Page 73 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

2.3 REDUCTIVE COUPLINGS 53
The hydrogen atom produced in the above reaction then combines with another one to form
hydrogen gas:
H H H H (2.4)

The overall balanced equation is thus
+
−
2M + 2H O → 2M OH + H 2 (2.5)
2
An analogous reaction also happens with alcohols (ROH).
The metals reduce halogens and other nonmetals to yield binary salts, as illustrated below
for chlorine:
2M + Cl → 2MCl (2.6)
2
−
− Cl +
M Cl Cl M + Cl
(2.7)
+ −
M Cl M + Cl

Under suitable conditions, the metals even reduce dihydrogen. Sodium hydride (NaH), for
example, is produced by the interaction of hydrogen gas and liquid sodium:

−
− H +
Na H H Na + H
(2.8)
+ −
Na H Na + H

Sodium hydride is widely used as a strong base in organic chemistry, whereas calcium
hydride is used as a drying agent for solvents.

REVIEW PROBLEM 2.1

Lithium metal is unique in terms of its ability to activate N at room temperature and
2
ordinary pressure:
3Li + N → 2Li N
3
2
Draw a mechanism using fishhooks and regular arrows. Can you rationalize the
unique reactivity of Li, relative to the heavier alkali metals, which do not react with
N under ordinary conditions?
2

2.3 REDUCTIVE COUPLINGS

The strong tendency of s-block metals to give up their valence electrons is the basis of
a variety of useful coupling reactions in organic chemistry. To moderate the potentially