The mechanism of the chapman rearrangement of N-arylbenzimidate on the basis of the molecular structure established by X-ray. Part II

Dibenz[c,h]acridine ( 13 ) was formed directly by the Chapman rearrangement of 2-methoxycarbonyl-1-naphthyl-N-1′-naphthylbenzimidate ( 11 ) without isolation of intermediate 12 . When the Chapman rearrangement was carried out under mild reaction conditions, the intermediate 12 was isolated in high yield, whose structure was determined by the X-ray studies. The mechanism of the Chapman rearrangement can be interpreted on the basis of the X-ray data of 11 and 12 .     

Amorphous celluloses stable in aqueous media: Regeneration from SO2–amine solvent systems

Amorphous celluloses were prepared by regeneration of cellulose from its solutions in the SO₂–diethylamine–dimethylsulfoxide (SO₂–DEA–DMSO) solvent system, and other selected SO₂–amine–organic solvents. The celluloses were amorphous whether regenerated in water or in alcohols or other organic solvents; in this respect the observations differ from all prior experience in the regeneration of cellulose. These celluloses retain their amorphous character even after extended soaking in water at room temperature. Viscosity measurements have shown that little or no depolymerization occurs during the dissolution, regeneration, and drying processes. Thus the procedures allow the preparation of amorphous celluloses of a wide range of molecular weights for use to model the behavior of amorphous domains in fibrous celluloses. The unusual stability of the amorphous cellulose structures prepared by these procedures is attributed to very rapid decomposition of the SO₂–amine complex with the cellulosic hydroxyl groups which is believed to occur in the solvated state. The rate of decomposition of this complex appears to be sufficiently high so that the cellulose chains aggregate in an amorphous state before they have any opportunity to realign into crystalline domains.     

Depolymerization of cellouronic acid during TEMPO-mediated oxidation

The mechanism of partial depolymerization of cellouronic acid (-1,4-linked polyglucuronic acid sodium salt) during 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose was studied by treating cellouronic acid with one reagent or a combination of TEMPO-NaBr-NaClO under various conditions. Although NaClO, NaBrO and an alkali at pH 11 brought about partial depolymerization of cellouronic acid, the use of these reagents themselves did not seem to be the primary reason for depolymerization. On the other hand, when all the reagents, i.e. TEMPO-NaBr-NaClO, were applied to cellouronic acid at pH 11, a remarkable decrease in weight-average degree of polymerization (DPw) from 430 to ca. 20 was observed within the initial 10 min. Probably hydroxyl radicals formed from NaBrO and TEMPO at pH 10–11 cause the depolymerization during the oxidation. Some radical scavengers were then used for the TEMPO-mediated oxidation of cellulose in order to suppress the depolymerization. Although the addition of crotonic acid under certain conditions gave cellouronic acid having higher DPw, none of the radical scavengers examined so far could completely prevent the depolymerization. When regenerated celluloses having higher DP were used as the starting materials, cellouronic acids having DPw of more than 1000 were obtained, although they still had large low-molecular-weight fractions.     

Optimization of preparation of thermally stable cellulose nanofibrils via heat‐induced conversion of ionic bonds to amide bonds

Improving the thermal stability of nanocelluloses is important for practical applications such as melt compounded nanocellulose‐reinforced polymer composites and flexible substrates for nanocellulose‐containing electronic devices. Here, we report optimum conditions for a straightforward surface modification strategy for improving the thermal stability of 2,2,6,6‐tetramethypiperidine‐1‐oxyl (TEMPO)‐oxidized cellulose nanofibrils (TOCNs); the heat‐induced conversion of TOCN alkyl ammonium carboxylates to amides. Different amine‐terminated compounds (R‐NH₂) were grafted onto the surface of TOCNs under aqueous conditions. The influences of R‐NH₂ molecular weight, R‐NH₂/TOCN‐COOH molar ratio, and thermal stability of R‐NH₂ on the properties of the grafted TOCN films were investigated through infrared spectroscopy and thermogravimetric analysis. For maximum thermal improvement of up to 90 °C, complete ionic bonding of TOCN carboxy groups with R‐NH₂ was required, as well as proper selection of the R‐NH₂ compound. A controlled heating process was also needed to achieve effective ionic‐to‐amide bond conversion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1750–1756     

X-ray studies on layer structure and bistability in ferroelectric liquid crystals

X-ray diffraction measurements of thin chiral smectic C (S_c*) liquid crystals between solid plates coated with rubbed polymer film were performed under an electric field. A variety of local layer structures which depend upon the boundary conditions could be observed, including bookshelf and chevron, and some distorted structures. Moreover, the method of layer deformation could be seen in a stepwise induced field, and seven deformation types could be detected. The relation between a bistability effect and the type of layer deformation was clarified and four deformation types were found favourable to bistability. A vertical layer structure at the boundary, like the bookshelf structure, was necessary to produce bistability. A high pretilt film seemed to have a smectic layer reform a tilted structure even under an induced field and it was difficult to produce bistability with the high pretilt one.     

Structure of β-amino acids in antibiotics iturin A

An antibiotic iturin A was separated into several components (A-1≈8) using HPLC and the structures of the β-amino acids of each component were established based on NMR and mass spectral analysis.     

Supported Noble Metal Catalysts and Adsorbents with Soft Lewis Acid Functions

Heterogeneous noble metal catalysts exhibit various functions. Although their redox functions have been extensively studied, we focused on their soft Lewis acid functions. Supported Au, Pt, and Pd catalysts electrophilically attack the π-electrons of soft bases such as alkynes, alkenes, and aromatic compounds to perform addition and substitution reactions. Hydroamination, intramolecular cyclization of alkynyl carboxylic acids, isomerization of allylic esters, vinyl exchange reactions, Wacker oxidation, and oxidative homocoupling of aromatics are introduced based on a discussion of the active species and reaction mechanisms. Furthermore, the adsorption of sulfur compounds, which are soft bases, onto the supported AuNPs is discussed. The adsorption and removal of 1,3-dimethyltrisulfane (DMTS), which is the compound responsible for the stale odor of “hine-ka” in alcoholic beverages, particularly Japanese sake, is described.     

Preparation of new nitrogen-bridged heterocycles. 59. Syntheses and intramolecular interactions of 3-(acylmethylthio)- and 3-[(3-ethoxycarbonyl-2-propenyl)thio]thieno[3,4-b]indolizine derivatives

Various thieno[3,4-b]indolizine derivatives having an acylmethylthio or (3-ethoxycarbonyl-2-propenyl)thio group at the 3-position which could not be obtained by a conventional method were prepared by a new procedure using cyanoethyl group as a protecting group and their intramolecular arene-pi interactions were investigated. In the (1)H-NMR spectra of these thieno[3,4-b]indolizines, the low-field shifts (delta 0.10-0.33 ppm) for the 5-protons were observed in comparison with those of 3-(methylthio)thieno[3,4-b]indolizines as a standard. The UV spectra also exhibited a characteristic absorption band at 425-445 nm attributable to the arene-pi interaction but their intensities were generally lower than those of 3-(arylmethylthio)thieno[3,4-b]indolizines. In their X-ray analyses, the anti conformation for 3-(acylmethylthio)thieno[3,4-b]indolizines and the gauche one for the 3-(3-ethoxycarbonyl-2-propenyl)thio derivatives were exhibited.