J.C. van der Waal

Zeolite titanium beta as a selective catalyst in the epoxidation of bulky alkenes

Abstract The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide. The Ti-beta catalyst is compared with TS-1, Ti,Al-beta and Ti-MCM-41 in the epoxidation of 1-octene and norbornene. The advantage of the larger pore size of Ti-beta is illustrated by the facile epoxidation of norbornene in which TS-1 displayed no activity. Rate differences in the epoxidation of terminal or internal alkenes are very small for Ti-beta, indicating that the Ti-site is rather spacious. The catalytic properties of Ti-beta were further investigated in the epoxidation of bulky alkenes such as cyclohexenes, cyclic terpenes and allylic alcohols. Ti-beta was found to catalyze the epoxidation of a wide variety of alkenes with aqueous hydrogen peroxide. In the epoxidation of linear alkenes two trends were observed. The lower alkenes were epoxidized fastest and the internal alkenes were slightly faster than the alkenes with a terminal double bond. The reactivity of methylenecyclohexane is about twice that of 1-methylcyclohexene. Based on electronic effects of substituents the reverse order would be expected, which suggests that here steric effects at the titanium site can play a dominant role in determining reactivity. Pronounced electronic effects were observed to be more important in the epoxidation of allylic alcohols: more highly substituted allylic alcohols are more reactive, whereas the reactivity of the substrates bearing a terminal, unsubstituted double bound is over an order of lower magnitude.

Synthesis of aluminium free titanium silicate with the BEA structure using a new and selective template and its use as a catalyst in epoxidations

The aluminium free titanium silicate analogue of zeolite beta is synthesized using di(cyclo-hexylmethyl)dimethylammonium as the template. The zeolite is characterized using XRD, DREAS and IR spectroscopy and evidence is obtained for the isolated incorporation of titanium in the zeolite lattice. The catalytic potential of Ti-beta is shown by the facile epoxidation of bulky olefins like norbornene and α-terpineol with aqueous hydrogen peroxide. The Ti-beta catalyst is compared with TS-1, Ti,Al-beta and Ti-MCM-41. In contrast to TS-1 and Ti-MCM-41, the Ti-beta has acidic properties when alcohols are applied as the solvent. This is explained by a higher lewis acid character of the titanium site in Ti-beta, which on coordination of an alcohol yields a Bronsted acid site.

Beta-type zeolites as selective and regenerable catalysts in the Meerwein-Ponndorf-Verley reduction of carbonyl compounds

Zeolite Beta, in the Al–form as well as in the Al–free, Ti–containing form, appears to be a selective and regenerable catalyst in the Meerwein–Ponndorf–Verley and Oppenauer (MPVO) reactions. In the liquid–phase MPV reduction of 4–tert–butylcyclohexanone with secondary alcohols, both catalysts display a high stereoselectivity to cis–4–tert–butylcyclohexanol, the isomer of industrial relevance. This stereoselectivity can be explained by considering the two transition states inside the pores of zeolite Beta. By using (S)–2–butanol as the reductant enantioselective reduction of phenylacetone was observed. 4–methylcyclohexanone was studied as the substrate in the gas–phase MPV reduction. Catalyst deactivation is much more pronounced with the acidic Al–Beta catalyst than with the non–acidic Ti–Beta.

Molecular Sieves, Multifunctional Microporous Materials in Organic Synthesis

Zeolites and molecular sieves are microporous materials with an increasing number of applications. Established applications of molecular sieves are in the field of oil refining processes, selective adsorption and ion exchange. Nowadays, zeolites come to the fore as clean, selective and recyclable catalysts in petrochemistry, e.g., in aromatic alkylation. Zeolites are considered to have a high potential for the synthesis of commodities and fine chemicals due to their molecular sized pores. Nevertheless, only a few commercial applications in fine chemical synthesis are known. Based on the essential criteria, extracted from the organic reaction under consideration, some of the potential pitfalls in selecting and screening zeolites as potential catalysts are discussed.Zeolites and molecular sieves are microporous materials with an increasing number of applications. Established applications of molecular sieves are in the field of oil refining processes, selective adsorption and ion exchange. Nowadays, zeolites come to the fore as clean, selective and recyclable catalysts in petrochemistry, e.g., in aromatic alkylation. Zeolites are considered to have a high potential for the synthesis of commodities and fine chemicals due to their molecular sized pores. Nevertheless, only a few commercial applications in fine chemical synthesis are known. Based on the essential criteria, extracted from the organic reaction under consideration, some of the potential pitfalls in selecting and screening zeolites as potential catalysts are discussed.

Meerwein-Ponndorf-Verley and Oppenauer reactions catalysed by heterogeneous catalysts

Summary Meerwein-Ponndorf-Verley and Oppenauer reactions (MPVO) are catalysed by metal oxides which possess surface basicity or Lewis acidity. Recent developments include the application of basic alkali or alkaline earth exchanged X-type zeolites and the Lewis-acid zeolites BEA and [Ti]-BEA. The BEA catalysts show high stereoselectivity, as a result of restricted transition state selectivity, in the MPV reduction of substituted alkylcyclohexanones with i-PrOH.

Zeolite titanium beta: A selective catalyst in the meerwein-ponndorf-verley-oppenauer reactions

Publisher Summary In recent times, the use of zeolite beta in the Meerwein–Ponndorf–Verley–Oppenauer (MPVO) reduction of 4- t -butylcyclohexanone has been under consideration. The high selectivity toward the thermodynamically less favored cis-alcohol is explained by a restricted transition-state around a Lewis-acidic aluminum in the zeolite pores. When using an aluminum-free zeolite titanium beta in the epoxidation of olefins, it has been shown that Ti-beta has acidic properties when alcoholic solvents were employed. Ti-beta is found to be an excellent catalyst in MPVO reactions with a tolerance for water. In this chapter, results are presented on the high selectivity, stability, and low by-product formation of the catalyst, Ti-beta, in both the liquid-phase and gas-phase MPVO reactions. Under liquid-phase conditions, a very high selectivity in the reduction of 4-substituted cyclohexanones toward the thermodynamically unfavorable cis-alcohols was observed. By-products were observed only during the oxidation of alcohols, using ketone solvents, and consisted primarily of aldol condensation products. Remarkable differences exist between the liquid-phase and gas-phase reactions under otherwise similar conditions. The selectivity toward the cis-alcohol is still above the thermodynamically expected value, but significantly lower than under liquid-phase conditions. In contrast to the liquid-phase reactions, dehydration of the alcohols to the corresponding alkene is an important side-reaction. The oxidation of both the cis- and the trans-alcohol clearly showed that the olefin is exclusively formed from the cis-alcohol. Dehydration of the trans-alcohol is assumed to proceed by isomerization via a MPVO mechanism to the corresponding cis-alcohol.

A new coupling reaction between α-pinene and acetone catalysed by beta zeolites

Abstract When pure ketones, like acetone, 2-butanone or cyclohexanone are used as solvents in the isomerization of α-pinene over zeolite beta, products of a coupling reaction between terpenes and the solvent, are formed. They were identified by GCMS analysis, as a-terpinyl acetone, 1-(α-terpinyl)-butan-2-one and 2-(a-terpinyl)-cyclohexanone, respectively.