Synthesis, spectral characterization, and crystal structure of two polymorphs of o,o'-dichloro dibenzyl disulfide

Article abstract of DOI:10.1080/10426500902813603

2-Chlorophenyl methanethiol undergoes air oxidation catalyzed by different selenides and yields the corresponding disulfide 1 in two polymorphic forms, 1a and 1b. In the molecular structures of the two new polymorphs of o,o-dichloro dibenzyl disulfide, th

Full text of DOI:10.1080/10426500902813603

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Synthesis, Spectral Characterization, and
Crystal Structure of Two Polymorphs of
o,o’-Dichloro Dibenzyl Disulfide
a
a
b
c
S. K. Srivastava , Rupali Rastogi , P. Rajaram , R. J. Butcher
&
d
Jerry P. Jasinski
a
School of Studies in Chemistry , Jiwaji University , Gwalior, India
School of Studies in Physics , Jiwaji University , Gwalior, India
Department of Chemistry , Howard University , Washington, DC,
b
c
USA
d
Department of Chemistry , Keene State College , Keene, New
Hampshire, USA
Published online: 03 Feb 2010.
To cite this article: S. K. Srivastava , Rupali Rastogi , P. Rajaram , R. J. Butcher & Jerry P. Jasinski
(2010) Synthesis, Spectral Characterization, and Crystal Structure of Two Polymorphs of o,o’-Dichloro
Dibenzyl Disulfide, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:2, 455-462
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Phosphorus, Sulfur, and Silicon, 185:455–462, 2010
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902813603
SYNTHESIS, SPECTRAL CHARACTERIZATION,
AND CRYSTAL STRUCTURE OF TWO POLYMORPHS
OF o,o’ -DICHLORO DIBENZYL DISULFIDE
1
1
2
3
S. K. Srivastava, Rupali Rastogi, P. Rajaram, R. J. Butcher,
4
and Jerry P. Jasinski
School of Studies in Chemistry, Jiwaji University, Gwalior, India
School of Studies in Physics, Jiwaji University, Gwalior, India
Department of Chemistry, Howard University, Washington, DC, USA
1
2
3
4
Department of Chemistry, Keene State College, Keene, New Hampshire, USA
2-Chlorophenyl methanethiol undergoes air oxidation catalyzed by different selenides and
yields the corresponding disulfide 1 in two polymorphic forms, 1a and 1b. In the molecular
ꢀ
structures of the two new polymorphs of o,o -dichloro dibenzyl disulfide, the dihedral angles
◦
◦
between the dibenzyl groups are 82.0(1) , (1a), and 73.7(4) , (1b), respectively [(1a): P-1,
◦
◦
a = 8.424(2) Å, b = 8.838(2) Å, c = 10.5823(19) Å, α = 90.122(18) , β = 112.19(2) ,
γ = 95.19(2) , V = 725.9(3) Å ; (1b): P21/n, a = 10.5888(10) Å, b = 9.1590(6) Å,
c = 15.2489(14) Å, β = 103.072(9) , V = 1440.6(2) Å ]. MOPAC computational studies
yield dihedral angles of 89.6(5) and 71.9(9) . Crystal packing is stabilized by weak π-ring
◦
3
◦
3
◦
◦
(
C
H· · ·Cg) intermolecular interactions in both 1a and 1b and by additional weak Cg · · ·
Cg intermolecular interactions in 1b, which influence the bond distances, bond angles, and
torsion angles of the dibenzyl groups in each polymorph. Additional characterization of each
polymorph has been carried out by TEM, IR, H and C NMR spectroscopy, microanal-
ysis, and by FAB mass spectrometry. TEM studies of a sample of 1a show that it contains
cigar-shaped crystallites.
1
13
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords 2-Chlorophenyl methanethiol; disulfides; polymorphs; selenides; TEM; X-ray
structure
INTRODUCTION
Conversion of thiols to disulfides is an important chemical synthetic scheme in
many biological systems.1 Dehydroascorbic acid, flavins, and cytochromes oxidize thiols
,2
Received 12 October 2008; accepted 11 February 2009.
One of the authors (R.R.) is grateful to UGC, New Delhi, India, for financial assistance. The authors are
thankful to the Director, Central Drug Research Institute, Lucknow, India, and Chairman CISC, Banaras Hindu
1
13
University, Varanasi, India, for C, H analysis, FAB measurements, and H, C NMR spectra, respectively. Further,
we are also thankful to the Head, School of Studies in Chemistry, and the Head, School of Studies in Physics, Jiwaji
University, Gwalior, India, for FTIR and TEM measurements, respectively. R.J.B. would like to acknowledge the
NSF-MRI program (CHE-0619278) for funds to purchase the X-ray diffractometer.
Address correspondence to S. K. Srivastava, School of Studies in Chemistry, Jiwaji University, Gwalior-
474011 (M.P.), India. E-mail: sksrivas7@yahoo.com
4
55

456
S. K. SRIVASTAVA ET AL.
to control the cellular redox potential and prevent biological oxidative damage.3–5 On
the other hand, certain organic disulfides are used as additives for lubricating oils, since
6
their presence increases the load-bearing properties of oil, especially at high pressures.
7
,8
9
The formation of diphenyl disulfide as well as dibenzyl disulfide and their molecular
10
structures are well characterized. Recently, three polymorphs of bis(5-methylthio-1,2-
dithiole-3-thione)-disulfide were obtained by the oxidation of the ammonium salt of 5-
methylthio-1,2-dithiole-3-thione-4-thiole. Because of the importance of these compounds,
we report the synthesis, spectral characterization, and crystal structure of two polymorphs
(
1a and 1b) of o,o’-dichloro dibenzyl disulfide (1). The structural data are compared to
9
those of dibenzyl disulfide, which crystallizes in the space group Cc.
RESULTS AND DISCUSSION
o,o’-Dichloro dibenzyl disulfide (1) was prepared by stirring an aqueous THF solution
−
+
of 2-chlorophenyl methanethiol with an ethanolic solution of Na2Se2 or C6H5Se Na
obtained by the reduction of elemental selenium or (C6H5)2Se2 in the presence of NaOH
(
with NaBH4 under N2 atmosphere) overnight. The resulting solution, which might contain
a selenium thiolate complex, was converted to o,o’-dichloro dibenzyl disulfide by air
oxidation for three days. However, the yield was only about 2%, due to the absence of
diselenides. Formation of a Fe-thiolate complex as an intermediate is also reported to
2−
account for the formation of [Fe(nta)Cl2] , which is generally observed in the catalyzed
air oxidation of thiols and dithiols.11
Crystal Structures
Most disulfide molecules exist in a skewed non-planar configuration like that typically
9
12
13
found in dibenzyl disulfide, peroxides, and disulfides. The degree of skewing is gen-
erally governed by steric hindrance of substituents at the disulfide moiety. In o,o’-dichloro
dibenzyl disulfide, the molecular structures of two polymorphs (1a and 1b) are observed
with chlorine atoms at the ortho position in each compound. A view of the molecular struc-
ture of 1a and 1b is shown in Schemes 1 and 2, respectively. Crystal and experimental data
for 1a and 1b are listed in Table I. Bond lengths and bond angles are all within the expected
1
4
◦
ranges (Table II). The dihedral angles between the dibenzyl groups are 82.0(1) in 1a and
◦
7
1
–
–
3.7(4) in 1b (Figures 1 and 2). The benzyl groups are twisted relative to each other in
a with S1A-C1A-C2A-C7A and S1B-C1B-C2B-C3B torsion angles of –94.03(14) and
77.24(16) and in 1b with S1B-C7B-C6B-C5B and S1A-C7A-C6A-C1A torsion angles of
101.47(14) and –78.39(16) , respectively. MOPAC calculations yield dihedral angles
between the benzyl groups of 89.6(5) (1a) and 71.9(9) (1b), respectively. In dibenzyl
disulfide, this angle is 89.0(9) , and the benzyl groups are twisted with respect to each
other with S2-C13-C14-C2 and S1-C1-C7-C8 torsion angles of –70.4(3) and –72.1(2) ,
respectively. It is apparent that these differences are influenced by the presence of the
chlorine atoms in the ortho position in each of the polymorphs. In polymorphs 1a and
◦
◦
◦
◦
15
◦
◦
9
◦
◦
◦
1b, the disulfide molecule itself is inherently chiral due to the twist orientation of the two
halves with respect to the S S vector. Since both polymorphs crystallize in a centrosym-
10
metric space group, they contain both P- or M-helical enantiomers. The S S bond length

TWO POLYMORPHS OF o,o’-DICHLORO DIBENZYL DISULFIDE
457
CH SH
2
Cl
NaOH
EtOH, N atm
,
2NaBH4
2
NaSeSeNa +
2
Se
2
CH2S
SH C
2
Cl
Cl
[Seleno thiolate complex]
intermediate
air oxidation
Polymorph 1a
Scheme 1 Synthetic scheme and chemical structure of polymorph 1a.
_
+
SeNa
CH SH
2
Se
Se
Cl
NaOH, 2NaBH4
2
2
+
EtOH, N atm
2
CH2S
SH C
2
air oxidation [Organoseleno thiolate complex]
intermediate
Cl
Cl
Polymorph 1b
Scheme 2 Synthetic scheme and chemical structure of polymorph 1b.
measures 2.025(1) Å (S1A-S1B) in 1a and 2.020(1) Å (S1A-S1B) in 1b, which closely
9
resembles the 2.020 Å (S1-S2) value observed in dibenzyl disulfide.
In polymorph 1a, there are intermolecular π-ring C H interactions with the center of
gravity of both chloro benzyl rings [C(5B)· · ·Cg1 = 3.792(3) Å, C(5B) H(5A)· · ·Cg1 =
◦
1
65 , (−1 + x, y, z); C(1A) H(1AB)· · ·Cg2, C(1A)· · ·Cg2 = 3.647(2) Å, C(1A)
◦
H(1AB)· · ·Cg2 = 155 , (x, y, z); C(1B)· · ·Cg2 = 3.742(2) Å, C(1B) H(1BB)· · ·
◦
Cg2 = 135 , (−x, 1−y, −z), where Cg1 = C(2A) C(7A) and Cg2 = C(2B) C(7B)] that
help to stabilize the crystal packing in the unit cell (see Figure 3S in the Supplemental
Materials online). In polymorph 1b there are both intermolecular π-ring C H interactions
◦
[
=
C(7A)· · ·Cg2 = 3.7291(19) Å, C(7A) H(7AA)· · ·Cg2 = 155 (x, y, z) where Cg2
C(1B) C(6B)] and intermolecular π–π stacking interactions between adjacent
chlorobenzyl rings [Cg2· · ·Cg2 = 3.8813(10) Å (−x, 2 − y, −z)], which also influence the
crystal packing in the unit cell (see Figure 4S in the Supplemental Materials online).

458
S. K. SRIVASTAVA ET AL.
Table I Crystal and structure refinement data for polymorphs 1a and 1b
Polymorph 1a
Polymorph 1b
Empirical formula
Formula weight
Temperature, K
Wavelength, Å
Crystal system
Space group
C14 H12 Cl2 S2
315.26
296(2)
0.71073
Triclinic
P-1
C14 H12 Cl2 S2
315.26
296(2)
0.71073
Monoclinic
P21/n
◦
Unit cell dimensions, Å,
a = 8.424(2)
α = 90.122(18) a = 10.5888(10)
b = 8.838(2)
β = 112.19(2)
b = 9.1590(6) β = 103.072(9)
c = 10.5823(19) γ = 95.19(2)
c = 15.2489(14)
Volume, Å3
Z
Density (calculated), g/cm
725.9(3)
1440.6(2)
2
4
3
1.442
1.454
Absorption coefficient, mm-1
F(000)
Crystal size, mm
Theta range for data collection,
Index ranges
0.713
324
0.719
648
3
0.51 × 0.43 × 0.23
0.51 × 0.45 × 0.18
◦
4.64 to 32.54
4.66 to 32.59
–12 ≤ h ≤ 12, –13 ≤ k ≤ 13,
–15 ≤ h ≤ 15, –12 ≤ k ≤ 13,
–22 ≤ l ≤ 12
–
15 ≤ l ≤ 15
Reflections collected
12565
13365
Independent reflections
4823 [R(int) = 0.0205]
4720 [R(int) = 0.0406]
◦
Completeness to theta = 25.00 ,% 99.1
97.4
Absorption correction
Semi-empirical from equivalents
Semi-empirical from equivalents
1.00000 and 0.66165
Full-matrix least-squares on F
4720 / 0 / 164
0.778
Max. and min. transmission
Refinement method
1.00000 and 0.80484
Full-matrix least-squares on F
4823 / 0 / 163
2
2
Data / restraints / parameters
2
Goodness-of-fit on F
1.029
Final R indices [I>2σ(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole, e·Å− 0.374 and –0.329
R1 = 0.0330, wR2 = 0.0901
R1 = 0.0667, wR2 = 0.1027
none
R1 = 0.0315, wR2 = 0.0669
R1 = 0.1136, wR2 = 0.0786
0.038(3)
3
0.204 and –0.258
Table II Selected geometric parameters for polymorphs 1a and 1b
◦
◦
Bond lengths [Å]
Bond angles [ ]
Torsion angles [ ]
Polymorph 1a
S1A S1B
C1A S1A
C1A C2A
C3A Cl1A
C1B S1B
C1B C2B
C3B Cl1B
Polymorph 1b
S1A S1B
C7A S1A
C7A C6A
C1A Cl1A
C7B S1B
C7B C6B
C1B Cl1B
2.025(1)
1.836(2)
1.492(2)
1.739(2)
1.837(2)
1.489(2)
1.740(2)
C1A S1A S2A
S1A C1A C2A
C1A C2A C3A
C1B S1B S1A
S1B C1B C2B
C1B C2B C3B
103.83(6)
114.20(9)
122.67(13)
103.66(6)
114.11(10)
123.02(14)
S1A S1B C1B C2B
S1B S1A C1A C2A
S1A C1A C2A C3A
S1A C1A C2A C7A
S1B C1B C2B C3B
S1B C1B C2B C7B
C1A S1A S1B C1B
−59.56(12)
67.25(11)
86.14(15)
−94.03(14)
−77.24(16)
101.78(15)
89.39(7)
2.020(1)
1.829(2)
1.488(2)
1.734(2)
1.827(2)
1.492(2)
1.735(2)
C7A S1A S2A
S1A C7A C6A
C7A C6A C1A
C7B S1B S1A
S1B C7B C6B
C7B C6B C1B
105.12(6)
114.15(9)
123.25(15)
104.94(6)
113.24(10)
122.78(13)
S1A S1B C7B C6B
S1B S1A C7A C6A
S1A C7A C6A C1A
S1A C7A C6A C5A
S1B C7B C6B C1B
S1B C7B C6B C5B
C7A S1A S1B C7B
60.38(12)
−59.63(13)
−78.39(16)
101.35(15)
75.62(17)
−101.47(14)
−89.45(7)

TWO POLYMORPHS OF o,o’-DICHLORO DIBENZYL DISULFIDE
459
Figure 1 ORTEP drawing of the molecular structure of polymorph 1a in the crystal showing the atom numbering
scheme of the asymmetric unit. Displacement ellipsoids are drawn at 50% probability level.
In summary, the dihedral angles between the benzyl groups of two new polymorphs of
o,o’-dichloro dibenzyl disulfide, are affected by weak π-ring (C H· · ·Cg) intermolecular
interactions in both 1a and 1b and by additional weak Cg· · ·Cg intermolecular interactions
in 1b. These intermolecular interactions also influence the bond distances, bond angles, and
torsion angles of the benzyl groups in each polymorph, which can be seen when comparing
9
with the geometric and crystal packing parameters of dibenzyl disulfide.
Figure 2 ORTEP drawing of the molecular structure of polymorph 1b in the crystal showing the atom numbering
scheme of the asymmetric unit. Displacement ellipsoids are drawn at 50% probability level.

460
S. K. SRIVASTAVA ET AL.
Spectral Data
+
In the FAB mass spectrum of polymorphs 1a and 1b, the molecular ion peak was
observed at m/z 315, which is in agreement with the molecular weight of the proposed
+
structure. The molecular ion further loses [C7H6SCl] , and a peak is observed at m/z 157,
+
whereas the base peak at m/z 125 corresponds to a [C7H6Cl] fragment. Figure 5S (in the
Supplemental Materials online) shows the transmission electron micrograph (TEM) of a
powder sample of polymorph 1a. The explicit feature in the IR spectra of all the polymorphs
−1
shows the absence of the band in the region 2590–2550 cm , which appears in the free
thiol as the S H vibration, indicating disulfide bond formation through this site. Because
of the presence of a center of symmetry in the molecule, the band, ν(S S), does not appear
1
in the IR spectra. The H NMR data show the absence of a signal due to an S H proton,
16
1
which again is in accord with the formation of an S S bond. Moreover, the H NMR
spectrum contains signals for the aromatic protons at 7.2–7.3 ppm. A singlet at 3.78 ppm is
13
1
assigned to the S CH2 protons. In the C{ H} NMR spectrum, the significant deshielding
of the S CH2 carbon atom in 1a and 1b, as compared to the free thiol, is in accord with
the presence of a disulfide moiety.
CONCLUSION
Air oxidation of 2-chlorophenyl methanethiol to o,o’-dichloro dibenzyl disulfide is
catalyzed by the addition of diselenides (Na2Se2 or (C6H5)2Se2); the disulfide is formed
upon standing on air for three days. It appears that both diselenides control the stereochem-
istry of the formation of the disulfide of two different polymorphs of the disulfide with
high yields. In the polymorphs 1a and 1b, the disulfide molecule itself is inherently chiral
due to the twist orientation of the two halves with respect to the S S vector. Since both
polymorphs crystallize in a centrosymmetric space group, they contain both P- or M-helical
enantiomers.
EXPERIMENTAL
Diphenyl diselenide,17 sodium phenyl selenolate,18 and disodium diselenide19 were
prepared according to published procedures. 2-Chlorophenyl methanethiol was obtained
from Aldrich. Selenium powder and sodium borohydride were purchased from CDH (India).
The C and H analysis were carried out with an Elementary Varo EL III Carlo Erba1108
1
13
analyzer. The H and C NMR spectra were recorded with a JEOL AL300 FT NMR
spectrometer at 300 and 75.45 MHz, respectively. TEM studies were performed on JEOL
JEM 1230 microscope using an accelerating voltage of 115kV. FAB mass spectra were
recorded with a JEOL SX-102/DA-6000 mass spectrometer using argon/xenon (6 kV, 10
mA) as the FAB gas. The accelerating voltage was 10 kV, and the spectrum was recorded
at room temperature using m-nitrobenzyl alcohol as matrix. IR spectra in the range of
−1
4
000–400 cm were recorded with a Shimadzu Prestige 21 FTIR spectrometer as KBr
pellets. The melting points were determined in open capillary and are reported as such.
Structure Determination and Refinement
X-ray data for 1a and 1b were collected with an Oxford Diffraction Gemini R CCD
area detector using CrysAlisPro software and graphite-monochromated Mo-Kα radiation

TWO POLYMORPHS OF o,o’-DICHLORO DIBENZYL DISULFIDE
461
(
λ = 0.71073 Å) at 200(2) K. The structure was solved by direct methods using
20
SHELXS97, and all of the non-hydrogen atoms were refined anisotropically by full-
2
20
matrix least-squares on F using SHELXL97. The hydrogen atoms were placed in their
calculated positions and included in the refinement using the riding model. An absorption
correction was performed using CrysAlis RED, and all calculations were performed using
21
SHELXTL.
Supporting Information
Crystallographic data (CIF) for the structures reported in this article have been de-
posited with the Cambridge Crystallographic Data Centre and allocated the deposition
numbers CCDC 667838 for 1a and CCDC 667839 for 1b, respectively. These data can be
obtained, free of charge, via www.ccdc.cam.ac.uk/data request/cif, by sending an e-mail
to data request@ccdc.cam.ac.uk, from the Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Synthesis of Polymorph 1a
To a stirred suspension of elemental selenium (0.79 g, 10 mmol) and NaOH (0.88 g,
2
2
2 mmol) in aqueous THF (20 mL + 0.2 mL H2O) under N2 atmosphere, NaBH4 (0.84 g,
2 mmol) was added. The reaction was exothermic, and the pink color of the diselenide
developed soon, which gradually faded to a colorless solution of the monoselenide (usually
taking only a few minutes). The colorless solution of sodium selenide was treated with
one equivalent of elemental selenium (0.79 g, 10 mmol), and the reaction solution became
purple in color. The reaction mixture was stirred for 2–3 h. During this period, a complete
dissolution of the selenium was observed and a brownish red aqueous solution of Na2Se2
was obtained. This solution was then treated with a solution of 2-chlorophenyl methanethiol
(5.46 g, 21 mmol) in THF (20 mL) under N2 atmosphere. The mixture was stirred for 24 h
at room temperature. It was hydrolyzed with 100 mL of water, extracted with 200 mL of
chloroform, washed with 100 mL of water, and dried over anhydrous magnesium sulfate.
The extract was concentrated to 15 mL under reduced pressure. After allowing the solution
to stand for 3 days, transparent block-like crystals were formed. The crystals were washed
◦
with petroleum-ether (60–80 C) to remove the yellowish oil that formed during the air
oxidation process. The yield of the compound obtained by this method was 80%; however
◦
in the absence of Na2Se2, the yield was only 2%. Yield: 80%. Mp: 74 C. Anal. Calcd. for
C14H12Cl2S2: C, 53.49; H, 3.84%. Found: C, 52.90; H, 3.81%.
Synthesis of Polymorph 1b
To an aqueous THF solution (20 mL + 0.2 mL H2O) of diphenyl diselenide (3.14 g,
1
0 mmol) and NaOH (0.80 g, 20 mmol) under N2 atmosphere, NaBH4 (0.75 g, 20 mmol) was
added in pinches. The yellow color of the diselenide darkened and then gradually faded to
colorless. To this colorless solution, 2-chlorophenyl methanethiol (5.46 g, 21 mmol) in THF
(20 mL) was added dropwise, and the solution was stirred for 24 h at room temperature.
The reaction mixture was hydrolyzed with 100 mL of water, extracted with 200 mL of
chloroform, washed with 100 mL of water, and dried over anhydrous magnesium sulfate.
The extract was concentrated to 15 mL under reduced pressure. After allowing the solution

462
S. K. SRIVASTAVA ET AL.
to stand for 3 days, yellow block-like crystals were formed. The crystals were washed with
◦
petroleum-ether (60–80 C) to remove the yellow crystals of diphenyl diselenide that were
formed during the air oxidation process. The compound obtained by this method was in
8
8
3
4% yield; however in the absence of diphenyl diselenide, the yield was only 2%. Yield:
◦
4%. Mp: 76 C. Anal Calcd. for C14H12Cl2S2: C, 53.49; H, 3.84%. Found: C, 53.36; H,
+
+
.64%. FAB: (1a, 1b) m/z = 315 (50%) for [M ], 157 (10%) for [C7H6SCl] , 125 (100%)
+
1
for [C7H6Cl] . H NMR (1a, 1b; CDCl3): δ = 3.78 (s, 4H, CH2S), 7.23–7.36 (m, 8H,
13
C6H4). C NMR (1a, 1b; CDCl3): δ = 41.2 (CH2 S), 135.1 (C Cl), 134.2 (C CH2),
31.7, 126.8, 129.8, 129.0.
1
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2
. D. C. Jocelyn, Biochemistry of the Thiol Group (Academic Press, New York, 1992).
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York, 1974), p. 785.
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4
5
6
7
8
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