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Tutorial: Nitrogen

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Abundance: Atmosphere (in the form of N 2, 78.1 Vol-%; 4·10 t); hydrosphere (N 2 dissolved in
12
17
water, 10 t); in minerals (saltpetre NaNO 3) and rocks (2·10 t); in organic form in the biomass of
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11
soil-bound microorganisms (3·10 t), plants and animals (10 t).
The bond in dinitrogen is a triple bond; the bond energy amounts to 949 kJ/mol, i.e. N 2 is
particularly inert.

Hydrogen compounds: NH 3 (ammonia; synthesis from H 2 and N 2 according to the Haber-Bosch
+
process) and ammonium ions (NH 4 ), N 2H 4 (hydrazine), HN 3 and salts derived thereof (azides, e.g.
NaN 3, commonly used as fungicide and bactericide in bio-assays). Nitrides, e.g. Na 3N, formally
+
derive from ammonia. Ammonia is an efficient complexing agent, e.g. for Ag : AgCl dissolved in
+
aqueous NH 3 forms soluble [Ag(NH 3) 2] , which gradually converts to silvernitride Ag 3N (highly
explosive). The ammonium ion is a Brønstedt acid; aqueous solutions of ammonium salts
consequently are acidic.

Oxygen compounds: N 2O (dinitrogen monoxide, “laughing gas“), NO (nitrogenmonoxide;
synthesis by combustion of ammonia according to the Ostwald process), NO 2 (nitrogendioxide, in
equilibrium with N 2O 4. NO 2 reacts with water to form nitrous acid HNO 2 + nitric acid HNO 3),
N 2O 5 (dinitrogen pentoxide). Salts derived from HNO 3 are termed nitrates, those derived from
HNO 2 nitrites.

Use: Fertilisers (ammonium compounds, nitrates), explosives (nitrate; gun powder is a mixture of
saltpetre, charcoal and flower of sulphur). HNO 3 is used for nitrosylations in organic synthesis.

Organic nitrogen compounds: Amines (NH 2R, R = phenyl: aniline; NHR 2; NR 3), heterocyclic
nitrogen compounds (for a selection see below), amides (1a) and peptide (1b), hydroxamic acids
(2), aminoacids (3), nitro compounds (4), nitrosamines (5), diazo compounds (6).
NH 2
NH
N N NH

N NH N NH NH N
Pyridin Piperidin Adenin Pyrrol Imidazol

O O
2
2
3
CH 2 C CH C H NCH CO H bzw. H N CH CO 2
R (1a) NH 2 R (1b) NH CH R (3) R
R'
O NO
CH 2 C RNO 2 RN R NN
N OH H R'
R
(2) R (4) (5) (6)
-
-
-
Other nitrogen compounds: Cyanide CN , cyanate NCO and thiocyanate NCS (can be formed in
metabolic processes and coordinate to transition metal ions). Cyanide in particular is toxic, but may
also occur as ligand in enzymes (iron-only hydrogenase). Amides of carbonic acid: carbamate, e.g.
+
-
NH 4 (CO 2NH 2) = sal volatile, and urea O=C(NH 2) 2.