Akinobu Shiga

The Catalysis of Vapor-Phase Beckmann Rearrangement for the Production of ε-Caprolactam

Recently, Sumitomo Chemical Co., Ltd. developed the vapor-phase Beckmann rearrangement process for the production of ε-caprolactam. In the process, cyclohexanone oxime is rearranged into ε-caprolactam using a zeolite as a catalyst instead of sulfuric acid. EniChem in Italy developed the ammoximation process that involves the direct production of cyclohexanone oxime without producing any ammonium sulfate. Sumitomo Chemical Co., Ltd. has commercialized the combined process of vapor-phase Beckmann rearrangement and ammoximation in 2003.In this paper, the authors focus on some aspects of the vapor-phase Beckmann rearrangement catalysis. A solid catalyst that is mainly composed of a high-silica MFI zeolite (Silicalite-1) has been developed for the vapor-phase Beckmann rearrangement. This catalyst does not possess acidity that can be detected by ammonia TPD. Methanol fed into the reactor with cyclohexanone oxime improves the yield of caprolactam. Methanol reacts with terminal silanols on the zeolite surface and converts them to methoxyl groups. The modification of the catalyst by methanol has an important role for the Beckmann rearrangement reaction.Nest silanols located just inside the pore mouth of the MFI zeolite are supposed to be the active sites of the catalyst. We propose that the coordination between the NOH group of cyclohexanone oxime molecule and the nest silanols through hydrogen bonding is responsible for the reaction. The reaction mechanism of Beckmann rearrangement under vapor-phase conditions is the same as in the liquid phase, namely, the alkyl group in anti-position against the hydroxyl group of the oxime migrates to the nitrogen atoms position.

A theoretical study of the insertion of olefins into Timethyl bonds by “Paired Interacting Orbitals”

Abstract Insertion of ethylene into the methylTi bond of ([CH 3 Ti(Cl) 4 /C 2 H 4 ] n , n = −1 or −3) Oh- d 0 , - d 2 and [CH 3 Ti(Cl) 2 /C 2 H 4 ] n , n = +1 or −1) Td- d 0 , - d 2 methyltitanium complexes has been studied by applying Paired Interacting Orbitals (PIO). It is important for the insertion that the PIOs are in-phase between the methyl carbon and the ethylene C β , and between the Ti and the ethylene C α . This condition is satisfied in d 0 complexes. In d 2 complexes the orbital pair in the PIO-1, which consists mainly of the occupied Ti d xz and the unoccupied ethylene π * MO, overlap out-of-phase between the methyl carbon and the ethylene C β . We can predict that, whereas the ethylene insertion is facile in d 0 methyltitanium complexes, it is not in d 2 complexes.

New reaction simulator “LUMMOX” and its application for prediction of catalytic activities

We developed a new reaction simulator, “LUMMOX.” It is an intermolecular interaction analyzer based on the theories of paired interacting orbitals (PIOs) and localized frontier orbitals (LFOs) that have been developed by Fujimoto et al. (Fukui, K.; Koga, N.; Fujimoto, H. J Am Chem Soc 1981, 103, 196; Fujimoto, H.; Koga, N.; Fukui, K. J Am Chem Soc 1981, 103, 7452; Fujimoto, H.; Satoh, S. J Phys Chem 1994, 98, 1436). LUMMOX runs on a Windows PC and displays graphic representation of orbital interactions. Prediction of activities, selectivities, and molecular weight of olefin polymerization catalysts are presented using PIO analysis and LFO calculation. Not only computational chemists but also experimental chemists can easily use this new system for catalyst design or molecular design from the point of view of orbital interaction.

New crystalline polymers: poly(2,5‐dialkyl‐1,4‐phenylene oxide)s

New heat-reversibly crystalline poly-(alkylated phenylene oxide)s are described, the oxidative polymerization of 2.5-dimethylphenol catalyzed by (1,4,7-triisopropyl-1,4,7-triazacyclononane) copper dichloride produced poly(2,5-dimethyl-1,4-phenylene oxide), which showed heat-reversible crystallinity with a high melting point at ca. 300°C, although the isomeric polymer, poly(2,6-dimethyl-1,4-phenylene oxide), never recrystallizes once melted. The polymerization of 2,5-diethylphenol and 2,5-dipropylphenol gave the polymers consisting of 1,4-phenylene oxide units; the latter polymer possessed heat-reversible crystallinity, however, the former one did not.

Coupling selectivity in the radical-controlled oxidative polymerization of 4-phenoxyphenol catalyzed by (1,4,7-triisopropyl-1,4,7-triazacyclononane)copper(II) complex

Various effects on the coupling selectivity of the oxidative polymerization of 4-phenoxyphenol catalyzed by (1,4,7-triisopropyl-1,4,7-triazacyclononane)copper(II) halogeno complex [Cu(tacn)X 2 ] are described. With respect to the amount of the catalyst and the nature of the halide ion (X) of Cu(tacn)X 2 , the coupling selectivity hardly changed. The Cu(tacn) catalyst possessed a turnover number greater than 1860. As the temperature of the reaction and the polarity of the reaction solvent were elevated, the C-O coupling at the o-position increased, but the C-C coupling was not involved. For the polymerization in toluene at 80 °C, poly(1,4-phenylene oxide), obtained as a methanol-insoluble part, showed the highest number-average molecular weight of 4000 with a melting point (T m ) of 195 °C. Only a slight change in the coupling selectivity was observed in the presence or absence of hindered amines as the base. Surprisingly, however, the C-O selectivity decreased from 100 to 24% with less hindered amines, indicating that the selectivity drastically changed from a preference for C-O coupling to a preference for C-C coupling.

'Radical-controlled' oxidative polymerization of m-cresol catalyzed by μ-η2 :η2-peroxo dicopper(II) complex

Abstract Described is an oxidative polymerization of m-cresol catalyzed by (1,4,7-triisopropyl-1,4,7-triazacyclononane)copper complex, from which a μ-η2:η2-peroxo dicopper(II) complex is formed under dioxygen and reacts with m-cresol to give ‘controlled’ phenoxy radical–copper(I) complex exclusively without formation of ‘free’ phenoxy radical. The present catalyst showed the highest activity in the metal complex catalysts reported for the polymerization of m-cresol with dioxygen. The resulting polymer consisted of oxyphenylene units and showed high molecular weight and high thermal stability. The high selectivity toward CO linkage would be due to the coupling from the phenoxy radical species controlled by this catalyst.

Theoretical study of ethylene polymerization on Ziegler–Natta catalysts and on metallocene catalysts

Abstract Ethylene insertion on Oh-d1CH3Tinchloride clusters/C2H4 (model systems of Ziegler–Natta catalysts) and Td-d0,-d1CH3TiCp2/C2H4 (model systems of metallocene catalysts) were studied by using paired interacting orbitals (PIO) analysis and LFO calculation. Electron delocalization from catalytic site to ethylene and that from ethylene to catalytic site played a crucial role in ethylene insertion. The former depends on the nucleophilicity of the active site and the latter on the electrophilicity of the active site. They were quantitatively estimated by LFO calculation. In the case of Oh systems, the electrophilicity of the catalyst decreased because of the Cl anion located trans to the ethylene in the reaction plane. In the case of Td systems, since the electrophilicity was not weakened because of the absence of the trans ligand to the ethylene, the nucleophilicity and electrophilicity were well balanced. The Oh-d1Ti4 cluster could be a suitable model of the active site on the TiCl3 crystalline surface.

A theoretical study of Ziegler-Natta olefin polymerization on the TiCl3 crystalline surface

Abstract Olefin insertion into Ti-methyl bonds of methyltitanium chloride clusters on a TiCl 3 crystalline surface has been studied by using paired interacting orbitals (PIO). We have shown that at least two types of active sites can be assumed on the edge of the basal face of violet TiCl 3 crystallites: a edge type active site which possesses a dangling bonded Cl atom, four bridged Cl atoms and a Cl vacancy and a corner type active site which possesses a dangling bonded Cl atom, three bridged Cl atoms and two Cl vacancies. The size effects on these active site have been estimated by changing the number of titanium atoms of the TiCl 3 model clusters. The most important interaction in the olefin coordinated state is electron delocalization from the occupied Ti d xz orbital of the methyltitanium chlorides to the π∗ orbital of the coordinated olefin molecule, while in the transition state is electron delocalization from the occupied C p and Ti d xz orbital of the methyltitanium chloride species to the π∗ orbital of the olefin. These interactions are compactly shown in PIOs. The coordination energy and the activation energy for the olefin insertion are almost independent of the cluster size when the number of Ti atoms is greater than three. The corner type active site has been shown to be stabilized at the transition state by the absence of one of the Cl atoms which are located orthogonal to the insertion plane. Thus, the olefin insertion on the corner type active site is more favorable than that on the edge type active site. In the case of propylene insertion, syn -orientation of propylene is favored. This regioselectivity should be lower on the corner type active site than that on the edge type active site.

Radical-controlled oxidative polymerization of 4-phenoxyphenol catalyzed by a dicopper complex of a dinucleating ligand

Abstract The oxidative polymerization of 4-phenoxyphenol (PPL) catalyzed by a dicopper complex with a dinucleating ligand, 1,2-bis[2-(bis(2-pyridyl)methyl)-6-pyridyl]ethane is described. The polymerization proceeded regioselectively to give crystalline unsubstituted poly(1,4-phenylene oxide) (PPO), in which μ-η 2 :η 2 -peroxo dicopper(II) species is probably involved as the active dioxygen intermediate. A copper complex with a mononucleating ligand of the similar structure, 1,1,1-tris(6-methylpyrid-2-yl)ethane, also catalyzed the oxidative coupling of PPL. The coupling selectivity for the dicopper/dinucleating ligand complex was close to that for the copper/mononucleating ligand complex. However, the initial reaction rate for the former was independent on the catalyst amount in a certain range, whereas that for the latter decreased with the decrease of the catalyst amount.

Prediction of reactivities of titanium—methyl bonds in Ohd0 methyltitanium chlorides for insertion of ethylene: Analysis by ‘paired interacting orbitals’ (PIO)

Abstract The effect of ligands on ethylene insertion into the methyl-titanium bond of Oh-d0 methyltitanium complexes was studied using paired interacting orbitals (PIO). The most important contribution to this insertion was shown to be electron delocalization from the methyltitanium compound to ethylene, and the next is electron delocalization from ethylene to the methyltitanium compound. The ligand effect, which favors ethylene insertion into the Ohd0 methyltitanum complexes, is summarized as follows: an electron-attracting ligand should be placed at a position trans to ethylene, and an electron-donating one trans to the methyl group; ligands placed at the positions perpendicular to the reaction plane play the role of introducing the ethylene monomer into the reaction site. The effect of coordination of MgCl2 on the insertion is also discussed.