Theoretical studies on the butene double bond isomerization catalyzed by 5-H of 1-ethyl-3-methyl-imidazolium fluoride

The isomerization of 1-butene to trans-2-butene catalyzed by 5-H proton of 1-ethyl-3-methyl-imidazolium fluoride (EMImF) has been studied with density functional theory of quantum chemistry. The equilibrium states geometries and transition state geometry are optimized at the levels of B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p), respectively. The apparent activation barrier of isomerization is about 208 kJ/mol theoretically. It indicates that the 5-H proton on the imidazole ring of EMImF has certain catalytic activity to the butene double bond isomerization, which is similar to that of the 4-H proton. According to the data of intrinsic coordinate path, it can be determined that the isomerization is an elementary course and the hydrogen exchange of butene with EMImF is synergetic.     

引发剂对离子液体催化正己烷异构化反应的影响

由无水三氯化铝与盐酸三乙胺按照摩尔比2∶1合成了离子液体2AlCl3/Et3NHCl,并考察了其催化正己烷异构化的反应性能。发现离子液体2AlCl3/Et3NHCl可用于催化正己烷的异构化反应,但所需的反应时间较长。考察了引发剂正丁醇、异丁烯、异丁烷和异戊烷对离子液体催化正己烷异构化反应的影响。发现异戊烷作为引发剂时,正己烷的转化率为84.54%,液体收率为80.08%,异构烷烃的选择性为94.74%,达到了较好的反应效果。引发剂异戊烷的用量对异构化反应有着较大的影响,较优的引发剂用量为30%。添加异戊烷引发剂能明显提高离子液体催化正己烷异构化的反应速度,达到相似反应程度的反应时间可由6h缩短为45min。     

The isomerization of n-butenes catalyzed by RhCl(PPh3)3. II. The isomerization of 1-butene

1-butene is catalytically isomerized by RhCl(PPh₃)₃ in dichloromethane solution. The slow reaction starts with an induction period and reaches the equilibrium distribution of the three n-butenes. The pseudo first order reaction rate, as taken from the second half of the reaction, depends on the square root of the catalyst concentration and the inverse of the concentration of free triphenylphosphine. At relatively low butene concentrations the reaction rates fall off. This is interpreted as meaning that a PPh₃—butene ligand exchange equilibrium is essential for the activation of the catalyst. ³¹P n.m.r. spectroscopy suggested that a trans-RhCl(PPh₃)₂(C₄H₈) complex existed in solution. Because of the high cis-2-butene/trans-2-butene ratio formed at the beginning of the reaction the activation of the olefinic double bond is thought to occur via a π-allyl mechanism.     

Addition of alcohols to isoprene catalyzed by hydrated rhodium trichloride: A way to improve the 1,4-addition regioselectivity

Synthesis of alkoxyolefins from alcohols and dienes can be achieved in the presence of hydrated rhodium trichloride. Because of the probable intermediate formation of π-allylic rhodium complexes, the regioselectivity of the addition varies according to the reaction conditions. Without any additives, the greatest selectivity in 1,4-addition is 53% for a 78% isoprene conversion. In the presence of zinc chloride, 1,4-addition is significantly increased (68% for a 70% conversion).     

Effect of potential shape on isomerization rate constants for the BGK model

As a model for isomerization reactions in liquids, we consider the motion, in a one-dimensional bistable potential, of a particle which suffers BGK collisions. We investigate how the relaxation rate constant as a function of collision frequency depends upon the shape of the potential. We discuss our results in relation to recent high-pressure NMR experiments involving cyclohexane isomerization. For a potential with narrow wells and a wide barrier, we find qualitative agreement between theory and experiment.     

Including anharmonicity in the calculation of rate constants. 1. The HCN/HNC isomerization reaction

A method for calculating anharmonic vibrational energy levels in asymmetric top and linear systems that is based on second-order perturbation theory in curvilinear coordinates is extended to the bound generalized normal modes at nonstationary points along a reaction path. Explicit formulas for the anharmonicity coefficients, x(ij), and the constant term, E0, are presented, and the necessary modifications for resonance cases are considered. The method is combined with variational transition state theory with semiclassical multidimensional tunneling approximations to calculate thermal rate constants for the HCN/HNC isomerization reaction. Although the results for this system are not very sensitive to the choice of coordinates, we find that the inclusion of anharmonicity leads to a substantial improvement in the vibrational energy levels. We also present detailed comparisons of rate constants computed with and without anharmonicity, with various approximations for incorporating tunneling along the reaction path, and with a more practical approach to calculating the vibrational partition functions needed for larger systems.     

Effect of solvent on the rate constants in solution polymerization. Part II. Vinyl acetate

Measurements were made of the value of the lumped kinetic constant k_p/k of vinyl acetate in different solvents and with different initiators. This quantity was evaluated using the well‐known conversion vs. time approach in dilute solutions using both azo‐bis‐isobutyronitrile and benzoyl peroxide (AIBN and BPO), and two different solvents (toluene and ethyl acetate) at 60°C. As was found for butyl acrylate in Part 1 of this series, it was found that the value of the lumped rate constant depends very strongly on the concentration of monomer in solution, decreasing as the solution becomes more and more dilute. However, unlike butyl acrylate, vinyl acetate is much more susceptible to changes in the solvent type, with toluene acting as a severe retarding agent of polymerization. The results of the present study suggest that at least two separate effects of solvent exist simultaneously in the case of vinyl acetate polymerization, and that both of them must be taken into account when attempting to model this type of system. The number‐ and weight‐average molecular weights of the different polymers were also measured, and excellent agreement was found between the measurements and model predictions. A linear relationship was shown to exist between the value of the lumped constant and the square root of the number‐average chain length. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 589–601, 1999     

Activation enthalpies and entropies for the microscopic rate constants of acetate-catalyzed isomerization of 5-androstene-3,17-dione

Both acetic acid and acetate catalyze the isomerization of 5-androstene-3,17-dione (1) to its conjugated isomer, 4-androstene-3,17-dione (3), through a dienol(ate) intermediate. The temperature dependence of the overall isomerization rate constants and of the microscopic rate constants for this isomerization was determined, and the Arrhenius plots give the activation enthalpy and entropy for each step. The source of the activation energy for the overall isomerization and for each of the individual steps is predominantly enthalpic, with a moderate to low entropic penalty. Additionally, the entropy and enthalpy for the keto-enol equilibrium of 1 and dienol were determined; this equilibrium is entirely controlled by enthalpy with no entropic contribution. The relevance of these results to the mechanism of the isomerization of 1 catalyzed by the enzyme 3-oxo-Delta(5)-steroid isomerase is discussed.     

Calculation of the elementary rate constants of polymer-analogous reactions and sequence analysis of products

A method has been developed for the calculation of elementary rate constants of deceleration and acceleration reactions on polymers in which the reactivity of the group is influenced only by the character of the closest adjacent groups. It is suggested that this method may be valid if the calculation yields a rate constant k′₃, which is independent of conversion. In this case, the sequence analysis of products can be performed by using Markovian first-order statistics, and the rate constants thus obtained can be used for calculating the relative frequencies of variously long sequences of reacted and unreacted groups and their number-average length. For markedly accelerated reactions, a simplified method of estimation of the average sequence length involving use of two of the three elementary rate constants, i.e., k₁ and k′₂, has been suggested.     

Effect of substituent in para-substituted anilines on the isomerization rate of 5-vinylbicyclo[2,2,1]hept-2-ene catalyzed by anilinepentacarbonyliron complexes

The isomerization kinetics of 5-vinylbicyclo [2,2,1]-hept-1ene to 5-enthylidenbicyclo [2,2,1] hept-2-ene in the presence of iron pentacarbonyl and parasubstituted anilines has been investigated. The kinetic data correlate with -constants of the substitutes according to Jaffe.

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5- [2,2,1]-2- 5- [2,2,1] -2- - . - .

     

Computation in kinetics, II. Simultaneous regression estimation of rate constants and initial concentrations

The general regression program KILET was used for simultaneous estimation of rate constants and initial concentrations. The method can be used either to improve the quality of fit calculating the possible analytical errors of some initial concentrations of a kinetic experiment or for analytical purposes, i.e. for the determination of analytes, while any side reactions can be taken into account.

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KILET - . - - , - , , .