Cyclohexene

Abstract: Tris(triphenylphosphine)chlororhodium(I), RhCl(PPh3)3, has been prepared by the interaction of an excess of triphenylphosphine with rhodium(III) chloride hydrate in ethanol; the corresponding bromide and iodide are also described. The dissociation of the complex in various solvents has been investigated, and its reactions with hydrogen, ethylene, and carbon monoxide and aldehydes studied. Dihydrido- and ethylene complexes have been isolated and studied by nuclear magnetic resonance (n.m.r.) spectroscopy. Approximate values for the formation constants of ethylene and propylene complexes have been obtained; the latter is lower by a factor of over 103. By electron spin resonance spectroscopy, the complex RhCl(PPh3)3 has been shown to contain trace amounts of a paramagnetic species, probably a rhodium(II) complex.In homogeneous solution the tris(triphenylphosphine) complexes are exceedingly active catalysts for the rapid and homogeneous hydrogenation, at ca. 1 atmosphere of hydrogen pressure and room temperature, of unsaturated compounds containing isolated olefinic and acetylenic linkages.The rates of hydrogenation of hept-1-ene, cyclohexene and hex-1-yne have been studied quantitatively and the dependence on factors such as substrate and catalyst concentration, temperature, and pressure determined. The data can be accommodated by a rate expression of the form: Rate =Kp[S][A]//1 +K1p+K2[S] where [S] and [A] are the olefin and catalyst concentrations, respectively, and p is the concentration of hydrogen in solution.From the data for cyclohexene the activation energy for the rate determining step is Ea= 22·9 kcal. mole–1(ΔH‡= 22·3 kcal. mole–1) and the value of ΔS‡= 12·9 e.u.It is shown that the rate of hydrogen–deuterium exchange under selected conditions is quite slow compared with the rates of hydrogenation of olefins and, furthermore, that when H2–D2 mixtures are used in the reactions, alkanes and dideuteroalkanes are the major products. Reductions of maleic and fumaric acids with deuterium shows that cis-addition occurs preferentially. Similarly, in the reduction of hex-2-yne to n-hexane, cis-hex-2-ene is found to be the major olefin intermediate.A mechanism for the hydrogenation is proposed in which the metal complex serves as a template to which a hydrogen molecule and an olefin molecule are briefly co-ordinated before transfer of one to the other takes place. The low kinetic isotope effect (rate H2/rate D2= 0·9) suggests that synchronous breaking of Rh–H bonds and making of C–H bonds takes place in the transition state involving two simultaneous three-centre interactions.

Abstract: Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.

Abstract: The reaction of 1-n-butyl-3-methylimidazolium chloride (BMIC) with sodium tetrafluoroborate or sodium hexafluorophosphate produced the room temperature-, air- and water-stable molten salts (BMI+)(BF4−) (1) and (BMI+)(PF6−) (2), respectively, in almost quantitative yield. The rhodium complexes RhCl(PPh3)3 and [Rh(cod)2][BF4] are completely soluble in these ionic liquids and they are able to catalyse the hydrogenation of cyclohexene at 10 atm and 25°C in a typical two-phase catalysis with turnovers up to 6000.

Abstract: The epoxidation of lower olefins, catalysed by titanium silicalite (TS-1) under mild conditions, is reported. The reaction may be performed at near room temperature, in dilute alcoholic or aqueous solutions of hydrogen peroxide. In methanol C 4 -C 8 linear olefins, allyl chloride, and allyl alcohol show fast reaction rates and high selectivities (72-97% on H 2 O 2 ). The solvolysis of the oxirane ring and the oxidation of the solvent are the main side reactions. Yields and kinetics are decreased by increasing the chain length or the cross-section of the olefin ( n -C n > n -C n +1 , 1-hexene ⪢ cyclohexene), by electron-withdrawing substituents (1-butene > allyl chloride > allyl alcohol), and by solvents in the order methanol > ethanol > t -butanol. The rate of reaction also depends on the position and steric configuration of the double bond and on the branching, as a result of inductive and shape selectivity effects: trans 2-butene cis 2-butene, 2-methyl-1-butene

Abstract: Currently, the industrial production of adipic acid uses nitric acid oxidation of cyclohexanol or a cyclohexanol/cyclohexanone mixture. The nitrous oxide emission from this process measurably contributes to global warming and ozone depletion. Therefore, the development of an adipic acid production process that is less damaging to the environment is an important subject in chemical research. Cyclohexene can now be oxidized directly to colorless crystalline adipic acid with aqueous 30 percent hydrogen peroxide under organic solvent- and halide-free conditions, which could provide an ideal solution to this serious problem.