Norio Saito

An in situ Raman spectroscopy study of subcritical and supercritical water: The peculiarity of hydrogen bonding near the critical point

The Raman spectra of water are measured at temperatures up to 510 °C and at pressures up to 40 MPa. The peak frequency increases with temperature, indicating the break of hydrogen bonding, and it changes only slightly at higher temperatures above the critical point. The peak frequency has a maximum near the critical pressure, and the extent of hydrogen bonding significantly changes with pressure in this near-critical region. The deviation of the maximum frequency Δf relative to that of the monomer is in good agreement with the chemical shifts with the literature NMR data. The extent of the hydrogen bonding can be estimated from the Δf values. The Δf values at the near-critical points are significantly lower compared with those in super- or sub-critical conditions, and the strength of the hydrogen bonding weakens uniquely in the near-critical region.

Promotion of a lipase-catalyzed esterification in supercritical carbon dioxide in the near-critical region

The ester syntheses from acyl donors and terpene alcohols catalyzed by Candida cylindracea (CCL) lipase have been carried out in supercritical carbon dioxide (SC-CO 2 ). In the near-critical region, the rate of esterification showed a sharp maximum and l-terpene esters were stereoselectively synthesized from acyl donors and a primary alcohol such as (dl)-citronellol. It was found that, in very limited pressure range near the critical point, the interactions between carbon dioxide and enzyme molecules are greatly increased and allowed to provoke drastic conformational changes of the enzyme, causing active sites to emerge and catalyze the stereoselective syntheses. Supercritical carbon dioxide medium in the near-critical region should be a trigger to the activation of the enzyme by causing the movement of the surface groups and creating an active site, producing stereoselective machinery.

Water/AOT/ethane microemulsion under supercritical conditions as a reaction medium

Abstract The alkaline fading of crystal violet (CV) is accelerated by using a W/O microemulsion of H2O/AOT/ethane under supercritical conditions. The rate of fading can be changed by three orders of magnitude with operating pressure and the molar ratio of water to AOT. The highest rate of CV fading observed is larger by a factor of 100 or more compared to those reported so far in the literature. The structure of AOT molecules and the type of interior water molecules seem to account for the rate enhancement with an increase in the H2O/AOT molar ratio. It is suggested that the intermicellar and AOT–ethane interactions are of significance for the promotion effect of pressure.

Acceleration of chemical reaction by AOT micelles under supercritical conditions

Abstract The alkaline fading of crystal violet (CV) is accelerated by using AOT micelles formed in supercritical ethane as a continuous phase. The rate of fading can be promoted by over two orders of magnitude by controlling operating pressure and molar ratio of water to AOT( W ). The structure of AOT molecules, the type of interior water molecules, and the E T (30) value indicative of micropolarity of a dye-organized cybotactic region in the micelle core seem to account for the rate enhancement with an increase in the W . It is further suggested that a decrease in the size of the micelle core due to significant changes in the intermicellar and AOT-ethane interactions with increasing pressure, which causes an increase in the micropolarity inside the core, is of importance for the promotion effect by pressure.

A simple method for the alkylation of diethyl malonate(速報)

Alkylmalonic esters, which have been recognized as important intermediates in the syntheses of various carboxylic acids, amino acids, etc., can be obtained by a variety of methods.1) Excepting the introduction of tertiary alkyl groups, the alkylation of malonic esters with alkyl halides in basic conditions, for example, in ethanol in the presence of sodium ethoxide, is one of the most important and popular methods. In this paper, we wish to report a simple and facile method for the alkylation of diethyl malonate. In connection with other work2), it was observed that diethyl malonate reacted with methyl iodide in N, N-dimethylformamide (DMF) solution in the