Selective decomposition of cyclohexyl hydroperoxide by copper ion-containing quaternary ammonium salts in alkali-free medium

Article abstract of DOI:10.1016/j.catcom.2013.05.022

A novel catalytic system composed of quaternary ammonium salts and copper (II) chloride was prepared. The catalyst showed high conversion and selectivity in the decomposition of cyclohexyl hydroperoxide to cyclohexanol and cyclohexanone (K/A oil) at room temperature in alkali-free medium. 93% conversion with 96% selectivity for cyclohexanone and cyclohexanol could be obtained.

Full text of DOI:10.1016/j.catcom.2013.05.022

Catalysis Communications 40 (2013) 55–58
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Selective decomposition of cyclohexyl hydroperoxide by copper
ion-containing quaternary ammonium salts in alkali-free medium
a,b
a
a
a,b
a
a,
Xi Zheng , Min Wang , Zhiqiang Sun , Junxia Liu , Jiping Ma , Jie Xu ⁎
a
Dalian National Lab for Clean Energy, State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, PR China
Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel catalytic system composed of quaternary ammonium salts and copper (II) chloride was prepared. The
catalyst showed high conversion and selectivity in the decomposition of cyclohexyl hydroperoxide to
cyclohexanol and cyclohexanone (K/A oil) at room temperature in alkali-free medium. 93% conversion
with 96% selectivity for cyclohexanone and cyclohexanol could be obtained.
Received 27 February 2013
Received in revised form 1 May 2013
Accepted 25 May 2013
Available online 31 May 2013
©
2013 Elsevier B.V. All rights reserved.
Keywords:
Quaternary ammonium salts
Copper
Cyclohexyl hydroperoxide
Decomposition
Alkali free
1
. Introduction
salts as green catalysts have aroused wide attention in many reactions
10–17]. It is reported that onium salts could promote the homolytic de-
[
The liquid-phase autoxidation of cyclohexane is an important
industrial process for producing cyclohexanone and cyclohexanol
K/A oil). K/A oil are precursors for caprolactam and adipic acid, which
are the building blocks for nylon-6 and nylon-6, 6, respectively.[1]
In order to maximize the yield of K/A oil, the industrial process is usually
divided into two steps: the first step is cyclohexane oxidation in ab-
sence of catalysts at high temperature (160 °C) with low conversion
composition of CHHP into radicals[18]. Metal ion-containing ionic liquid
is a kind of onium cation with metal ion-containing complex as counter
anions, which may possess potential applications in the decomposition
of CHHP.
In a continuation of our research to develop high-efficiency catalysts
for the decomposition of CHHP in alkali-free medium[2–5], herein, copper
(
ion-containing hexadecyl trimethyl ammonium chloride ([HTA]
2
[CuCl
4
])
(
(
3.5–4.5%) to maximize the selectivity of cyclohexyl hydroperoxide
CHHP) (60–70%); the second step is the catalytic decomposition of
was prepared and applied for the decomposition of CHHP. CuCl
2
could be
easily introduced to quaternary ammonium salts via the formation of
four-coordinated CuCl2
−
complex. It is found that this catalyst was highly
CHHP to K/A oil. Great efforts have been made to develop high active
catalysts for the decomposition of CHHP[2–9]. Currently, the most
commonly used catalyst is NaOH aqueous containing Co2 in the indus-
trial process. However, this catalyst suffers from economic and environ-
mental drawbacks: (1) low selectivity of K/A oil and a number of
ring-opening side reaction products; (2) reaction process consumes a
large amount of alkali leading to environmental pollution and increas-
ing costs; (3) not conductive recycling by-product of organic acids in
the alkali medium. Thus, it is significant to explore new catalyst for
the efficient decomposition of CHHP in alkali-free medium.
4
active in the decomposition of CHHP at room temperature.
+
2
. Experimental
2 4
2.1. General procedure for the synthesis of [HTA] [CuCl ]
The copper ion-containing quaternary ammonium salts were
prepared as follows: A stoichiometric amount of anhydrous CuCl
2
was added to the anhydrous ethanol solution of quaternary ammoni-
um salts. The reaction mixture was refluxed for 1 h. Then the solvent
was evaporated completely, golden solid was obtained. The solid was
recrystallized in anhydrous ethanol before use. Calculation for
Recently, metal ion-containing ionic liquids, especially those based
on dialkylimidazolium, N-alkylpyridinium and quaternary ammonium
2
+
[
2 4
HTA] [CuCl ]: C, 58.84%; N, 3.61%; H, 10.84%; Cu , 8.26%. Found:
2
+
C, 58.63%; N, 3.62%; H, 10.57%, Cu , 8.44%. Other catalysts were
prepared using the same method (Table S1).
⁎
Corresponding author. Tel./fax: +86 411 84379245.
E-mail address: xujie@dicp.ac.cn (J. Xu).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.05.022

56
X. Zheng et al. / Catalysis Communications 40 (2013) 55–58
2
.2. Synthesis of n-heptane solution containing CHHP
organic component in [HTA]
TGA and DR UV–vis, it could be deduced that the molar ratios of HTAC
and CuCl is 2, that is consistent with the above-mentioned elemental
2 4
[CuCl ] (82.6%). Based on the results of
Raw material CHHP dissolved in cyclohexane was provided by
2
2
−
Liaoyang Synthetic Fiber Co. Ltd. (China). In order to eliminate the
influence of cyclohexanol and cyclohexanone that consist in raw
material on the results of CHHP decomposition, the raw material was
purified before use. Meanwhile, in order to get rid of the phenomenon
of cyclohexane oxidation in the process of CHHP decompostion,
n-heptane was used as alternative solvent. The reaction solution was
prepared as follows: the CHHP solution (raw material) was first reacted
with NaOH in water, leading to an aqueous solution of the peroxide sodi-
4
analysis result, and the counter anion should be CuCl .
3.2. Catalytic activity
Different catalysts were used for decomposition of CHHP at room
temperature. When the reaction was performed without catalyst
or with CuCl as catalyst, the decomposition reaction almost did not
2
um salt, which was neutralized by NaHCO
n-heptane. The organic phase was dried by anhydrous MgSO
tion contains CHHP (0.597 mmol/mL), cyclohexanol (0.006 mmol/mL),
cyclohexanone (0.004 mmol/mL), acid and ester (0.011 mmol/mL).
3
followed by extraction with
. The solu-
occur at room temperature (Table 1, entries 1–2). When HTAC was
used as catalyst, the conversion of CHHP reached 33% (Table 1,
entry 3). It means that quaternary ammonium salt was active in the
4
2 4
decomposition of CHHP. Further, [HTA] [CuCl ] showed much higher
activity (video in the supporting information), 93% conversion could
be obtained under the same conditions (Table 1, entry 7). The CuCl2
−
2
.3. Decomposition procedure
4
complex formed by the interaction between copper chloride and qua-
ternary ammonium salts might be able to promote the decomposition
The reaction was carried out in a 50 mL stainless steel autoclave
under magnetic stirring. In a typical procedure, 0.02 g catalyst and
0 mL n-heptane solution containing CHHP (0.597 mmol/mL) were
added into the reactor. The reaction was conducted at room temper-
ature for 30 min under N atmosphere.
of CHHP. In order to display the activity of [HTA]
designed catalysts such as cobalt-containing SiO
with multi-nanochambers (Co–SiO ) and α-Co(OH)
nanoflowers were also tested at room temperature and much lower ac-
tivity than that of [HTA] [CuCl ] for CHHP decomposition were obtained
(Table 1, entries 4–5). Furthermore, industrial catalyst of Co in alkali
medium was also used to decompose CHHP at room temperature, only
45% conversion and 84% selectivity of K/A oil were obtained. Thus,
2
[CuCl
-based nanosphere
hierarchical
4
], our former
1
2
2
2
2
2
4
2
+
3
. Results and discussions
3
.1. Characterization of the materials
2 4
[HTA] [CuCl ] might be a more appropriate choice for CHHP decompo-
2 4
X-ray diffraction pattern of [HTA] [CuCl ] recrystallized in ethanol
sition from both economic and environmental perspectives.
was presented in Fig. S1. A series of diffraction peaks of (0 0 l; l = 2,
, 6, 8, 10, …) were observed, suggesting [HTA] [CuCl ] process a high
ordered two-dimensional layered perovskite structure.
To further investigate the structure of [HTA] [CuCl
The influence of different quaternary ammonium cations on the
decomposition of CHHP was studied. Octyl trimethyl ammonium
chloride, decyl trimethyl ammonium chloride, dodecyl trimethyl
ammonium chloride, and tetradecyl trimethyl ammonium chloride
4
2
4
2
4
], diffuse
reflectance UV–visible spectra (DR UV–vis) were carried out (Fig. 1).
Two distinct absorption bands centered at 292 and 402 nm were ob-
served, which could be ascribed to the transition between the Cl (3p)
valence band and Cu (4s) conduction band and the transition from
the top of the valence band composed of Cl (3p) orbital to the bottom
of the Cu (3d) conduction band, respectively. It has been reported
that these bands are characteristic absorption of the inorganic sheets
of corner-sharing copper chloride octahedral sandwiched with organ-
ic layers.[19–22] This indicated that copper chloride was introduced
to hexadecyl trimethyl ammonium chloride (HTAC) via the formation
2
combined with CuCl were also effective in the decomposition of
CHHP (Table 2). It was found that the activity of catalysts increased
with the increase of the length of alkyl chain. The hydrophobicity of
this catalyst is enhanced with the length of alky chains increasing.
We previously showed that the activity in hydrocarbon oxidation
could be enhanced by the increase of the hydrophobicity of catalyst
[23–26]. Similarly, catalysts with longer alky chains were more easily
dispersed in the nonpolar solvent, and thus the interaction between
CHHP and the catalyst was enhanced.
The effect of other metal on the CHHP decomposition was further
studied. The results were summarized in Fig. 2. Mn and Cu showed good
performances for CHHP decomposition. While, Ni and Zn showed lower
activity than that of Cu. These results may be related to the Lewis acidity
and coordination ability of metal ions [27]. The change of the metal ion
has a great influence on the catalyst activity. Metal ion might be the
major influence factor of our catalytic system.
2
−
of four-coordinated CuCl
4
complex.
The TGA curve (Fig. S2) showed a drastic weight loss at 235–435 °C,
which could result from the decomposition of HTAC. The corresponding
weight loss was 83.1%, which was similar to the weight fraction of
0.15
0.10
0.05
0.00
Table 1
a
Catalytic decomposition of CHHP with different catalysts.
c
Entry
Catalysts
CHHP/
catalyst
Conversion
(%)
Selectivity
(%)
K/A oil
(%)
b
A
K
Others
1
2
3
4
5
6
7
none
–
trace
trace
33
24
18
–
–
–
–
CuCl
2
40
93
27
478
176000
231
–
–
–
–
HTAC
Co(OH)2
57
61
65
48
59
38
34
29
36
37
5
5
6
16
4
95
95
94
84
96
a
b
Co–SiO
Co + NaOH
[HTA] [CuCl
2
d
45
93
2
4
]
a
Reactions were carried out with 0.02 g catalyst in 10 mL n-heptane solution
containing cyclohexyl hydroperoxide (0.597 mmol/mL) at 25 °C for 30 min.
2
50
300
350
400
450
500
550
600
b
Wavelength (nm)
molar ratio of CHHP and catalyst.
A, cyclohexanol; K, cyclohexanone; others, mainly adipic acid and esters.
c
d
Reaction was carried out with 2 mL NaOH aqueous solution (5 wt.%) and 2 ppm Co2+.
2 4
Fig. 1. DR UV–vis spectra of [HTA] [CuCl ] (a) and HTAC (b).

X. Zheng et al. / Catalysis Communications 40 (2013) 55–58
57
Table 2
Catalytic performance of different quaternary ammonium salts in the decomposition of
CHHP.a
Catalysts
CHHP/catalystb Conversion (%) Selectivityc (%)
K/A oil (%)
A
K
Others
[
[
[
[
[
OTA]
DTA]
2
[CuCl
[CuCl
[CuCl ]
2 4
4
4
]
]
164
181
198
215
231
74
77
83
87
93
49 46
50 44
56 40
55 41
59 37
5
6
4
4
4
95
94
96
96
96
2
DDTA]
TTA] [CuCl
4
HTA] [CuCl ]
2
4
]
2
a
Reactions were carried out with 0.02 g of catalyst in 10 mL of n-heptane solution
containing cyclohexyl hydroperoxide (0.597 mmol/mL) for 30 min at 25 °C.
b
molar ratio of CHHP and catalyst.
A, cyclohexanol; K, cyclohexanone; others, mainly adipic acid and esters.
c
The pathway for CHHP decomposition was studied through real-
time in situ Fourier transform infrared (FT-IR) spectral measurements
(
Fig. 3). Before the addition of catalyst, with the background correc-
tion (Supporting information), the CHHP revealed intense absorption
−
1
at 1369 cm (vibrational absorption peaks of C–O) could be used to
measure the CHHP changes in the reaction process (point-in-time A
2 4
in Fig. 3). After the addition of [HTA] [CuCl ], CHHP decomposed rap-
idly and intermediate specie was observed with a broad absorption
−
1
band at 1680–1600 cm (point-in-time B in Fig. 3a). As the reaction
proceeded, this peak then disappeared followed by the emerging
of vibrational absorption peaks of C–O and C = O in cyclohexanol
−
1
and cyclohexanone at 1120 and 1725 cm
respectively. The broad
−
1
absorption band at 1680–1600 cm manifested that new intermediate
species formed in the reaction process. Catalyst could rapidly interact
with CHHP to form intermediate species, so that accelerating the
decomposition of CHHP. Because the reaction proceeds very rapidly,
intermediate species are difficult to be separated from the reaction
medium. We are currently unable to determine the structure of the
intermediate species.
Furthermore, the mechanism of CHHP decomposition was investi-
gated tentatively. When radical inhibitor 2,6-tert-butyl-p-cresol (BHT)
was added to the reaction system, the reaction was markedly inhibited
and trace amounts of CHHP was decomposed. This indicates that a free
radical process might be involved in CHHP decomposition. This result
was consistent with other previous research.[18,28,29] What's more,
radicals that formed by the homolytic activation of CHHP might be sta-
bilized by BHT radical. The structures of the corresponding free radicals
formed in chain initiation were studied by GC-MS preliminarily
Fig. 3. a) A segment of in situ FT-IR for the CHHP decomposition with [HTA]
catalyst at room temperature (A: no catalyst; B: catalyst was added; C: the end of the
reaction). b) FT-IR spectra of point-in-time A, B and C.
2
[CuCl
4
] as
decomposes mainly into alkyl radical R• and alkoxy radical RO• by the
homolytic activation. R• and RO• react very quickly in presence of
CHHP to cyclohexanol and cyclohexanone in propagation and termina-
tion steps. The detailed mechanism remains to be further studied.
In summary, we have developed copper ion-containing quaternary
ammonium salts for the catalytic decomposition of CHHP at room
temperature in alkali-free medium. Copper chloride is successfully in-
(
Fig. S3). Based on the above results, CHHP decomposition mechanism
might be a free radical homolytic mechanism. Through the effect
2 4
of [HTA] [CuCl ], CHHP acts as radical initiator, which subsequently
2
−
troduced to quaternary ammonium salts via the formation of CuCl
4
complex. The presence of CuCl2
−
complex in the catalytic system is
4
Conversion of CHHP decomposition
Selectivity of K/A oil
crucial to ensure high efficiency of CHHP decomposition. The relationship
between the high activity and structures is now under investigation.
[
HTA] [CuCl ]
2 4
Acknowledgment
[
[
[
HTA] [MnCl ]
This study was financially supported by the National Natural Science
Foundation of China (21233008, 21103175 and 21103206).
2
4
HTA] [NiCl ]
2
4
Appendix A. Supplementary data
HTA] [ZnCl ]
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2013.05.022.
2
4
0
20
40
60
80
100
References
Conversion (%) and selectivity (%)
[
1] U. Schuchardt, D. Cardoso, R. Sercheli, R. Pereira, R.S. de Cruz, M.C. Guerreiro, D.
Mandelli, E.V. Spinace, E.L. Fires, Applied Catalysis A 211 (2001) 1.
Fig. 2. Catalytic performance of different metal (II) ion-containing catalysts. Reaction
conditions: 0.02 g catalyst in 10 mL n-heptane solution containing cyclohexyl hydroperoxide
[2] X. Zheng, M. Wang, Z.Q. Sun, C. Chen, J.P. Ma, J. Xu, Catalysis Communications 29
(2012) 149.
(0.597 mmol/mL) at 25 °C for 30 min.

58
X. Zheng et al. / Catalysis Communications 40 (2013) 55–58
[
[
3] M. Wang, C. Chen, J.P. Ma, X. Zheng, Q.W. Li, Y.Q. Jin, J. Xu, Journal of Materials [18] L.J. Csanyi, K. Jaky, Z. Kota, T. Pali, Journal of Molecular Catalysis A: Chemical 209
Chemistry 22 (2012) 11904.
(2004) 59.
4] M. Wang, J.P. Ma, C. Chen, X. Zheng, Z.T. Du, J. Xu, Journal of Materials Chemistry
[19] G.S. Li, D.M. Camaioni, J.E. Amonette, Z.C. Zhang, T.J. Johnson, J.L. Fulton, The Journal
of Physical Chemistry B 114 (2010) 12614.
21 (2011) 12609.
[
[
5] Z.Q. Sun, J. Xu, Z.T. Du, W. Zhang, Applied Catalysis A 323 (2007) 119.
6] D. Loncarevic, J. Krstic, J. Dostanic, D. Manojlovic, Z. Cupic, D.M. Jovanovic, Chemical
Engineering Journal 157 (2010) 181.
[20] T. Sasaki, M. Tada, C. Zhong, T. Kume, Y. Iwasawa, Journal of Molecular Catalysis A:
Chemical 279 (2008) 200.
[21] Y.Y. Zheng, G. Wu, M. Deng, H.Z. Chen, M. Wang, B.Z. Tang, Thin Solid Films 514
(2006) 127.
[22] J. Brugger, D.C. McPhail, J. Black, L. Spiccia, Geochimica et Cosmochimica Acta 65
(2001) 2691.
[23] M. Wang, C. Chen, J.P. Ma, J. Xu, Journal of Materials Chemistry 21 (2011) 6962.
[24] C. Chen, J. Xu, Q.H. Zhang, Y.F. Ma, L.P. Zhou, M. Wang, Chemical Communications
47 (2011) 1336.
[7] R.P. Saint-Arroman, B. Didillon, A. de Mallmann, J.M. Basset, F. Lefebvre, Applied
Catalysis A 337 (2008) 78.
[8] A. Ramanathan, M.S. Hamdy, R. Parton, T. Maschmeyer, J.C. Jansen, U. Hanefeld,
Applied Catalysis A 355 (2009) 78.
[
9] R.P. Saint-Arroman, J.M. Basset, F. Lefebvre, B. Didillon, Applied Catalysis A 290 (2005)
81.
10] C. Zhong, T. Sasaki, A. Jimbo-Kobayashi, E. Fujiwara, A. Kobayashi, M. Tada, Y. Iwasawa,
1
[
[25] M. Wang, C. Chen, Q.H. Zhang, Z.T. Du, Z. Zhang, J. Gao, J. Xu, Journal of Chemical
Technology and Biotechnology 85 (2010) 283.
Bulletin of the Chemical Society of Japan 80 (2007) 2365.
[
[
[
[
[
[
[
11] Q.H. Zhang, S.G. Zhang, Y.Q. Deng, Green Chemistry 13 (2011) 2619.
12] T. Welton, Chemical Reviews 99 (1999) 2071.
[26] C. Chen, L.P. Zhou, Q.H. Zhang, H. Ma, H. Miao, J. Xu, Nanotechnology 18 (2007)
215603.
[27] S. Kobayashi, T. Busujima, S. Nagayama, Chemistry - A European Journal 6 (2000)
3491.
[28] L.J. Csanyi, K. Jaky, I. Palinko, A. Rockenbauer, L. Korecz, Physical Chemistry Chemical
Physics: PCCP 2 (2000) 3801.
[29] P.P. Toribio, J.M. Campos-Martin, J.L.G. Fierro, Applied Catalysis A 294 (2005) 290.
13] J.P. Hallett, T. Welton, Chemical Reviews 111 (2011) 3508.
14] H. Olivier-Bourbigou, L. Magna, D. Morvan, Applied Catalysis A 373 (2010) 1.
15] V.I. Parvulescu, C. Hardacre, Chemical Reviews 107 (2007) 2615.
16] H.B. Zhao, J.E. Holladay, H. Brown, Z.C. Zhang, Science 316 (2007) 1597.
17] D. Betz, P. Altmann, M. Cokoja, W.A. Herrmann, F.E. Kuhn, Coordination Chemistry
Reviews 255 (2011) 1518.