Regioselective chlorination of phenols in the presence of tetrahydrothiopyran derivatives

Article abstract of DOI:10.1080/17415993.2019.1620230

Four six-membered cyclic sulfides, namely tetrahydrothiopyran, 3-methyltetrahydrothiopyran, 4-methyltetrahydrothiopyran and 4,4-dimethyltetrahyrdrothiopyran have been used as moderators in chlorination reactions of various phenols with sulfuryl chloride in the presence of aluminum or ferric chloride. On chlorination of phenol, ortho-cresol and meta-cresol the para/ortho chlorination ratios and yields of the para-chloro isomers are higher than when no cyclic sulfide is used for all of the cyclic sulfides, but chlorination of meta-xylenol is less consistent, with some cyclic sulfides producing higher p/o ratios and others producing lower ratios than reactions having no sulfide present.

Full text of DOI:10.1080/17415993.2019.1620230

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
Regioselective chlorination of phenols in the
presence of tetrahydrothiopyran derivatives
Keith Smith, Des Williams & Gamal A. El-Hiti
To cite this article: Keith Smith, Des Williams & Gamal A. El-Hiti (2019): Regioselective
chlorination of phenols in the presence of tetrahydrothiopyran derivatives, Journal of Sulfur
Chemistry, DOI: 10.1080/17415993.2019.1620230
To link to this article: https://doi.org/10.1080/17415993.2019.1620230
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2019.1620230
Regioselective chlorination of phenols in the presence of
tetrahydrothiopyran derivatives
c
Keith Smitha, Des Williamsb and Gamal A. El-Hiti
aSchool of Chemistry, Cardiff University, Cardiff, UK; bDepartment of Chemistry, University of Wales Swansea,
Swansea, UK; cDepartment of Optometry, College of Applied Medical Sciences, King Saud University, Riyadh,
Saudi Arabia
ABSTRACT
ARTICLE HISTORY
Received 15 March 2019
Accepted 11 May 2019
Four six-membered cyclic sulfides, namely tetrahydrothiopyran,
3-methyltetrahydrothiopyran, 4-methyltetrahydrothiopyran and
4,4-dimethyltetrahyrdrothiopyran have been used as moderators in
chlorination reactions of various phenols with sulfuryl chloride in
the presence of aluminum or ferric chloride. On chlorination of phe-
nol, ortho-cresol and meta-cresol the para/ortho chlorination ratios
and yields of the para-chloro isomers are higher than when no cyclic
sulfide is used for all of the cyclic sulfides, but chlorination of meta-
xylenol is less consistent, with some cyclic sulfides producing higher
p/o ratios and others producing lower ratios than reactions having
no sulfide present.
KEYWORDS
Chlorination; cyclic sulfides;
para/ortho ratio; phenols;
regioselectivity
1. Introduction
Several chlorinated phenols are employed as or used in the production of herbicides, pes-
ticides, disinfectants, dyes, and pharmaceuticals [1,2]. For example, 2,4-dichlorophenol is
an important intermediate in the production of commercial herbicides, while 4-chloro-
3,5-dimethylphenol is used as a household antiseptic. Traditional phenol chlorination
CONTACT Gamal A. El-Hiti
gelhiti@ksu.edu.sa
Department of Optometry, College of Applied Medical
Sciences, King Saud University, PO Box 10219, Riyadh 11433, Saudi Arabia
© 2019 Informa UK Limited, trading as Taylor & Francis Group

2
K. SMITH ET AL.
processes are not selective and produce significant waste [3]. Several chlorinating sys-
tems have been reported for regioselective chlorination of phenols [4–16], including
the use of Merrifield resin/sulfuryl chloride (SO2Cl2) [5], aluminum-pillared mont-
morillonite clay or L type zeolites/SO2Cl2 [6], manganese(II) sulfate/hydrogen perox-
ide/hydrogen chloride [7], ammonium chloride/1,3-dichloro-5,5-dimethylhydantoin [8],
[bis(trifluoroacetoxy)iodo]benzene/aluminum chloride (AlCl3) [9], and Nagasawa’s bis-
thiourea catalyst/N-chlorosuccinimide [10]. However, such chlorinating systems lead to
either limited para-selectivity, or to high ortho-selectivity, or cannot be applied on a large
scale. Therefore, development of para-selective chlorination processes is still needed.
Several sulfides have been used as selective catalysts for the production of para-
chlorophenols [17–21]. For example, chlorination of phenol using SO2Cl2/diphenyl
sulfide/AlCl3 led to a para/ortho chlorophenol ratio of 10.5 [17]. Similarly, chlorination
of o-cresol and m-cresol with such a system led to para/ortho ratios of 19.0 and 7.5,
respectively [17]. The para-selectivity was attributed to the bulk of the active intermediate
complex Ph2SCl+AlCl4 . Dialkyl sulfides (R–S–R’) have also been used as selective mod-
–
erators for production of para-chlorophenols. In this case, interesting variations were seen
depending on the nature of the alkyl groups. In the absence of any Lewis acid, dibutyl and
dipentyl sulfides showed greater para-selectivity for chlorination of phenol using sulfuryl
chloride than other symmetrical dialkyl sulfides with either shorter or longer alkyl groups,
and the para-selectivity was further enhanced in the presence of Lewis acids, especially
AlCl3 [18]. Also, with m-cresol as substrate, it was shown that the para-selectivity dropped
as the level of steric hindrance of the alkyl group of alkyl n-butyl sulfides was increased
from n-butyl to tert-butyl [18]. Clearly, these results are not consistent with the simple
–
notion that the selectivity depends on the bulk of the complex RR’SCl+AlCl4 .
High para/ortho ratios have also been achieved in chlorination of phenols in the pres-
ence of dithiaalkanes [R–S–(CH2)n–S–R]. In chlorination of m-cresol, compounds with
longer spacer groups and with R groups around butyl in length provided the highest ratios
(para/ortho ratio of 20.7 for n = 12 and R group n-butyl in the presence of AlCl3) [19]. A
more extensive study revealed that 1,ω-bis(methylthio)alkanes with longer spacer groups
(ω = 6 or 9) showed greatest para-selectivity in chlorination of m-cresol (para/ortho
ratio = 18.0) and m-xylenol (para/ortho ratio = 19.6), while 1,ω-bis(methylthio)alkanes
with shorter spacer groups (ω = 2 or 3) showed greater para-selectivity in chlorination of
phenol (para/ortho ratio = 11.4) and o-cresol (para/ortho ratio = 20.0) [20]. DFT calcu-
lations suggested that dithiaalkanes with shorter and longer spacer groups adopt different
intermediate structures, with short spacer intermediates involving a S–Cl+–S arrangement
of heteroatoms, while longer spacer intermediates involve a S–S+–Cl arrangement. How-
ever, use of disulfides as the moderators did not always follow the same pattern. For exam-
ple, 1,2-dithiocane (hexamethylene disulfide) showed a higher para-selectivity (para/ortho
ratio = 20.6) than 1,2-dithiolane (trimethylene disulfide) in chlorination of o-cresol,
while 1,2-dithiolane was the more selective in para-chlorination of m-xylenol (para/ortho
ratio = 19.1) [21]. On the other hand, para-selectivity in chlorination of both o-cresol and
m-xylenol was higher with poly(trimethylene disulfide) than with poly(hexamethylene
disulfide) [21]. Therefore, the factors influencing the levels of selectivity provided by
different sulfur compounds as moderators are still unclear.
As part of our continuing contribution to the field of regioselective aromatic substi-
tution reactions [22–39], in the current work we report the chlorination of a number

JOURNAL OF SULFUR CHEMISTRY
3
of commercially important phenols using SO2Cl2 in presence of various tetrahy-
drothiopyran derivatives and a Lewis acid. The four tetrahydrothiopyrans chosen for
the study were the parent tetrahydrothiopyran (1), 3-methyltetrahydrothiopyran (2),
4-methyltetrahydrothiopyran (3) and 4,4-dimethyltetrahydrothiopyran (4). Since earlier
work had indicated that α-branching in the alkyl group of alkyl n-butyl sulfides caused
significant diminution of the para-selectivity when used as the moderator in phenol chlo-
rination reactions [18], 2-methyltetrahydrothiopyran was not included in the study. Com-
pounds 2 and 3 offer alternative configurational/conformational arrangements between
the active chlorine and the distal methyl group in the presumed chlorosulfonium inter-
mediates, whereas compounds 1 and 4, which will have different steric interactions at
a distance from the active chlorine in the intermediate, would not show configurational
differences. It was hoped, therefore, that some meaningful insight might be gained into
the subtle effects that influence the selectivity induced by sulfur-containing activators in
phenol chlorination reactions.
2. Results and discussion
The four tetrahydrothiopyrans 1–4 were synthesized by reactions of the appropriately sub-
stituted 1,5-dibromopentanes with sodium sulfide nonahydrate at 170°C for 7 h (Scheme
1). The crude products obtained were purified by Kugelrohr distillation to give the pure
cyclic sulfides 1−4 in 58–80% yield (Table 1) as colorless oils.
First, we attempted chlorination of phenol (5, R = H; 50 mmol) using freshly dis-
tilled SO2Cl2 (55 mmol) in the presence of 1−4 (0.28 mmol) and AlCl3 (50 mg) at room
temperature (RT; Scheme 2). Also, the reaction was attempted in the absence of cyclic
sulfides both with and without AlCl3 to provide a baseline. The results are presented in
Table 2. Clearly, the presence of any one of the cyclic sulfides 1−4 led to production of
4-chlorophenol (6, R = H) in a better yield (83.2–89.0%) and with higher para-selectivity
(para/ortho ratio = 12.7–18.2) than when no catalyst was used (yield 63.7–70.1% and
Scheme 1. Synthesis of tetrahydrothiopyrans 1−4.
Table 1. Yields of tetrahydrothiopyrans 1−4 according to
Scheme 1.
Sulfide
R1
R2
R3
Yield (%)
1
2
3
4
H
Me
H
H
H
Me
Me
H
H
H
80
75
79
58
H
Me

4
K. SMITH ET AL.
Scheme 2. Chlorination of phenols in the presence of cyclic sulfides 1−4 and AlCl3 or FeCl3.
Table 2. Chlorination of phenol (5, R = H) according to Scheme 2.a
Yield (%)b
Sulfide
5 (R = H)
10.7(8.2)
5.8
10.8
2.3
6.7
6 (R = H)
70.1 (63.7)
89.0
83.2
88.1
7 (R = H)
17.1 (21.1)
Other
1.0 (0.7)d
p/o ratio
Mass balance (%)c
—
1
2
3
4
4.1 (3.0)
17.8
14.7
12.7
18.2
98.8 (93.8)
99.8
99.6
97.3
99.3
5.0
5.6
6.9
4.8
—
—
—
—
87.8
aSO2Cl2 (4.44 ml, 55.0 mmol) was slowly added to a mixture of 5 (R = H; 4.71 g, 50.0 mmol), AlCl3 (50 mg) and 1−4
(0.28 mmol) at RT over 2 h.
bYield (%) based on quantitative GC and the yields in parentheses are for the reaction conducted without AlCl3.
cTotal yield (%) for all identified products, as a check for losses due to unidentified materials.
d2,4-Dichlorophenol.
para/ortho ratio = 3.0–4.1). The unsubstituted tetrahydrothiopyran (1) led to the high-
est yield (89.0%) of 4-chlorophenol, while 4,4-dimethyltetrahyrdrothiopyran 4 provided
the highest para/ortho ratio (18.2), but differences between the various moderators were
not great and it is difficult to draw any general conclusions from such small differences,
especially since significantly different quantities (2.3–10.8%) of unreacted phenol (5; R =
H) were present in the different reaction mixtures.
Next, we investigated the chlorination of o-cresol (5, R = 2-Me; 50 mmol) under
the same conditions that were used for phenol, in the absence and presence of cyclic
sulfides (Scheme 2). The results obtained are recorded in Table 3. The yield of 4-chloro-
2-methylphenol (6, R = 2-Me) was only 75.1% when the reaction was carried out in
the presence of AlCl3 without any of the cyclic sulfides 1−4. In the presence of catalysts
Table 3. Chlorination of o-cresol (5, R = 2-Me) according to Scheme 2.a
Yield (%)b
Sulfide
5 (R = 2-Me)
6 (R = 2-Me)
7 (R = 2-Me)
p/o ratio
Mass balance (%)c
—
1
2
3
4
9.6 (2.0)
—
4.6
—
4.0
75.1 (78.2)
96.4
93.6
96.6
90.0
11.9 (15.4)
7.8 (5.1)
45.7
40.0
40.4
33.2
99.0 (99.8)
98.5
100.5
99.0
2.1
2.3
2.4
2.7
96.7
aSO2Cl2 (4.44 ml, 55.0 mmol) was slowly added to a mixture of 5 (R = 2-Me; 5.41 g, 50.0 mmol), AlCl3 (50 mg) and 1−4
(0.28 mmol) at RT over 2 h.
b,cSee footnotes b and c to Table 1.

JOURNAL OF SULFUR CHEMISTRY
5
1−4, the yield of 6 (R = 2-Me) was very high (90.0–96.6%) and the para/ortho ratio
was improved from 7.8, when no sulfide was used, to 33.2–45.7. Such results highlight the
importance of the sulfur atom within the cyclic sulfides for the para-selectivity of the chlo-
rination reaction. Tetrahydrothiopyran (1) was the most para-selective catalyst and led to
the highest para/ortho ratio (45.7) and yield of 6 (96.4%). Again, however, the differences
between the different cyclic sulfides were not great.
Chlorination of m-cresol (5, R = 3-Me; 50 mmol) with SO2Cl2 (55 mmol) and AlCl3
gave the results recorded in Table 4. The yields of 4-chloro-3-methylphenol (6, R = 3-Me)
obtained when cyclic sulfides were present were broadly comparable to that obtained when
no sulfide was used (87.2%), but the para/ortho ratios were significantly increased from 9.2
in the absence of sulfide to 15.6–19.2 in the presence of 1–4 because the reaction mixtures
contained significantly lower quantities of the ortho-isomer 7 (R = 3-Me) and significantly
larger quantities of unreacted m-cresol (4.5–15.4%). 4,4-Dimethyltetrahydrothiopyran (4)
provided the highest para/ortho ratio (19.2) and yield of 6 (R = 3-Me; 90.4%), although
the differences with the different sulfides were again not large.
Finally, chlorination of m-xylenol (5, R = 2,3-di-Me; 50 mmol) was attempted under
conditions similar to those used for the chlorination of other phenols. However, since
m-xylenol is solid at RT and unlike the other phenols cannot be melted and then
retain its liquid form in the presence of the other reaction components, a solvent (per-
chloroethylene) had to be used. Also, AlCl3 was replaced by ferric chloride (FeCl3) as
the activator, since in order to be consistent with the requirements for use of the prod-
uct 6 (R = 2,3-di-Me) as a commercial household antiseptic the product would have
to contain a very low proportion of Al. The results (Table 5) are in contrast with those
obtained for other phenols. Cyclic sulfides 1 and 2 provided higher proportions of 4-
chloro-3,5-dimethylphenol (para/ortho ratio = 9.0–13.5 compared with a para/ortho ratio
of 6.9–7.0 when no sulfide was used), but sulfides 3 and 4 provided very low propor-
tions of 4-chloro-3,5-dimethylphenol (para/ortho ratio = 1.9–3.7). Such results clearly
indicate that steric hindrance within the moderator is not the only driving force for
the regioselectivity of these reactions. Clearly, the sulfur atom within the cyclic sul-
fides has a significant effect on the regioselectivity of the chlorination reaction of phe-
nols using SO2Cl2, but the wider structure of the sulfur-containing molecule is also
important.
Table 4. Chlorination of m-cresol (5, R = 3-Me) according to Scheme 2.a
Yield (%)b
Sulfide
5 (R = 3-Me)
6 (R = 3-Me)c
7 (R = 3-Me)
p/o ratio
Mass balance (%)d
—
1
2
2.5 (3.2)
4.3
7.9
87.2 (86.0)
89.6
82.9
9.5 (10.0)
5.7
5.2
9.2 (8.6)
15.6
15.9
99.2 (99.2)
99.6
96.0
3
4
15.4
4.7
78.4
90.4
4.5
4.7
17.3
19.2
98.3
99.8
aSO2Cl2 (4.44 ml, 55.0 mmol) was slowly added to a mixture of 5 (R = 3-Me; 5.41 g, 50.0 mmol), AlCl3 (0.25 g) and 1−4
(0.40 mmol) at RT over 2 h.
bSee footnote b to Table 1.
cSum total of mixture of 2-chloro-3-methylphenol and 6-chloro-3-methylphenol (the two ortho-chlorinated products),
which were not fully resolved by the GC system used.
dSee footnote c to Table 1.

6
K. SMITH ET AL.
Table 5. Chlorination of m-xylenol (5, R = 3,5-di-Me) according to Scheme 2.a
Yield (%)b
Sulfide
5 (R = 3,5-di-Me) 6 (R = 3,5-di-Me)
7 (R = 3,5-di-Me) Otherd p/o ratio Mass balance (%)c
—
1
2
15.4 (13.4)
2.8
71.1 (68.6)
89.1
78.1
10.3 (9.8)
6.6
— (—)
0.7
2.9
6.9 (7.0)
13.5
9.0
96.8 (91.8)
99.2
96.8
7.1
8.7
3
4
15.4
5.8
53.8
73.6
27.7
19.7
—
—
1.9
3.7
96.9
99.1
aSO2Cl2 (4.44 ml, 55.0 mmol) was slowly added to a mixture of 6 (R = 3,5-di-Me; 6.11 g, 50.0 mmol), FeCl3 (25 mg) and 1−4
(0.05 mmol) in tetrachloroethylene (TCE; 25 ml) at RT over 2 h.
bYield (%) based on quantitative GC and the yields in parentheses are for the reaction conducted without FeCl3.
cSee footnote c to Table 1.
d2,4-Dichloro-3,5-dimethylphenol.
3. Conclusion
Four cyclic sulfides have been synthesized and used as potential moderators for chlori-
nation of phenols with freshly distilled sulfuryl chloride and a Lewis acid promoter. For
three of the phenols tested (phenol, ortho-cresol and meta-cresol) the para-isomers were
produced more regioselectively and usually in (often substantially) higher yields than in
corresponding reactions carried out in the absence of cyclic sulfide, regardless of the cyclic
sulfide used. However, the situation with meta-xylenol was different, with two of the sul-
fides (1 and 2) giving an increased proportion of para-chlorinated product and two (3
and 4) giving a higher proportion of ortho-chlorinated product than in the absence of any
sulfide. Since the methyl group(s) in these latter sulfides are further away from the active
sulfur atom than the methyl group in 2 it does not appear that the only driving force for
the selectivity changes is steric hindrance, providing further support for the idea that the
effects of sulfur compounds on such chlorination reactions are more subtle.
4. Experimental Section
4.1. General
Chemicals purchased from Aldrich and Lancaster Chemicals were mostly used as pur-
chased. Sulfuryl chloride was distilled under an inert atmosphere at atmospheric pressure.
Gas chromatography (GC) was carried out using a Shimadzu GC-2014 instrument with a
capillary ZB Carbowax column (30 m, 0.32 mm ID) and temperature programed (40°C for
3 min, then ramped at 10°C/min to 220°C, then held for 8 min) with an injection tempera-
ture of 300°C and a detection temperature 250°C. To allow quantification, tetradecane was
added as a standard. Commercial samples of expected phenol chlorination products were
used to determine retention times and response factors for each product. 1H (400 MHz)
and 13C NMR (100 MHz) spectra were recorded on a Bruker AV400 spectrometer. Chemi-
cal shifts δ are reported in parts per million (ppm) relative to TMS and coupling constants J
in Hz have been rounded to the nearest integer. DEPT spectra were used to determine 13
C
multiplicities. Assignments of NMR signals are based on expected chemical shifts, integra-
tion values and coupling patterns and have not been rigorously confirmed. Low-resolution
mass spectra were recorded on a Quattro II spectrometer at 70 eV. High-resolution mass
spectra data were obtained on a MAT900 instrument.

JOURNAL OF SULFUR CHEMISTRY
7
4.2. Typical procedure for the preparation of cyclic sulfides 1−4
A mixture of the appropriately substituted 1,5-dibromopentane and sodium sulfide non-
ahydrate (for quantities, see individual compound sections) was heated at 170°C for 7 h in
an oil bath. After cooling, water (20 ml) and dichloromethane (DCM, 20 ml) were added.
The phases were separated and the aqueous layer was re-extracted with DCM (3 × 20 ml).
The combined organic phases were washed with H2O (30 ml) and dried over anhydrous
MgSO4. Removal of the solvent under reduced pressure gave the crude product, which was
purified by Kugelrohr distillation to give the pure cyclic sulfides 1−4.
4.2.1. Tetrahydrothiopyran (1)
Yield 1.60 g (80%) from 1,5-dibromopentane (4.00 g, 17.4 mmol) and sodium sulfide non-
ahydrate (6.27 g, 26.1 mmol) as a colorless oil (Bp 50−55°C at 15 mmHg; lit. 140−141°C
at RT [40]). 1H-NMR (CDCl3) δ (ppm): 1.60 (m, 2 H), 1.85 (m, 4 H), 2.65 (m, 4 H); 13C-
NMR (CDCl3) δ (ppm): 26.8, 28.1, 29.4; MS- EI+ m/z (%) 102 ([M]+, 100), 87 (95), 67
(60), 46 (75), 39 (80).
4.2.2. 3-Methyltetrahydrothiopyran (2)
Yield 1.44 g (75%) from 1,5-dibromo-2-methylpentane (4.01 g, 16.4 mmol) and sodium
sulfide nonahydrate (7.88 g, 32.8 mmol) as a colorless oil (Bp 70°C at 20 mmHg; lit. 158°C
1
at RT [41]). H-NMR (CDCl3) δ (ppm): 0.89 (d, J = 7.5 Hz, 3 H), 1.61−2.00 (m, 5 H),
2.22−2.53 (m, 4 H); 13C-NMR (CDCl3) δ (ppm): 23.1, 28.1, 28.8, 33.5, 35.2, 36.1; MS EI+
m/z (%) 116 ([M+] 90), 101 (100).
4.2.3. 4-Methyltetrahydrothiopyran (3)
Yield 0.38 g (79%) from 1,5-dibromo-3-methylpentane (1.00 g, 4.1 mmol) and sodium sul-
fide nonahydrate (1.48 g, 6.1 mmol) as a colorless oil (Bp 50−55°C at 20 mmHg; lit. 54°C
at 22 mmHg [41]). 1H-NMR (CDCl3) δ (ppm): 0.85 (d, J = 6 Hz, 3 H), 1.10−1.40 (m, 4
H), 1.90 (m, 1 H), 2.45−2.55 (m, 4 H). 13C-NMR (CDCl3) δ 23.4, 29.2, 32.6, 36.3; MS EI
m/z (%) 116 ([M]+, 100), 101 (95), 67 (90), 41 (85).
4.2.4. 4,4-Dimethyltetrahyrdrothiopyran (4)
Yield 0.26 g (58%) from 1,5-dibromo-3,3-dimethylpentane (1.00 g, 3.87 mmol) and
sodium sulfide nonahydrate (1.40 g, 5.81 mmol) as a colorless oil (Bp 60−65°C at
1
15 mmHg; lit. 57−58°C at 15 mmHg [42]). H-NMR (CDCl3) δ (ppm): 0.75 (s, 6 H),
1.40−1.60 (m, 4 H) 2.50−2.60 (m, 4 H); 13C-NMR (CDCl3) δ (ppm): 24.8, 26.9, 28.8, 40.2;
MS EI+ m/z (%) 130 ([M]+, 90), 115 (95), 69 (70), 41 (80).
4.3. Chlorination of phenol, o-cresol and m-cresol
Phenol (melted), o-cresol (melted) or m-cresol (50.0 mmol), AlCl3 (25−50 mg) and the
appropriate cyclic sulfide 1−4 (0.28−0.40 mmol; see Tables 1–4 for details) were placed in
a dried round bottomed flask (50 ml). The mixture was stirred as sulfuryl chloride (4.44 ml,
55.0 mmol) was added slowly over 2 h via a pressure equalizing dropping funnel and for 2 h
further. The reaction was quenched with water (20 ml) and the organic components were
then extracted with diethyl ether (3 × 30 ml). The combined ether layers were dried over

8
K. SMITH ET AL.
MgSO4, which was removed by filtration. The solvent was removed under reduced pressure
to give the crude product, which was weighed. Quantitative GC analysis was conducted on
a weighed aliquot of the product with a known quantity of tetradecane.
4.4. Chlorination of m-xylenol
m-Xylenol (6.11 g, 50.0 mmol), FeCl3 (25 mg), tetrachloroethylene (25 ml) and the appro-
priate cyclic sulfide 1−4 (0.05 mmol) were placed in a dried round bottom flask (50 ml).
The mixture was stirred as freshly distilled sulfuryl chloride (4.44 ml, 55.0 mmol) was
added slowly over 2 h via a pressure equalizing dropping funnel and then for another 2 h.
The work-up and analysis of the products by GC were as previously described for other
phenols.
Acknowledgments
The authors extend their appreciation to Cardiff and Swansea Universities for their support of this
research. G. A. El-Hiti thanks the College of Applied Medical Sciences Research Centre and the
Deanship of Scientific Research at King Saud University for funding his research.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The authors extend their appreciation to Cardiff and Swansea Universities for their support of this
research.
ORCID
Gamal A. El-Hiti http://orcid.org/0000-0001-6675-3126
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