Page 157 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

5A.5 THERMAL DECOMPOSITION OF NH NO AND NH NO
4 2 4 3 137

REVIEW PROBLEM 5A.7
The N–N-bonded hyponitrite anion [O–N=N–O] 2– can be accessed via the following
solution-phase synthesis:

RONO + NH OH + 2 EtONa → Na N O + ROH + 2EtOH
2
2
2
2
Suggest a mechanism for the process. (The hyponitrite anion can exist as either cis
or trans isomers. The cis isomer serves as a chelating ligand for metal ions.)

5A.5 THERMAL DECOMPOSITION OF NH NO AND NH NO 3
2
4 4
When heated, ammonium nitrite (NH NO ) and ammonium nitrate (NH NO ) decompose
4
4
3
2
as follows:
NH NO → N + 2H O (5A.22)
4 2 2 2
NH NO → N O + 2H O (5A.23)
4 3 2 2
Although both these reactions are common in undergraduate laboratories, where they are
typically carried out with just a few milligrams of the salts, the solids are explosive and
appropriate precautions are essential. Both reactions involve N–N bond formation, so we
must identify a nitrogen nucleophile and a nitrogen electrophile in each case. In the case
+ –
of NH NO , proton transfer from NH 4 to NO 2 yields NH , a potential nucleophile, and
2
4
3
HNO , a potential electrophile, which should link up as follows:
2
−
O H H OH H OH
N +
N (5A.24)
N H N N N
+ −
O H H O H O
H H H
Observe that a N–N bond has been created. Additional proton transfers followed by elimi-
nation of water lead to a N–N double bond, as shown below.
H
+
H OH O H H
+ N N (5A.25)
N N N N + O
− − H OH H
H H
H O H O
Elimination of a second molecule of water then leads to a N–N triple bond, that is, N :
2
N N H
− HOH
H OH N N + O
(5A.26)
O H
H
H