Takashi Kamitanaka

Reactions of supercritical alcohols with unsaturated hydrocarbons

Abstract The reactions of some supercritical alcohols were investigated using 1,1-diphenylethylene, styrene, allylbenzene, and diphenylacetylene as the reaction partners. 1,1-Diphenylethylene in supercritical methanol was hydroxymethylated to afford 3,3-diphenyl-1-propanol as the major product. The alkenes containing a single and no conjugate phenyl group were also hydroxymethylated in supercritical methanol, but the reaction rates were significantly reduced when compared with that for 1,1-diphenylethylene. Styrene was converted to the hydroxyalkylated products in supercritical ethanol and 2-propanol as well as in supercritical methanol. The rates of the hydroxyalkylation of styrene were strongly dependent on the structures of the supercritical alcohols; the order of reactivity was 2-propanol>ethanol>methanol. The relation between the structures of the alcohols and the rates of hydroxyalkylation suggests that the reaction begins with an attack on the electrophile ( + CR 2 OH or δ+ CR 2 OH) by the pi electrons of the styrene double bond. All the examined alkenes afforded their hydrogenated derivatives other than the hydroxyalkylated ones. In addition, supercritical alcohols acted as hydroxyalkylating or hydrogenating reagents for the triple bond in the reaction with diphenylacetylene.

Photoinduced reversible topographical changes on diarylethene microcrystalline surfaces with biomimetic wetting properties.

Reversible topographical changes were observed on a photochromic diarylethene microcrystalline film surface by alternate irradiation with UV and visible light. Two types of surfaces were prepared from this film: 1) Storage of the film at 30 °C for 24 hours in the dark after UV irradiation afforded a surface that was covered with needle-shaped crystals, whose diameter and length were approximately 1 μm and 10 μm, respectively, and showed a superhydrophobic lotus effect. 2) Storage of the film at 70 °C for 3 hours in the dark caused the needle-shaped crystals to be converted into larger rod-like crystals (5~8 μm wide and 20~30 μm long) by Ostwald ripening and a disappearance of the lotus effect. The obtained activation energy of the formation of the needle- and rod-shaped crystals was 143 and 162 kJ mol(-1), respectively. Subsequent UV irradiation to the surface, which was followed by storage at 50 °C for 1 hour in the dark, gave a doubly rough structure; small needle-shaped crystals were formed between the larger rod-shaped crystals. The surface showed both superhydrophobic properties and the pinned effect of the water droplet: the petal effect. Fractal analysis of both surfaces were carried out using a box-counting method, and the lotus effect was observed in the presence of smaller-sized crystals, whilst the petal effect was observed with larger sized crystals (ca. 100 μm). We demonstrated that the hydrophobic property was controlled by the distribution in crystal size of the closed-ring isomer of the diarylethene. Visible-light irradiation of both rough surfaces afforded surfaces with cubic-shaped micro-crystals of the open-ring isomer.

Reduction of acetophenone using supercritical 2-propanol: the substituent effect and the deuterium kinetic isotope effect

Abstract The reductions of several substituted acetophenones using supercritical 2-propanol were carried out to estimate the Hammetts reaction constant ( ρ =0.33). Also, the reduction of acetophenone using supercritical deuteriated 2-propanol was carried out to determine the rate-determining step. The kinetic isotope effects were observed in the reduction using 2-deuterio-2-propanol ( k H / k D =1.6) and O -deuterio-2-propanol ( k H / k D =2.0). These findings suggest that the reaction proceeds via a cyclic transition state between acetophenone and 2-propanol similar to that of the Meerwein–Ponndorf–Verley reduction.

Biocatalytic reduction of ketones by a semi-continuous flow process using supercritical carbon dioxide.

The immobilized resting-cell of Geotrichum candidum was used as a catalyst for the reduction of a ketone in a semi-continuous flow process using supercritical carbon dioxide for the first time; it was also applied for the asymmetric reduction of a ketone and resulted in excellent enantioselectivity (ee > 99%) and a higher space-time yield than that of the corresponding batch process.