Modified guanidines could effectively mediate asymmetric silylation of secondary alcohols as recyclable bases under simple and mild conditions.

The extraction of gold(III) from 0.10 mol dm −3 hydrochloric acid into various aprotic ionic liquids (ILs) was investigated at 25 °C. Eleven kinds of ILs were examined as the extraction solvents; the cations were 1-butyl-3-methylimidazolium ([BMIm] + ), 1-hexyl-3-methylimidazolium, 1-methyl-3-octylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-butyl-1-methylpyrrolidinium, and methyltrioctylammonium; the anions were t e t r a fl u o r o b o r a t e , h e x a fl u o r o p h o s p h a t e , b i s -(trifluoromethanesulfonyl)amide ([NTf 2 ] − ), and bis-(pentafluoroethanesulfonyl)amide. The metal was extracted as anionic tetrachloroaurate ([AuCl 4 ] − ) into all the nonprotic ILs with high distribution ratios (>100). The distribution ratio of gold(III) differs largely (480-fold at most) depending on the IL species and also depends on the amount of extracted gold(III). These dependences of the distribution ratio were quantitatively explained as functions of the solubility product of the IL used, where we considered the equilibrium model comprising the ion pair extraction of [AuCl 4 ] − with the IL cation in the aqueous phase and the ion exchange of [AuCl 4 ] − with the IL anion in the IL phase. From a practical purpose, the back extraction of gold(III) from an IL ([BMIm][NTf 2 ]) phase was also examined; nearly quantitative stripping was possible using acidic thiourea solutions.

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Solid-state excimer emission of anthracene and its derivatives is a rare case at ambient conditions. We have designed organic salts composed of 9,10-bis(4-aminophenyl)anthracene (BAPA) and mineral acids in order to regulate the anthracene arrangement for investigation of the plausible geometry. From fluorescence measurement of three BAPA salts (nitrate: salt 1, chloride: salt 2, phosphate: salt 3), emission colors were changed by the effect of the mineral acids on the crystal structure. Notably, salt 3 crystal exhibited a bluish-green color derived from excimer emission at ambient conditions. On the basis of X-ray crystallographic analysis, the excimer emission of the salt 3 crystal was attributed to a tilt–slide type of anthracene geometry. In the geometry, π-planes of the anthracene moieties partially overlapped next to each other, an angle between the π-planes is 44°, and the nearest C–C distance is 3.7 Å. Such molecular geometry of partial overlapping of the anthracene rings and slightly longer C–C distance than that of common active π–π interaction (3.4–3.5 Å) was constructed of OH···O hydrogen bonds among mineral acid ions. These results suggest that the hydrogen bonds among mineral acid ions lead to the proximity of BAPA, following the excimer emission.

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