Synthesis of new symmetric disubstituted dithioether dithiols

Article abstract of DOI:10.1080/10426507.2012.668984

The β, β'-dihydroxydithioethers, derived from oxirane, have been converted into dithioethers dithiols in good yields. A colloidal solution of gold nanoparticles (AuNPs) with 5,8-dithiadodecane-3,10-dithiol was prepared and showed a good stability from tight binding offered by the thiol group on the Au surfaces. Copyright

Full text of DOI:10.1080/10426507.2012.668984

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Phosphorus, Sulfur, and Silicon and the
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Synthesis of New Symmetric
Disubstituted Dithioether Dithiols
Moufida Romdhani-Younes a , Ines Gara a , Amine Mezni b & Mohamed
Moncef Chaabouni a
a Laboratoire de Chimie Organique Structurale, Département de
Chimie, Faculté des Sciences de Tunis, Université Tunis El Manar,
Tunis, Tunisia
b Unité de Recherche Synthèse et Structure des Matériaux
Inorganiques 99/UR12-30, Département de Chimie, Faculté des
Sciences de Bizerte, Jarzouna, Tunisia
Accepted author version posted online: 02 Mar 2012.Version of
record first published: 19 Jun 2012.
To cite this article: Moufida Romdhani-Younes , Ines Gara , Amine Mezni & Mohamed Moncef
Chaabouni (2012): Synthesis of New Symmetric Disubstituted Dithioether Dithiols, Phosphorus, Sulfur,
and Silicon and the Related Elements, 187:9, 1074-1081
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Phosphorus, Sulfur, and Silicon, 187:1074–1081, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.668984
SYNTHESIS OF NEW SYMMETRIC DISUBSTITUTED
DITHIOETHER DITHIOLS
Moufida Romdhani-Younes,1 Ines Gara,1 Amine Mezni,2
and Mohamed Moncef Chaabouni1
1Laboratoire de Chimie Organique Structurale, De´partement de Chimie,
Faculte´ des Sciences de Tunis, Universite´ Tunis El Manar, Tunis, Tunisia
2Unite´ de Recherche Synthe`se et Structure des Mate´riaux Inorganiques
99/UR12-30, De´partement de Chimie, Faculte´ des Sciences de Bizerte,
Jarzouna, Tunisia
GRAPHICAL ABSTRACT
R2
R1
S
S
S
R2
R1
R1
Triton B
R2
HS
SH
+
solvent free
O
OH HO
R2
R2
S
1. S=C(NH2)2, HCl
2. KOH, H2O, reflux
R1
R1
SH HS
R1, R2 = H, Me; H, Et; (CH2)4; H, CH2OPh; H, Ph
Abstract The β,βꢁ-dihydroxydithioethers, derived from oxirane, have been converted into
dithioethers dithiols in good yields. A colloidal solution of gold nanoparticles (AuNPs) with
5,8-dithiadodecane-3,10-dithiol was prepared and showed a good stability from tight binding
offered by the thiol group on the Au surfaces.
Keywords Epoxides; gold nanoparticles; hydroxy thioethers; thiols
INTRODUCTION
Since their discovery, thioetherthiol derivatives have been the subject of several
studies.1–4 Interest in such compounds is due to their applications in various fields such
5–8
as the synthesis of polymers
and in the field of biochemistry.9 The ability of thiols
to penetrate in cellular tissues under physiological conditions and their fixation on DNA
Received 8 December 2011; accepted 8 February 2012.
Address correspondence to Moufida Romdhani-Younes, Laboratoire de Chimie Organique Structurale,
De´partement de Chimie, Faculte´ des Sciences de Tunis, Universite´ Tunis El Manar, 2092 Tunis, Tunisia. E-mail:
moufida.romdhani@gmail.com
1074

SYNTHESIS OF NEW SYMMETRIC DISUBSTITUTED DITHIOETHER DITHIOLS
1075
branches10,11 demonstrates their importance in the medical field.12,13 Compounds which
contain two sulfur atoms are excellent precursors in organic synthesis,14 particularly in the
preparation of thiacrown ethers,15–18 which are excellent chelating agents of some metallic
ions.19
For instance, the incorporation of thiol groups into organic molecules allows their
coordination to noble metal surfaces to form self-assembled monolayers (SAMs)20,21 that
have applications in molecular electronics22–24 and in the synthesis of stable colloidal
nanoparticles of noble metals, even under extreme conditions of pH and ionic strength due
to strong interactions between gold and sulfur atoms.25
In the course of our work on the synthesis of sulfur containing compounds, we
have prepared a number of polydentate ligands26–29 exhibiting either a thioether or an
oxathioether moiety as an additional donor function. We herein report the synthesis of a
new series of symmetrically disubstituted dithioether dithiols 3a–e (Table 1), accessible
from substituted β,βꢁ-dihydroxydithioethers 2a–e. The starting compounds 2a–e were
prepared, as previously described,27 from alkyl or aryl oxiranes in one step (Scheme 1).
R2'
R2'
R1'
S
S
R1
Triton B
R2
HS
SH
+
solvent free
O
R1'
S
OH HO
R2'
R1'
R2'
S
1. S=C(NH2)2, HCl
2. KOH, H2O, reflux
R1'
SH HS
1, 2, 3: a: R1 = Me, R2 = H; b: R1 = Et, R2 = H; c: R1/R2 = (CH2)4; d: R1 = PhOCH2, R2 = H
2, 3: e1: R1 = Ph, R2 = H; e2: R1' = Ph/H, R2' = H/Ph; e3: R1' = H, R2' = Ph
Scheme 1 Synthesis of disubstituted dithioether dithiols 3a.
RESULTS AND DISCUSSION
In our first attempts to study the reactivity of β,βꢁ-dihydroxydithioethers 2a–e, we
tried to prepare the corresponding tosylates according to standard protocols30,31 in order to
synthesize the dithiols containing six sulfur atoms by condensation of dimercaptoethane
with these tosylates. In all cases, no tosylation reaction was observed and the starting com-
pounds were recovered unchanged. This is presumably due to the existence of an adjacent
sulfur atom. Consequently, a direct thiolation of the two hydroxyl groups was attempted.
According to the literature,1,32 the condensation of alcohols in concentrated hydrochloric
acid with thiourea followed by hydrolysis of the thiouronium salt intermediate under basic
conditions is considered to be a good thiolation method, which is widely used for the
preparation of primary and secondary thiols. Therefore, the new symmetric disubstituted
dithioetherdithiols 3a–e have been prepared in this way. In the case of styrene oxide, we

1076
M. ROMDHANI-YOUNES ET AL.
Table 1 Symmetric disubstituted dithioethers dithiols
Yield
(%)
bp
Epoxide 1
Thioetherdiols 2
Thioetherdithiolsa 3
(◦C/0.01 mmHg)
87
87
Me
S
S
S
S
Me
Me
Me
Me
OH
HO
O
SH
HS
1a
2a
3a
3b
85
134
Et
S
S
S
S
O
Et
Et
Et
Et
OH
HO
SH
HS
1b
2b
70
70
oil
oil
S
S
S
S
O
OH HO
SH HS
1c
2c
3c
PhO
S
S
S
S
OPh
OPh
O
PhO
PhO
SH
HS
OH
HO
1d
2d
3d
70b
176c
Ph
S
S
S
S
O
Ph
Ph
Ph
Ph
O H
H O
SH
HS
1e
3e1 53%
2e1 52%
Ph
Ph
Ph
Ph
S
S
S
S
O H
H O
SH
HS
3e2 32%
2e2 31%
Ph
Ph
S
S
S
S
Ph
Ph
OH
HO
SH
HS
3e3 15%
2e3 17%
c
aThe ratio of the three isomers was determined by 1H NMR. bTotal yield of three isomers. The mixture of
isomeric products was purified by distillation.
showed in a previous letter27 that the ring opening of this epoxide with dimercaptoethane
using benzyltrimethylammonium hydroxide (Triton B) as catalyst led to a mixture of three
regioisomers of β,ꢁ-dihydroxydithioethers 2e1–e3 (Table 1). The three isomers were con-
verted into their homologous thioether thiols 3e1–e3 and the mixture of isomers was purified
1
by distillation. The ratio of the three isomers was determined by H spectroscopy. Com-
pounds 3a, 3b, 3d, and 3e should be obtained as mixtures of diastereomers. However, since
the two stereogenic centers within the molecule are far from each other, the diastereoiso-
mers could not be discerned by NMR techniques as in the case of their precursors 2a, 2b,
2d, and 2e.27 The 1H NMR spectrum shows a sharp singlet for the two methylene groups

SYNTHESIS OF NEW SYMMETRIC DISUBSTITUTED DITHIOETHER DITHIOLS
1077
of the dimercaptoethane moiety ( SCH2 CH2S ) at around δ = 2.80 ppm. As the com-
pounds 3a, 3b, and 3d are symmetric, the 13C NMR spectra show the existence of only three
different signals corresponding to the three aliphatic carbon atoms of one isomer, besides
the peaks related to the carbon atoms of the alkyl groups. In addition of the peaks related
to the aromatic carbon atoms, six distinct signals were observed in the 13C NMR spectrum
of the mixture of 3e1, 3e2, and 3e3. This is not the case for the cyclohexane derivative 3c,
for which two singlets of the same intensity were observed for these methylene groups at
δ = 2.80 ppm and at δ = 2.83 ppm. The existence of two diastereomers for the cyclohexane
derivative was shown in our previous work.27 This may be explained if we assume that
the cyclohexene oxide 1c gave exclusively trans-products 2c,33 formed as an equimolar
mixture of the meso- and threo-isomers which are transformed into the homologous meso-
and threo-isomers 3c too (Scheme 2). Examination of the 13C NMR spectra of 3c showed
doubling of a number of the peaks. 1H NMR spectra of 3c exhibited correct integrals but
it showed two signals for the CH2S group. The isomeric ratio is determined from CH2S
signals intensity.
S
S
S
S
SH HS
OH HO
threo 50%
threo 50%
i)SC(NH2)2/HCl
Triton B 25°C
Solvant free
O
SH
HS
+
+
+
ii)KOH/H2O/reflux
S
S
S
S
SH HS
meso
OH HO
meso
50%
50%
Scheme 2 Formation of stereoisomers of 3c.
It should be noted that in all cases variable amounts of the corresponding disulfide
and trisulfide compounds (dimers and trimers) were formed by air oxidation of the aqueous
1
thiolates. The formation of compounds 3a–e was confirmed by H and 13C NMR spec-
1
troscopy and HRMS. In all cases, the H NMR spectra showed the absence of a singlet
around δ 3.77 ppm due to the two (OH) protons and the presence of a multiplet between
δ 1.70 and 1.80 ppm assigned to the protons of SH groups. The 13C NMR spectra display
characteristic signals of all carbons.
As compounds 3 are expected to be excellent chelating agents toward soft metal ions,
we used 3b as a ligand to prepare gold nanoparticles (AuNPs) due to the soft character of
both Au and S.34,35 These AuNPs could have applications in biological fields and catalytic
reactivity. The preparation was carried out in aqueous solution using tetrachloroauric(III)
acid (HAuCl4·3H2O) as precursor and sodium borohydride (NaBH4) as a reducing agent
with the ligand 3b in a molar ratio of Au:ligand = 600:1. Tetrachloroauric acid and the
ligand 3b were first mixed in water to promote the formation of metal-ligand precursors.
The precursor formation showed a rapid color change of the originally yellow solution to
colorless. Addition of NaBH4 initiates reduction of the Au ions and rapid growth of the Au
nanocrystals.

1078
M. ROMDHANI-YOUNES ET AL.
Figure 1 TEM images (a) and UV-Vis spectrum (b) of AuNPs of 3b.
The AuNPs were characterized by transmission electron microscopy (TEM) and
UV-vis absorption spectroscopy. The results are shown in Figure 1.
The TEM image shows the formation of a clear distribution of colloidal nanoparticles
formed between gold atoms and the ligand 3b. This image does not show any nanocrystal
clumping, and also shows that the AuNPs exhibit a spherical shape with a diameter of 10
nm. The UV-Vis spectroscopy result is in good agreement with the TEM image and reveals
that AuNPs have a maximum absorption band at 530 nm which indicates the formation
of AuNPs with a size of 10 nm. These nanoparticles appear to exhibit good stability.
Indeed, the peak characteristic of AuNPs absorbance shows no shift after several months
of synthesis. In addition, no change in color of the solution is observed.
Compared to other ligands as PEG-SH25 used in the complexation of gold, the ligand
3b is highly stable even though it has a short chain. Furthermore, the two SH functions of
3b increase the stability of the AuNPs.
The importance of the synthesis of colloidal solutions with thiols mainly rests on
biological applications. In fact, working in this area under extreme conditions of pH, which
involves particles with good stability, the use of thiols have the greatest gold affinity.
In summary, we have achieved the conversion of β,βꢁ-dihydroxydithioethers 2a–e
into their corresponding disubstituted dithioethers dithiols 3a–e in good yields. To our
knowledge, these compounds, except the product 3a36 have not been reported previously and
may be useful intermediates for the synthesis of lipophilic thiacrown ethers. We have also
demonstrated that compounds 3 can be used for the preparation of colloidal gold solution in
aqueous phase using HAuCl4·3H2O. These colloidal solutions exhibit remarkable stability.
EXPERIMENTAL
1H and 13C NMR, UV-Vis Spectroscopy, and Transmission
Electron Microscopy
The 1H (300 MHz) and 13C NMR (75 MHz) spectra were recorded in CDCl3 as solvent
on a Bruker AC 300 spectrometer. The chemical shifts are reported in ppm relative to TMS
1
(internal reference). For the H NMR, the multiplicities of signals are indicated by the

SYNTHESIS OF NEW SYMMETRIC DISUBSTITUTED DITHIOETHER DITHIOLS
1079
following abbreviations: s: singlet, d: doublet, t: triplet, m: multiplet. Coupling constants
J are given in Hz. HRMS spectra were obtained by use of a MAT 95 SBE instrument.
TEM measurements were made on a JEOL 2011 microscope operating at 100 kV. This
microscope is equipped with a Gatan Imaging Filter 2000 so as to conduct an electron
energy-loss spectroscopy (EELS) analysis. Such an analysis is a powerful technique to
provide a cartographic picture of the distribution of chemical elements in the observed
nanoparticles. The absorption spectra were obtained with a PERKIN ELMER UV/VIS
spectrometer lambda11.
Preparation of Dithiols
To a stirred solution of thiourea (2.51 g, 33 mmol) in 8 mL of conc. aqu. HCl, were
added the thioetherdiol 2 (15 mmol) at room temperature. The mixture was refluxed for 9 h.
The resulting solution was then cooled in an ice bath and 5.65 g (0.101 mol) of KOH in 35 mL
of H2O were cautiouslyadded. This mixturewas refluxed for 3h. Then, the resultingsolution
was allowed to cool, acidified with 10% aqu. HCl to pH = 2–3, and extracted with diethyl
ˆ
ether (3 I 50 mL). The combined organic layers were dried over anhydrous MgSO4, filtered,
and concentrated in vacuo. The residue was purified by distillation except the product 3d
which was isolated by column chromatography (silica gel 60F254, heptane /EtOAc 80:20).
Preparation of AuNPs
AuNPs were prepared following literature methods25: an amount of 156 µL of
50.8 mM HAuCl4·3H2O solution and the desired molar concentration of 3b-ligand were
dissolved in 25 mL of deionized H2O; the mixture was then stirred for 1 h. An amount
of 72 µL of 880 mM NaBH4 stock solution in deionized H2O was added (in aliquots of
18 µL) over 30 min with vigorous stirring. The mixture was then left under stirring for at
least 3 h. In our experimental protocol, we used 10 times total molar excess of the reducing
agent during the growth and passivation steps, i.e., a total NaBH4:Au molar ratio ∼10.
1
4,7-Dithiadecane-2,9-dithiol (3a). Yield = 87%. H NMR: 1.36 (d, 6H, J = 6,
2CH3); 1.74 (m, 2H, 2SH); 2.55–2.78 (m, 4H, CH2S); 2.81 (S, 4H, SCH2CH2S); 2.92–3.09
(m, 2H, CHSH). 13C NMR: 20.0 (CH3); 31.87 (C, SCH2CH2S); 38.67(CH2); 43.62 (CHSH).
HRMS: calcd. 265.0189 for C8H18S4Na, found 265.0193 (M+Na)+.
1
5,8-Dithiadodecane-3,10-dithiol (3b). Yield = 85%. H NMR: 0.99 (t, 6H, CH3);
1.54 (m, 4H, CH2); 1.80 (m, 2H, SH); 2.70 (m, 4H, CH2S); 2.75 (s, 4H, SCH2CH2S);
2.89 (m, 2H, CHSH). 13C NMR: 11.23 (CH3); 29.48 (CH2CH3); 31.14 (SCH2CH2S);
42.36 (CH2S); 43.49 (CHSH). HRMS: calcd. 293.0502 for C10H22NaS4, found 293.0508
(M+Na)+.
1
2,2ꢁ-[Ethane-1,2-diylbis(sulfanediyl)]dicyclohexanethiol (3c). Yield = 72%. H
NMR: 1.27–1.41 [m, 8H, (CH2)2]; 1.50–1.90 [m, 8H, (CH2)2]; 1.77 (m, 2H, SH); 2.42 (m,
2H, CH), 2.70–2.75 (m, 2H, CH), 2.80, 2.83 (two singlets, 4H, SCH2CH2). 13C NMR: 24.10,
24.30 (two peaks, CH2); 24.02, 25.90 (two peaks, CH2); 31.09, 31.77 (two peaks, CH2);
32.45, 32.92 (two peaks, SCH2CH2S); 33.42, 33.78 (two peaks, CH2); 46.30, 46.70 (two
peaks, CH); 48.32, 48.90 (two peaks, CHSH). HRMS: calcd. 345.0815 for C14H26NaS4,
found 345.0811 (M+Na)+.
1
1,10-Diphenoxy-4,7-dithiadecane-2,9-dithiol (3d). Yield = 70%, Yellow oil. H
NMR: 1.85 (m, 2H, SH); 2.58–2.83 (m, 4H, CH2S); 2.81 (s, 4H, SCH2CH2S); 3.35 (m, 2H,
CH); 4.02–4.30 (m, 4H, CH2O); 6.80–7.40 (m, 10H, Har). 13C NMR: 32.91 (SCH2CH2S);

1080
M. ROMDHANI-YOUNES ET AL.
35.42 (CH2S); 57.10 (CH); 70.30 (CH2O); 114.92–159.38 (Car). HRMS: calcd. 449.0713
for C20H26O2SNa, found 449.0715 (M+Na)+.
1,8-Diphenyl-3,6-dithiaoctane-1,8-dithiol (3e1), 2,7-Diphenyl-3,6-dithiaoctane-
1,8-dithiol (3e2) and 2,7-Diphenyl-3,6-dithiaoctane-1,8-dithiol (3e3). Total yield = 70%.
1,8-Diphenyl-3,6-dithiaoctane-1,8-dithiol (3e1). 1H NMR: 1.50–1.70 (m, 2H, SH); 2.80
(s, 4H, SCH2CH2S); 2.75–3.10 (m, 4H, CH2S); 3.95 (m, 2H, CH); 6.90–7.50 (m, 10H,
Har). 13C NMR: 33.56 (SCH2CH2S); 41.90 (CHPh); 43.46 (CH2S); 127.14–141.77 (Car).
HRMS: calcd. 389.0502 for C18H22NaS4, found 389.0505 (M+Na)+.—2,7-Diphenyl-3,6-
dithiaoctane-1,8-dithiol (3e2). 1H NMR: 1.50–1.70 (m, 2H, SH); 2.80 (s, 4H, SCH2CH2S);
3.10–3.40 (m, 4H, CH2S); 4.15 (m, 2H, CH); 6.90–7.50 (m, 10H, Har). 13C NMR:
31.34 (SCH2CH2S); 35.15 (CH2SH); 48.77 (CHPh); 127.14–139.99 (Car). HRMS: calcd.
389.0502 for C18H22NaS4, found 389.0505 (M+Na)+.—2,7-Diphenyl-3,6-dithiaoctane-
1,8-dithiol (3e3). 1H NMR: 1.50–1.70 (m, 2H, SH); 2.81 (s, 4H, SCH2CH2S); 2.90–3.15
(m, 2H, CH2SH); 3.10–3.35 (m, 2H, SCH2CH); 4.12 (m, 2H, CHPh); 6.90–7.50 (m, 10H,
Har). 13C NMR: 31.34 (CH2SC-Ph); 33.56 (SCH); 35.15 (CH2SH); 41.90 (HSCHPh),
43.46 (CH2CHPh), 48.77 (SCHPh), 127.14–141.77 (Car). HRMS: calcd. 389.0502 for
C18H22NaS4, found 389.0505 (M+Na)+.
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