CHED 73 |
| Teaching the challenging concept of kinetic and thermodynamic control is helped by a rapid colorful demonstration involving the competitive metallation of octaethylporphyrin by zinc(II) acetate and nickel(II) acetate. Treating equimolar solutions of octaethylporphyrin, nickel acetate and zinc acetate in warm glacial acetic acid forms zinc(II) octaethylporphyrin (the kinetically controlled product) in seconds. The solution changes color from red-brown to pink. There is also a change in fluorescence from scarlet to orange. On heating to reflux, the zinc is rapidly and quantitatively displaced, forming nickel (II) octaethylporphyrin (the thermodynamically controlled product). The experiment is monitored either by eye, although the color change is somewhat subtle, or by the disappearance of fluorescence. The reaction is complete in less than 10 minutes. The utility of the reaction as a laboratory class experiment using thin layer chromatography and visible spectroscopy is also discussed. |
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General Posters
7:30 PM-9:30 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Chemical Education |