The free radical oxidation of CH2O in the presence of NO2 and NO

NO₂ was photolyzed at 366 nm and 296 K in the presence of CH₂O and O₂ and in some runs with added NO or N₂. The measured products were CO, CO₂ and HCOOH. H₂ and N₂O were not produced. Both the CO and the CO₂ were produced in a linear fashion with irradiation time, but the HCOOH grew after a marked induction period. From the CO₂ quantum yields at high [O₂]/[NO₂] ratios an upper limiting value of 0.16 ± 0.02 was found for k_3b/k₃ where reactions (3a) and (3b) are

This is lower than the value of approximately 0.30 reported for k_3b/k₃ by Chang and Barker. From the CO and CO₂ yields the competition for HCO between O₂ and NO₂ could be measured.

The ratio k₉/k_7a was found to be 0.21 ± 0.07 and was independent of pressure. The analysis required knowledge of some other rate coefficients. If those rate coefficients are completely in error, k₉/k_7a could be as high as 0.63. With the literature value of 5.6 × 10⁻¹² cm³ s⁻¹ for k₉, the best value for k_7a is (2.7 ± 0.9) × 10⁻¹¹ cm³ s⁻¹ with a lower limiting value of (8.9 ± 3.0) × 10⁻¹² cm³ s⁻¹.Information was also obtained on the reaction of HO₂ with CH₂O which produces HCOOH. An approximate value of (1.4 – 3.2) × 10⁻¹³ cm³ s⁻¹ was found for the rate coefficient for this reaction which is about 14 – 32 times greater than the estimate of Su et al.     

Synthesis and reactivity of a stable precursor of 2-cyano-1,3-butadiene

A new, productive synthesis of 3-cyano-2,5-dihydrothiophene-1,1-dioxide (3) is described. This substituted sulfolene serves as a stable precursor of 2-cyano-1,3-butadiene and can be used in the Diels-Alder reactions without isolation of the unstable diene.The Diels-Alder reactions of 2-cyano-1,3-butadiene appear to proceed in high yield only with electron-deficient dienophiles, but ¹³C NMR shows that in some cases the products are a mixture of regioisomeric cycloadducts.     

2-carbethoxy-1,3-butadiene irontricarbonyl : chemical transformations and reactivity of the corresponding free dienes.

Chemical transformations on the 2-carbethoxy-1,3-butadiene irontricarbonyl complex were performed. The dienic and dienophilic reactivities of the corresponding free dienes are studied.     

Tuning the shape of nanoparticles to control their catalytic properties: selective hydrogenation of 1,3-butadiene on Pd/Al2O3

Shape-controlled Pd nanoparticles supported on powder alumina are more efficient for selective butadiene hydrogenation to butene when they exhibit high fractions of (111) facets.     

Cycloaddition of a 1,2-diaza-1,3-butadiene to phenylpropiolic acid: an efficient route to pyridazinoquinolone derivatives

Diazocoupling of dihydroquinolin-4-ones with aryldiazonium nitrates gave the corresponding diazo derivatives, which undergo facile (4+2) cycloaddition reactions with phenylpropiolic acid to afford 2-aryl-4a-methyl-10-oxo-4-phenyl-2,4a,5,10-tetrahydropyridazino[4,3-b]quinoline-3-carboxylic acid derivatives 3. However, with β-nitrostyrene a mixture of three isomeric products 4a-c was obtained.     

Copper/H2O2-mediated oxidation of 2'-deoxyguanosine in the presence of 2-naphthol leads to the formation of two distinct isomeric adducts

Exposure of cells to phenolic compounds through exogenous and endogenous sources can lead to deleterious effects via nucleobase modifications of DNA occurring under oxidative conditions. 2'-Deoxyguanosine (dG) is the most electron rich of the four canonical bases and includes many nucleophilic sites; it is also susceptible to oxidation with numerous reactive oxygen species. In these studies, dG was allowed to react with 2-naphthol in the presence of copper or iron salts yielding two principal isomeric products. Spectroscopic analysis and reactions with alkylated nucleosides support the assignment of compound 1a/1b as a pair of atropisomer N(2) adducts and compound 2a/2b as a diastereomeric mixture of tricyclic [4.3.3.0] adducts. Both products are the result of an overall four-electron oxidation process and consequently have the same masses, though drastically different structures, providing mechanistic insight into their formation. Thus, dG alkylation by 2-naphthol under oxidative conditions yields products whose structural properties are altered, leading to potentially mutagenic effects in genomic DNA.     

Measurements of the kinetics of the OH-initiated oxidation of β-pinene: Radical propagation in the OH + β-pinene + O2 + NO reaction system

The mechanism of the OH-initiated oxidation of β-pinene in the presence of NO has been investigated using a discharge-flow system at 5 Torr and 300 K. OH radical concentrations were measured as a function of reaction time by laser-induced fluorescence (LIF). The rate constant for the OH +β-pinene reaction was measured to be (7.68 ± 0.72) ×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. OH radical propagation was observed after the addition of O₂ and NO, and the measured OH concentration profiles were compared to simulations based on both the Master Chemical Mechanism and the Regional Atmospheric Chemistry Mechanism for β-pinene oxidation in order to determine the ability of these mechanisms to describe the observed efficiency of radical propagation. Both models are able to reproduce the observed OH concentrations profiles to within 15%. Expanding the MCM to include isomerization of the β-hydroxy alkoxy radicals improves the agreement with the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 522–531, 2005     

Development of a highly selective and efficient catalyst for 1,3-butadiene dimerization

A selective dimerization reaction of 1,3-butadiene in the presence of 2-propanol to give 1,3,7-octatriene has been developed. By modification of palladium carbene catalysts an unexpected selectivity switch from the telomerization to the dimerization product occurred. In applying the 1,3-bis(2,6-diisopropylphenyl)-4,5-dimethyl-3H-imidazolidenylpalladium(0) complex 9, unprecedented catalyst efficiency (TON > 80 000 and TOF > 5000 h(-1)) has been obtained for this transformation. [reaction: see text]     

Electrochemical reduction of CO2 in the presence of 1,3-butadiene using a hydrogen anode in a nonaqueous medium

The possibility of anodic generation of a solvated proton on a gas-diffusion electrode in an aprotic medium in the presence of carbon dioxide and 1,3-butadiene has been demonstrated. Formic acid was shown to be the only product of the reaction in the initially aprotic medium with the use of a hydrogen gas-diffusion anode. The influence of the counterion on the reactivity of the CO₂ ^.− radical anion in electrocarboxylation was shown experimentally. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 295–300, February, 1999.     

On the mechanism of the OH initiated oxidation of acetylene in the presence of O2 and NO x

The mechanism of the oxidation of acetylene, in the presence of O₂ and NO _x , has been studied. Different levels of theory have been tested for the first step of the mechanism: the acetylene + OH radical reaction. Based on these results the meta-hybrid functional MPWB1K has been chosen for modeling all the other steps involved in the oxidation of acetylene. Different reaction paths have been considered and the one leading to glyoxal formation and OH regeneration is predicted to be the main channel, independently of the presence of NO _x . Two different mechanisms were modeled to account for formic acid formation, both of them involving cyclic intermediates. According to the computed activation free energies, the three-membered intermediate seems to be more likely to occur than the four-membered one. However, reaction barriers are very high and only a very small proportion of formic acid is expected to be formed through such intermediates. In the presence of NO _x , considered in this work for the first time, the main product of the tropospheric oxidation of acetylene is also expected to be glyoxal.     

Polymerization and copolymerization of 2-phthalimidomethyll 1,3-butadiene. II. Kinetic study of the polymerization of 1,3-butadiene and of the copolymerization of 1,3-butadiene with 2-phthalimidomethyl 1,3-butadiene initiated by bis-(η3-allyl nickel trifluoroacetate)

The kinetics of the polymerization of 1,3-butadiene initiated by bis(η³-allyl nickel trifluoroacetate) prepared in benzene was studied in methylene chloride at 40°C. The reaction is first order with respect to the monomer, second order with respect to the catalyst in contrast to the case in which solvent is benzene. We have shown that the presence of a polar molecule (fe, N-methyl phthalimide) decreases the overall rate of polymerization. The apparent reactivity ratios for the system 2-phthalimidomethyl 1,3-butadiene (1)-1,3-butadiene (2) are r₁ = 0.65 ± 0.006 and r₂ = 0.48 ± 0.015.     

The radical cation of hexafluoro-1,3-butadiene: An ESR study

Two distinct radical cations have been observed by ESR in a γ-irradiated solid solution of hexafluoro-1,3-butadiene in freon. INDO calculations of ES     

Chloroform infrared multiphoton dissociation in the presence of O2 and NO2

The infrared multiphoton dissociation (IRMPD) of CDCl3 in the presence of O2 and NO2 as acceptor gases has been studied. We have worked with both pure CDCl3 and mixtures with CHCl3. The reaction mechanism following IRMPD of CDCl3 is discussed in detail. CCl2O, CCl4 and DCl were found to be the main products. With added O2, the observed CDCl3 dissociation was larger than with nonoxygenated acceptor gases. The reaction mechanism probably involves a catalytic cycle initiated by the oxidation of CCl3. With the aim of discriminating the different CDCl3 dissociation mechanisms, the IRMPD of CDCl3 in the presence of NO2 was first studied. In order to make evident the CDCl3 dissociation produced by the catalytic cycle, we then studied the IRMPD of CDCl3 in mixtures with CHCl3 with O2 as the acceptor gas. In this case, the dissociation mechanism subsequent to IRMPD is evidenced in the competence between the two isotopic species.     

Ir/SiO2 as a highly active catalyst for the selective reduction of NO with CO in the presence of O2 and SO2

Coexisting SO2 considerably enhanced the catalytic activity of Ir/SiO2 for NO reduction with CO in the presence of O2 because of the formation of a cis-type coordinated species of NO and CO to one iridium atom ([formula: see text]), a possible reaction intermediate leading to N2 formation.     

Synchrotron photoionization measurements of OH-initiated cyclohexene oxidation: ring-preserving products in OH + cyclohexene and hydroxycyclohexyl + O2 reactions

Earlier synchrotron photoionization mass spectrometry experiments suggested a prominent ring-opening channel in the OH-initiated oxidation of cyclohexene, based on comparison of product photoionization spectra with calculated spectra of possible isomers. The present work re-examines the OH + cyclohexene reaction, measuring the isomeric products of OH-initiated oxidation of partially and fully deuterated cyclohexene. In particular, the directly measured photoionization spectrum of 2-cyclohexen-1-ol differs substantially from the previously calculated Franck-Condon envelope, and the product spectrum can be fit with no contribution from ring-opening. Measurements of H(2)O(2) photolysis in the presence of C(6)D(10) establish that the addition-elimination product incorporates the hydrogen atom from the hydroxyl radical reactant and loses a hydrogen (a D atom in this case) from the ring. Investigation of OH + cyclohexene-4,4,5,5-d(4) confirms this result and allows mass discrimination of different abstraction pathways. Products of 2-hydroxycyclohexyl-d(10) reaction with O(2) are observed upon adding a large excess of O(2) to the OH + C(6)D(10) system.