The kinetics and mechanism of n-butyraldehyde photolysis in the vapor phase at 313 nm

The photolysis was investigated at 313 nm wavelength, 253–529 K temperatures, and 4 × 10^?11-2 × 10^?9 mol·photon/cm²·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.     

Kinetics and mechanism of the atmospheric oxidation of Ethyl tertiary butyl ether

Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10^?13 cm³ molecule^?1 s^?1 at 298 K. The primary products and molar yields for the OH reaction with ETBE in the presence of NO_x were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.     

Polymer reactions—Part VII: Thermal pyrolysis of polypropylene

Polypropylene has been pyrolysed in a carrier stream of helium from 388° to 900°C in both the programmed heating and flash pyrolysis modes. The products were on-line identified and quantitatively analysed by an interfaced GC peak identification system. The first order rate constants for pyrolysis are 3·7 × 10^?4 sec^?1 and 4·0 × 10^?4 sec^?1, respectively, for atactic and isotactic polypropylene at 388°C; the corresponding overall activation energies are 56 ± 6 and 51 ± 5 kcal mole^?1. The main products in decreasing yields are 2,4-dimethyl-1-heptene, 2-pentene, propylene, 2 methyl-1-pentene and 2,4,6-trimethyl-1-nonene. Also isolated, but in much smaller quantities, are: ethane, isobutylene, 4,6-dimethyl-2-nonene, 2,4,6-trimethyl-1-heptene, 3-methyl-3,5-hexadiene and methane. Propylene is the product of an unzipping reaction. Most of the other products can be accounted for by a mechanism involving first, random scission of carbon-carbon bonds to produce methyl, primary and secondary alkyl radicals, followed by intramolecular hydrogen transfer processes. Methane and ethane are formed from the methyl radicals. All the products found in high yields are derived from the secondary alkyl radicals.     

Kinetics and mechanism of the atmospheric oxidation of tertiary amyl methyl ether

Tertiary-amyl methyl ether (TAME) is proposed for use as an additive to increase the oxygen content of gasoline as stipulated in the 1990 Clean Air Amendments. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of TAME. The kinetics of the reaction of OH with TAME was examined by using a relative rate technique in which photolysis of methyl nitrite or nitrous acid was used as the source of OH. The OH rate constant for TAME and two major products (t-amyl formate and methyl acetate) were measured and yields for ten products were determined as primary products from the reaction. Values determined for the rate constants for the reaction with OH were 5.48 × 10^?12 (TAME), 1.75 × 10^?12 (t-amyl formate), and 3.85 × 10^?13 cm³ molec^?1 s^?1 (methyl acetate) at 298 ± 2 K. The primary products (with corrected yields where required) from the OH + TAME that have been observed include (1) t-amyl formate (0.366), methyl acetate (0.349), acetaldehyde (0.43, corrected), acetone (0.036), formaldehyde (0.549), t-amyl alcohol (0.026), 3-methyoxy-3-methyl-butanal (0.044, corrected), t-amyloxy methyl nitrate (0.029), 3-methyoxy-3-methyl-2-butyl nitrate (0.010), and 2-methoxy-2-methyl butyl nitrate (0.004). Mechanisms leading to these products involve OH abstraction from each of the four different hydrogen atoms of TAME. © 1995 John Wiley & Sons, Inc.     

Production and decomposition of highly excited 2-butyl radicals by the addition of hot hydrogen atoms to but-2-ene. Cross section for the addition reaction

Highly excited 2-butyl radicals have been generated by addition of hot hydrogen atoms to but-2-ene. Atoms of initial energy 130 kJ mol^?1 and 161 kJ mol^?1 were produced by photolysis of H₂S. Rates of decomposition of the highly excited 2-butyl radicals were monitored by analysis of stabilization and decomposition products, and the extent of energy-loss of the hydrogen atoms in nonreactive collisions assessed by measuring the effect of added xenon on product yields. A model involving the cross-section for the addition reaction, energy transfer in nonreactive collisions between hydrogen atoms and but-2-ene, RRKM rate constants for decomposition of excited 2-butyl radicals, and collisional energy transfer from the radicals, has been used to calculate product yields for comparison with experimental values. It is concluded that the cross-section for addition of hydrogen atoms of energy about 130 kJ mol^?1 to but-2-ene is 0.055 ± 0.028 nm². This value is compatible with the A factor for the thermal addition reaction.     

The mechanisms of the homogeneus,unimolecular elimination kinetics of ethyl 4-chlorobutyrate and 4-chlorobutyric acid in the gas phase

Ethyl 4-chlorobutyrate, which is reexamined, pyrolyzes at 350–410°C to ethylene, butyrolactone, and HCl. Under the reaction conditions, the primary product 4-chlorobutyric acid is responsible for the formation of γ-butyrolactone and HCl. In seasoned vessels, and in the presence of a free-radical inhibitor, the ester elimination is homogeneous, unimolecular, and follows a first-order rate law. For initial pressures from 69–147 Torr, the rate is given by the following Arrhenius expression: log k₁(s^?1) = (12.21 ± 0.26) ? (197.6 ± 3.3) kJ mol^?1 (2.303RT)^?1. The rates and product formation differ from the previous work on the chloroester pyrolysis. 4-Chlorobutyric acid, an intermediate product of the above substrate, was also pyrolyzed at 279–330°C with initial pressure within the range of 78–187 Torr. This reaction, which yields γ-butyrolactone and HCl, is also homogeneous, unimolecular, and obeys a first-order rate law. The rate coefficient, is given by the following Arrhenius equation: log k₁(s^?1) = (12.28 ± 0.41) ? (172.0 ± 4.6) kJ mol^?1 (2.303RT)^?1. The pyrolysis of ethyl chlorobutyrate proceeds by the normal mechanism of ester elimination. However, the intermediate 4-chlorobutyric acid was found to yield butyrolactone through anchimeric assistance of the COOH group and by an intimate ion pair-type of mechanism. Additional evidence of cyclic product and neighboring group participation is described and presented.     

Photo-oxygenation of Styrenic Estrogens: Structural Analysis of 8,9-Didehydro-, 6,7-Didehydro-, and 9,11-Didehydroestrone Derivatives and Their Reactivity towards Singlet Oxygen

A series of didehydro-3-O-methyl-estrones having a styrenic framework, with the ring-A-conjugated double bond in all three possible positions (8,9-didehydro- ( 6 ),9,11-didehydro- ( 1b ), 6,7-didehydro- ( 9 ), and the 12,18-di-nor-8,9-didehydroestrone analog 11 ), were compared for their reactivity towards singlet oxygen. Under dye-sensitized photo-oxygenation conditions, both, products derived from ene-type reactions with the isolation of a stable hydroperoxide and a fragmentation product, were obtained from 6 (see Scheme 3), while only fragmentation took place for 1b (Scheme 1), Kinetic studies indicated that 6 is more reactive towards ¹O₂ than 1b (β = 9.2·10^?3 mol·1^?1 vs 3.3·10^?2 mol·1^?1, resp.). The observed reactivity, apparently, does not match with ene-type reaction and [2 + 2]cycloaddition being in competition, since the most activated substrate 6 preferentially yields ene-type products and their derivatives. Conformational analysis on the structure of 6 and 1b , both calculated by molecular-mechanic techniques (MMPMI) and determined by X-ray diffraction, show that the allylic H-atoms satisfy the orthogonality rule for ene-type reactions. The product distribution is best rationalized by applying Fukui's rule which takes into account a combination of electronic and geometric factors. Substrates 9 and 11 yielded photo-products arising from ene-type reaction with no stable primary products isolated (Scheme 4). Geometric considerations based on the calculated structures by molecular mechanics are consistent with the observed results.     

Lower photoreactivity of 3-methyl-3-(4′-biphenylyl)-t-butene

Direct and sensitized photolyses of 3-methyl-3-(4′-biphenylyl)-1-butene gave 1,1-dimethyl-2-(4′-biphenylyl)cyclopropane as primary product and 2-methyl-4-(4′-biphenylyl)-1-butene as secondary product with quantum yields of 7.6×10^?3 and 5.6×10^?3, respectively. On direct photolysis, the triplet reactant rearranged with a quantum yield of 4.4×10^?3 and is more reactive than the singlet. The exceptionally low photoreactivity shows that the excitation energy is largely localized on the biphenylyl portion but can be delivered to the reaction center slowly.     

The photooxidation of methyl tertiary butyl ether

Methyl tertiary butyl ether (MTBE) has been proposed and is being used as an additive to increase the octane of gasoline without the use of tetraethyl lead and alkylbenzenes. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of MTBE. The kinetics of the reaction of OH with MTBE was examined by using a relative rate technique in which photolysis of methyl nitrite was used as the source of OH. With n-butane as the reference compound a value of (2.99 ± 0.12) × 10^?12 cm³ molecule^?1 s^?1 at a temperature of 298 K was obtained for the rate constant. The products (and product yields) for the OH reaction with MTBE in the presence of NO_x were also determined and found to be t-butyl formate (0.68 ± 0.05), methyl acetate (0.14 ± 0.02), acetone (0.026 ± 0.003), t-butanol (0.062 ± 0.009), and formaldehyde (0.48 ± 0.05) in mols/mol MTBE converted. The OH rate constant for the major product formed, t-butyl formate was also measured and found to be (7.37 ± 0.05) × 10^?13 cm³ molecule^?1 s^?1. Mechanisms to rationalize the formation of the products are presented.     

A flash photolysis–resonance fluorescence kinetics study of ground-state sulfur atoms. II. Rate parameters for reaction of S(3P) with C2H4

Absolute rate constants for the reaction of S(³P) with ethylene were measured over an ethylene concentration range of 7, a total pressure of 50 to 400 torr, and a flash intensity range of 10. At 298°K, the bimolecular rate constant was found to be invariant over this range of variables and had a measured value of 4.96 × 10^?13 cm³ molec^?1 s^?1. Over the temperature range of 218° to 442°K, the rate data could be fit to a simple Arrhenius equation of the form Units are cm³ molec^?1 s^?1. The dependence of the measured value of k₁ on the concentration of the reaction product ethylene episulfide is discussed.     

OH radical reaction rate constants for polycyclic alkanes: Effects of ring strain and consequences for estimation methods

Using a relative rate method, rate constants for the gas-phase reactions of the OH radical with trans-pinane [(1R, 2R)-2, 6, 6-trimethylbicyclo[3.1.1]heptane], tricyclene (1, 7, 7-trimethyltricyclo[2.2.1.0^{2, 6}]heptane), and quadricyclane (quadricyclo[2.2.1.0^{2, 6}.0^{3, 5}]heptane) of (1.34 ± 0.29) × 10^?11 cm³ molecule^?1 s^?1, (2.86 ± 0.62) × 10^?12 cm³ molecule^?1 s^?1 and (1.83 ± 0.41) × 10^?12 cm³ molecule^?1 s^?1, respectively, have been determined at 296 ± 2 K. These rate constants are compared with values calculated from an empirical estimation method and used to refine this estimation technique for the calculation of OH radical reaction rate constants for polycyclic systems. © John Wiley & Sons, Inc.     

Kinetic and product study of the gas‐phase reaction of sabinaketone with OH radical

Sabinaketone is one major photooxidation product of sabinene, an important biogenic volatile organic compound. This article provides the first product study and the second rate constant determination of its reaction with OH radicals. Experiments were investigated under controlled conditions for pressure and temperature in the LISA indoor simulation chamber using FTIR spectrometry. Kinetic study was carried out at 295 ± 2 K and atmospheric pressure using the relative rate technique with isoprene as the reference compound. The rate constant was found to be k_{sabinaketone + OH} = (7.1 ± 1.0) × 10^?12 molecule^?1 cm³ s^?1. Acetone and formaldehyde were detected as products of the reaction with the respective yields of R_acetone = 0.9 ± 0.2 and R_HCHO = 1.2 ± 0.3. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 415–421, 2007     

Pyrolysis of Hailar lignite in an autogenerated steam agent

An in situ pyrolysis process of high moisture content lignite in an autogenerated steam agent was proposed. The aim is to utilize steam autogenerated from lignite moisture as a reactant to produce fuel gas and additional hydrogen. Thermogravimetric analysis revealed that mass loss and maximum mass loss rate increased with the rise of heating rates. The in situ pyrolysis process was performed in a screw kiln reactor to investigate the effects of moisture content and reactor temperature on product yields, gas compositions, and pyrolysis performance. The results demonstrated that inherent moisture in lignite had a significant influence on the product yield. The pyrolysis of L _R (raw lignite with a moisture content of 36.9 %, wet basis) at 900 °C exhibited higher dry yield of 33.67 mL g^?1 and H₂ content of 50.3 vol% than those from the pyrolysis of the predried lignite. It was also shown that increasing reaction temperature led to a rising dry gas yield and H₂ yield. The pyrolysis of L _R showed the maximum dry yield of 33.7 mL g^?1 and H₂ content of 53.2 vol% at 1,000 °C. The LHV of fuel gas ranged from 18.45 to 14.38 MJ Nm^?3 when the reactor temperature increased from 600 to 1,000 °C.     

Overwhelming decomposition of 4-bromo-4''''-cyanomethylbiphenylyl radical anion without electron transfer to 4,4''''-dibromobiphenyl

Dibromobiphenyl reacted with cynomethyl anion in ammonia under irradiation to form nucleophilic bis-substituted product in high yield without substantial monosubstituted product. Quantum yields for the formations of bis- and monosubstituted products were found to be 85.6 and 2.3×10-6 respectively, while the corresponding pseudo-first-order rates were 6.9×10-3 and 5.2×10-10 mol.L-1.S-1. Block up the possible electron transfer of 4-brome-4'-cyanomethylbiphenylyl radical anion to 4-cyanometbyl-biphenylyl radical and bromine ion.     

Diffusion of ethylene glycol accompanied by reactions in poly(ethylene terephthalate) melts

Diffusion coefficients of ethylene glycol (EG) have been measured in poly(ethylene terephthlate) (PET) melts by a quartz-spring sorption apparatus. A simple mathematical model was developed to investigate the sorption behavior accompanied by chemical reactions of EG and PET at high temperatures. Diffusion coefficients are deduced from experimental data for an asymptotically thin sample in order to minimize the effects of reactions. The diffusion coefficient of EG is strongly dependent on the vapor pressure of EG and temperature but not on the molecular weight of PET in this experimental range (degree of polymerization 80–120). The diffusion coefficient of EG in PET melt at 265°C is 2.58 × 10^?7 cm²/s at the limit of zero concentration of EG. The activation energy for diffusion is 38.4 kcal/gmol, and the heat of solution for sorption is ?44.9 kcal/gmol. The concentrations of the volatile materials resulting from reactions in PET-EG system were analyzed with gas chromatography. In addition, a fit of the current model to experimental data yields frequency factors for the polymerization reaction (k₁) and the acetaldehyde formation reaction (k₂) to be 5.84 × 10⁸ cm³/mol ? min and 3.90 × 10¹¹ min^?1, respectively.     

An FTIR study of the Cl-atom-initiated reaction of glyoxal

The kinetics and mechanism of Cl-atom-initiated reactions of CHO? CHO were studied using the FTIR detection method to monitor the photolysis of Cl₂–CHO? CHO mixtures in 700 torr of N₂–O₂ diluent at 298 ± 2 K. The observed product distribution in the [O₂] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHO? CHO → HCl + CHO? CO with a rate constant of [3.8 ± 0.3(σ)] × 10^?11 cm³ molecule^?1 s^?1; (2) the primary product CHO? CO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10^?7 s; (3) alternatively, the CHO? CO reacts with O₂ leading to the formation of CO, CO₂, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO₂ radical, formed in the secondary reaction CHO + O₂ → HO₂ + CO, reacts with the CHO? CHO with a rate constant ca. 5 × 10^?16 cm³ molecule^?1 s^?1 to form HCOOH and a new transient product resembling that detected previously in the HO₂ reaction with HCHO.     

Using only the very accurately known experimental enthalpy of hydrogenation of ethylene as a reference standard in the atomization method

Theoretical Gn model chemistries yield slightly different values for the enthalpy of formation of the hydrogen molecule from the constituent protons and electrons. For example, the G3 model yields ?1.92 kJ mol^?1 at 298 K, which differs from zero by an acceptably small amount. However, using this G3 value for a stepwise series of hydrogenations of polyunsaturated molecules multiplies the error, e.g., by five times for the hydrogenation of naphthalene. For polyunsaturates, this can produce errors considerably greater than experimental uncertainties. We calculate enthalpies of hydrogenation by referring the calculated values to the accurately known experimental enthalpy of hydrogenation of ethylene. This approach is simpler than the atomization method that depends on several experimental enthalpies of formation of the constituent atoms of the target molecules. This method yields enthalpies of hydrogenation and of formation in excellent agreement with experiment for many polyunsaturated compounds and lends confidence to results obtained for others, for which no accurate experimental values exist or are disparate, for example azulene. Some new and surprising results are that the formally conjugated triple bonds of cyanoacetylene do not lead to stabilization, but to destabilization by 10.2 kJ mol^?1. The conjugated triple bonds of cyanogen cause thermodynamic destabilization by 47.5 kJ mol^?1. Stabilization by conjugation in acrylonitrile is near zero. The remarkable endothermic monohydrogenation of benzene (25 kJ mol^?1), first noted by Kistiakowsky, is also found in toluene and naphthalene, leading to stability of the reactant relative to the product of ~30 and 22 kJ mol^?1, respectively.     

OH‐Initiated Photooxidations of 1‐Pentene and 2‐Methyl‐2‐propen‐1‐ol: Mechanism and Yields of the Primary Carbonyl Products

The products of the gas‐phase reactions of OH radicals with 1‐pentene and 2‐methyl‐2‐propen‐1‐ol (221MPO) at T=298±2 K and atmospheric pressure were investigated by using a 4500 L atmospheric simulation chamber that was built especially for this work. The molar yield of butyraldehyde was 0.74±0.12 mol for the reaction of 1‐pentene. This work provides the first product molar yield determination of formaldehyde (0.82±0.12 mol), 1‐hydroxypropan‐2‐one (0.84±0.13 mol), and methacrolein (0.078±0.012 mol) from the reaction of 221MPO with OH radicals. The mechanism of this reaction is discussed in relation to the experimental results. Additionally, taking into consideration the complex mechanism, the rate coefficients of the reactions of OH with formaldehyde, 1‐hydroxypropan‐2‐one, and methacrolein were derived at atmospheric pressure and T=298±2 K.; the obtained values were (8.9±1.6)×10^?12, (2.4±1.4)×10^?12, and (22.9±2.3)×10^?12 cm³ molecule^?1 s^?1, respectively.     

Rate constants for the reactions of Br atoms with a series of alkanes,alkenes, and alkynes in the presence of O2

Rate constants of Br atom reactions have been determined using a relative kinetic method in a 20 l reaction chamber at total pressures between 25 and 760 torr in N₂ + O₂ diluent over the temperature range 293–355 K. The measured rate constants for the reactions with alkynes and alkenes showed dependence upon temperature, total pressure, and the concentration of O₂ present in the reaction system. Values of (6.8 ± 1.4) × 10^?15, (3.6 ± 0.7) × 10^?14, (1.5 ± 0.3) × 10^?12, (1.6 ± 0.3) × 10^?13, (2.7 ± 0.5) × 10^?12, (3.4 ± 0.7) × 10^?12, and (7.5 ± 1.5) × 10^?12 (units: cm³ s^?1) have been obtained as rate constants for the reactions of Br with 2,2,4-trimethylpentane, acetylene, propyne, ethene, propene, 1-butene, and trans-2-butene, respectively, in 760 torr of synthetic air at 298 K with respect to acetaldehyde as reference, k = 3.6 × 10^?12 cm³ s^?1. Formyl bromide and glyoxal were observed as primary products in the reaction of Br with acetylene in air which further react to form CO, HBr, HOBr, and H₂O₂. Bromoacetaldehyde was observed as an primary product in the reaction of Br with ethene. Other observed products included CO, CO₂, HBr, HOBr, BrCHO, bromoethanol, and probably bromoacetic acid.     

Synthesis and Properties of Poly(Organophosphazenes) Electrolyte

Abstract

To prepare electrolytes using poly(organophosphazenes), poly(bisanilinophosphazene) selected was carried out with the various concentration of sulfonic chloride in tetra-chloroethane solvent using vigorously sterring at room temperature for 4 hr. The products prepared were determined with IR and chemical analysis. It was found that the -SO₃H groups in the product appeared at 1,1050 cm^?1, 1,030 cm^?1 and 550 cm^?1, and the reaction rate of sulfonic chloride was about 34%-55% under this experimental conditions. Also, the products had two kind of glass transition temperatures such as 63°C and -18°C, respectively, and the values were lower in comparison with that of starting polymer. Furthermore, the conductivity of the product at room temperature was determined and the conductivity was increased the concentration of -SO₃H groups. It was found that the product having -SO₃H groups was able to ion exchange with Li⁺ or Cu²⁺ ions under aqueous solution. Also, the ion exchange rate was determined with the titration of alkaline aqueous solution with a standard solution of HCl. The products formed after the ion exchange reaction had higher conductivity in comparison with that of the polymer.