Michael addition of ethyl acrylate and acetone over solid bases

The catalytic behaviour of the superbases Na/NaOH/-Al₂O₃ and Cs_xO/-Al₂O₃ as well as of the basic zeolites Na/NaX and Cs_xO/CsX were investigated in the Michael addition of ethyl acrylate and acetone. The reactions were carried out in the liquid phase at catalyst loadings varying from 0.05 to 0.1 mol ester/g catalyst.     

Zeolite effect in the enantioselective transhydrogenation over a Co‐salen “ship‐in‐the‐bottle” complex

Our investigations were focused on the transhydrogenation of carbonyl groups using Co(II)‐salen complexes entrapped in zeolites. The Co‐salen 1 complex was occluded in the zeolite as a “ship‐in‐the‐bottle” (SIB) catalyst, as could be demonstrated by means of DRIFT‐IR spectra, DTG, nitrogen adsorption isothermes and soxhlet extraction. The results of the test reactions show that an immobilization of the Co‐salen 1 complex in the zeolite as a “SIB” complex results in an enantiomeric excess as high as in the homogeneous case. The Co‐salen 1 USY SIB catalyst shows its best ee‐value at higher temperature (25°C) than the homogeneous one (-10°C). The reason could be the steric constraints of the Co‐salen complex in the zeolite framework. This revised version was published online in July 2006 with corrections to the Cover Date.     

Epoxidation of propylene and direct synthesis of hydrogen peroxide by hydrogen and oxygen

The autoreduction of palladium–platinum-containing titanium silicalite leads to an effective catalyst for the epoxidation of propylene to propylene oxide by O₂ in the presence of H₂. The one-pot reaction is favoured compared to the two-step reaction path.     

Effect of temperature on the ageing behaviour of unsaturated ester‐based lubricants

The ageing behaviour of trimethylolpropane trioleate was investigated at different temperatures in a modified rotary bomb test apparatus. Some physicochemical properties of ageing oil samples, such as acid value, kinematic viscosity, and iodine value, were measured. The oil samples were analysed using gas chromatography, gas chromatography‐mass spectrometry, and gel permeation chromatography to assess the influence of temperature on the ageing behaviour of ester‐based oils. The results revealed that an increase in temperature could greatly speed up the ageing reaction and increase the formation of decomposition products. However, the degree of oil ageing remained similar when the same quantity of oxygen was consumed.     

Baeyer–Villiger-oxidation of cyclopentanone with aqueous hydrogen peroxide by acid heterogeneous catalysis

Using aqueous hydrogen peroxide containing 30% H₂O₂, solid acid catalysts were compared in their performance as catalysts for the transformation of cyclopentanone to δ-valerolactone. It could be shown that organic ion exchange resins with sulphonic acid groups providing acid functionality are promising catalysts for this reaction. The variation of several reaction parameters was studied in more detail. The obtained results were compared to investigations of zeolites and Nafion^® composite materials.     

Novel zeolitic hosts for “ship-in-a-bottle” catalysts

Modified faujasites have been employed in order to incorporate sterically demanding organometallic complexes such as the Jacobsen catalyst in zeolites X and Y. The new heterogeneous catalysts have been tested in the diastereoselective epoxidation of (R)-(+)-limonene in the liquid phase in an autoclave at elevated pressure using O₂ as the oxidant as well as in a glass reactor at ambient pressure using NaOCl as the oxidizing agent. In both catalytic systems conversions of 100% could be achieved. Selectivities were up to 70% and de values up to 55% in the autoclave experiments whereas in the experiments at atmospheric pressure they remained below 10 and 30%, respectively. This revised version was published online in November 2006 with corrections to the Cover Date.     

Theoretical and experimental study on the selectivity of dehydrogenation of α-limonene in ZSM-5 and zeolite-Y

Dehydrogenation of the natural terpene α-limonene to the industrially important p-cymene was studied over two zeolite-supported Pd catalysts, ZSM-5 and zeolite-Y. Reactor tests indicate that transalkylation of the p-cymene product can be avoided by employing the shape-selective properties of a medium-pore ZSM-5 catalyst. The diffusion properties of the three isomers of cymene were then calculated in the two zeolites using molecular mechanics. In case of ZSM-5, p-cymene was found to have the lowest barrier of the three isomers for diffusion through the straight, spherical channel of the zeolite. For zeolite-Y, differences in diffusivity for the three isomers were very small. Theory and experiments showed, in excellent agreement, that only ZSM-5 selectively produces p-cymene. This work shows that molecular mechanics is a powerful and reliable method for the screening of zeolites for performing shape-selective catalysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dimerization of α-methylstyrene over Nafion/silica composite catalysts

The dimerization of α-methylstyrene (AMS) 1 over highly dispersed strongly acidic ion exchange resins based on Nafion and entrapped in a porous silica matrix has been investigated in the continuous liquid phase. Over these new catalysts the dimerization rate is independent of the choice of solvent, which highlights the increased accessibility of the acid sites. Depending upon the reaction conditions different dimerization products are obtained. Complete conversion is achieved even at very high space velocities. This revised version was published online in July 2006 with corrections to the Cover Date.