Published on the web November 13, 2010
1319
Catalytic Beckmann Rearrangement of Cyclododecanone Oxime
Satoshi Sato,*1 Hideaki Hoshino,1 Tsunemi Sugimoto,2 and Kohichi Kashiwagi2
1Graduate School of Engineering, Chiba University, Yayoi, Inage-ku, Chiba 263-8522
2Ube Industries Ltd., 1978-19 Kogushi, Ube, Yamaguchi 755-8633
(Received September 28, 2010; CL-100828; E-mail: satoshi@faculty.chiba-u.jp)
The catalytic Beckmann rearrangement of cyclododecanone
O
N OH
oxime (CDOX) was investigated in silane-nitrile-solvent systems.
We have found that chlorosilanes, such as trimethylchlorosilane
and tetrachlorosilane, are effective catalysts to produce ½-
laurolactam (LRL) at 100 °C. Tetrachlorosilane is the most active
catalyst, and hydrocarbon solvents such as cyclohexane, hexane,
and decane are suitable for the system. Nitriles such as acetonitrile
and benzonitrile would play an important role as a remover of
silane species from the produced LRL-silane salt.
NH
Scheme 1.
Table 1. Effect of solvents in the Beckmann rearrangement of
CDOX at 100 °C for 2 ha
Selectivity/mol %
Conversion
/mol %
Entry Solvent
TON
LRL
CD
The Beckmann rearrangement of ketoximes such as CDOX
is an important reaction to produce LRL for the production of
Nylon-12 (Scheme 1). LRL is industrially produced using
fuming sulfuric acid catalyst in the Beckmann rearrangement
of CDOX, and the produced LRL-sulfate adduct is neutralized
with ammonia to produce ammonium sulfate. Efficient catalyst
systems are required for the reduction of waste ammonium
sulfate and for the simplification of the process.
Catalyst: Me3SiCl
1
2
3
4
5
MeCN
EtCN
PhCN
MeNO2
Me2NCHO
100
99.1
96.1
12.9
29.1
90.0
94.9
95.8
0
8.5
0.1
1.8
65.0
43.6
23.6
24.7
24.7
0
0
0
In the liquid-phase Beckmann rearrangement of CDOX,
solid catalysts such as zeolites and heteropolyacid cesium salt
have been reported.1-4 One of the answers to the question of how
to reduce the use of sulfuric acid is to apply the vapor-phase
process: ¢-zeolite is proposed as a catalyst in a vapor-phase
reaction at 320 °C.5
Catalyst: SiCl4
6
7
8
MeCN
Et2NCHO
CHCl3
100
24.4
9.6
31.0
75.4
97.7
38.4
49.6
0
0.6
20.0
18.8
7.4
26.2
2.5
1.3
0
9
10
n-Hexane
MeCNb
In the liquid-phase Beckmann rearrangement of CDOX,
homogeneous catalysts, which effectively work in specific
solvents such as acetonitrile6-8 and nitromethane,6 are reported.
In the Beckmann rearrangement of cyclohexanone oxime, solid
catalysts have been proposed by several research groups.9-13 In
the successful reports of the Beckmann rearrangement, various
liquid-phase processes have employed nitrile solvents such as
acetonitrile4,6-10,14 and benzonitrile3,11-14 since 2002. There is a
report of the effect of solvent in the homogeneous Beckmann
rearrangement of cyclohexanone oxime:14 linear correlation
between dielectric constant of the solvent and the initial reaction
rate. However, the role of nitriles in the liquid-phase Beckmann
rearrangement has not been clarified. In this paper, we examined
the Beckmann rearrangement of CDOX using silane-nitrile
catalyst systems with various solvents to elucidate the effect of
nitriles in the liquid phase, and found that LRL was selectively
formed from CDOX in silane-nitrile-hexane systems.
Commercially available reagents were purchased from
Wako Pure Chemical Industries Ltd., Tokyo Chemical Industries
Co., Ltd., or Kokusan Chemical Co., Ltd., while CDOX was
supplied by Ube Industries Ltd. The Beckmann rearrangement
of CDOX was performed in a pressure vessel with a volume of
50 cm3. The reactor vessel with catalyst (0.19 mmol), CDOX
(1.0 g, 5.1 mmol), and solvent (10 g) was placed in an oven at
100 °C. After the prescribed period, the vessel was cooled at
0 °C. The reaction mixture recovered was analyzed on a gas
95.8
3.9
336
aSolvent: 10 g, catalyst/CDOX: 0.19/5.1 (mmol/mmol). bReacted
at 130 °C for 6 h, catalyst/CDOX: 0.011/5.1 (mmol/mmol).
chromatograph (FID-GC, Shimadzu GC-8A), using a 60-m
capillary column (TC-WAX, GL Science, Japan).
Table 1 shows the effect of solvents on the Beckmann
rearrangement of CDOX catalyzed by chlorotrimethylsilane,
Me3SiCl, and tetrachlorosilane, SiCl4, at 100 °C. The silanes
effectively worked as a catalyst to produce selectively LRL with
high turnover number, TON, in nitrile solvents (Entries 1-3 and
6). The results are in good harmony with the previous reports:
nitriles are the specific solvents for the Beckmann rearrange-
ment.3,4,6-14 The large TON promises that this catalytic system
could drastically reduce catalyst waste (Entry 10).
Table 2 lists the conversion of CDOX in benzonitrile solvent
using various catalyst candidates. Acidic halides and silane
compounds were effective catalysts for the rearrangement. In
particular, SiCl4 is the most active and selective catalyst among
the candidates we tested: it completed the Beckmann rearrange-
ment of CDOX at 100 °C in 2 h (Entry 14). Although HCl
showed TON larger than 1, HCl was less active than chlorosi-
lanes (Entry 15). Other compounds without halogen, such as
acetic anhydride, sulfuric acid, ethoxytrimethylsilane, and
triethylsilane, were not effective (Entries 1-4). These findings
suggest that chlorosilanes produce silyl cations as active species.
Chem. Lett. 2010, 39, 1319-1320
© 2010 The Chemical Society of Japan