Page 74 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

THE s-BLOCK ELEMENTS: ALKALI AND ALKALINE EARTH METALS
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violent nature of the reactions, the metals are often used in amalgam form (i.e., as solid
solutions in mercury). With alkyl halides, alkyl radicals are generated:

−
− X + (2.9)
Na R X Na + R

The radicals then dimerize to form alkanes:

R R R R (2.10)

The overall reaction then is

+ −
2R−X + 2 Na → R−R + 2Na X (2.11)

This reaction is called the Wurtz reaction after the French chemist Charles-Adolphe Wurtz
(1817–1884).

REVIEW PROBLEM 2.2
Although it’s one of organic chemistry’s classic reactions, the Wurtz reaction
is seldom used for alkane synthesis. Alkanes are typically much more con-
veniently obtained from petroleum, natural gas, and the reduction of fatty acids.
The Wurtz reaction is most valuable for specialized applications, particularly for
closing cyclopropane rings, as in the synthesis of bicyclo[1.1.0]butane, shown
below:

Cl

+ 2 Na

Br

Draw a mechanism for this reaction.

A much more widely used reductive coupling is the pinacol coupling of carbonyl com-
pounds, depicted below for acetone:

Me Me
Me Me 1. Mg Me Me
C C C (2.12)
+
2. H 3 O
O HO OH