Investigations in supercritical fluids

In recent years, supercritical fluids (SCF) have drawn substantial interest as modern solvents for chemical reactions, separations, and extractions in the area of basic research as well as in industrial processes. Especially, supercritical carbon dioxide (scCO(2)) is a desirable replacement for organic solvents because it is inexpensive, nontoxic, nonflammable, environmentally benign, and exhibits ease of recycling and disposal. This contribution provides for an overview of the basic physical properties of SCFs, such as density tuning, diffusivity, viscosity and interaction with fluorinated compounds. In addition, in situ NMR spectroscopy in toroid cavity autoclaves and the specialized technique of parahydrogen-induced polarization are introduced as superior and beneficial for investigating physical properties and chemical reaction in SCFs. The concept of turnover frequencies and active sites in catalysis is reviewed, while specific examples are given for homogeneous hydrogenations and hydroformylations in scCO(2). The emerging field of colloid catalysis in SCFs is illustrated with the ultrafast single-phase hydrogenation of alkynes using bimetallic colloids in inverted polymer micelles as the catalyst.