Synthesis and characterization of benzylidene bis-dithiobenzoate

Article abstract of DOI:10.1080/104265090885138

Benzal chloride reacts with sodium sulfide in alcoholic solution to yield three main products: benzyl disulfide, benzyl dithiobenzoate, and a new interesting compound 5, C₂₁H₁₆S₄, which was isolated and characterized as benzylidene bis-dithiobenzoate. The intermediates obtained from the autoxidation-reduction of the unisolable thiobenzaldehyde are implied in subsequent nucleophilic addition and substitution processes. NMR spectra and X-Ray structure analysis of 5 are discussed. Copyright Taylor & Francis Inc.

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Phosphorus, Sulfur, and Silicon
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Synthesis and Characterization
of Benzylidene Bis-
Dithiobenzoate
M Gloria Quintanilla a , Eva Guerra a , Jessica Dotor
a , Jirina Maresova a , Fructuoso Barba a & Avelino
Martín b
a Departamento de Química Orgánica, Universidad
de Alcalá , Madrid, Spain
b Departamento de Química Inorgánica, Universidad
de Alcalá , Madrid, Spain
Published online: 01 Feb 2007.
To cite this article: M Gloria Quintanilla , Eva Guerra , Jessica Dotor , Jirina
Maresova , Fructuoso Barba & Avelino Martín (2005) Synthesis and Characterization
of Benzylidene Bis-Dithiobenzoate, Phosphorus, Sulfur, and Silicon and the Related
Elements, 180:7, 1691-1699, DOI: 10.1080/104265090885138
To link to this article: http://dx.doi.org/10.1080/104265090885138
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Phosphorus, Sulfur, and Silicon, 180:1691–1699, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090885138
Synthesis and Characterization of Benzylidene
Bis-Dithiobenzoate
Ma Gloria Quintanilla
Eva Guerra
Jessica Dotor
Jirina Maresova
Fructuoso Barba
Departamento de Qu´ımica Orga´nica, Universidad de Alcala´,
Madrid, Spain
´
Avelino Martın
Departamento de Qu´ımica Inorga´nica, Universidad de Alcala´,
Madrid, Spain
Benzal chloride reacts with sodium sulfide in alcoholic solution to yield three
main products: benzyl disulfide, benzyl dithiobenzoate, and a new interesting
compound 5, C
H
S , which was isolated and characterized as benzylidene
21 16 4
bis-dithiobenzoate. The intermediates obtained from the autoxidation-reduction of
the unisolable thiobenzaldehyde are implied in subsequent nucleophilic addition
and substitution processes. NMR spectra and X-Ray structure analysis of 5 are
discussed.
Keywords Benzal chloride; benzyl dithiobenzoate; benzylidene bis-dithiobenzoate;
dibenzyl disulfide; sodium sulfide; thiobenzaldehyde
Received March 25, 2004; accepted July 12, 2004.
This research was supported by the Spanish Ministry of Education and Culture,
CTQ2004-05394/BQU.
The authors are very indebted to Jose Maria Arribas and Ana Albasanz for their help
with the elemental analysis and mass spectra. Also we record with appreciation the help
rendered by Luis Manuel Frutos by the Theoretical Studies.
Crystallographic data (excluding structure factors) for the structure in this paper
have been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC-231178. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44-(0)1223-336033
or e-mail: deposit@ccdc.cam.ac.uk].
Address correspondence to M. Gloria Quintanilla, Departamento de Qu´ımica
Orga´nica, Universidad de Alcala´, 28871 Madrid, Spain. E-mail: gloria.quintanilla@
uah.es
1691

1692
M. G. Quintanilla et al.
INTRODUCTION
The study of dithiocarboxylic acids and its esters is still a rather
unexplored field in organic chemistry. Most of the work on this sul-
fur chemistry was done around 1900 and many of the described
results are not coincident.1 In 1882 Klinger2 reported the reaction
between benzal chloride 1 and potassium hydrogen sulfide, where-
upon potassium dithiobenzoate and dibenzyl disulfide were obtained.
Fromm and Schmoldt3 tried to reproduce Klinger’s results. When they
treated benzal chloride with sodium sulfide, mainly β-thiobenzaldehyde
(trithiobenzaldehyde) was produced. However, if sodium hydrogen sul-
fide was employed (similar as Klinger did), only dibenzyl disulfide was
isolated. Therefore, those authors deduced that Klinger was wrong:
Gem-dihalides do not lead to dithiocarboxylic salts; perhaps Klinger
obtained it because of a contamination with trihalogenated compound
(which is known as a source to obtain dithiocarboxylic salts4). Wood
and Bost5 asserted that benzal chloride and sodium sulfide react in
alcoholic solution to form monomeric thiobenzaldehyde. This com-
pound can not be isolated, but undergoes different reactions to yield
β-trithiobenzaldehyde, benzyl mercaptan, sodium dithiobenzoate,
small amounts of benzyl dithiobenzoate, and benzyl mercaptal of
thiobenzaldehyde. The same authors described the reaction of benzalde-
hyde with H2S in alcoholic solution either saturated with HCl or in al-
kaline medium. In both cases viscous pink oils are obtained, together
with trithiobenzaldehyde or benzyl dithiobenzoate. Upon distillation,
the pink oil decomposed to form mostly stilbene and sulfur. No more
progresses concerning the study of this reaction have been found in the
recent years. With this article, we intend to put some light on this pro-
cess, with the isolation and identification of the obtained products and
with a proposal of this formation route.
RESULTS AND DISCUSSION
The reaction between benzal chloride 1 and sodium sulfide nonahy-
drate in ethanol under the experimental conditions described below led
to the following products (Scheme 1): dibenzyl disulfide 2 (39%), benzyl
dithiobenzoate 3 (6%), benzaldehyde 4 (8%), unreacted benzal chloride
SCHEME 1

Benzylidene Bis-Dithiobenzoate
1693
(9%), and a new red product 5 (38%) which was characterized by analyti-
cal and spectroscopic techniques as benzylidene bis-dithiobenzoate
and its structure confirmed by X-Ray studies.
It has been reported in the literature2 that the thiobenzaldehyde
initially formed is not isolable and undergoes, under the slightly basic
conditions of the process, a Cannizzaro-type reaction to yield benzyl
mercaptan and dithiobenzoate. We propose for this reaction the redox
process shown in the Scheme 2. The thiobenzaldehyde 6 disproportion-
ates to the corresponding radical cation (which would immediately re-
act with the anion S2− and loses an electron and a proton to give the
dithiobenzoate anion) and the radical anion, which takes up both an
electron and a proton leading to the benzyl thiolate.
SCHEME 2
The formation of dibenzyl disulfide 2, the most important of the
side products, can be explained either as an air oxidation of benzyl
thiolate or as an alternative of the reduction process: The radical an-
ion, after taking up a proton, might also dimerise to give the benzyl
disulfide.
The reaction between benzyl thiolate and the thiocarbonyl group of
the dithiobenzoate would lead to the benzyl dithiobenzoate 3.
The amount of undesired benzaldehyde 4, produced by hydrolysis
of benzal chloride, was considerably reduced by improving the dryness
method of hydrated sodium sulfide, as described in the Experimental.
The red crystals of the unknown compound 5 exhibited no car-
bonyl bands in its IR spectrum. EI mass spectra showed an ap-
parent molecular peak at 332, which would not be in accordance

1694
M. G. Quintanilla et al.
with the molecular formula obtained from the elemental analysis:
C21H16S4.
It was necessary to use two soft ionization methods to find the correct
molecular weight of our compound: ESI (Electro Spray Ionization) and
APCI (Atmospheric Pressure Chemical Ionization).6 The EI might be
too aggressive, breaking the molecule and losing elementary sulfur,
which displays peaks at 64 and 128 in the spectrum. Both techniques
confirmed what we were expecting: a molecular weight of 396 for the
molecular formula C21H16S4 as the elemental analysis predicted.
These results and the 1H and 13C NMR spectra led us to assign
to compound 5 the structure of benzylidene bis-dithiobenzoate, which
1
was confirmed by X-ray structural analysis. In the H-NMR spectrum
5 showed peaks which correspond to the presence of three phenyl rings
of two different types: two of them are more unshielded than the ben-
zaldehyde protons, and the third one appears at a lower frequency:
7.94 ppm (d, 4H (o-)); 7.61 ppm (d, 2H (oꢀ-)); 7.51 ppm (t, 2H (p-)); a
multiplet from 7.37 ppm to 7.30 ppm, with a predominant triplet at
7.35 ppm (7H (m-), (mꢀ-), (pꢀ-)); 6.97 ppm (s, 1H*, methynic proton). From
the proton-coupled 13C-NMR spectra, we could emphasize the following
signals: 223.98 ppm, corresponding to two equivalent thiocarbonyl car-
3
bons (q, J = 3.3 Hz, by coupling with two aromatic and the methynic
proton); 144.16 ppm corresponding to two equivalent ipso carbons of
3
4
the A, Aꢀ rings (td, JC−Hm = 8 Hz, JC−Hp = 1.48 Hz); 136.14 ppm
3
ꢀ
corresponding to the ipso carbon of the B ring (td, JC−Hm = 7.5 Hz,
2JC−H∗ = 4.5 Hz); 127.14–132.88 ppm (aromatic carbons); 62.11 ppm
corresponding to the methynic group (dt, 1JC−H∗ = 158.43 Hz, 3JC−Ho
=
ꢀ
4.72 Hz). (It has been described that in aromatic systems the
coupling constants C H at two bond is smaller than at three
bonds.)7
Compound 5 would be produced by a nucleophilic substitution
of the benzalchloride (Scheme 3) by the dithiobenzoate anion (see
Scheme 2).
SCHEME 3

Benzylidene Bis-Dithiobenzoate
1695
FIGURE 1
X-Ray Structural Analysis
Compound 5 crystallizes in the monoclinic space group P21/c. Selected
bond distances, interactions and angles are presented in Table 1. Two
independent molecules were found in the asymmetric unit. As can be
seen in Figure 1, the tetrahedral environment of C101 and C201 is
slightly distorted with angles in the range 105.0(3)–114.8(3)◦. Distances
from H101 and H201 to the nearest sulfur atoms H101· · ·S12 = 2.53
˚
˚
(4) A and H201· · ·S22 = 2.43 (4) A are shorter than the sum of the Van
der Waals radii, which could indicate some interaction and hindrance
of the free rotation around the C101–H101 or C201–H201 bonds. At
the same time, the distance between S12 and the S11 of the nearest
˚
molecule in the unit cell is 3.516 (2) A, again shorter than the sum of
the Van der Waals radii. This interaction does not appear in the second
˚
molecule (distance S21 to S22 of the nearest molecule 3.861 (2)A) and
could be responsible for the spatial arrangement and the existence for
the two different molecules.

1696
M. G. Quintanilla et al.
˚
˚
TABLE I Selected Bond Lengths (A), Interactions (A) and
Angles (◦) of 5
C101-S11
C101-S13
1.821 (5)
1.813 (5)
3.174 (5)
1.00 (4)
2.53 (4)
1.627 (5)
105.0 (3)
110.4 (3)
123.5 (4)
126.0 (3)
−26 (3)
38 (3)
C201-S21
C201-S23
1.816 (5)
1.817 (5)
3.146 (5)
1.06 (4)
2.43 (4)
1.626 (5)
108.5 (3)
111.1 (3)
122.7 (4)
126.1 (3)
−19 (3)
C101· · ·S12
C201· · ·S22
C101-H101
C201-H201
H101· · ·S12
H201· · ·S22
C108-S12
C208-S22
S13-C101-S11
S11-C108-C109
C109-C108-S12
S12-C108-S11
H101-C101-S11-C108
H101-C101-S13-C115
S11-C108-C109-C110
S23-C201-S21
S21-C208-C209
C209-C208-S22
S22-C208-S21
H201-C201-S21-C208
H201-C201-S23-C215
S21-C208-C209-C210
−44 (2)
30.3 (6)
32.7 (6)
At sight of these results, theoretical calculations were made in order
to find out whether the apparent absence of free-rotation could imply
the existence of two real enantiomers.
Theoretical Predictions
The HF (Hartree-Fock)8 method with B3Lyp hybrid exchange-
correlation energy functional, using 3-21G∗ basis set, were used in order
to determine the structures of the molecular conformations predicted by
X-Ray technique. All the structures were optimized, in order to identify
them as stationary points in the potential energy surface (PES), and
analysis of approximate Hessian of the energy confirms them as a min-
imum in the PES. The results show that the two conformers found have
the same energy, in fact, the structures are enantiomers. The structures
are in equilibrium through a transition state, which has energy around
1 kcal/mol over the minima, so the interconversion is very fast in solu-
tion at room temperature, and it is not expected to detect any optical
activity.
EXPERIMENTAL
Benzal chloride, absolute ethanol (99.9%), and sodium sulfide nonahy-
drated were obtained commercially. IR measurements were performed
on a Perkin-Elmer Model 583 spectrophotometer; liquid samples were
measured neat on NaCl plates; solid samples as KBr pellets. 1H-NMR
(300 MHz) and 13C-NMR (300 MHz and 500 MHz) spectra were recorded
on Varian Unity 300 and Unity Plus 500 spectrometers; the chemical

Benzylidene Bis-Dithiobenzoate
1697
shifts are given in ppm. Melting points were determined on a Re-
ichert Thermovar microhot stage apparatus. Elemental analysis was
performed on a LECO CHNS-932 analyzer. Mass Spectra (EI, ionizing
voltage 70 eV) were determined using a Hewlett Packard Model 5988A
mass selective detector equipped with a Hewlett Packard MS Chem
Station. APCI and ESI6 were performed on an Automass Multi of Ther-
moQuest, font Aqua, and solvent systems: MeOH (AcOH 5%) for ESI
and H2O/MeOH for APCI.
The study of the stoichiometry has been very important in this pro-
cess, since the proportional amount of both starting materials causes a
big influence in the results.
After several attempts the best results were obtained starting the
reaction with a mixture of 3 moles of benzal chloride and 4 moles of
sodium sulfide.
From the procedure we could remark the following steps:
A carefully drying process of the Na2S · 9H2O is necessary, where
it is previously crashed and then heated in a wide plate at 105◦C for
20 hours to evaporate the water of hydration.
It is also of deciding importance how the reagents are added. To the
mixture of dried sodium sulfide in ethanol the benzal chloride is added
in two portions (see below).
The water of hydration of the Na2S · 9H2O must be removed because
of the undesirable production of benzaldehyde as a consequence of the
benzal chloride hydrolysis under basic conditions.
General Procedure: 7.25 g (4.5 · 10−2 moles) of benzal chloride were
added to a solution of 7.21 g (3 · 10−2 moles) of previously dried sodium
sulfide and 100 mL of absolute ethanol in a double neck round bottomed
flask. The reaction mixture was heated and stirred for 2 h, after which
3 · 10−2 moles of the previously dried sodium sulfide were again added
to complete the proportion 3:4.
After filtration of the white solid precipitated at the bottom of the
flask, (NaCl) and evaporation of solvent 4.56 g of a red oil was obtained.
A steam distillation was carried out of that red mixture to remove the
benzaldehyde 4 (0.37 g, 8%).
The distillate was extracted with ether; the organic layer was sep-
arated, concentrated, and dried over anhydrous MgSO4. After solvent
evaporation a red amorphous mass was obtained where an important
amount of red crystals was included. The crude, product was separated
by column chromatography (hexane/chloroform, 29:1) leading to 0.45 g
benzal chloride 1 (9%), 1.81 g benzyl disulfide3,9 2 (39%), 0.26 g benzyl
dithiobenzoate5 3 (6%), 1.65 g benzal bis-dithiobenzoate 5 (36%).

1698
M. G. Quintanilla et al.
Benzyl dithiobenzoate5,10(3): (0.26 g, 6% yield). 1H-NMR
(300 MHz, CDCl3)δ: 8.02 (d, 2H, J = 6.10 Hz); 7.54 (t, 1H, J = 6.32 Hz);
7.42–7.30 (m, 7H); 4.61 (s, 2H). 13C-NMR (300 MHz, CDCl3) δ: 227.64,
144.74, 134.96, 132.39, 129.28, 128.7, 128.52, 128.34, 127.74, 126.90.
MS (EI) m/e (%): 244 (M+, 35), 121 (100), 91 (88), 77 (43).
Benzylidene bis-dithiobenzoate (5): (1.65 g, 36.% yield, red crys-
tals, m.p. 73–75◦C).1H-NMR (300 MHz, CDCl3) δ: 7.945 (d, 4H, J =
7.3Hz), 7.61 (d, 2H, J = 7.8 Hz), 7.51 (t, 2H, J = 7.3 Hz), 7.37–
7.30 (m, 7H), 6.97 (s, 1H); 13C-NMR (500 MHz, CDCl3) δ: 223.98 (q,
4
J = 3.3Hz); 144.6 (td,3JC−Hm = 8 Hz, JC−Hp = 1.48 Hz); 136.14 (td,
3
JC−Hm = 7.5 Hz, 2JC−H∗ = 4.5 Hz); 127.14–132.88 (aromatic carbons),
ꢀ
62.11 (dt, 1JC−H∗ = 158.43 Hz, 3JC−Ho = 4.72 Hz). IR υmax (KBr/cm−1):
ꢀ
3058.68; 3027.75; 2919.40; 1674.15; 1589.45; 1493.63; 1444.37; 1236.52;
1043.22; 872.68; 760.05. MS (EI) m/e(%): 332(M+–64, 18), 274(14)
210(20), 121(100), 77(26). Anal.Calc. for C21H16S4: C, 63.636; H, 4.040;
S, 32.327. Found: C, 63.630; H, 4.013; S, 33.77. ESI: Peaks correspond-
ing to Molecule + H+: 397.0; Molecule + Na+: 419.0; Molecule + K+:
435.1; Dimer + Na+: 815.0; Dimer + K+: 830.0, APCI: Molecule + H+:
397.0.
X-ray data were collected on a Bruker-Nonius Kappa CCD difrac-
tometer at 150◦K. Crystal data: monoclinic, C21H16S4 (Mw:396.58),
˚
space group P21/c with a = 15.637(2), b = 6.329(1) and c = 37.846(6) A,
◦
3
β = 95.06(1) , V = 3730(1)A , Z = 8, and Dcalc = 1.412 gcm−3. Of the
44006 measured reflections for 5, 7966 [R(int) = 0.258] were indepen-
dent; R1 = 0.078, wR2 = 0.134 (for 3292 reflections with F > 4σ(F)).
The structure was solved, using the WINGX package,11 by direct meth-
ods (SHELXS-97) and refined by least-squares against F2 (SHELXL-
97).12 All nonhydrogen atoms were anisotropically refined, while the
hydrogen atoms were located in the difference Fourier map and isotrop-
ically refined with a fixed thermal factor of 0.03.
˚
REFERENCES
[1] S. Scheithauer and R. Mayer, Thio and Dithiocarboxylic Acids and Their Deriva-
tives, In Topics in Sulfur Chemistry, A. Senning (Ed.) Vol. 4 (Georg Thieme Verlag,
Stuttgart, 1979).
[2] H. Klinger, Ber. Dt. Chem . Ges. 15, 861 (1882).
[3] E. Fromm and P. Schmoldt, Ber. Dt. Chem. Ges. 40, 2861 (1907).
[4] A. Engelhardt and P. Latschinoff, Z. Chem. 4, 455 (1868).
[5] J. H. Wood and R. W. Bost, J. Am. Chem. Soc. 59, 1011 (1937).
[6] Bob Ardrey, Liquid Chromatography–Mass Spectrometry: An Introduction. (John
Wiley & Sons Inc., West Sussex; England, 2003).
[7] Horst Friebolin, Basic One- and Two-Dimensional NMR Spectroscopy. (VCH Verlag,
Weinheim, Germany, 1993).

Benzylidene Bis-Dithiobenzoate
1699
[8] Gaussian 98, Revision A.7, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr., R. E.
Stratman, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C.
Strain, O. Farkas, J. Tomasi, U. Barone, M. Cossi, R. Cammi, B. Menucci, C. Pomelli,
C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma,
D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Feresman, J. Cioslowski, J. V.
Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts,
R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P. M. W. Gill, B. G. Johnson, W. Chen, M. W. Wong, J. L.
Andres, C. Gonzalez, M. Head-Gordon, E. S. Replogle, and J. A. Pople.
[9] Spectra Data collected from SDBS (Integrated Spectral Data System for Organic
Compounds). Web Page: http://www.aist.go.jp/RIODB/SDBS/menu-e.html
[10] N. H. Leon and R. S. Asquith, Tetrahedron, 26, 1719–25, (1970).
[11] WinGX—A Windows Program for Crystal Structure Analysis. L. J. Farrugia (Uni-
versity of Glasgow, Glasgow, 1998).
[12] SHELX97—Programs for Crystal Structure Analysis (Release 97-2). G. M.
Sheldrick, Institu¨t fu¨r Anorganische Chemie der Universita¨t, Tammanstrasse, 4
(D-3400 Go¨ttingen, Germany, 1998).