Environmental Engineering Reference
In-Depth Information
½
H
R
R
O
NO
2
!
OH
þ
NH
3
The essential difference between nitrate esters and nitro compounds can be found
in the reaction. In the same reaction conditions, nitro compounds would be con-
verted to amines. Though the structure of ester group (
NO
2
) is the same as the
-
nitro group (C
NO
2
) in nitro compounds, the reactivity of nitrate esters is higher
and the product distribution after hydrolysis reaction is more complicated. It
indicates that nitrate esters might have the structure of hyperoxide group
-
R
O
O
-
-
-
-
NO.
However, the hyperoxide structure was not found in nitrate esters after multiple
chemical structure analysis techniques [
1
,
3
,
15
]. The only structure of nitrate esters
is:
The structure of nitrate esters was further characterized by techniques of Raman
spectroscopy, Infrared spectroscopy, Electron Diffraction, dipole moment, and
X-ray. The results supported the
finding of no hyperoxide structure in nitrate esters.
Symmetrical structure was demonstrated for nitrate esters.
The bond length and bond angle of nitrate esters are similar with those of nitro
compounds [
3
,
16
].
5.1.2 Physical Properties of Nitrate Esters
Lower alcohol esters formed through the reaction between nitric acid and alcohol
-
OH are usually liquid with a slightly higher boiling point than the corresponding
alcohols. However, the boiling point of the corresponding nitrous esters is much
lower than the alcohols. The C-nitro compounds have higher boiling point than the
corresponding nitrate esters. The boiling points of monohydric alcohols and esters
are listed in Table
5.1
.
The highly associated structure, mainly through hydrogen bonds, of liquid
alcohols can be used to explain why the boiling points of alcohols are lower than
the corresponding nitrate esters. Because of the molecular association, the viscosity
of alcohols is higher than that of the corresponding nitrate esters. On the other hand,
semipolar bonds of nitro groups are existed in nitrate esters, like nitro compounds.
