Darren F. Lee

Epoxidation of allyl alcohol to glycidol using titanium silicalite TS-1: effect of the method of preparation

The epoxidation of allyl alcohol with hydrogen peroxide catalysed by the microporous titanium silicalite TS-1 has been investigated with respect to the effect of the method of catalyst preparation. Three methods of TS-1 synthesis have been studied using the standard tetrapropyl-ammonium cation as template (i) using tetraethyl orthosilicate, tetraethyl orthotitanate as reagents, (ii) using a fluoride method and (iii) using tetrabutyl orthotitanate as the titanium source. The TS-1 samples were characterised by electron microscopy, X-ray diffraction and infrared spectroscopy. The method of preparation controlled the morphology of the TS-1 crystals and in particular the crystallisation time was found to be an important parameter. Data are presented that correlate the activity for the epoxidation of allyl alcohol with the morphology of TS-1. In addition it is found that the catalytic activity of TS-1 for this reaction is not related to the intensity or presence of the infrared absorption band at ca. 960 cm−1.

Epoxidation of allyl alcohol to glycidol using titanium silicalite TS-1 : effect of the reaction conditions and catalyst acidity

The epoxidation of allyl alcohol to glycidol using the titanium silicalite TS-1 with hydrogen peroxide as the oxidant is described and discussed in detail. The reaction conditions (alcohol, solvent, temperature) required to obtain 100% selectivity to glycidol are described and this selectivity has been observed at conversions of allyl alcohol of up to 20%. Addition of excess hydrogen peroxide enhances conversion but does not appear to affect selectivity to glycidol deleteriously, whereas addition of hydrogen peroxide over an extended time period is not particularly beneficial. The major side reactions are the oxidation of the alcohol solvent and the ring opening solvolysis of the glycidol that leads to the formation of alkoxy diols. Base treatment of the TS-1 using sodium azide enhances the glycidol selectivity, whereas the incorporation of Brønsted acid sites by addition of aluminium into the framework structure of TS-1 enhances the selectivity to the products of solvolysis ring opening reactions.

Acetone conversion to isobutene in high selectivity using zeolite β catalyst

The catalytic activity of the proton forms of zeolite β and ZSM-5 are compared for the conversion of acetone. Zeolite β demonstrates markedly enhanced selectivity to isobutene and selectivities of >80% can be achieved for conversions up to 65%. In contrast high selectivities to isobutene with ZSM-5 can be attained only at very low conversions (≤5%).

Oxidation of thioethers and sulfoxides with hydrogen peroxide using TS-1 as catalyst

A combined experimental and molecular simulation study of the oxidation of thioethers with hydrogen peroxide using Ti-containing zeolites as catalysts is described and discussed. Two aspects of reaction selectivity were explored. First, regioselectivity was studied for the oxidation of allyl methyl thioether with TS-1 as catalyst, and only products for the oxidation at sulfur, i.e., the sulfoxide and sulfone, were observed. Second, shape-selective oxidation was studied using four isomeric butyl methyl thioethers. For n-, iso- and sec-butyl methyl thioethers the dominant product in the TS-1 catalysed reaction was the sulfone, but for tert-butyl methyl thioether, the dominant product was from partial oxidation to the sulfoxide. Molecular simulations were used to investigate the origin of this effect. For all substrates used in this study, the oxidation of the thioether to the sulfoxide was found to occur readily by a non-catalysed solution reaction and this was studied in detail. However, the oxidation of the sulfoxide to the sulfone was only observed in the catalysed reactions. It was observed that the non-catalysed reaction can be suppressed by carrying out the catalysed reaction in the presence of a base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), that is too large to diffuse into the intracrystalline pore structure of TS-1. In the presence of DBU, the rate of reaction with TS-1 as catalyst was much lower and the relative ratios of the sulfoxide and sulfone products can be explained through a combination of intramolecular steric hindrance and the shape selectivity of the zeolite.

Heterogeneous aziridination of alkenes using Cu2+ exchanged zeolites

Abstract Copper-exchanged zeolite Y (CuHY) is found to be a highly effective heterogeneous catalyst for the aziridination of alkenes using ( N -( p -tolylsulfonyl)imino)phenyliodinane (PhI=NTs) as the nitrogen source: Download full-size image Exchange of zeolite Y with other cations (Ag + , Co 2+ , Fe 3+ , Mg 2+ , Ni 2+ , Zn 2+ ) was found to be ineffective and the yield of the aziridine was lower than that obtained if no catalyst was present. This is considered to be due to the ability of these metals to catalyze the breakdown of the PhI=NTs reagent into iodobenzene and toluene sulfonamide. Modification of the CuHY catalyst with bis(oxazolines) leads to the preparation of the first heterogeneous enantioselective aziridination catalyst and the results showing the effect of temperature and modifier concentration are described and discussed. The optimum reaction conditions for the aziridination of styrene are found to be using acetonitrile solvent at −10°C with a Cu 2+ : bis(oxazoline) ratio of 2:1, and under these conditions, e.e. of 34–35% have been observed. The catalyst can be recovered and reused without significant loss of catalyst performance.

Methanol conversion to hydrocarbons over zeolite H-ZSM-5 : comments on the formation of C4 hydrocarbons at low reaction temperatures

Abstract Pulsed flow microreactor studies are described for the methanol conversion reaction. The reactor is incorporated into a standard gas Chromatograph injector and this system enables complete analysis of the products exiting the reactor to be made for each pulse. It is found that the carbon mass balance for the pulse studies are low for microporous zeolites and that it is unsafe to use such a technique to investigate the nature of the initially desorbed reaction products. Experiments at 112°C using 1 μl pulses of liquid methanol demonstrate that a C 4 hydrocarbon is formed in trace amounts for the initial two pulses (equivalent to 1 methanol per aluminium atom). However, this effect is not observed for subsequent pulses and it is considered to be the product of a non-catalytic reaction. Pretreating the zeolite with ethanol is found not to enhance this effect and no hydrocarbons are observed in similar experiments using SAPO-34. Possible mechanisms for the low-temperature formation of C 4 hydrocarbon products are discussed.

Catalytic heterogeneous aziridination of alkenes using microporous materials

Copper-exchanged zeolite Y is a highly active catalyst for the aziridination of alkenes; modification using bis(oxazolines) leads to preparation of the first heterogeneous enantioselective aziridination catalyst.

Shape selective epoxidation of crotyl alcohol with H2O2 in the presence of TS-1

Publisher Summary The use of alcohols as solvents was investigated for allyl and cis- and trans-crotyl alcohols; methanol was found to be the best solvent for allyl alcohol and ethanol for crotyl alcohol. However, the reaction was possible, using water as solvent, without loss of selectivity of the oxirane, because of triol formation at short reaction times (1–3 h). A number of studies have demonstrated that alkenes can be readily epoxidised by hydrogen peroxide, using the titanium silicalite TS-1. However, it has been found that substitution of the alkene by electron withdrawing groups significantly decreases the reactivity of the carbon–carbon double bond, because the decrease of the electron density renders it less susceptible to electrophilic attack by the oxidant. Although TS-1 has been investigated for the epoxidation of a range of molecules, for example, butene, pentene, hexene, allyl chloride, and allyl alcohol, little attention has been given to the effect of shape selectivity in the MFI zeotype framework in these reactions. In this paper, it is possible to address this aspect and exemplify the shape selective epoxidation, using a range of allylic alcohols. In particular, the shape selective epoxidation of crotyl alcohol is compared and contrasted with the reaction of allyl alcohol in a range of solvents.

Selective conversion of allyl alcohol to oxygenates and hydrocarbons using ion exchanged zeolite Y

The reaction of allyl alcohol using zeolite Y as catalyst has been investigated and it is shown that it can be converted into a range of products, including hydrocarbons, acrolein and diallyl ether. Control of product selectivity can be achieved by careful selection and manipulation of the charge balancing cation, a series of catalysts can be prepared which, for the conversion of allyl alcohol, lead almost exclusively to the initial formation of either (a) C2-C6 hydrocarbons and coke (H-NaY), (b) acrolein (H-CsY), (c) propene (Li-NaY) or (d) diallyl ether (Cs-NaY). The effects of addition of H2 and H2O to the reactant are described and discussed with respect to the reaction mechanism and the reaction of potential intermediates (2-propanol and propene oxide) is also described. Mechanisms of formation of the major products are proposed that involve the concerted action of Brønsted acid and basic sites within the zeolite. In particular, since the addition of H2O does not affect the product distribution, it is considered that the mechanism of hydrocarbon formation does not involve the allyl cation as an intermediate.

A combined MAS nuclear magnetic resonance spectroscopy, in situ FT infrared spectroscopy and catalytic study of the conversion of allyl alcohol over zeolite catalysts

A combined study of allyl alcohol conversion over zeolite catalysts using catalytic measurements in a flow microreactor, in situ FTIR and MAS NMR spectroscopy is reported. Rate constants for the conversion in the flow reactor and the static in situ reactor used in the FTIR studies are in broad agreement, emphasising the viability of the experimental approach. In the flow microreactor allyl alcohol conversion over the zeolite catalyst is shown to form diallyl ether, hydrocarbons and acrolein. The in situ study successfully models the formation of diallyl ether and hydrocarbon as initial reaction products, but unfortunately acrolein is found to be rapidly converted to hydrocarbons under the condition used in the in situ cells. The studies are combined to provide a model for the reaction which involves two parallel pathways for the formation of the hydrocarbons and acrolein.