Cyclohexene kinetics

No results have yet been reported for the kinetics of the pyrolysis of vinylcyclobutane though there is some indirect evidence that one of the reaction paths would yield cyclohexene. Kinetic results are available for isopropenylcyclobutane and by analogy with cyclopropane systems the behaviour of this compoimd should be very similar to vinylcyclobutane. It has been reported (Ellis and Frey, 1963) that the pyrolysis of isopropenylcyclobutane gives rise to ethylene, isoprene and 1-methyl-cyclohexene. These products arise by two simultaneous first-order processes which are both homogeneous ... 

Ru(NO)(EDTA) is made from K[RuCl(EDTA.H)] and NOCl, and was characterised by IR, ESR and electronic spectroscopy. The system Ru(NO)(EDTA)/Oj or PhlO/aq. EtOH oxidised 1-hexene to 2-hexanone and epoxidised cyclohexene kinetic data were measured and 0-substimtion shows that the oxygen atom in the products derives from the [783],... 

Decomposition of more complex diaziriries follows first order kinetics also. Chlorophenyl-carbene adds to cyclohexene to give a norcarane derivative. Substituent effects of m-Cl, m-NOa or m-Me groups, as well as solvent effects, are small. Chlorotrichloromethyldiazirine yields tetrachloroethylene chlorocyclooctyldiazirine also leads to an alkene 74CJC246). 

Among the cases in which this type of kinetics have been observed are the addition of hydrogen chloride to 2-methyl-1-butene, 2-methyl-2-butene, 1-mefliylcyclopentene, and cyclohexene. The addition of hydrogen bromide to cyclopentene also follows a third-order rate expression. The transition state associated with the third-order rate expression involves proton transfer to the alkene from one hydrogen halide molecule and capture of the halide ion from the second ... 

The simultaneous determination of a great number of constants is a serious disadvantage of this procedure, since it considerably reduces the reliability of the solution. Experimental results can in some, not too complex cases be described well by means of several different sets of equations or of constants. An example would be the study of Wajc et al. (14) who worked up the data of Germain and Blanchard (15) on the isomerization of cyclohexene to methylcyclopentenes under the assumption of a very simple mechanism, or the simulation of the course of the simplest consecutive catalytic reaction A — B —> C, performed by Thomas et al. (16) (Fig. 1). If one studies the kinetics of the coupled system as a whole, one cannot, as a rule, follow and express quantitatively mutually influencing single reactions. Furthermore, a reaction path which at first sight is less probable and has not been therefore considered in the original reaction network can be easily overlooked. 

This is the same case with which in Eqs. (2)-(4) we demonstrated the elimination of the time variable, and it may occur in practice when all the reactions of the system are taking place on the same number of identical active centers. Wei and Prater and their co-workers applied this method with success to the treatment of experimental data on the reversible isomerization reactions of n-butenes and xylenes on alumina or on silica-alumina, proceeding according to a triangular network (28, 31). The problems of more complicated catalytic kinetics were treated by Smith and Prater (32) who demonstrated the difficulties arising in an attempt at a complete solution of the kinetics of the cyclohexane-cyclohexene-benzene interconversion on Pt/Al203 catalyst, including adsorption-desorption steps. 

The quantitative solution of the problem, i.e. simultaneous determination of both the sequence of surface chemical steps and the ratios of the rate constants of adsorption-desorption processes to the rate constants of surface reactions from experimental kinetic data, is extraordinarily difficult. The attempt made by Smith and Prater 82) in a study of cyclohexane-cyclohexene-benzene interconversion, using elegant mathematic procedures based on the previous theoretical treatment 28), has met with only partial success. Nevertheless, their work is an example of how a sophisticated approach to the quantitative solution of a coupled heterogeneous catalytic system should be employed if the system is studied as a whole. 

The unreactivity of cyclohexene (Section II.A) may be explained by the fact that in this case the ring strain of the dimer is much higher than that of the monomer. The observation that cyclohexene can be a reaction product [Eq. (8)] supports the assumption that thermodynamic rather than kinetic limitations prevent cyclohexene from polymerizing. Calderon and Ofstead (24, 100) have observed that bicyc o-[2.2.2]2-octene can be polymerized via ring opening ... 

Models of this type were used successfully in the interpretation of the kinetic data of Maennig and Kolbel as well as of kinetic data obtained for the hydrogenation of a-methylstyrene and cyclohexene. 

What concerns us here are three topics addressing the fates of bromonium ions in solution and details of the mechanism for the addition reaction. In what follows, we will discuss the x-ray structure of the world s only known stable bromonium ion, that of adamantylideneadamantane, (Ad-Ad, 1) and show that it is capable of an extremely rapid degenerate transfer of Br+ in solution to an acceptor olefin. Second, we will discuss the use of secondary a-deuterium kinetic isotope effects (DKie) in mechanistic studies of the addition of Br2 to various deuterated cyclohexenes 2,2. Finally, we will explore the possibility of whether a bromonium ion, generated in solution from the solvolysis of traAU -2-bromo-l-[(trifluoromethanesulfonyl)oxy]cyclohexane 4, can be captured by Br on the Br+ of the bromonium ion, thereby generating olefin and Br2. This process would be... 

Where Br nucleophilically promotes the Br+/OTf- elimination to generate free Br2 and cyclohexene. This process requires that the rate of solvolysis of 4 be linearly dependent on [Br ]. However, control (ref. 15) kinetics experiments indicate that the rate constant for solvolysis of 4 in HOAc or MeOH are independent of Br" thus generation of free Br2 must occur after the rate limiting step. This nicely confirms the previous conclusion based upon the invariance of the n0a+10hV9h ratio on [Br]. 

In the present study, the HDN of decahydroq unohne (DHQ) was studied over NiMo(P)/Al20.T catalysts in the presence and absence of H2S. The reaction took place at 593 K and 3.0 MPa, thus allowing us to observe the most important reaction intermediate, propylcyclohexylamine, and to calculate the kinetic constants from the experimental results. Rate and adsorption constants for the different reaction steps were determined by separate and by combined HDN studies of DHQ and cyclohexene. 

The cyclohexene hydrogenation is a well-studied process especially in conventional trickle-bed reactors (see original citations in [11,12]) and thus serves well as a model reaction. In particular, flow-pattern maps were derived and kinetics were determined. In addition, mass transfer can be analysed quantitatively for new reactor concepts and processing conditions, as overall mass transfer coefficients were determined and energy dissipations are known. In lieu of benchmarking micro-reactor performance to that of conventional equipment such as trickle-bed reactors, such a knowledge base facilitates proper, reliable and detailed comparison. 

GL 16] [R 12] [P 15] As excess of cyclohexene was used, the kinetics were zero order for this species concentration and first order with respect to hydrogen [11]. For this pseudo-first-order reaction, a volumetric rate constant of 16 s was determined, considering the catalyst surface area of 0.57 m g and the catalyst loading density of1g cm. ... 

Using the titanocene-catalyzed co-hydrogenation of cyclohexene, we have studied the kinetics of the polymerization of a number of primary silanes ( 20 ). The rate law was found to be ... 

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

The stoichiometry and kinetics of gas phase epoxidation of cyclohexene by silica-supported Ti(0 Pr)4 upon treatment with /< r/-butyl hydro peroxide were the... 

Metal-modified silicas were exposed to excess BuOOH vapor in order to generate the supported feri-butylperoxide complexes, followed by evacuation to remove PrOH and unreacted BuOOH. Reaction kinetics were monitored as the uptake of cyclohexene from the gas phase, using a ThermoNicolet Nexus FTIR spectrometer to measure the intensity of the o(C=C) mode. In situ spectra were recorded in custom-made glass reactors under vacuum. Formation of cyclohexene oxide was confirmed by GC/MS on an HP 6890 equipped with a DBI capillary column (J W Scientific). 

The kinetics of epoxidation were measured in situ as the rate of uptake of olefin by the catalyst, since the epoxide product remains adsorbed on the catalyst surface in the absence of solvent. Addition of 2 Torr cyclohexene vapor (30 pmol) to a 14.2 mg sample of 3 (9.0 pmol Ti, 4.5 pmol V) at room temperature resulted in the loss of the o(C=C) mode in the gas phase IR spectrum over the... 

The catalyst can be regenerated by evacuation to remove cyclohexene oxide and addition of fresh BuOOH at the end of the first kinetic run. When a second dose of cyclohexene vapor was introduced to 3, very similar kinetic behavior was observed, Figure lb. However, the smaller absorbance change imphes that less cyclohexene was epoxidized, likely because of incomplete removal of the epoxide which blocks the active sites. 

As mentioned above, V(0 Pr)3-modiricd silica treated with BuOOH shows no activity towards cyclohexene at room temperature. However, the material obtained by grafting Ti(0 Pr)4 directly on unmodified silica heated at 500°C, eq 4, does convert olefins to their epoxides upon treatment with BuOOH. The catalyst 4 also shows biphasic kinetic behavior towards cyclohexene, Figure lc. 

Dvorko and Shilov [Kinetics and Catalysis, 4 (212), 1964] have studied the iodine catalyzed addition of HI to cyclohexene in benzene solution. 

Bennet, P.J., Harris, S.J., Kerr, J. A. (1987) A reinvestigation of the rate constants for the reactions of ozone with cyclopentene and cyclohexene under atmospheric conditions. Int. J. Chem. Kinet. 19, 609-614. 

The formation of multinuclear clusters is much more favorable for rhodium than for cobalt. Additional evidence was obtained in comparative hydroformylation rate studies of 1-heptene and of cyclohexene at 75°C and 150 atm 1/1 H2/CO (19). For the acyclic olefin the kinetics followed the kinetic expression (except at low olefin) ... 

In the case of cyclohexene, no change was noted in the initial spectrum of Rh4(CO)12 at temperatures below 100°C and not too long reaction times. This agrees with the kinetic data in that the reaction of the olefin with HRh(CO)3 is the rate-limiting step with this less reactive olefin, and that the HRh(CO)3 is in equilibrium with Rh4(CO)12. At higher temperatures and/or longer reaction times, Rh6(CO)16 was seen in the infrared spectrum and the reaction was slower. The thermodynamically favored cluster under these conditions is Rh6(CO)16, and the equilibrium would be less favorable for formation of HRh(CO)3. 

The hydrogens within the octahedral olefin-dihydride intermediate are transferred consecutively with overall cis addition, and the rate-determining step (k9) is olefin insertion to give the alkyl- hydride. Kinetic and thermodynamic parameters for nearly all the steps of Fig. 1 have been estimated for the cyclohexene system. Because the insertion reaction is generally believed to require a cis disposition of the hydride and olefin... 

Kinetic data on cyclohexene hydrogenation catalyzed by RhClL species (n = 1, 2, or 3 L = p-dimethylaminophenyl phosphines) were interpreted in terms of active dimer catalysts (cf. 1), possibly involving coordination through nitrogen as well as phosphorus (82). 

The cyclohexadienyl radicals decay by second-order kinetics, as proven by the absorption decay, with almost diffusion-controlled rate (2k = 2.8 x 109 M 1 s 1). The cyclohexyl radicals 3 and 4 decay both in pseudo-first-order bimolecular reaction with the 1,4-cyclohexadiene to give the cyclohexadienyl radical 5 and cyclohexene (or its hydroxy derivative) (equation 15) and in a second order bimolecular reaction of two radicals. The cyclohexene (or its hydroxy derivative) can be formed also in a reaction of radical 3 or... 

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