butanol and 2-methyl-2-propanol. The ultrasonic sound velocity data were used to compute isentropic compressibilities (k _s). The deviations in the value of k _s from ideal value were computed. Except cyclohexanone all the binary mixtures formed by NMP with ketones at 303.15?K exhibit negative deviation from ideal behaviour over the entire range of composition. Cyclohexanone with NMP exhibit positive deviation over the entire range of composition. An inversion in the sign of Δk _s from positive to negative was observed for 2-propanol system and negative deviation was observed in four binary mixtures formed by NMP with other branched alcohols at 303.15?K. The ultrasonic sound velocities of these mixtures have been analysed is terms of Free Length Theory (FLT), Collision Factor Theory (CFT) and Nomoto's relation.     

Thermal and physical properties of ZrO2–AlO(OH) nanopowders synthesised by microwave hydrothermal method

Journal of Thermal Analysis and Calorimetry - Industrially relevant nanopowder was synthesised by microwave hydrothermal synthesis to obtain well-controlled composition (ZrO2–AlO(OH) system)...     

Experimental and Theoretical Study of the Effect of Moisture on Methane Adsorption and Desorption by Activated Carbon at 273.5 K

Adsorption and desorption of methane by activated carbon (AC) at constant temperature and at various pressures were investigated. The effect of moisture was also studied. A volumetric method was used, up to 40 bar, at a temperature of 273.5 K. Results of a dry AC sample were compared with those obtained from a moist sample and two different ACs with different physical and surface properties were used. As expected, the results showed that the existence of moisture, trapped in the AC pores, could lead to a decrease in the amount of methane adsorbed and a decrease in the amount of methane delivered during desorption. To model the experimental results, a large variety of adsorption isotherms were used. The regressed parameters for the adsorption isotherms were obtained using the experimental data generated in the present study. The accuracy of the results obtained from the different adsorption isotherms was favorably compared.     

Studies of curcumin and curcuminoids. XXXVI. The stoichiometry and complexation constants of cyclodextrin complexes as determined by the phase-solubility method and UV–Vis titration

Cyclodextrin (CD) complex stoichiometry and complexation constant with two symmetric curcuminoids and two unsymmetric curcuminoid-like compounds were investigated and compared by two independent methods, the phase-solubility method and ultraviolet-visible absorption spectroscopy (UV–Vis) titration. Two different methods were applied in an effort to increase the apparent intrinsic solubility of the compounds and make the investigation of stoichiometry and complexation constants possible. The intrinsic solubility could be determined for all four compounds in aqueous 10% (v/v) ethanolic solutions. Higher order complexation or solubilization through complex aggregation was observed for the symmetric molecules, while 1:1 complexation was observed for the unsymmetric molecules in the phase-solubility diagram. The UV–Vis investigation showed 1:1 complexation for all compounds, with some indication of higher order complexation for the symmetric molecules. Thus the stoichiometry found with the two methods correlated well for the unsymmetric, but not for the symmetric compounds where the phase-solubility investigations clearly indicated higher order complexation and possible aggregation of complexes. There was also a difference between the 1:1 complexation constants found with the two methods, especially for the compounds with low intrinsic solubility (i.e. the symmetric curcuminoids). However, they agree in the ranking of complexes according to the strength of the association. The 1:2 complexation constant observed with the phase-solubility method was more than 100 times the complexation constant found with the UV–Vis method, which explains why solubility is poorly predicted from the UV–Vis data. This discrepancy may be explained by solubilization by aggregation of complexes or some phenomena other than inclusion complexation.     

Evidence for the occurrence of electrochemical reactions and their interaction with chemical reactions during the corrosion of pure Fe with solid NaCl deposit in water vapor at 600 °C

The results of this work prove that electrochemical reactions are involved in the whole corrosion process of pure Fe with a solid NaCl deposit in water vapor at 600 °C. The interaction of chemical and electrochemical reactions accelerates the corrosion rate of pure Fe significantly. The electrochemical reaction is coupled with a preceding chemical reaction process (ce), in which Fe first reacts chemically with NaCl and water vapor to generate HCl_(g). And then, the electrochemical reaction proceeds via a one-electron electrochemical reduction to form H₂.     

Study on the synthesis of ZnO/K2SO4 composite material by sol–gel method and its photocatalytic properties

A novel photocatalytic composite material ZnO/K₂SO₄ was prepared using sol–gel method. The samples were characterized by means of wide-angle X-ray diffraction, Fourier-transform infrared spectroscopy, and high-resolution scanning electron microscopy. The preliminary experimental results indicated that the as-prepared composite material exhibited good photocatalytic performance in the degradation of methyl orange in aqueous solution. The results indicate that 92.54% of the initial methyl orange was degraded after 30 min of ultraviolet light irradiation by adding 0.15 g ZnO/K₂SO₄ composite material into 50 mL methyl orange solution.