Kinetic regularities of conversion of ozone complexes with arenes

The kinetic regularities of conversion of ozone complexes with several substituted benzenes (ArX = C₆H₅Me, C₆H₅Et, C₆H₅CHMe₂, C₆H₅CMe₃, C₆H₅F, C₆H₅Cl,m-BrC ₆ H ₅ Me, and C₆H₅CH₂Cl) were studied by spectrophotometry. The rate of consumption of [ArX · O₃ in a CH₂Cl₂-ArX solution obeys the kinetic equationW =k ₀[ArX · O₃]+k ₁ [ArX · O3][ArX]. The values of the rate constants ko andk ₁for the complexes studied were determined at -60+0 °C.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 371–374, 'February, 1996.     

Studies of decomposition kinetics for ozone complexes with cumene and chlorobenzene

Kinetic regularities in decomposition of complexes of aromatic compounds with O₃ have been studied for ozone complexes with cumene and chlorobenzene. Oxidation effect of these complexes on both aromatic compounds and olefins has been established.

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O₃. .

     

Decomposition kinetics of ozone complexes with toluene and its deuterated derivatives

Decomposition rate of O₃ complexes with aromatic hydrocarbons (ArX·O₃) in ArXO₃-ArX-CH₂Cl₂ system (ArX=C₆H₅CH₃, C₆H₅CD₃ and C₆D₅CD₃) is described by the equation:

Reduction kinetics of gold(III) complexes with calix[4]arenes derivatized with thioether groups on the upper rim

Gold(III) reduction with polydentate calix[4]arenes having thioether groups on their upper rim yields gold(I) complexes and sulfoxides. The reaction can proceed by both intramolecular and intermolecular mechanisms, whose rates depend considerably on the steric and donor properties of the radicals at the sulfur atoms. Rate constants and activation energies are determined for both reaction pathways in the temperature range 293–323 K. The higher the polarity of the solvent, the higher the reduction rate; in passing from toluene or CCl₄ to 1,2-dichloroethane, the reduction rate increases by one order of magnitude, following the increasing order of dielectric constants.     

Stoichiometric complexes of calix[4]arenes with solvent molecules

Some calix[4]arenes were found to form complexes with solvent molecules which retained their stoichiometric composition when sublimed. Saturated vapor pressures of calix[4]arenes and their complexes with solvents were for the first time determined by the Knudsen effusion method over a wide temperature range. Changes in the standard thermodynamic parameters of complex formation in the transfer from the condensed to gas phase were calculated. The enthalpy contribution to the Gibbs energy grew as conformational ligand mobility increased, and the entropy contribution increased as flexibility decreased and rigidity increased.     

Coupled hydrogenation of arenes and alkenes or dienes with cobalt phosphine complexes

Coupled hydrogenation of arenes with alkenes and dienes proceeds under mild conditions in the presence of a phosphine-modified cobalt system as well as of H₃Co[P(C₄H₉)₃]₃. Benzene hydrogenation products are cyclohexene (up to 25%) and cyclohexane. By the ESR method, a Co(0) complex containing P(C₄H₉)₃, an arene molecule and AlR₃ as ligands has been identified in the catalytic system Al(C₂H₅)₃+Co(C₅H₇O₂)₂+P(C₄H₉)₃. The nature of the active complex and the possible mechanism of the coupled process are discussed.

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, , H₃Co[P(C₄H₉)₃]₃ . ( 25%) . Al(C₂H₅)₃+Co(C₅H₇O₂)₂+P(C₄H₉)₃ Co(0), P(C₄H₉)₃, AlR₃. .

     

Unsaturated iridium pyridinedicarboxylate pincer complexes with catalytic activity in borylation of arenes

Unsaturated σ,π-cyclooctenyl and hydrido Ir(III) complexes bearing an unusual tridentate dianionic ONO pincer-type ligand have been straightforwardly obtained from 2,6-pyridinedicarboxylic acid and standard Ir(I) starting materials. These complexes efficiently catalyzed the arene C-H borylation under thermal conditions.     

Supramolecular polymeric complexes of calix[8]arenes

Formation of ionic complexes of calix[8]arenes with polymers of various basicities was studied, and previously unknown ternary polymeric complexes of calix[8]arenes of the ion-ion (polymer-calixarene-uranyl ion) and ion-hydrophilic molecule-hydrophobic molecule (polymer-calixarene-fullerene) types were prepared.     

Direct C-H bond arylation of arenes with aryltin reagents catalysed by palladium complexes

Direct C-H bond arylation of simple arenes with aryltin reagents has been successfully catalysed by PdCl2 in the presence of CuCl2. CuCl2 proved to be an activator for a palladium intermediate as well as an oxidant.     

Thermochemistry of molybdenum tricarbonyl complexes of arenes and cyclic polyolefins

The heats of reaction of arene, cycloheptatriene, and cyclooctatetraene complexes of molybdenum tricarbonyl with pyridine yielding (py)₃Mo(CO)₃ have been measured by solution calorimetry. Reaction of toluene molybdenum tricarbonyl with cyclopentadiene yielding HMo(CO)₃C₅H₅ and with tetrahydrofuran yielding (THF)₃Mo(CO)₃ have also been studied thermochemically. These measurements yield accurate values for the enthalpy of arene exchange in methylene chloride solution for a number of organomolybdenum complexes. The order of stability: benzene < toluene < cyclooctatetraene < mesitylene < hexamethylbenzene < cycloheptatriene < (tris)-tetrahydrofuran < η⁵-cyclopentadienylhydrido < (tris)-pyridine spans a range of 31 kcal/mol.The enthalpy of isomerization of cycloheptatriene to toluene is reduced by 7.1 ± 1.2 kcal/mol upon coordination to molybdenum tricarbonyl, indicative of a loss of “resonance” energy for the complexed arene. The MoH bond strength in HMo(CO)₃C₅H₅ is estimated as 66 ± 8 kcal/mol. The importance of entropic factors in arene exchange is discussed.     

Molecular dynamics of host-guest complexes of small gas molecules with calix[4]arenes

The unexpected sorption of gases by a low-density p-tert-butylcalix[4]arene crystal polymorph raises fundamental questions about differential gas transport and sequestration in the organic solid state. To gain insight into the processes underlying these observations, we have used molecular dynamics simulations, augmented with calculations of potentials of mean force, to investigate the stability of isolated host-guest complexes and the relationship between the dynamics of these complexes and the dynamics of a solvated host molecule. Thermal fluctuations of the calixarenes themselves are found to be consistent with proposed mechanisms for gas entry into the host cavities, while relative host-guest stabilities correlate well with experimental absorption-desorption isotherms in some cases (CO2 and CH4) but not in others (C2H2). In these isolated systems, stable complexes characteristically form when the attractive interactions of the guest with the ring of negative charge density on the inner surface of the host cavity are not disrupted by thermal motion. The experimentally observed efficient uptake of gases such as C2H2 by the host crystals suggests, however, that stabilization of host-guest complexes in some systems may derive from dynamical constraints imposed by the crystal lattice.     

Products and kinetics of the heterogeneous reaction of suspended vinclozolin particles with ozone

Vinclozolin is a widely used fungicide that can be released into the atmosphere via application and volatilization. This paper reports an experimental investigation on the heterogeneous ozonation of vinclozolin particles. The ozonation of vinclozolin adsorbed on azelaic acid particles under pseudo-first-order conditions is investigated online with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The ozonation products are analyzed with a combination of VUV-ATOFMS and GC/MS. Two main ozonation products are observed. The formation of the ozonation products results from addition of O(3) on the C-C double bond of the vinyl group. The heterogeneous reactive rate constant of vinclozolin particles under room temperature is (2.4 ± 0.4) × 10(-17) cm(3) molecules(-1) s(-1), with a corresponding lifetime at 100 ppbv O(3) of 4.3 ± 0.7 h, which is almost comparable with the estimated lifetime due to the reaction with atmospheric OH radicals (～1.7 h). The reactive uptake coefficient for O(3) on vinclozolin particles is (6.1 ± 1.0) × 10(-4).     

Degradation of lignin by ozone. I. The kinetics of lignin degradation of ozone

The ozonolysis of spruce periodate and cuoxam lignins and protolignin in spruce wood has been studied in 45% aqueous acetic acid at room temperature. Stirring affected the rate of reaction and a tentative explanation is given. Degradation followed first-order kinetics characterized by a rate constant K with values of 6.96 × 10^?4s^?1 for periodate lignin, 5.10 × 10^?4s^?1 for cuoxam lignin, and 5.09 × 10^?4s^?1 for protolignin in spruce wood. The similarity of the rate constants shows (1) that periodate and cuoxam lignins are good models for wood lignin and (2) that the carbohydrate matrix has an insignificant effect on the rate of delignification of the protolignin by ozone. The average rate of ozone consumption per C₉ unit for periodate lignin was determined as 0.12 mol/min and 0.08 mol/min for cuoxam lignin. The implications of the various results are discussed.     

A new paradigm for cationic cyclization of iron tricarbonyl diene complexes with pendant alkenes and arenes

A new example of stereospecific cationic cyclization of iron tricarbonyl diene complexes with pendant alkenes and arenes is provided. Protonation of a double bond vicinal to the iron tricarbonyl diene moiety is employed to trigger the cyclization, rather than the previously reported Lewis/protic acid dehydroxylation of diastereomeric alcohols, eliminating one step of separation and avoiding some reactivity problems previously encountered for one of the alcohol diastereoisomers. [reaction: see text]     

Sulfonylation of arenes with sulfonamides

In the presence of triflic anhydride, sulfonylation of arenes with sulfonamides proceeded smoothly in Cl₂CHCHCl₂ at 80-140 °C, which gave rise to the desired products in good to excellent yields.     

Evolutional kinetics of metal-polymer complexes formation

Under the conditions of polydental binding, metal ions couple azacrown ether links of the polymer, limiting segmental chain mobility and decreasing statistical weight of the states available for complex formation. According to the rate constant dependence on conversion extent two different regimes of the complex formation reaction may be given: 1) retardation resulting from decreasing reactivity, the measured rate constant decreases by a few orders of magnitude in the course of time; 2) retardation followed by increasing reactivity, the observed rate constant remains unchangeable. The process covering conformational nonequilibrium states of macromolecular coil makes it dependent on the system prehistory which violates the law of mass action. The couplings being labile, the instantaneous value of pseudomonomolecular rate constant of the reaction is a function of conversion extent on metal and is not dependent on absolute polymer uptake by metal. The reaction rate in each point does not depend only on reagents concentration ratio but also on the character of metal ion distribution along the polymer chain obtained to the given moment. At complex formation with “hard” couplings the increase of metal concentration makes the effective retardation of the process change, whereas initial parts of the kinetic curves remain practically the same. In this system pseudomonomolecular rate constant does not seem to be a function of conversion extent, but is defined by absolute quantity of the formerly bound metal. Formal application of the law of mass action in this case is useless, it is necessary to apply distribution function on reactivity. Unlike solid phase systems nonequivalent character of reaction sites in the polymer is of evolution character, i.e.it arises in the course of the reaction on the account of polymer coil conformation change.