Chemoselective hydrogenation method catalyzed by Pd/C using diphenylsulfide as a reasonable catalyst poison

While Pd/C is one of the most useful catalysts for hydrogenation, the high catalyst activity of Pd/C causes difficulty in its application to chemoselective hydrogenation between different types of reducible functionalities. In order to achieve chemoselective hydrogenation using Pd/C, we investigated catalyst poison as a controller of the catalyst activity. We found that the addition of Ph₂S (diphenylsulfide) to the Pd/C-catalyzed hydrogenation reaction mixture led to reasonable deactivation of Pd/C. By the use of the Pd/C-Ph₂S catalytic system, olefins, acetylenes, and azides can be selectively reduced in the coexistence of aromatic carbonyls, aromatic halides, cyano groups, benzyl esters, and N-Cbz (benzyloxycarbonyl) protecting groups. The present method is promising as a general and practical chemoselective hydrogenation process in synthetic organic chemistry.     

Production of multi-hollow polymer particles by the stepwise acid/alkali method

 Recently, we reported that multi-hollow polymer particles can be prepared from carboxylated polymer particles by the stepwise alkali/acid method. In this article, an attempt was made to prepare similar particles from acid-swellable polymer particles by the stepwise treatment with acid and alkali, which was named the stepwise acid/alkali method. The acid-swellable particles were produced by emulsion terpolymerization of styrene, butyl acrylate, and dimethyl 2-amino ethyl methacrylate. The effects of initial pH value, temperature, and time in the acid and alkali treatment processes on the multi-hollow structure were examined. Received: 18 December 1996 Accepted: 11 March 1997     

Novel [2 + 2] photocycloaddition-induced rearrangement of bichromophoric naphthalene-tethered resorcinol ethers

The first examples of sequential photocycloaddition-rearrangement reactions of naphthalene-tethered resorcinol ethers are described. Bichromophoric aromatic compounds with naphthalene and resorcinol ether moieties were irradiated in the presence/absence of a small amount of acid to give the corresponding cycloaddition-rearrangement products. From the determination of quantum yields, steady-state fluorescence spectral studies, and fluorescence lifetime measurements, the mechanism of this novel photoinduced multistep reaction was elucidated to involve the initial intramolecular exciplex formation, followed by the intramolecular [2 + 2] photocycloaddition between the two aromatic rings and the subsequent acid-catalyzed skeletal rearrangement of the resulting cyclobutane derivative leading to the final products.     

Smectic layer structure of ferroelectric liquid crystal formed between fine polymer fibres

This paper describes the alignment of ferroelectric liquid crystal (FLC) structures formed between aligned polymer fibres, where the FLC smectic layers are determined by polarising microscopy and X-ray diffraction. The FLC/polymer composite films were formed from a nematic phase FLC/monomer solution using a photopolymerisation-induced phase separation method. It was found that bending of the FLC smectic layers was induced in both the film plane and the cross-sectional plane at the phase transition from smectic A to chiral smectic C of the FLC material. The light transmittance properties of the composite film between crossed polarizers was analysed by light propagation simulation in several optical anisotropic media, based on the evaluated smectic layer model.     

Cluster-size dependence of alloying behavior in gold clusters

Cluster-size dependence of alloying behavior in nm-sized atom clusters has been studied by transmission electron microscopy, using clusters in the Au-Cu system. It was revealed that occurrence of rapid spontaneous alloying becomes more difficult with increasing cluster size. In gold clusters of approximately 4 nm in the mean size, a rapid dissolution of copper atoms took place and homogeneously mixed Au-Cu alloy clusters were formed. In gold clusters of approximately 10 nm in the mean size, rapid alloying of copper took place only at a shell-shaped region beneath the free surface of individual clusters and pure gold was retained at the central region of clusters. In gold clusters of approximately 30 nm in the mean size, no rapid alloying of copper was induced. The ease with which spontaneous alloying takes place is discussed in terms of the lattice softening in atom clusters.