The use of polymeric sulfides as catalysts for the para-regioselective chlorination of phenol and 2-chlorophenol

Article abstract of DOI:10.1080/17415993.2019.1688815

Various poly(alkylene sulfide)s have been synthesized and used as catalysts to enhance the para-regioselectivity in chlorination of phenol and 2-chlorophenol using freshly distilled sulfuryl chloride in the presence of AlCl₃ as an activator. Poly(alkylene sulfide)s having alternating spacers, one having three methylene groups and the second having three, six or nine methylene groups were the most para-regioselective catalysts in chlorination of both phenol and 2-chlorophenol. For example, chlorination of phenol and 2-chlorophenol in the presence of optimal examples of such poly(alkylene sulfide)s gave 4-chlorophenol and 2,4-dichlorophenol as the major products in 94.8 and 95.4% yields, respectively, compared with 75.4 and 55.0% yields in the absence of catalysts. In addition, double chlorination of phenol in the presence of poly(alkylene sulfide)s gave 2,4-dichlrophenol in up to 97.1% yield compared with only 58.6% in the absence of catalysts.

Full text of DOI:10.1080/17415993.2019.1688815

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
The use of polymeric sulfides as catalysts for the
para-regioselective chlorination of phenol and 2-
chlorophenol
Keith Smith, Amany S. Hegazy & Gamal A. El-Hiti
To cite this article: Keith Smith, Amany S. Hegazy & Gamal A. El-Hiti (2019): The use of polymeric
sulfides as catalysts for the para-regioselective chlorination of phenol and 2-chlorophenol, Journal
of Sulfur Chemistry, DOI: 10.1080/17415993.2019.1688815
To link to this article: https://doi.org/10.1080/17415993.2019.1688815
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2019.1688815
The use of polymeric sulfides as catalysts for the
para-regioselective chlorination of phenol and
2-chlorophenol
Keith Smith a, Amany S. Hegazya,b and Gamal A. El-Hiti
c
a
b
School of Chemistry, Cardiff University, Cardiff, UK; Department of Chemistry, University of Wales Swansea,
c
Swansea, UK; Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King
Saud University, Riyadh, Saudi Arabia
ABSTRACT
ARTICLE HISTORY
Various poly(alkylene sulfide)s have been synthesized and used
as catalysts to enhance the para-regioselectivity in chlorination
of phenol and 2-chlorophenol using freshly distilled sulfuryl chlo-
ride in the presence of AlCl3 as an activator. Poly(alkylene sul-
fide)s having alternating spacers, one having three methylene
groups and the second having three, six or nine methylene groups
were the most para-regioselective catalysts in chlorination of both
phenol and 2-chlorophenol. For example, chlorination of phenol
and 2-chlorophenol in the presence of optimal examples of such
poly(alkylene sulfide)s gave 4-chlorophenol and 2,4-dichlorophenol
as the major products in 94.8 and 95.4% yields, respectively, com-
pared with 75.4 and 55.0% yields in the absence of catalysts. In addi-
tion, double chlorination of phenol in the presence of poly(alkylene
sulfide)s gave 2,4-dichlrophenol in up to 97.1% yield compared with
only 58.6% in the absence of catalysts.
Received 3 October 2019
Accepted 30 October 2019
KEYWORDS
Para-regioselective
chlorination; catalysts;
aluminum chloride;
2,4-dichlorophenol; phenol;
poly(alkylene sulfide)s
1. Introduction
Chlorophenols are used in the production of many industrial products such as herbi-
cides, pharmaceuticals and dyes [1]. For example, 2,4-dichlorophenoxyacetic is used in
weed control for many crops such as maize and rice [2,3]. It is still widely used mainly
due to its low production cost and can be produced from the reaction of molar equiva-
lents of chloroacetic acid and 2,4-dichlorophenol (2,4-DCP) in the presence of an excess
CONTACT Keith Smith
Place, Cardiff CF10 3AT, UK; Gamal A. El-Hiti
Optometry, College of Applied Medical Sciences, King Saud University, PO Box 10219, Riyadh 11433, Saudi Arabia
smithk13@cardiff.ac.uk
School of Chemistry, Cardiff University, Main Building, Park
gelhiti@ksu.edu.sa
Cornea Research Chair, Department of
©
2019 Informa UK Limited, trading as Taylor & Francis Group

2
K. SMITH ET AL.
of sodium hydroxide [4]. Therefore, there is continuing interest in the development of
low-cost processes for the selective production of chlorophenols.
Recently, several processes have been developed for the selective halogenation of
aromatic compounds [5–10]. For example, chlorination systems involving the use of
[
bis(trifluoroacetoxy)iodo]benzene and aluminum chloride (AlCl ) in acetonitrile [5], 1,3-
3
dichloro-5,5-dimethylhydantoin in the presence of ammonium chloride in toluene [6],
hydrogen chloride, manganese(II) sulfate and hydrogen peroxide in water [7], and N-
chlorosuccinimide and Nagasawa’s bisthiourea catalyst in chlorinated solvent [8] have
been reported. However, such systems are often selective towards the ortho-isomers and
involve use of solvent, which are not applicable for the commercial production of bulk
chlorophenols.
We have reported a number of efficient processes that employ solid catalysts to enhance
the regioselective production of para- or linear isomers in electrophilic substitution of
aromatic compounds [11–25]. Sheldon’s group has used a similar approach for chlo-
rination of phenol (P) using SO Cl in the presence of L type zeolite in isooctane
2
2
to give 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) in 10.7 and 85.3% yields,
respectively [26]. Under similar reaction conditions, the use of Al-pillared montmo-
rillonite clay as a catalyst gave 2-CP and 4-CP in 13.4 and 75.7% yields, respectively
[
26]. Others have adopted different approaches to chlorination of phenols with various
chlorinating agents [27,28]. However, one of the most promising approaches for commer-
cially relevant selective para-chlorination of phenols involves the use of sulfur-containing
catalysts.
Selective chlorination of phenols using SO Cl in the presence of sulfur-containing cata-
2
2
lysts and Lewis acids was first reported by Watson [29,30]. For example, mono-chlorination
of P using SO Cl in the presence of diphenyl sulfide (Ph S) and AlCl at 25°C gave 2-CP
2
2
2
3
and 4-CP in 8.5 and 89.5% yields, respectively [29,30]. Similarly, chlorination of 2-CP in
the presence of ferric chloride (FeCl ) at 35°C gave 2,4-DCP and 2,6-dichlorophenol (2,6-
3
DCP) in 94.0 and 4.2% yields, respectively [29,30]. Double chlorination of P using SO Cl
2
2
in the presence of Ph S and FeCl at 25°C gave 2,4-DCP (97.3%), 2,6-DCP (0.4%) and
2
3
2
,4,6-trichlorophenol (2.0%) [29,30].
Since then, various other sulfur compounds have been investigated as catalysts in the
chlorination of P and 2-CP. For example, chlorination of P using SO Cl and di-n-butyl
2
2
sulfide in the absence of a Lewis acid at 25°C gave 2-CP, 4-CP, and 2,4-DCP in 8.7, 84.8,
and 1.0% yields, respectively, along with unreacted starting material (5.4%) [31,32]. Chlo-
rination of P using SO Cl in the presence of the cyclic disulfide 1,2-dithiocane and AlCl
2
2
3
at 25°C gave 2-CP (7.4%), 4-CP (91.2%), and 2,4-DCP (1.1%) [33], while use of the poly-
meric equivalent, poly(hexamethylenedisulfide), under similar conditions gave 2-CP, 4-CP
and 2,4-DCP in 8.8, 89.0, and 2.2% yields, respectively [33]. The use of tetrahydrothiopy-
ran as catalyst in chlorination of P using SO Cl in the presence of AlCl at 25°C gave
2
2
3
2
-CP and 4-CP in 5.0 and 89.0% yields, respectively [34], while chlorination of P using
SO Cl in the presence of 5,18-dithiadocosane and AlCl at 35°C gave 2-CP and 4-CP in
2
2
3
6
.6 and 76.4% yields, respectively, along with unreacted starting material (11.4%) [35,36].
Methylthio alcohols, methoxy(methylthio)alkanes, and bis(methythio)alkanes have also
been investigated as catalysts in chlorination of P using SO Cl in the presence of AlCl
2
2
3
at 25°C and led to the production 2-CP (8.2–12.7%) and 4-CP (83.1–88.8%) along with
,4-DCP (1.6–2.3%) [37].
2

JOURNAL OF SULFUR CHEMISTRY
3
We have previously had occasion to synthesize a series of poly(alkylene sulfide)s [38],
which we have used to make stable borane complexes [39,40], and in the patent litera-
ture we have also reported a more complex poly(alkylene sulfide) with a repeating unit
[
(CH ) S(CH ) S] [36]. Such solid sulfur-containing materials could combine some of
2 8 2 6
the advantages of solid reagents (such as ease of removal by filtration, lack of odor) with
some of the benefits of sulfur compounds (as regioselective catalysts). Therefore, we now
report the preparation of further examples of more complex poly(alkylene sulfide)s hav-
ing alternating alkylenethio groups of different chain lengths and their use, along with the
use of symmetrical poly(alkylene sulfide)s, in the regioselective chlorination of phenol and
2
-chlorophenol using SO Cl and AlCl .
2 2 3
2. Results and discussion
A range of poly(alkylene sulfide)s was synthesized using two different synthetic
approaches. The first one involved lithiation of 1,ω-alkanedithiols (one mole equivalent)
using n-butyllithium (n-BuLi; two mole equivalents) in tetrahydrofuran (THF) at low
temperature followed by reaction with 1,ω-dibromoalkanes (0.9 mole equivalent) and
1
-bromobutane (0.2 mole equivalent) at room temperature (Scheme 1). Such a procedure
allowed the production in 75–96% yields of poly(alkylene sulfide)s 1–19 that have alter-
nating spacer units of different chain lengths (number of methylene groups) (Table 1). The
second procedure involved reaction of 1,ω-dibromoalkanes (one mole equivalent) and
sodium sulfide nonahydrate (Na S.9H O; 1.4 mole equivalents) under reflux conditions
2
2
for 4 h (Scheme 2), in accordance with the reported procedure [38]. This method was used
to synthesize poly(alkylene sulfide)s 20–24 that had just one type of spacer unit in 83–97%
yields (Table 2). This method was successfully applied for the production of poly(alkylene
sulfide)s that had 2–8 methylene units as spacers. The latter approach was also used on an
equimolar mixture of two different dibromoalkanes, resulting in a poly(alkylene sulfide)
2
5 with two different spacer groups, but not uniformly distributed (Scheme 3). The gen-
eral natures of the synthesized poly(alkylene sulfide)s 1–25 were confirmed by the use of
1
H NMR spectral data and where comparisons were possible were consistent with those
previously reported [38].
Chlorination of P (100 mmol) using distilled SO Cl (110 mmol) in the presence of
2
2
poly(alkylene sulfide)s (100 mg) as catalysts and AlCl (100 mg) as a Lewis acid in the
3
absence of solvent was attempted at 25°C (Scheme 4; route a). In addition, the reaction
was carried out in the absence of poly(alkylene sulfide)s under the same conditions for
comparison. The yields of the chlorinated products obtained (2-CP, 4-CP and 2,4-DCP)
are reported in Table 3.
Scheme 1. Synthesis of poly(alkylene sulfide)s 1–19 using alkanedithiols.

4
K. SMITH ET AL.
Table 1. Synthesis of poly(alkylene sulfide)s 1–19 according to Scheme 1.
Polymer
n
m
Melting point (°C)
Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
3
3
3
3
3
4
4
4
4
4
5
6
6
6
6
8
8
8
2
3
4
6
9
12
4
6
165–168
64–67
60–63
63–65
71–73
83–85
68–70
69–72
75–78
80–84
86–90
69–70
74–77
74–77
78–81
78–83
82–84
78–81
85–88
75
82
94
83
84
93
90
80
95
92
96
96
84
92
93
89
88
90
91
8
0
1
2
3
4
5
6
7
8
9
10
12
5
6
8
10
12
8
10
12
Scheme 2. Synthesis of poly(alkylene sulfide)s 20–24 using sodium sulfide.
Table 2. Synthesis of poly(alkylene sulfide)s 20–24 according to Scheme 2.
Polymer
m
Melting point (°C)
Yield (%)
2
2
2
2
2
0
1
2
3
4
2
3
4
6
8
185–186
55–57
66–69
70–77
58–64
90
90
83
97
94
Scheme 3. Synthesis of mixed poly(alkylene sulfide) 25 using sodium sulfide.
The yield of 4-CP was only 75.4% when the reaction was carried out in the absence of
any catalyst (Table 3). The yield of 4-CP improved in all cases when a poly(alkylene sulfide)
was used as a catalyst. Catalysts containing at least one shorter spacer unit (at most three
methylene groups) invariably provided higher yields of 4-CP (87.2–91.4%) than those hav-
ing only longer spacers containing at least five methylene groups (78.2–85.0%). Catalysts
in which the shortest spacer group was four methylene units provided intermediate yields
(
82.4-90.3%), depending on the length of the longer spacer group (catalysts with longer
second spacers giving lower yields of 4-CP). The same trends can be seen in the 4-CP/2-
CP ratios (p/o ratios). Poly(alkylene sulfide) 5, which contains alternating spacers of three

JOURNAL OF SULFUR CHEMISTRY
5
Table 3. Chlorination of phenol according to Scheme 4 (route a).a
Repeatingunits
Yield (%)b
Polymer
n
m
Terminal group
P
2-CP
4-CP
2,4-DCP
p/o ratio
Mass balance (%)c
–
1
–
2
–
3
–
3
3
–
–
–
3
3
3
3
4
–
4
4
4
4
5
6
–
6
6
6
8
–
8
8
–
2
2
3
3
4
6
3/6
3/6
3/6
9
9
9
12
4
4
6
8
10
12
5
6
6
8
10
12
8
8
10
12
–
Bu
Br
Bu
Br
Bu
Bu
Br
0.3
3.5
0.7
3.9
0.2
0.5
5.9
–
–
–
3.4
–
3.8
6.0
3.6
0.6
4.8
2.4
3.5
–
5.9
5.0
1.5
4.0
2.8
4.0
1.7
5.3
1.5
0.7
21.9
8.3
9.7
5.9
7.9
8.3
5.2
7.5
7.6
7.5
4.8
4.7
5.3
5.6
5.9
8.5
8.3
12.7
12.2
13.9
9.4
13.0
12.5
11.4
13.2
9.7
16.7
15.6
17.5
17.0
75.4
87.2
88.5
89.8
90.9
90.5
88.3
91.3
90.9
90.8
91.4
94.8
90.1
87.9
90.0
90.3
85.6
83.4
83.0
82.4
84.1
80.5
85.0
83.4
82.2
85.0
79.7
78.2
79.1
80.5
2.4
0.4
0.8
0.2
0.8
0.4
–
1.0
1.4
1.5
–
3.4
10.5
9.1
100
99.4
99.7
99.8
99.8
99.7
99.4
99.8
99.9
99.8
99.6
99.5
99.5
99.5
99.6
99.9
99.5
99.5
99.5
99.4
99.9
99.5
99.8
99.5
99.5
99.5
99.6
99.8
99.7
99.4
2
2
2
3
4
2
2
2
5
5
5
6
7
2
8
9
1
1
1
1
2
1
1
1
1
2
1
1
0
15.2
11.5
10.9
17.0
12.2
12.0
12.1
19.0
20.2
17.0
15.7
15.2
10.6
10.3
6.6
6.8
5.9
8.9
6.2
6.8
7.3
6.2
8.8
1
5
5
5
d
e
Br
Br
Bu
Bu
Bu
Bu
Bu
Br
Bu
Bu
Bu
Bu
Bu
Bu
Br
f
–
0.3
–
g
0.1
0.5
0.8
1.0
0.8
3.1
0.5
1.0
0.8
0.7
1.3
0.8
1.5
0.7
1.6
1.2
2
0
1
2
3
3
4
5
6
7
4
8
9
Bu
Bu
Bu
Bu
Br
4.8
5.0
4.5
4.7
Bu
Bu
aSulfuryl chloride (8.90 ml, 110 mmol) was slowly added to a mixture of phenol (9.41 g, 100 mmol), AlCl3 (100 mg) and
poly(alkylene sulfide)s (100 mg) at RT over 2 h.
b
Yield (%) based on quantitative GC.
c
Total yield (%) for all identified products, to confirm no other significant products formed.
d
Polymer 25 (50 mg) was used.
Polymer 25 (20 mg) was used.
e
f
Sulfuryl chloride (105 mmol) was used.
g
Sulfuryl chloride (105 mmol) and polymer 5 (50 mg) were used.
and nine methylene groups (i.e. n = 3, m = 9), was the most para-regioselective catalyst
in chlorination of P, producing 4-CP in 91.4% yield under the standard conditions, which
increased to 94.8% when the mixture was stirred at 55°C for 1 h before work-up. This was
the highest 4-CP yield achieved from any of the reactions. Reducing the quantity of 5 to
5
0 mg and SO Cl to 105 mmol led to the production of 4-CP in 90.1% yield along with
2 2
a significant quantity of unreacted P (3.8%). Poly(alkylene sulfide) 25 (m = 3/6) was also
highly selective, leading to the production of 4-CP in 91.3% under the standard condi-
tions and giving very similar results with lower quantities (50 mg or 20 mg) of 25 under
otherwise similar reaction conditions.
Polymers with similar spacer groups but prepared by the different methods, one major
difference therefore being the nature of the terminal group (Bu or Br), gave broadly similar
results when direct comparisons were possible, suggesting that the length of the spacer
groups has more effect than the nature of the terminal groups or the method of preparation.
Nevertheless, in the cases with at least one short spacer group (at least one group being no

6
K. SMITH ET AL.
OH
OH
Cl
Cl
+
2
-CP
4-CP
OH
route a
route b
route c
P
OH
OH
Cl
Cl
Cl
+
Cl
2
,4-DCP
2,6-DCP
Reagents used in different routes (all at RT for 2h unless otherwise stated)
route a: P (100 mmol), SO2Cl2 (110 mmol), polymer 1-25 (0.1 g), AlCl3 (0.1 g)
route b: 2-CP (100 mmol), SO2Cl2 (110 mmol), polymer 1-25 (0.1 g), AlCl3 (0.1 g)
route c: P (100 mmol), SO2Cl2 (210 mmol), polymer 1-25 (0.1 g), AlCl3 (01 g)
Scheme 4. Chlorination of phenol (P) or 2-chlorophenol (2-CP) using sulfuryl chloride in the presence
of poly(alkylene sulfide)s 1–25 and AlCl3.
longer than trimethylene, or both being tetramethylene, which were the polymers giving
higher p/o ratios), the p/o ratio was somewhat greater with the polymer made using the
alkanedithiol route shown in Scheme 1 (i.e. 1 > 20; 2 > 21; 4 > 25; 7 > 22). By contrast,
for polymers with longer spacers, which generally did not give high p/o ratios, the polymer
made using Scheme 2 gave a somewhat greater p/o ratio than the corresponding example
made by the alkanedithiol route (i.e. 23 > 13; 24 > 17).
The fact that the presence of any of the polymers resulted in a higher p/o ratio than in
their absence is consistent with the previously expressed view that the sulfur-containing
catalyst forms a bulky electrophilic complex with the AlCl and SO Cl that attacks the P
3
2
2
at the least hindered 4-position to produce 4-CP as the major product [29,30]. However,
this simplistic idea does not explain the subtleties displayed by the polymers with different
spacer groups.
In view of the commercial importance of 2,4-dichlorophenol, and in recognition that
further chlorination of 4-CP would give virtually exclusively 2,4-DCP, it was of interest to
investigate the further chlorination of 2-CP (Scheme 4, route b), which could give both
2
,4-DCP and 2,6-DCP, under similar conditions to those used for the chlorination of P.
The yields and p/o ratio for the chlorinated products (2,4-DCP and 2,6-DCP) are reported
in Table 4.
Under the standard conditions, in the absence of any poly(alkylene sulfide), the yields
of 2,4-DCP and 2,6-DCP were 55.0 and 12.5%, respectively, along with a high proportion

JOURNAL OF SULFUR CHEMISTRY
7
Table 4. Chlorination of 2-chlorophenol according to Scheme 4 (route b).a
Repeatingunits
Yield (%)b
2,4-DCP
Polymer
n
m
Terminal group
2-CP
2,6-DCP
p/o ratio
Mass balance (%)c
–
2
2
5
7
7
2
8
8
9
1
1
1
1
1
1
1
1
1
–
3
3
3
4
4
–
4
4
4
4
4
6
6
6
6
8
8
8
–
3
3
9
4
4
4
6
6
–
32.4
11.5
0.4
9.6
5.9
2.0
13.0
9.9
1.4
3.7
55.0
84.0
95.4
84.1
84.6
90.7
80.7
84.5
92.1
89.8
85.7
73.7
76.8
76.3
72.6
71.9
78.8
70.8
70.5
12.5
4.2
3.7
5.7
8.5
6.8
5.9
5.3
5.7
6.0
6.1
6.4
8.9
11.1
9.9
10.0
6.6
9.7
12.1
4.4
20.0
25.8
14.8
10.0
13.3
13.7
15.9
16.2
15.0
14.0
11.5
8.6
99.9
99.7
99.5
99.4
99.0
99.5
99.6
99.7
99.2
99.5
99.8
99.7
99.6
99.5
99.7
99.5
99.7
99.5
99.0
Bu
Bu
Bu
Bu
Bu
Br
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
d
d
2
d
8
0
1
3
4
5
6
7
8
9
10
12
6
8.0
19.6
13.9
12.1
17.2
17.6
14.3
19.0
16.4
8
6.9
7.3
7.2
11.9
7.3
10
12
8
10
12
5.8
aSulfuryl chloride (8.90 ml, 110 mmol) was slowly added to a mixture of 2-chlorophenol (12.86 g, 100 mmol), AlCl3 (100 mg)
and poly(alkylene sulfide) (100 mg) at RT over 2 h.
b
Yield (%) based on quantitative GC.
c
Total yield (%) for all identified products, to confirm no other significant products formed.
d
The mixture was stirred at 55°C for 1 h before work-up.
(32.4%) of unreacted 2-CP (Table 4). In the presence of any one of the poly(alkylene sul-
fide)s, the yield of 2,4-DCP increased significantly (up to 89.9%) while the yield of 2,6-DCP
decreased, leading in all cases, therefore, to a higher p/o ratio. However, there were sig-
nificant differences in the level of selectivity observed with the different poly(alkylene
sulfide)s. Generally, poly(alkylene sulfide)s with shorter spacers (n = 3, 4 and m = 3–8)
led to higher yields of 2,4-DCP and higher p/o ratios than the ones with longer spacer units
(
n = 6, 8 and m = 6–12). However, a significant quantity (3.7–19.0%) of unreacted 2-CP
still remained in the product mixtures and this could complicate the interpretation of the
results. For example, with the only poly(alkylene sulfide) prepared by the sodium sulfide
method (Scheme 2), polymer 22, 13% of 2-CP remained, resulting in a lower yield of 2,4-
DCP (80.7%) than for the corresponding polymer prepared according to Scheme 1 (i.e. 7,
8
4.6%), despite giving a higher p/o ratio (13.7 compared to 10.0). Therefore, three of the
poly(alkylene sulfide)s that produced high yields of 2,4-DCP were used in reactions con-
ducted under more forcing conditions (stirred at 55°C for 1 h before work-up). The yield of
2
,4-DCP increased to over 90% in all three cases and poly(alkylene sulfide) 2 (n, m = 3)
provided a p/o ratio of 25.8 and the highest yield of 2,4-DCP (95.4%) ever recorded on
chlorination of 2-CP using SO Cl .
2
2
With the benefit of the information derived from monochlorination of phenol and chlo-
rination of 2-CP, it was of interest to investigate the direct double chlorination of phenol.
A significant quantity of starting material was recovered in chlorination of 2-CP under the
general conditions, which negatively affected the yield of 2,4-DCP. Therefore, for the dou-
ble chlorination of P (100 mmol) (Scheme 4, route c) a small excess of SO Cl (210 mmol)
2
2
was used, along with a poly(alkylene sulfide) and AlCl , in an attempt to produce 2,4-DCP
3

8
K. SMITH ET AL.
Table 5. Double chlorination of phenol according to Scheme 4 (route c).a
Repeatingunits
Yield (%)b
2,4-DCP
Polymer
n
m
Terminal group
2-CP
4-CP
2,6-DCP
p/o ratio
Mass balance (%)c
–
1
–
2
–
3
–
3
3
–
3
3
3
3
3
3
4
–
4
4
4
4
6
–
6
6
6
8
–
8
8
–
2
2
3
3
4
6
3/6
9
9
9
9
9
12
4
4
6
8
10
12
6
6
8
10
12
8
8
10
12
–
Bu
Br
Bu
Br
Bu
Bu
Br
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Br
Bu
Bu
Bu
Bu
Bu
Br
9.0
0.4
0.3
1.6
0.8
0.8
2.0
0.4
1.1
0.4
–
29.2
3.7
4.6
37.8
23.0
21.7
34.4
18.7
28.3
9.6
58.6
95.1
94.0
59.7
75.7
76.9
62.9
80.4
69.9
89.2
93.3
96.6
97.1
68.9
65.6
60.4
66.7
54.9
70.1
61.4
66.0
77.1
67.9
63.3
71.8
49.4
84.3
61.2
74.1
3.0
0.7
0.7
0.4
0.4
0.4
0.6
0.4
0.2
0.3
0.3
0.3
0.9
0.7
0.2
0.2
1.1
1.6
1.5
1.6
2.1
2.0
2.3
1.8
2.1
2.0
3.2
2.5
2.7
19.5
135.9
134.3
149.2
189.3
192.3
104.8
201.0
349.5
279.3
331.0
321.7
107.9
98.4
328.0
302.0
60.6
34.3
46.7
38.4
31.4
38.6
29.5
99.8
99.9
99.6
99.5
99.9
99.8
99.9
99.9
99.5
99.5
99.1
99.0
98.8
99.9
99.5
99.5
99.7
99.6
99.6
99.5
99.5
99.9
99.4
99.4
99.5
99.5
99.7
99.4
99.4
2
2
2
3
4
2
5
5
5
5
5
6
7
2
8
9
1
1
1
2
1
1
1
1
2
1
1
0
1
5
d
e
f
5.5
2.1
0.4
–
g
0.4
1.8
1.8
1.3
4.5
6.6
3.6
4.3
5.6
2.5
4.8
4.9
4.1
8.7
2.3
6.9
4.5
28.5
31.9
37.6
27.4
36.5
24.4
32.2
25.8
18.3
24.4
29.4
21.5
39.4
9.9
2
0
1
3
3
4
5
6
7
4
8
9
Bu
Bu
Bu
Bu
Br
35.2
34.2
24.7
26.3
29.0
27.4
Bu
Bu
28.8
18.1
aSulfuryl chloride (17.00 ml, 210 mmol) was slowly added to a mixture of phenol (9.41 g, 100 mmol), AlCl3 (100 mg) and
poly(alkylene sulfide) (100 mg) at RT over 2 h.
b
Yield (%) based on quantitative GC.
c
Total yield (%) for all identified products, to confirm no other significant products formed.
d
The mixture was stirred at 55°C for 1 h before work-up.
Sulfuryl chloride (220 mmol) was used and the mixture was stirred at 55°C for 1 h before work-up.
e
f
Sulfuryl chloride (230 mmol) was used and the mixture was stirred at 55°C for 1 h before work-up.
g
Sulfuryl chloride (215 mmol) was used and the reaction was carried out at 55°C.
directly in one step and in high yield without over-chlorination. The yields of 2,4-DCP and
2
,6-DCP obtained are recorded in Table 5.
In the absence of poly(alkylene sulfide) and AlCl , the yields of 2-CP, 4-CP, 2,4-DCP,
3
and 2,6-DCP were 9.0, 29.2, 58.6, and 3.0%, respectively, and the 2,4-/2,6-DCP ratio was
less than 20 (Table 5). The yield of 2,4-DCP under the general conditions increased in all
cases when poly(alkylene sulfide)s were used and the yield was highest for poly(alkylene
sulfide)s containing at least one short spacer unit (n = 2 or 3 and m = 2-9). For example,
poly(alkylene sulfide)s 1 and 20 (n, m = 2) provided the highest yields of 2,4-DCP (94.0
and 95.1%, respectively) with a 2,4-/2,6-DCP ratio of ca. 135 in each case. Even higher
2
,4-/2,6-DCP ratios of over 300 were achieved when poly(alkylene sulfide)s 5 (n = 3,
m = 9), 7 (n = m = 4), or 22 (m = 4) were used under the standard conditions, but in
these cases the second chlorination step was slow and there were substantial quantities
of 4-CP remaining, so that the actual yields of 2,4-DCP were not particularly high. The
highest ratio (349.5) was with polymer 5, so in this case a period at higher temperature
(55°C) and/or addition of extra sulfuryl chloride were used to try to increase the yield of

JOURNAL OF SULFUR CHEMISTRY
9
2
,4-DCP. Indeed, the yield of 2,4-DCP increased from 69.9 to 89.2% when the standard
mixture was stirred at 55°C for 1 h before work-up. The 2,4-DCP yield increased further
to 93.3–96.6%), with little change in the 2,4-/2,6-ratio, when more sulfuryl chloride was
used and the reaction mixture was stirred at 55°C for 1 h before work-up. The highest yield
of 2,4-DCP was 97.1%, achieved when the amount of SO Cl was 215 mmol for 100 mmol
(
2
2
of P and the reaction was heated at 55°C for 1 h before work-up, but it is not clear why
in this case the selectivity was lower (possibly poorer temperature control). Increasing the
reaction time in the double chlorination of P at RT showed little significant effect on the
yield of 2,4-DCP.
Clearly, polymer 5 was the most efficient catalyst in both monochlorination and dou-
ble chlorination of phenol in terms of para-selectivity and yields of 4-CP and 2,4-DCP,
respectively. The best 4-CP/2-CP ratio obtained from monochlorination of phenol was ca.
2
0 (Table 3), while, the 2,4-DCP/2,6-DCP ratio obtained from double chlorination of phe-
nol was ca. 320, when polymer 5 was used. Therefore, this catalyst provides a ca. 16-fold
increase in para-selectivity during the second chlorination step.
3
. Conclusion
Highly para-regioselective chlorination systems for the chlorination of phenol and
-chlorophenol have been developed. The systems consist of a poly(alkylene sulfide),
2
aluminum chloride and sulfuryl chloride. Such systems provide high yields of the para-
chlorinated phenols compared with those obtained in the absence of a poly(alkylene sul-
fide). The length of the spacer units (number of methylene groups) within the poly(alkylene
sulfide) was found to be important for the regioselectivity of the chlorination reactions.
High yields of the corresponding para-chlorinated phenols were obtained when at least one
of the spacer units in the poly(alkylene sulfide) was short (2-4 methylene groups long). By
use of one such poly(alkylene sulfide) it was possible to achieve direct double chlorination
of phenol to give over 96% of 2,4-dichlorophenol with a 2,4-/2,6-DCP ratio of over 300.
The polymers are odorless, used at a low concentration, and can be recycled and reused at
a commercial scale; therefore, such catalysts have potential for industrial use.
4. Experimental section
4.1. General
Chemicals and reagents were purchased from Aldrich Chemical Company. Sulfuryl chlo-
ride was freshly distilled under nitrogen. The GC analyses were performed on a Shimadzu
GC-2014 Gas Chromatograph using a capillary ZB Carbowax column (30 m, 0.32 mm ID)
and tetradecane was added as a standard. The column temperature was adjusted at 40°C
for 3 min, ramped to 220°C (10°C/min) and held for 10 min. The injector and detector
temperatures were 300 and 250°C, respectively.
4.2. Synthesis of poly(alkylene sulfide)s
4.2.1. Alkanedithiol method (Scheme 1)
A solution of n-butyllithium in hexane (24.00 ml, 2.5 M, 60.00 mmol) was added over
0 min to a stirred solution (−78°C) of the appropriate alkanedithiol (30.00 mmol) in
1

10
K. SMITH ET AL.
dry THF (40 ml) under nitrogen. The mixture was stirred for 30 min at −78°C and then
allowed to warm to room temperature. The appropriate dibromoalkane (27.00 mmol) was
added and the mixture was stirred at room temperature for 60 min. 1-Bromobutane (0.82 g,
6
.00 mmol) was added and the mixture was stirred for 18 h at room temperature. The
white solid obtained was collected by filtration, washed successively with water (3 × 25 ml),
and dried at 50°C under reduced pressure to give a white solid. The melting points of the
solids were recorded (see Table 1) and their proton NMR spectra were recorded in order
to confirm the general nature of the polymers.
4.2.2. Sodium sulfide method (Schemes 2 and 3)
A mixture of an appropriate dibromoalkane (or an equimolar mixture of two dibromoalka-
nes; 3.00 mol in total) and sodium sulfide nonahydrate (1000 g, 4.17 mol) were placed in
a round bottom flask (3 l) equipped with a magnetic bar and a water condenser. The mix-
ture was heated under reflux for 4 h with vigorous stirring, by which time a very viscous
material resulted. The mixture was poured into a clean beaker and cold water (350 ml) was
added slowly with stirring, and the mixture was left to cool. The solid obtained was col-
lected by filtration, washed thoroughly with water (3 × 200 ml), and dried at 50°C under
reduced pressure to give a white solid. Again, melting points of the solids were recorded
(
see Table 2) and their proton NMR spectra were recorded.
4
.3. Chlorination of phenol
To a stirred mixture of melted phenol (9.41 g, 0.10 mol), AlCl (100 mg) and the appropri-
3
ate poly(alkylene sulfide) (100 mg), SO Cl (8.90 ml, 0.11 mmol) was slowly added over 2 h
2
2
at room temperature (RT). The mixture was stirred at RT for 2 h and then quenched with
water (20 ml). The products were extracted using Et O (3 × 30 ml) and the combined solu-
2
tion was dried over MgSO . The drying reagent was removed by filtration and the solvent
4
was removed under reduced pressure until the weight was constant. A weighed aliquot of
the products and a known quantity of tetradecane were used for the GC analysis. In some
cases (see results and discussion) the mixture was warmed to 55°C for 1 h prior to work up
or extra SO Cl was used in the reaction.
2
2
4
.4. Chlorination of 2-chlorophenol
The procedure was identical to that used for phenol, but 2-chlorophenol (12.86 g, 0.10 mol)
was used instead of phenol.
4
.5. Double chlorination of phenol
The procedure was identical with that used for phenol except that SO Cl (17.00 ml,
2
2
0.21 mmol) was used instead of 8.90 ml.
Acknowledgements
A. S. Hegazy thanks Swansea and Cardiff Universities for financial support. G. A. El-Hiti is grateful
to the Deanship of Scientific Research, King Saud University for funding through Vice Deanship of
Scientific Research Chairs.

JOURNAL OF SULFUR CHEMISTRY
11
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by Cardiff University; King Saud University [Grant Number Research
Chairs]; Swansea University.
ORCID
Keith Smith http://orcid.org/0000-0003-4838-5651
Gamal A. El-Hiti http://orcid.org/0000-0001-6675-3126
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