Bis(2,3-dichlorophenyl) disulfide

The title compound, C12H6Cl4S2, features an S—S bond [2.0252 (8) Å] that bridges two 2,3-dichlorophenyl rings with a C—S—S—C torsion angle of 88.35 (11)°. The benzene rings are normal one to the other with a dihedral angle of 89.83 (11)°. The crystal structure features intermolecular Cl⋯Cl [3.4763 (11) Å] and π–π stacking interactions [centroid–centroid distances = 3.696 (1) and 3.641 (2) Å]. Intramolecular C—H⋯S interactions are also observed.

Supporting information for this paper is available from the IUCr electronic archives (Reference: BX2456).

Introduction
The disulfide bonds are found in proteins (Sevier and Kaiser, 2006), natural products and pharmacologically active compounds. Disulfide compounds have shown to exhibit activity as fungicide, mildew-proofing (Crowley, 1964) and antitumor agents (Hashash et al., 2002). In organic synthesis disulfides are used in cross-coupling reactions catalyzed by transition metal compounds such as palladium, nickel and copper (Gomez-Benitez et al., 2006;Yu et al., 2010).
Several methods for the synthesis of disulfides have been reported. These processes involve the oxidative coupling of mercaptans by various oxidants such as molecular oxygen, nitric oxide, solvent-free permanganate, metal ions and promoted by sulfonyl chloride in aqueous media (Xiao et al., 2009;Shaabani et al., 2008;Ogilby, 2010).
Thus, in this report we present the crystal structure of the bis(2,3-dichlorophenyl)disulfide obtained by a nucleophilic substitution reaction. The structure is represented in figure 1.

Synthesis and crystallization
The title compound was obtained as a by-product of the reaction between 2-(chloromethyl)benzimidazole (0.2 g) and the lead salt of 2,3-dichlorobenzethiol ([Pb(SC 6 H 3 -2,3-Cl 2 ) 2 ]) (0.337 g) in toluene. The resulting reaction mixture was allowed to proceed under reflux by 8 h after which time the formation of PbCl 2 was observed indicating completion of the reaction. The reaction mixture was then filtered through a short Celite plug to afford a colorless solution, the solvent was evaporated under vacuum and the residue column chromatographed (silica gel 60, eluted with 3/2 ethyl acetate/hexane system). Slow Evaporation of the first fraction collected produced crystals of the title compound suitable for X-ray diffraction analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were included in calculated positions (C-H = 0.93 A for aromatic H) and refined using a riding model with Uiso(H) = 1.2 Ueq of the carrier atoms.

Results and discussion
The asymmetric unit of the title compound consists of one molecule on the disulfide. The rings of the bis(2,3-dichlorophenyl)disulfide show a dihedral angle of 89.83° between the two planes and a torsion angle C1-S1-S2-C7 of 88.35 (11)°. The value of the C-S-S-C torsion angle is similar to those found in similar compounds, such as bis- (pentachlorophenyl)disulfide (Deng et al., 2003), diphenyldisulfide (Korp & Bernal, 1984) and bis(4-amino-2-chlorophenyl)disulfide (Tang et al., 2011). The S-S distance is 2.0252 (8) Å, whereas the C-S distances are 1.784 (2) and 1.7835 (19) Å. These values are similar and close in value to compounds such as bis(pentachlorophenyl)disulfide with a S-S distance of 2.063 (2) Å and bis(4-amino-2-chlorophenyl)disulfide of 2.0671 (16) Å. The crystal packing is stabilized by π-π and Cl···Cl interactions ( Figure 2). The π-π interactions of the 2,3-dichlorophenyl rings presents distances between centroids of 3.696 (1) and 3.641 (2) Å. The Cl1···Cl2 contact distance is of 3.476 Å that is close to the sum of the van der Waals radii of the chloride atoms (Bondi, 1964). The sulphur atoms present C-H···S intramolecular interactions, these values are in the table 1.

Figure 1
The molecular structure of the title compound showing 40% probability of displacement ellipsoids for the non-hydrogen atoms.

Figure 2
Representation of the π-π and Cl···Cl interactions shown by dashed lines. Hydrogen atoms are omitted. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.41 e Å −3 Δρ min = −0.30 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.