The influence of triethylamine on the hydrodechlorination reactivity of chlorophenols over Raney Ni catalyst

Article abstract of DOI:10.1016/j.catcom.2010.09.023

The hydrodechlorination (HDCl) of 2,4-dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) over Raney Ni in liquid phase with triethylamine (Et₃N) under mild conditions was studied. The results showed that Et₃N together with solvents significantly affected the HDCl reactivity or selectivity, in which ortho-positioned Cl of chlorophenols (CPs) was easier to be dechlorinated in methanol (MeOH) and ethanol (EtOH), whereas para-positioned Cl was preferentially dechlorinated in water. Different species and action mechanisms of Et₃N in water and organic solvents possibly affected the HDCl reactivity or selectivity of CPs over Raney Ni.

Full text of DOI:10.1016/j.catcom.2010.09.023

Catalysis Communications 12 (2010) 282–285
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
The influence of triethylamine on the hydrodechlorination reactivity of
chlorophenols over Raney Ni catalyst
a,b
a
a
a
a
a,
Xuanxuan Ma , Shiwei Zhou , Cuiyun Yang , Sujing Liu , Xiaoli Bi , Chuanhai Xia ⁎
a
Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China
Graduate School of Chinese Academy of Sciences, Beijing 100049, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 May 2010
Received in revised form 8 September 2010
Accepted 17 September 2010
Available online 25 September 2010
The hydrodechlorination (HDCl) of 2,4-dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and 4-chlorophenol
(
4-CP) over Raney Ni in liquid phase with triethylamine (Et
showed that Et N together with solvents significantly affected the HDCl reactivity or selectivity, in which
ortho-positioned Cl of chlorophenols (CPs) was easier to be dechlorinated in methanol (MeOH) and ethanol
EtOH), whereas para-positioned Cl was preferentially dechlorinated in water. Different species and action
3
N) under mild conditions was studied. The results
3
(
mechanisms of Et
over Raney Ni.
3
N in water and organic solvents possibly affected the HDCl reactivity or selectivity of CPs
Keywords:
Hydrodechlorination (HDCl)
Triethylamine (Et
3
N)
© 2010 Elsevier B.V. All rights reserved.
Raney Ni
Chlorophenol (CP)
Catalytic reactivity/selectivity
1
. Introduction
Chlorophenols (CPs) have been widely used as wood preserva-
of Pd/C for the dehalogenation of 4-bromobiphenyl (4-BB) and 2-
chlorophenol (2-CP) under mild conditions [17,18].
During the HDCl process of chlorinated organic compounds, HCl
by-product formed, which might result in the deactivation of
catalysts. So, some bases were often used as scavengers of HCl to
eliminate and minimize the poison of HCl to catalysts [8,9,19]. As an
organic base, triethylamine (Et N) has been used in a series of the
3
HDCl reactions over Pd catalysts to remove HCl formed [20–24].
Additionally, Monguchi et al. [22] thought that, besides playing a role
of a base in the HDCl of aryl chlorides, Et N also could act as an
3
tives, and as pesticides/herbicide precursors. Furthermore, they can
also be found in effluent streams associated with the pulp and paper
industries. Due to the high toxicity and hard biodegradability of these
compounds, they have been long regarded as a major source of
environmental pollution [1]. Therefore, development of efficient
methods to dispose them is very necessary and important. In the
last few years, various destructive techniques including biological,
thermal and chemical treatments have been developed for the
detoxification of organic pollutants [2,3]. Among them catalytic
hydrodechlorination (HDCl) has received attention as one of the
most promising and innovative technologies for the disposal of toxic
organochlorines, which can convert the toxic organic chlorides into
the corresponding hydrocarbons under mild conditions [4–6].
electron donor for the reactants and expedite the HDCl reaction.
In this work, the HDCl reactivities of CPs such as 2,4-DCP, 2-CP and
4-CP were investigated in liquid phase over Raney Ni with Et
room temperature and atmospheric pressure. It was found that Et
obviously affected the HDCl reactivity or selectivity of CPs, and played
different roles in water and organic solvents. The effect of Et N on the
3
N at
3
N
3
Usually, supported Pd catalysts were chosen in the HDCl of CPs in
liquid phase [7–12], but it was limited in the practical use due to the
high cost of these catalysts. In recent years, the use of low-cost
catalysts such as Raney Ni has received considerable attention in the
HDCl of aryl chlorides. Many studies have indicated that organo-
chlorines could be completely HDCl in liquid system over Raney Ni
under mild conditions [13–16]. In our previous studies, it was also
proved that the catalytic activity of Raney Ni was comparable to that
HDCl reactivity or selectivity of aryl chlorides has not been reported in
literature.
2. Experimental
2.1. Experimental materials
Raney Ni catalyst (RTH-311) used in experiments was supplied by
Dalian Tongyong Chemical Co., Ltd., Liaoning, China. The weight
percentage of nickel and aluminum in the catalyst was more than 90%
and less than 7%, respectively. The catalyst was not pre-treated before
experiments and only kept in water-sealing storage.
⁎
Corresponding author. Tel.: +86 535 2109173; fax: +86 535 2109000.
E-mail address: chxia@yic.ac.cn (C. Xia).
1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.09.023

X. Ma et al. / Catalysis Communications 12 (2010) 282–285
283
All CPs used in experiments were purchased from Alfa Aesar with a
minimum purity of 98%. The other analytical reagents such as
methanol (MeOH), ethanol (EtOH), Et N and NaOH were supplied
Table 1
The hydrodechlorination reactivity of 2,4-DCP over Raney Ni catalyst with Et
NaOH in liquid phase.
3
N or
a
3
by Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. De-ionized
water and high purity hydrogen and nitrogen (N99.99%) were used in
experiments.
Base
Solvent
Methanol
Ethanolb
Water
Time
min)
Products distribution (%)
(
DCP
2-CP
4-CP
Phenol
Et
3
N
10
81.6
64.6
49.3
90.9
76.3
64.3
70.2
24.4
7.1
3.4
3.9
3.7
0
2.2
2.6
4.6
2.7
0.9
0
6.8
10.4
11.4
5.4
10.9
13.9
0.9
0
8.2
21.1
35.6
3.7
10.6
19.2
24.3
72.9
92.0
100
7.8
17.6
29.2
11.7
34.4
68.6
100
3
6
0
0
2
.2. Experimental process
10
3
6
0
0
5
5
0
0
The reaction was carried out in a three-neck flask at 40 °C, which
was attached with a thermometer, a condenser and a hydrotreater
including a hydrogen cylinder, hydrogen flowmeter, three-way valve
1
2
3
(
0
0
and a nitrogen cylinder), with a magnetic stirrer. Under atmospheric
pressure, 80 mL solutions (water or MeOH/EtOH) were added into the
0
NaOH
Methanol
Water
10
30
60
5
90.3
80.3
69.0
85.0
60.8
29.3
0
1.1
1.2
1.1
3.3
4.0
2.1
0
0.8
0.9
0.7
0
0.8
0
flask, containing 2,4-DCP (3.13 mmol), 2-CP/4-CP (6.22 mmol), Et
3
N
(
9.29 mmol) or NaOH (6.85 mmol). After the air in the flask was
completely replaced by nitrogen, Raney Ni (0.2 g or 0.4 g) was added.
Then the reaction mixture was stirred vigorously with a magnetic
stirrer and was kept at 40 °C using a thermostated water bath. During
the reaction, an aliquot of the reactant was taken and centrifuged, and
then analyzed by gas chromatography (GC).
1
3
5
5
0
0
0
a
3
Reaction conditions: 80 mL solutions containing 2,4-DCP (3.13 mmol), Et N
(
9.29 mmol) or NaOH (6.85 mmol) and Raney Ni (0.4 g for organic solvents and 0.2 g
−
1
for water), 40 °C, 10 mL H
2
min
.
b
3
Et N (4.45 mmol).
2
.3. Product analysis
The intermediate products in the HDCl of CPs were determined by
3
However, when Et N as a base was used, more 2-CP as an
intermediate product was produced in water, and more 4-CP was
formed in MeOH and EtOH (Table 1). It indicated that in the presence
of Et N, ortho-positioned Cl of 2,4-DCP was easier to be dechlorinated
3
by Raney Ni in organic solvents; on the contrary, para-positioned Cl
GC/MS (Thermo Scientific ITQ 900) with a column of HP-5
30 m×0.25 mm×0.25 μm). The composition of the reaction system
was analyzed by GC/FID (Agilent 7890A) with a column of DB-1701
30 m×0.32 mm×0.25 μm).
(
(
was easier to be dechlorinated in water. The result in organic solvents
3
. Results and discussion
3
with Et N was inconsistent with those of previous studies, where 2-CP
was the only reactive intermediate product in the HDCl of 2,4-DCP in
Usually, 2,4-DCP was catalytically hydrogenated within 60 min in
liquid system [8–10,12,25–28].
water with hydrogen gas over Raney Ni under mild conditions
Table 1). According to the analytical results of GC/MS, 2-CP and 4-CP
3
Consequently, we concluded that Et N together with solvents
(
affected greatly the HDCl reactivity or selectivity of CPs over Raney Ni,
where the ortho-positioned Cl was easier to be dechlorinated in
organic solvents, whereas para-positioned Cl was easier to be
dechlorinated in water. Scheme 1 described the HDCl process of 2,4-
were the dechlorinated intermediate products in the HDCl of 2,4-DCP,
and then they could be further converted to phenol, and even, to
cyclohexanone and cyclohexanol with hydrogen gas over Raney Ni. In
the end, phenol was the main product, and only a small amount of
cyclohexanone and cyclohexanol formed. Therefore, the HDCl of 2,4-
DCP was a stepwise process and the HDCl reaction pathway of 2,4-
DCP was shown in Scheme 1. Compared to CPs, phenol, cyclohexa-
none and cyclohexanol are less toxic and useful as intermediates in
chemical manufacturing. Thus, the HDCl method with Raney Ni
catalyst could effectively decrease and eliminate the toxicity and
pollution of CPs.
DCP affected by Et
understand the influence of Et
3
N/NaOH and solvents. In order to further
N on the HDCl reactivity of CPs, the
3
HDCl processes of single and mixed 2-CP and 4-CP were investigated.
The HDCl processes of single 2-CP and 4-CP over Raney Ni with
Et N in different solvents under mild conditions were shown in Fig. 1.
3
It was seen that the HDCl of 2-CP was always faster than that of 4-CP
in organic solvents (MeOH and EtOH), whereas the HDCl reactivity
was just the opposite in water. In order to more visually display the
Additionally, it was clearly observed in Table 1 that the
dechlorination reactions were faster in water than that in EtOH and
MeOH under the same conditions. It means that solvent effects
showed a very important influence on the HDCl reaction. This result
was possibly attributed to a lesser catalyst deactivation as a result of
3
effect of Et N on the HDCl reactivity of 2-CP and 4-CP, we further
researched the HDCl processes of mixed 2-CP and 4-CP under the
same reaction conditions, as shown in Fig. 2. It was clearly observed
that there was the same trend as Fig. 1, that is, the HDCl of 2-CP was
always faster than that of 4-CP in organic solvents, whereas the HDCl
of 4-CP was always faster than that of 2-CP in water. In a word,
whether in single system or in mixed system of 2-CP and 4-CP, ortho-
positioned Cl was easier to be dechlorinated in organic solvents,
whereas the priority HDCl of para-positioned Cl occurred in water,
which was the same as the results obtained in the HDCl of 2,4-DCP.
increased solubility of HCl and/or NaCl and Et
3
NHCl (formed during
HCl neutralization with NaOH or Et N) which facilitated their removal
3
from the active surface of the catalyst in water [20–24].
In some literature, 2-CP was the only reactive intermediate
product in the HDCl of 2,4-DCP in liquid system [8–10,12,25–28]. In
this study, it could be seen that when NaOH was used as a base in
liquid system, the amount of 2-CP formed was more than that of 4-CP
in organic solvent (MeOH) and in water by GC/MS during the HDCl of
3
As an organic base, Et N possibly played different roles in water and
organic solvents. It is easy to ionize to form ammonium ion and hydroxyl
ion in water. And then, HCl formed in the HDCl processes can be
neutralized by hydroxyl ion (Scheme 2). So, it could eliminate the poison
of HCl to catalysts, and promote the catalytic HDCl processes [20–24]. In
2
,4-DCP (Table 1). It means that para-positioned Cl was easier to be
hydrogenated than ortho-positioned Cl of 2,4-DCP, whether in water
or in organic solvents. This trend was coincident with the results
reported in the literature [8–10,12,25–28]. It was possibly due to the
steric hindrance of hydroxyl group where the ortho-positioned Cl
experienced a more restricted HDCl [8–10,12,25–28].
any case, Et
3
N played an important role of a base in water, the same as
N is
NaOH. However, in organic solvents such as MeOH and EtOH, Et
3
usually difficult to ionize and present in molecular state. As a base, it could
directly react with HCl to form triethylamine-hydrochloride in the HDCl of

284
X. Ma et al. / Catalysis Communications 12 (2010) 282–285
OH
Cl
Water
Main pathway
Raney Ni, H2
Et3
OH
Main pathway
OH
OH
Organic solvent
O
OH
Cl
Cl
+
OH
Cl
Cl
Water
Main pathway
Raney Ni, H2
OH
Organic solvent
Cl
Scheme 1. The hydrodechlorination process of 2,4-DCP over Raney Ni catalyst.
CPs (Scheme 2), by which the poison of HCl to catalysts could be
effectively removed [20–24]. Furthermore, triethylamine-hydrochloride
formed in the HDCl could be a modifier to coat the catalyst, which possibly
influenced the outcome of the reactions by mediating the substrate–
catalyst interactions [29]. Tundo et al. [29,30] had found that some amines
and onium salts could change significantly the reactivity and regio-,
chemo- and stereoselectivities of Pt/C, Pd/C and Raney Ni in the
hydrodehalogenation reactions of haloaromatics.
3
word, Et N not only played an important role of bases but also acted as
an organic modifier in the HDCl processes in organic solvents.
In conclusion, it was believed that the different existing species and
3
action mechanisms of Et N in water and organic solvents possibly affected
and determined the HDCl reactivity or selectivity of CPs over Raney Ni.
4. Conclusions
3
Additionally, Et N having an electron pair on N-atom, can provide
an electron pair to the surface and the active sites of the metal
catalysts such as Pt, Pd, Rh and Ni [31,32]. Due to the interaction
between Et N and Ni, the electron transfer from N to d orbital of Ni
3
probably occurred, thereby changing the surface properties of the Ni
catalyst, which might influence the reactivity or selectivity toward
ortho- and para-positioned Cl of 2,4-DCP in the HDCl processes. In a
3
In the presence of Et N, ortho-positioned Cl was easier to be
dechlorinated over Raney Ni under mild conditions in organic
solvents, whether for dichlorophenol (2,4-DCP) or for monochlor-
ophenols (2-CP and 4-CP); however, the priority dechlorination of
para-positioned Cl occurred in water. That is, Et N had a significant
3
influence on the HDCl reactivity or selectivity in different solvents.
(
a)
(b)
1
2
0
8
6
4
2
0
12
1
10
8
6
4
2
0
0
10
20
30
40
50
60
0
10
20
30
40
50
60
Time (min)
Fig. 1. In the presence of Et
Reaction conditions: 80 mL solution, 2-CP or 4-CP (6.22 mmol), Et
3
N the hydrodechlorination of single 2-CP (a) and 4-CP (b) over Raney Ni in different solvents under mild conditions (● water; ○ methanol; ▼ ethanol).
−
1
3
N (9.29 mmol) and Raney Ni (0.4 g for organic solvent and 0.2 g for water), 40 °C, 10 mL H
2
min
.

X. Ma et al. / Catalysis Communications 12 (2010) 282–285
285
(
a)
(b)
(c)
6
6
6
5
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
0
10
20
30
40
50
60
0
10
20
30
40
50
10
20
30
40
Time (min)
3
Fig. 2. In the presence of Et N the hydrodechlorination of mixed 2-CP and 4-CP over Raney Ni under mild conditions in methanol (a) ethanol (b) and water (c) (● 2-CP and ○ 4-CP).
−
1
Reaction conditions: 80 mL solution, 2-CP (3.11 mmol) and 4-CP (3.11 mmol), Et
3
N (9.29 mmol) and Raney Ni (0.4 g for organic solvent and 0.2 g for water), 40 °C, 10 mL H
2
min
.
In water
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[
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(
CH CH ) N H O
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(
(CH CH ) NHCl
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