Organic 2 Review Problem 297

Organic 2 Review Problem 297 - P REPARATIONS 281 For the...

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PREPARATIONS 281 For the preparation of the Grignard reagent, the following factors should be noted: (1) Alkyl and aryl iodides usually react with magnesium more rapidly than the corresponding bromides, and the bromides very much more rapidly than the chlorides. Aryl (as distinct from alkyl) chlorides have usually only a slow reaction with magnesium and are there- fore very rarely used. With alkyl and aryl iodides in particular, however, a side reaction often occurs with the formation of a hydro- carbon and magnesium iodide: 2RI + Mg= R-R+ MgI 2 Hence as a general rule the bromides are used. (2) The formation of the Grignard reagent is inhibited by traces of water, which also decompose the reagent when it is formed. Therefore the apparatus used must be thoroughly dry, and the ether anhydrous (p. 82). Specially prepared magnesium turnings* should preferably be used: if magnesium ribbon is employed, it should first be drawn through two layers of fine emery paper to remove the superficial film
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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