CHEMISTRY: Going with the Flow

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Science  28 Nov 2003:
Vol. 302, Issue 5650, pp. 1481a
DOI: 10.1126/science.302.5650.1481a

Many industrial-scale catalytic processes use a fixed bed reactor, in which a solution containing the reactants flows continuously over a heterogeneous catalyst that is immobilized on a solid porous support; the product emerges in the output stream. Hillerich and Plenio have adapted this reactor for use with homogeneous catalysts. In their biphasic system of two immiscible liquids, a polar tag is attached to the catalyst to keep it in the polar solvent (dimethyl sulfoxide), while the reactants and products reside primarily in the nonpolar solvent (n-heptane). The lower-density, reactant-containing n-heptane is fed into the bottom of a glass tube filled with the higher-density catalyst phase. Vigorous stirring creates small droplets that rise slowly to the top of the tube. During transit upward, the reactants partition into the catalyst phase, where they are converted into products that are extracted back into the buoyant droplets. At the top of the tube, the product-containing effluent is drawn off. Filling the tube with various sizes of glass beads provides an easy way to control the transit speed of the reactants. This method, which does not require expensive solvents or pressurized equipment, should be applicable to a range of organic reactions. — JFU

Chem. Comm. 10.1039/b310504k (2003).

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