Chemistry Reference
In-Depth Information
A by-product of the above reaction is ammonium sulfate. To avoid the necessity of disposing of
ammonium sulfate, many caprolactam producers sought other routes to the oxime. One approach is to
form it directly by reacting cyclohexanone with ammonia and hydrogen peroxide in the presence of
tungstic acid catalyst [
56
]:
8H
2
0
H
3
PW
2
O
40
+
NH
3
O
+
H
2
O
NOH
The reaction is conducted in water and the product oxime is extracted with an organic solvent.
Another process is based on photo-nitrosyl chlorination. Here cyclohexane is converted in one step to
cyclohexanone oxime hydrochloride [
57
]:
h
u
+
NOCl
NO
Cl
+
Cl
+
HCl
+
+
NO
NOH
HCl
Another process uses ketene to form cyclohexene acetate [
58
]:
NO
2
O
O
O
HNO
3
O
O
[H]
H
2
O
O
2
N
COOH
O
N
H
Among some more recent developments is a one-step synthesis of caprolactam from
cyclohexanol [
59
]:
O
LiCl
2
OH
+
O
Ca(SCN)
2
90-100
o
C
N
H
There are other processes for caprolactam syntheses as well; however, a thorough discussion of
this subject belongs in topics dedicated to the subject.
The mechanism of the reaction of ring opening polymerization of lactams is discussed in
Chap.
5
. Several important side reactions accompany this polymerization. One is formation of
cyclic oligomers [
58
]. The cyclic oligomers, soluble in water and alcohol mixtures, range in size
from cyclic dimers to cyclic nonamers [
60
-
62
]. Formation of these compounds may be governed
by equilibrium [
63
]. The polyamide will also thermally oxidize upon prolonged exposure to heat
and air. Another important side reaction is decarboxylation that occurs at high temperatures. This
