Synthesis of Acetoaldehyde,Acetic Acid,and Others by the Dehydrogenation and Oxidation of Ethanol

Following gradual shift of primary resources from fossil towards renewable ones in chemical industry, biomass based ethanol has been attracting growing interests as a fuel to replace gasoline and as a chemical feed stock to replace ethylene. This paper reviews major work reported in the last 10 years for the production of acetaldehyde, acetic acid, and other related compounds from ethanol. At present acetic acid can be industrially produced more economically from methanol than from ethylene, the production of acetic acid from ethanol is not profitable. Acetaldehyde, which is more expensive than ethanol, can be selectively produced in gas phase by dehydrogenation over supported Cu catalysts and by oxidation with O₂ over V and Mo based oxides. It is noteworthy that gold nanoparticles deposited on basic and acidic metal oxides are highly selective to acetaldehyde by oxidation with O₂. Acetic acid can be produced in water solvent over Au catalysts supported on MgAl₂O₄ or on Cu doped NiO, while in gas phase over Mo–V–Nb mixed oxides combined with TiO₂ colloids.     

13C chemical shifts of propane molecules encaged in structure II clathrate hydrate

Experimental NMR measurements for (13)C chemical shifts of propane molecules encaged in 16-hedral cages of structure II clathrate hydrate were conducted to investigate the effects of guest-host interaction of pure propane clathrate on the (13)C chemical shifts of propane guests. Experimental (13)C NMR measurements revealed that the clathrate hydration of propane reverses the (13)C chemical shifts of methyl and methylene carbons in propane guests to gaseous propane at room temperature and atmospheric pressure or isolated propane, suggesting a change in magnetic environment around the propane guest by the clathrate hydration. Inversion of the (13)C chemical shifts of propane clathrate suggests that the deshielding effect of the water cage on the methyl carbons of the propane molecule encaged in the 16-hedral cage is greater than that on its methylene carbon.     

Preparation of organic/inorganic hybrid and hollow particles by catalytic deposition of silica onto core/shell heterocoagulates modified with poly[2-(N,N-dimethylamino)ethyl methacrylate

The organic/inorganic hybrid particles PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) were prepared by catalytic hydrolysis and subsequent polycondensation of tetraethoxysilane in the poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA) layers grafted on the PSt/P(St-CPEM)(θ) core/shell heterocoagulates. The micron-sized PSt core and the submicron-sized P(St-CPEM) shell particles bearing ATRP initiating groups were synthesized by dispersion polymerization of styrene (St) and emulsifier-free emulsion polymerization of St with 2-chloropropionyloxyethyl methacrylate (CPEM), respectively. The raspberry-shaped PSt/P(St-CPEM)(θ) heterocoagulates with a controlled surface coverage (θ=0.51, 0.81) were prepared by hydrophobic coagulation between the core and the shell particles in an aqueous NaCl solution near the T(g) of P(St-CPEM). Surface modification of heterocoagulates was carried out by ATRP of DMAEMA from the shell particles adsorbed on the core particles. Silica deposition was performed by simply adding tetraethoxysilane to a water/methanol dispersion of PSt/P(St-CPEM)(θ)-g-PDMAEMA. The SEM and TGA revealed that the resulting PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) composites maintain a raspberry-like morphology after deposition of silica onto the PDMAEMA layer grafted on heterocoagulates. The micron-sized, raspberry-shaped or the submicron-sized, hole-structured silica hollow particles were obtained selectively by thermal decomposition of the PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2). The oriented particle array was fabricated by dropping anisotropically perforated silica particles onto a glass substrate settled at the bottom of a bottle filled with chloroform.     

Rhodium acetate/base-catalyzed N-silylation of indole derivatives with hydrosilanes

In the presence of Rh(2)(OAc)(4) (OAc = acetate) and TBA(2)WO(4) (TBA = tetra-n-butylammonium), the N-silylation of indole derivatives with hydrosilanes efficiently proceeded to give the corresponding N-silylated indoles in high yields. Pyrrole and carbazole were also N-silylated with the combined catalysts.     

A highly negatively charged γ-Keggin germanodecatungstate efficient for Knoevenagel condensation

A tetra-n-butylammonium (TBA) salt of a γ-Keggin -6-charged germanodecatungstate, [γ-H(2)GeW(10)O(36)](6-) (I), could act as an efficient homogeneous catalyst for Knoevenagel condensation of active methylene compounds with carbonyl compounds.     

Redesign of enzyme for improving catalytic activity and enantioselectivity toward poor substrates: manipulation of the transition state

Secondary alcohols having bulky substituents on both sides of the hydroxy group are inherently poor substrates for most lipases. In view of this weakness, we redesigned a Burkholderia cepacia lipase to create a variant with improved enzymatic characteristics. The I287F/I290A double mutant showed a high conversion and a high E value (>200) for a poor substrate for which the wild-type enzyme showed a low conversion and a low E value (5). This enhancement of catalytic activity and enantioselectivity of the variant resulted from the cooperative action of two mutations: Phe287 contributed to both enhancement of the (R)-enantiomer reactivity and suppression of the (S)-enantiomer reactivity, while Ala290 created a space to facilitate the acylation of the (R)-enantiomer. The kinetic constants indicated that the mutations effectively altered the transition state. Substrate mapping analysis strongly suggested that the CH/π interaction partly enhanced the (R)-enantiomer reactivity, the estimated energy of the CH/π interaction being -0.4 kcal mol(-1). The substrate scope of the I287F/I290A double mutant was broad. This biocatalyst was useful for the dynamic kinetic resolution of a variety of bulky secondary alcohols for which the wild-type enzyme shows little or no activity.     

Reversible deprotonation and protonation behaviors of a tetra-protonated γ-Keggin silicodecatungstate

The potentiometric titration of a γ-Keggin tetra-protonated silicodecatungstate, [γ-SiW(10)O(34)(H(2)O)(2)](4-) (H(4)·I), with TBAOH (TBA = [(n-C(4)H(9))(4)N](+)) showed inflection points at 2 and 3 equiv of TBAOH. The (1)H, (29)Si, and (183)W NMR data suggested that the in situ formation of tri-, doubly-, and monoprotonated silicodecatungstates, [γ-SiW(10)O(34)(OH)(OH(2))](5-) (H(3)·I), [γ-SiW(10)O(34)(OH)(2)](6-) (H(2)·I), and [γ-SiW(10)O(35)(OH)](7-) (H·I), with C(1), C(2v), and C(2) symmetries, respectively. Single crystals of TBA(6)·H(2)·I suitable for the X-ray structure analysis were successfully obtained and the anion part was a monomeric γ-Keggin divacant silicodecatungstate with two protonated bridging oxygen atoms. Compounds H(3)·I, H(2)·I, and H·I were reversibly monoprotonated to form H(4)·I, H(3)·I, and H(2)·I, respectively.     

Strategic design and refinement of Lewis acid-base catalysis by rare-earth-metal-containing polyoxometalates

Efficient polyoxometalate (POM)-based Lewis acid-base catalysts of the rare-earth-metal-containing POMs (TBA(6)RE-POM, RE = Y(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), or Dy(3+)) were designed and synthesized by reactions of TBA(4)H(4)[γ-SiW(10)O(36)] (TBA = tetra-n-butylammonium) with RE(acac)(3) (acac = acetylacetonato). TBA(6)RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic oxygen-enriched surfaces of negatively charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, respectively. Consequently, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-containing POMs via the simultaneous activation of coupling partners on the same POM molecules. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C═O bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examined, the neodymium-containing POM showed remarkable catalytic performance for cyanosilylation of various kinds of structurally diverse ketones and aldehydes, giving the corresponding cyanohydrin trimethylsilyl ethers in high yields (13 substrates, 94-99%). In particular, the turnover frequency (714,000 h(-1)) and the turnover number (23,800) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts.     

Polarons, bipolarons, and side-by-side polarons in reduction of oligofluorenes

The nature of charge carriers in conjugated polymers was elucidated through optical spectroscopy following single- and multielectron reduction of 2,7-(9,9-dihexylfluorene) oligomers, F(n), n = 1-10, yielding spectra with the two bands typical of polarons upon single reduction. For short oligomers addition of a second electron gave a single band demonstrating the classic polaron-bipolaron transition. However, for long oligomers double reductions yielded spectra with two bands, better described as two polarons, possibly residing side-by-side in the F(n) chains. The singly reduced anions do not appear to delocalize over the entire length of the longer conjugated systems; instead they are polarons occupying approximately four fluorene repeat units. The polarons of F(3) and F(4) display sharp absorption bands, but for longer oligomers the bands broaden, possibly due to fluctuations of the lengths of these unconfined polarons. DFT calculations with long-range-corrected functionals were fully consistent with the experiments describing polarons in anions, bipolarons in dianions of short oligomers, and side-by-side polarons in dianions of long oligomers, while results from standard functionals were not compatible with the experimental results. The computations found F(10)(2-), for example, to be an open-shell singlet ( ≈ 1), with electrons in two side-by-side orbitals, while dianions of shorter oligomers experienced a gradual transition to bipolarons with states of intermediate character at intermediate lengths. The energies and extinction coefficients of each anionic species were measured by ultraviolet-visible-near-infrared absorption spectroscopy with chemical reduction and pulse radiolysis. Reduction potentials determined from equilibria mirrored oxidation potentials reported by Chi and Wegner. Anions of oligomers four or more units in length contained vestigial neutral (VN) absorption bands that arise from neutral parts of the chain. Energies of the VN bands correspond to those of oligomers shorter by four units.