Page 155 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

5A.4 MULTIPLE BOND FORMATION: SYNTHESIS OF SODIUM AZIDE 135

REVIEW PROBLEM 5A.5
Another synthesis of hydrazine involves the oxidation of urea, (NH ) C=O, with
2 2
sodium hypochlorite:

(H N) C=O + NaOCl + 2NaOH → N H + H O + NaCl + Na CO
2 2 2 4 2 2 3
Suggest a mechanism.

MULTIPLE BOND FORMATION: SYNTHESIS OF SODIUM AZIDE
5A.4
Nitrogen-on-nitrogen attack followed by elimination leads to N–N multiple bonds. A good
example is the synthesis of sodium azide (NaN ). Sodium azide has been widely used as the
3
gas-forming agent in automobile airbags; nowadays, however, a milder explosive is gen-
erally preferred. The synthesis involves the interaction of nitrous oxide (N O) and molten
2
∘
sodium amide (NaNH ) at about 190 C.
2
2NaNH + N O → NaN + NaOH + NH (5A.16)
2 2 3 3
–
The structure of the azide anion (N ) indicates that the NH – and N O nitrogens must
3 2 2
somehow come together and the H and O atoms somehow stripped away. A reasonable
–
working hypothesis is that the amide ion (NH ) acts as a nucleophile and attacks one of
2
the N O nitrogens. For NH 2 – attacking the terminal nitrogen of N O, the following pathway
2
2
may be envisioned:
N N
+ − − N N
N N O H N O
H N OH (5A.17)
H N H −
−
H
–
The NH proton of the intermediate can then be picked up by a second NH , producing
2
–
–
NH ,N , and OH , as shown below:
3
3
H
H N N − −
− N H N OH N + N N N
− H
H H OH
(5A.18)
− − − + − −
N N N N N N + OH
OH