Reaktionen in überkritischem Kohlendioxid

Solvation Effects in Organic Chemistry: A Short Historical Overview

This short overview describes the historical development of the physics and chemistry of organic solvents and solutions from the alchemist era until the present time based on some carefully selected examples that can be considered landmarks in the history of solution chemistry.

DABCO-based ionic liquids: green and recyclable catalysts for the synthesis of barbituric and thiobarbituric acid derivatives in aqueous media

A new and straightforward method for the synthesis of 5-arylidine barbituric and thiobarbituric acids through a reaction between barbituric acid and its thio-analogue with aldehydes using [DABCO](SO₃H)₂(HSO₄)₂) as an efficient catalyst has been reported.

Near-critical CO2 in mesoporous silica studied by in situ FTIR spectroscopy

Attenuated total reflection Fourier transform infrared spectroscopy was used to correlate the band shift of the nu2 vibrational band of carbon dioxide with the density of the fluid. Upon adsorption of CO2 on mesoporous silica and a nonporous SiO2 film, additional bands were detected due to interactions of CO2 with SiO2. Near the saturation pressure for the porous samples, the absorbance of the nu2 band increased strongly, which was concluded to be caused by liquidlike CO2 inside the pores. Integration of single-beam-sample-reference spectra between bulk CO2 and CO2 adsorbing on the mesoporous silica coated on one part of the internal reflection element revealed excess adsorption type isotherms with sharp maxima at 21 degrees C. A flatter curve shape could be observed at 25 degrees C, which allowed estimating the pore critical temperature. Moreover, the density of the fluid inside and outside the pores could be compared. Over the investigated ranges of pressure, temperature, and pore size, the results evidenced that the CO2 density was always higher in the silica pores than in the bulk, even under supercritical conditions. This has important consequences on the pressure dependence of dissolution power and diffusivity of fluids in mesoporous solids. An overview is given on the influences of fluid phase behavior in the bulk and in the pores at various conditions on solubility and diffusivity.

Fixation of CO(2) by Zinc(II) Chelates in Alcoholic Medium. X-ray Structures of {[Zn(cyclen)](3)(&mgr;(3)-CO(3))}(ClO(4))(4) and [Zn(cyclen)EtOH](ClO(4))(2)

The fixation of CO(2) on Zn(II) chelates in alcoholic medium was studied in efforts to synthesize alkyl carbonates. In the presence of a base, such as NEt(3), the tetraazacyclododecane complex of Zn(II) in alcoholic solution binds CO(2) and forms a &mgr;(3)-carbonate complex. This complex was characterized by NMR spectroscopy and X-ray analysis. Crystal data: orthorhombic; space group Pcba; a = b = c = 21.850(5) Å; alpha = beta = gamma = 90 degrees; V = 10431.7(6) Å(3); Z = 8. The central Zn atom is coordinated to the four nitrogen donor atoms and to one oxygen of the bridging carbonate group. In an organic solvent such as DMSO, the complex exists in equilibrium with the decarboxylated Zn(II) complex. In addition, a Zn(II)(cyclen)(ethanol) complex was isolated and characterized by X-ray analysis. Crystal data: monoclinic; space group P2(1)/n; a = 12.707(5), b = 11.780(5), c = 15.642(5) Å; alpha = gamma = 90 degrees; beta = 105.250(5) degrees; V = 2259.0 (6) Å(3); Z = 4. The central Zn atom is coordinated to four nitrogen donor atoms and the oxygen of ethanol. We were not successful in converting this complex to the ethyl carbonate complex. The results of this study are discussed in reference to those published in the literature.