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Ch_322b_15.07

Ch_322b_15.07 - dissolving metal reductions in organic...

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Synthetic Applications of Friedel-Crafts Acylation: The Clemmensen Reduction Acylation is often the preferred way to introduce a side-chain onto a benzene ring because rearrangements and polysubstition do not occur. Example: The Synthesis of Propylbenzene Reduction of the ketone to an alkyl group may be accomplished by any of several standard methods. + CH 3 CH 2 CCl O = propanoyl chloride AlCl 3 CCH 2 CH 3 O + HCl ethyl phenyl ketone (90%)
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The Clemmensen Reduction In 1913, E. Clemmensen developed a standard reduction that involves refluxing the ketone in a heterogeneous mixture of amalgamated zinc and hydrochloric acid. Often, acetic acid is added to improve the solubility of the ketone. Good yields of the alkylbenzene are typically obtained. CCH 2 CH 3 O = Zn(Hg) HCl, HOAc reflux CH 2 CH 2 CH 3 propylbenzene (80%)
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A Dissolving Metal Reduction The Clemmensen reduction is one of many
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Unformatted text preview: dissolving metal reductions in organic chemistry where a metal serves as a source of electrons. As the metal releases electrons and is oxidized, it dissolves as metal ions. Some Group 1 (Li, Na, K), Group 2 (Mg, Ca), and other metals (Al, Fe, Sn) with their favorable oxidation potentials (E o ) are in this category. ox Zn Zn 2+ + 2e-E o ox = +0.762 V In the Clemmensen reduction, the surface of the zinc metal is activated by amalgamation with Hg. Mossy zinc is stirred in a mixture of mercuric chloride and concentrated HCl for a few minutes. The electrochemical potential of the metal surface is changed slightly by amalgamation and a more active surface is formed. It is believed that the redox reaction with the ketone occurs on the metal surface. The detailed mechanism is not known....
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Ch_322b_15.07 - dissolving metal reductions in organic...

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