Page 153 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

5A.3 N–N BONDED MOLECULES: SYNTHESIS OF HYDRAZINE 133

REVIEW PROBLEM 5A.2
Nitronium tetrafluoroborate can be isolated as a solid salt and is even commercially
available. It is prepared as follows:

BF 3 , HF
+ −
N 2 O 5 NO 2 BF 4
CH 3 NO 2
Suggest a mechanism for this reaction.

REVIEW PROBLEM 5A.3

Solid nitrosonium and nitronium salts are moisture sensitive and need to be protected
even from moist air. Can you explain why?

REVIEW PROBLEM 5A.4
Anhydrous nitric acid (dangerous!) serves as a starting material for a number of reac-
tive pentavalent nitrogen compounds, including nitryl chloride (NO Cl) and chlorine
2
nitrate (ClONO ), as shown below:
2
1. HNO + ClSO H → ClNO + H SO 4
3
2
2
3
2. HNO + ClF → ClONO + HF
3
2
Suggest mechanisms for the two reactions.
5A.3 N–N BONDED MOLECULES: SYNTHESIS OF HYDRAZINE

Given the variety of nitrogen-based nucleophiles and electrophiles, it’s no surprise that
reactions involving nitrogen-on-nitrogen attack, leading to N–N bond formation, are fairly
common. We will discuss several such reactions, beginning with the Olin–Raschig process
for the synthesis of hydrazine (NH NH ). The synthesis involves two operational steps. In
2 2 ∘
the first step, ammonia interacts with chilled (5 C) aqueous sodium hypochlorite (NaOCl)
to form chloramine (NH Cl):
2
NH + NaOCl → NH Cl + NaOH (5A.10)
3 2
The resulting solution is then added to anhydrous ammonia under pressure and heated to
∘
130 C, to yield hydrazine:
NH Cl + NH + NaOH → N H + NaCl + H O (5A.11)
2
4
2
3
2