Addition Of Cyclohexene Research Articles

The effect of temperature on the properties of the NBR/PVC blend exposed to ethanol fuel and different gasolines

The use of ethanol fuel or ethanol/gasoline mixtures has greatly increased in recent years. The effect of the fuels on the stability of the polymeric components of vehicles is an important point of investigation, especially taking into account that other solvents are sometimes used to adulterate the ethanol/gasoline mixtures. To assess the compatibility of the fuel with the NBR/PVC blend, we studied the changes in the weight, hardness and mechanical properties of this polymeric blend during the immersion tests with different gasolines (regular, premium, regular doped with rubber solvent and regular with addition of cyclohexene) and with bioethanol fuel. The immersion tests were performed by 20days at immersion temperatures of 30°C, 60°C and 110°C. The diffusion coefficients related to the fuel sorption and desorption processes were calculated. The values of the parameters Tau3 and I3 were obtained by positron annihilation lifetime spectroscopy (PALS) to investigate the free volume of the NBR/PVC blend. All of the blend samples became less elastomeric and more rigid after the exposure tests. The swelling of the NBR/PVC blends exposed to the different gasolines increased with the immersion temperature. The NBR/PVC blend samples exposed to the gasoline doped with cyclohexene showed a two-fold increase in swelling compared with the other gasolines. The samples immersed in bioethanol showed the highest weight loss due to the polar character of the alcohol, which caused the extraction of a large quantity of the polymeric blend constituents. The pure ethanol was more aggressive for NBR/PVC blend than all of the Brazilian gasolines studied.

Effects of Dispersion in Density Functional Based Quantum Mechanical/Molecular Mechanical Calculations on Cytochrome P450 Catalyzed Reactions.

Density functional theory (DFT) based quantum mechanical/molecular mechanical (QM/MM) calculations have provided valuable insight into the reactivity of the cytochrome P450 family of enzymes (P450s). A failure of commonly used DFT methods, such as B3LYP, is the neglect of dispersion interactions. An empirical dispersion correction has been shown to improve the accuracy of gas phase DFT calculations of P450s. The current work examines the effect of the dispersion correction in QM/MM calculations on P450s. The hydrogen abstraction from camphor, and hydrogen abstraction and C-O addition of cyclohexene and propene by P450cam have been modeled, along with the addition of benzene to Compound I in CYP2C9, at the B3LYP-D2/CHARMM27 level of theory. Single point energy calculations were also performed at the B3LYP-D3//B3LYP-D2/CHARMM27 level. The dispersion corrections lower activation energy barriers significantly (by ∼5 kcal/mol), as seen for gas phase calculations, but has a small effect on optimized geometries.These effects are likely to be important in modeling reactions catalyzed by other enzymes also. Given the low computational cost of including such dispersion corrections, we recommend doing so in all B3LYP based QM/MM calculations.

Synthetic and mechanistic studies of metal-free transfer hydrogenations applying polarized olefins as hydrogen acceptors and amine borane adducts as hydrogen donors

Metal-free transfer hydrogenation of polarized olefins (RR'C=CEE': R, R' = H or organyl, E, E' = CN or CO(2)Me) using amine borane adducts RR'NH-BH(3) (R = R' = H, AB; R = Me, R' = H, MAB; R = (t)Bu, R' = H, tBAB; R = R' = Me, DMAB) as hydrogen donors, were studied by means of in situ NMR spectroscopy. Deuterium kinetic isotope effects and the traced hydroboration intermediate revealed that the double H transfer process occurred regio-specifically in two steps with hydride before proton transfer characteristics. Studies on substituent effects and Hammett correlation indicated that the rate determining step of the H(N) transfer is in agreement with a concerted transition state. The very reactive intermediate [NH(2)=BH(2)] generated from AB was trapped by addition of cyclohexene into the reaction mixture forming Cy(2)BNH(2). The final product borazine (BHNH)(3) is assumed to be formed by dehydrocoupling of [NH(2)=BH(2)] or its solvent stabilized derivative [NH(2)=BH(2)]-(solvent), rather than by dehydrogenation of cyclotriborazane (BH(2)NH(2))(3) which is the trimerization product of [NH(2)=BH(2)].

Time-resolved resonance Raman and density functional theory investigation of iodocyclopropanation and addition reactions with alkenes after ultraviolet photolysis of iodoform.

A time-resolved resonance Raman spectroscopic investigation is reported for the ultraviolet photolysis of CHI(3) in pure cyclohexane and mixed cyclohexane/cyclohexene solvents. The ICHI-I species is observed in pure cyclohexane solvent. Upon addition of cyclohexene, the ICHI-I species lifetime is reduced and new bands from an I(2):cyclohexene complex are observed. Density functional theory computations show that ICHI-I and CHI(2) species have similar barriers of reaction toward addition to the C=C of ethylene. The addition reaction of ICHI-I with ethylene results in formation of an iodocyclopropane and I(2) molecule while addition of.CHI(2) results in initial formation of a diiodopropyl radical intermediate. Ultraviolet photolysis of CHI(3) in the presence of cyclohexene is known to produce a reasonable yield of iodonorcarane product and some addition reaction products. We present a mechanism for the iodocyclopropanation reaction that is consistent with both experimental and theoretical characterization of reaction intermediates formed after ultraviolet photolysis of CHI(3). We briefly discuss the concentration dependence of the time-resolved resonance Raman spectra and photochemistry in relation to the competition between the reaction of the ICHI-I and CHI(2) species with the C=C bond of olefins.

Changes in the hydrogenative ring-opening mechanism of cyclohexene oxide over Cu/SiO2 resulting from the addition of cyclohexene, a major product

The ring-opening mechanism influencing effect of a major product in the cyclohexene oxide–D2 system was investigated over a Cu/SiO2 catalyst. This product is cyclohexene, thus, the hydrogenative ring opening of a 1:1 cyclohexene oxide–cyclohexene mixture was studied in the presence of D2 at 403 K in a closed circulation reactor. It was found that the mechanism of single C–O scission was not affected, but that of the double C–O scission was changed. Simultaneous bond cleavage was the major route of ring opening in the additive-free system and it became consecutive on cyclohexene addition. Added cyclohexene was hydrogenated with a very low rate, but it transformed the surface of the catalyst and, thus, facilitated the change in the mechanism. An explanation concerning the seemingly anomalous lack of deuterium in a product (cyclohexane) not seen in the additive-free system is also suggested.

Studies of Acetylperoxy Radicals Produced by Photolysis of Biacetyl in Aerated Benzene Solutions. Ion-Pair Formation with Tetramethyl-p-phenylenediamine

Spin-trapping studies of the radicals produced by photolysis of biacetyl in degassed benzene confirmed the formation of acetyl radicals as a major product and methyl radicals as a minor one. In aerated benzene, the trapped radicals are ascribed to the acetylperoxy radical yielded by the reaction of the acetyl radical and oxygen. The laser photolysis studies of biacetyl in aerated benzene containing tetramethyl-p-phenylenediamine, TMPD, demonstrate that the acetylperoxy radicals react with TMPD to give the weakly interacting complex which turns to the ion-pair complex with the rate constant 6.7 × 105 s-1. The absorption spectrum of the ion-pair complex resembles that of the cation radical of TMPD. The quantum yield for the formation of the acetylperoxy radicals produced by photolysis of biacetyl in benzene is estimated as 0.41. The addition of cyclohexene and norbornadiene is found to increase the rate for the formation of the ion-pair complex, indicating that the acetylperoxy radicals react with these ole...

Halogenation par voie electrochimique de composes ethyleniques—II. Chloration du cyclohexene dans differents solvants nucleophiles

The electrochemical chlorination of cyclohexene has been studied in the same solvents (acetonitrile, N,N-dimethylformamide, dimethylsulfoxide and methanol) as those previously used for the bromination of this alkene. The oxidation peaks of the chloride ion are modified by addition of cyclohexene in a different way according to the solvent used. The simultaneous formation of mixed compounds with dichlorocyclohexane shows the solvents participation to the nucleophilic attack of the chloronium ion.

Evidence for intermediates involved in Fischer-Tropsch synthesis over Ru

Recent studies of Fischer-Tropsch synthesis over Ru catalysts have suggested that the growth of hydrocarbon chains may involve the addition of methylene groups to either alkylidene or alkyl species present on the catalyst surface. In the present investigation an attempt was made to detect the growing chains by their reaction with an olefin, an approach suggested by recent experiments with metal complexes containing alkylidene or alkyl ligands. The addition of ethylene to the feed of CO and H 2 enhanced the formation of propylene, while the addition of cyclohexene led to the formation of methyl- and ethylcyclohexane and ethyl-, propyl-, and butylcyclohexane. While the observed reaction products did not permit an unambiguous distinction between the two possible surface species, the distribution of products obtained from cyclohexene addition and the influence of cyclohexene on the production of normal alkanes, suggests that the olefin reacts with species involved in chain propagation.

On the kinetics of polymer degradation in solution—III: Pulse radiolysis studies on polyisobutene using the light-scattering detection method

Polyisobutene (PIB) dissolved in saturated hydrocarbons was degraded by irradiation with 2 μs impulses of 15 MeV electrons. The time dependence of the change of light-scattering intensity (LSI) (due to the decrease of molecular weight) was measured. The half life τ 1 2 (LS) of the decrease of LSI was not influenced by the addition of cyclohexene, which on the other hand drastically reduced the extent of degradation, leading to the conclusion that the time of establishing bond scissions in the main chains is much shorter than τ 1 2 (LS) and the latter corresponds to disentanglement diffusion. This is furthermore evidenced by the following experimental findings: τ 1 2 (LS) increases with decreasing PIB concentration, i.e. with decreasing macroviscosity. However, τ 1 2 (LS) increases linearly with increasing microviscosity as shown by measuring τ 1 2 (LS) in different hydrocarbon solutions (C 5-C 16) τ 1 2 (LS) is proportional to M 0.34, i.e. significantly weaker dependence on M̄ than expected for translational diffusion. Thus, it is believed that disentanglement diffusion and translational diffusion may be distinguished. As n-propanol was successively added to n-hexane solutions of PIB. τ 1 2 (LS) increased. indicating that disentanglement diffusion is easier for loosely than for tightly coiled macromolecules.

Hochdruckversuche: Umsetzungen von kohlenstoffdisulfid mit aminen, amiden und olefinen—V

Suitable tertiary amines react with CS 2, 100°C, 10 4 atm to give N,N-disubstituted thioformamides. Salts of dialkyldithiocarbamic acids decompose at the same conditions into dialkylthioformamide and sulphur. After addition of cyclohexene, mainly N,N-dialkyldithiocarbamic acid cyclohexyl ester has been obtained. Carbon disulfide and sulphur add to olefins yielding trithiocarbonates. Dimethyl formamide reacts with CS 2 giving dimethyl thioformamide. Mechanisms are discussed with help of 14CS 2 and 14C-dimethyl formamide.

The gas-phase unimolecular thermal isomerization of pentachlorocyclopropane

The gas-phase thermal isomerization of pentachlorocyclopropane to 1,1,3,3,3-pentachloropropene has been studied in the temperature range 440–490 K at pressures between 10 and 50 Torr. The reaction is of the first order and was unaffected by changes in surface:volume ratio or by the addition of cyclohexene. The rate constants log10k/s–1=(14·16 ± 0·23)–(39,963 ± 500)/4·576T(i) fit the Arrhenius equation (i). The reaction is interpreted as a unimolecular process taking place with chlorine-atom migration through a concerted transition state.

The hydrogen chloride catalysed decomposition of t-butyl isopropyl ether

Hydrogen chloride catalyses the decomposition of t-butyl isopropyl ether at 319-420�. The major products are isobutene and isopropyl alcohol; traces of propene and t-butyl alcohol are formed. The reaction is first order in each reagent and the Arrhenius equation is followed. K2 = 1012.97�0.14exp(-32110 � 400/RT) The rate is not affected by the addition of cyclohexene or by an increase in the surface-to-volume ratio of the reaction vessel. The formation of traces of propene is discussed.

Isomerization of C<sub>8</sub>-Cyclohexanes in the Presence of Aluminum Chloride

Liquid-phase isomerization of ethylcyclohexane, 1, 2-dimethylcyclohexane, 1, 3-dimethylcyclohexane, and 1, 4-dimethylcyclohexane has been investigated at temperatures ranging from 50 to 120°C using aluminum chloride as catalyst. The isomerization reaction takes place producing eight C8-cyclohexane isomers which are in their equilibrium compositions. C8-cyclopentanes are also formed, but they do not exceed 4% of the total isomerization products. Because of the carbonium ion chain mechanism involved, the isomerization is pronouncedly accelerated by the addition of cyclohexene, hexene-1, cyclohexylchloride, and t-butylchloride. Some comments are also given on the values of kinetic parameters of the reaction as well as the apparent reaction order with respect to catalyst concentration.