Cyclohexene experimental results

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. 

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. 

Mechanistic and theoretical studies of the Diels-Alder reaction have resulted in the characterization of this reaction as a concerted, although not necessarily synchronous, single-step process28-31 45. The parent reaction, the addition of 1,3-butadiene to ethylene yielding cyclohexene, has been the subject of an ongoing mechanistic debate. Experimental results supported a concerted mechanism, whereas results from calculations seemed to be dependent on the method used. Semi-empirical calculations predicted a stepwise mechanism, whereas ab initio calculations were in favor of a concerted pathway. At the end of the 80s experimental and theoretical evidence converged on the synchronous mechanism29-31. 

Cyclohexene. The experimental results are summarized in Table IV. The product ratios are similar for CH2 generated by CH2N2 photolysis and by CH2N2 pyrolysis at 265°C., but for CH2 generated by the benzophenone-photosensitized decomposition of CH2N2 the addition product norcarane is favored. 

Figure 2. Experimental results of cyclohexene epoxidation with H202 over Ti-MCM-41 catalysts ( ) TM-1 ( ) TM-2 (a) TM-3.

Based on the experimental results, one can propose a reaction mechanism for epoxidation of cyclohexene over Ti-beta and Ti-MCM-41 as follows ... 

We know of no experimental measurements for the enthalpy-of-formation difference of (Z)- and ( )-cycloheptene or cyclohexene. Admitting for now the 1-phenyl derivative, the (Z)-/(E)-differences are 56, 121 and 197 kJ mol-1 for the substituted cyclooctene, cycloheptene and cyclohexene. [These results derived from photoacoustic calorimetric measurements were reported... 

Based on the experimental results, a conclusion is that the present TPPMn-NaBH4-02 reaction with cyclohexene proceeded mostly through formation of a potent oxidizing species (X). 

Attempts to trap dimethylcarbene by photolysis of the 3,3 -dimethyl-diazirine in cyclohexene in the liquid phase were unsuccessful. The evidence for the intermediacy of this carbene thus rests entirely on the analogy of this decomposition with other similar systems. The experimental results obtained can be accounted for equally well if it is assumed that the excited propylene molecules are formed directly from the di-methyldiazirine after the absorption of light. 

Further applications of TPSC have been attempted in the hydroformylation of cycloolefins, cyclohexene being a model substrate (Eq. 1). The experimental results indicate that the catalytic activity of PETPP/Rh complex is higher than that of the... 

The examination of the experimental results presented in Fig. 4 (b) shows an enhancement of cyclohexene selectivity by using of the catalyst C6 with shorter pores. This is an evidence for the fact that short pores suppress the successive reactions of cyclohexene. The potential of the egg-shell catalysts with tailor-made pore structure can be further improved by their assembling in microchannel reactors. The good thermal conductivity of the metallic substrate... 

Several additions have been kinetically studied by more than one research group, but most of them were studied in solution and different workers used different solvents, so that the published data cannot be compared for reproducibility, Such a difficulty does not arise for reactions in the gas and in the pure liquid phases. Two popular Diels-Alder reactions, the dimerisation of cyclopentadiene to endo-dicyclopentadiene and that of butadiene to 4-vinyl-cyclohexene are suitable for a comparison of experimental results. Rate coefficients from 8 different sources for the former reaction in the pure liquid phase at various temperatures (in the range where comparison is possible) are given in Table 2. The coefficients are all extrapolated to zero time, as both secondary reactions and variation of the environment during the reaction cause a drift in the observed values of k. Rate coefficients for butadiene dimerisation in the gas phase, from different sources, are collected in Table 3. In this case also the temperature range has been limited to that where comparison is possible. In both Tables 2 and 3 activation parameters, as given by the authors (unless otherwise indicated) are also listed. 

The proposed reaction mechanism involves initially the activation of cyclohexenone by the thiourea group and subsequently a Michael addition of the tertiary amine at the p-position. The resulting enolate intermediate attacks the aldehyde performing an aldol reaction. Finally, a retro-Michael addition releases the catalyst to afford the product (Scheme 19.22). This mechanism supports the experimental results of the authors diethyl analogue 16b showed similar enantioselectivities, but significant lower yield for the reaction between 2-cyclohexen-l-one and 3-phenylpropionaldehyde, presumably because of the difficulty of the amine to perform the Michael addition due to confined space in the presence of the more flexible ethyl substituents. 

Experimental results and theoretical analyses have enabled rational predictions for the regiochemical preferences in Diels-Alder reactions. Known as the ortho, para rule, the strongest electron donating group on the diene ends up either ortho (1,2) or para (1,4) to the strongest electron-withdrawing group on the dienophile in the final cyclohexene product. For example, combination of isoprene (7) with methyl acrylate (8) yields mostly para product 9, while reaction of 8 with 1-methylbutadiene 11 furnishes ortho cyclohexene 12 as the major product. As shown in these cases, formation of mixtures is common under thermal conditions. ... 

The presence of ascorbic acid as a co-substrate enhanced the rate of the Ru(EDTA)-catalyzed autoxidation in the order cyclohexane < cyclohexanol < cyclohexene (148). The reactions were always first-order in [H2A]. It was concluded that these reactions occur via a Ru(EDTA)(H2A)(S)(02) adduct, in which ascorbic acid promotes the cleavage of the 02 unit and, as a consequence, O-transfer to the substrate. While the model seems to be consistent with the experimental observations, it leaves open some very intriguing questions. According to earlier results from the same laboratory (24,25), the Ru(EDTA) catalyzed autoxidation of ascorbic acid occurs at a comparable or even a faster rate than the reactions listed in Table III. It follows, that the interference from this side reaction should not be neglected in the detailed kinetic model, in particular because ascorbic acid may be completely consumed before the oxidation of the other substrate takes place. 

Table 4 shows that benzene is formed at almost identical rates from cyclohexene, hexadiene, methylcyclohexene and cyclohexadiene react under low partial pressure over Ga-HZSM-5. which suggests that over these catalysts benzene is formed from the same intermediate. In contrast over H-ZSM-5, under identical experimental conditions, the rate of benzene formation from the hydrocarbons cited was one to two orders of magnitude lower. These results prove again that gallium plays a decisive role in aromatization. Over H-ZSM-5 the major hydrocarbon formed is methylcyclopentene from cyclohexene (ring contraction)... 

Although it is generally accepted that the exo approach to norbomene is favored over the endo, the magnitude of the AAE is rarely measurable experimentally unless some fraction of the endo product can be detected. The exo approach to norbomene is favored over the endo orientation by nearly 3 kcalmol for both PFA and DMDO, while the exo TS for benzonorbomadiene is favored by nearly 5 kcalmol (Figure 27). The preferred exo approach does not appear to result from steric interactions. It is of particular interest that the AE for norbomene is only 0.9 kcalmol greater than that for cyclohexene despite the SE = 19.2 kcalmol" for the strained bicyclic alkene. Thus, in the absence of twist-strain we observe little rate enhancement due to strain energy. 

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