Ethane-1,2-diyl bis(benzenedithioate)

In the crystal structure, the title compound, C16H14S4, is located on an inversion center and exhibits a gauche+–trans–gauche− conformation in the S—CH2—CH2—S bond sequence. The S—C=S plane makes a dihedral angle of 30.63 (17)° with the phenyl ring. An intermolecular C—H⋯π interaction is observed.

In the crystal structure, the title compound, C 16 H 14 S 4 , is located on an inversion center and exhibits a gauche + -transgauche À conformation in the S-CH 2 -CH 2 -S bond sequence. The S-C S plane makes a dihedral angle of 30.63 (17) with the phenyl ring. An intermolecular C-HÁ Á Á interaction is observed.
Cg1 is the centroid of the C1-C6 phenyl ring.

Comment
The S-CH 2 -CH 2 -S part of crystallized poly(ethylene sulfide) (PES, [-CH 2 CH 2 S-] x ) lies in the gauche + -transgauche -(g + tg -) conformation (Takahashi et al., 1968); the two S-C bonds are in opposite gauche states, and dipole moments are formed along bisectors of the C-S-C angles. The dipole-dipole interaction was suggested to be the source of its high melting point (215-220 °C) in comparison with that (66-69 °C) of poly(ethylene oxide), [-CH 2 CH 2 O-] x (Sasanuma & Watanabe, 2006). Therefore, poly(thioethylenethioterephthaloyl) ([-SCH 2 CH 2 SCOC 6 H 4 CO-] x ) and poly(thioethylenethiodithioterephthaloyl) ([-SCH 2 CH 2 SCSC 6 H 4 CS-] x ), having the same S-CH 2 -CH 2 -S bond sequence as PES, are expected to be superior in some physical properties to their homologous polyester, poly(ethylene terephthalate) ([-OCH 2 CH 2 OCOC 6 H 4 CO-] x ). Crystal conformations of polymers are requisite to derive their configurational properties and thermodynamic quantities. Because a polymer tends to have a crystal conformation similar to that of its small model compounds, the models provide the physicochemical information on the polymer.
The crystal structure of 1,2-bis(benzoylthio)ethane (BBTE, C 6 H 5 C(=O)SCH 2 CH 2 SC(=O)C 6 H 5 ), a model compound of poly(thioethylenethioterephthaloyl), was determined already (Deguire & Brisse, 1988); its S-CH 2 -CH 2 -S part also lies in the g + tgstate. We have investigated structure-property relationships of the above-mentioned polyester, polythioester, and polydithioester. As part of the work, this study has dealt with 1,2-bis(dithiobenzoyl)ethane (BDTBE, C 6 H 5 C(=S)SCH 2 CH 2 SC(=S)C 6 H 5 ), a model compounds of poly(thioethylenethiodithioterephthaloyl); the crystal structure has been determined and compared with those of BBTE and PES. Figure 1 shows the molecular structure of BDTBE. Its S-CH 2 -CH 2 -S bond sequence adopts the g + tgconformation, as found for PES and BBTE. The g + tgconformation renders the two phenyl rings parallel to each other; however, this is partly because the BDTBE molecule is located on the center of symmetry. The C 6 H 5 -C(=O)-S part of BBTE is essentially coplanar, whereas the C=S bond of BDTBE is out of the phenyl plane; the S-C═S plane makes a dihedral angle of 30.63 (17)°w ith the phenyl ring. This is probably due to the van der Waals radius (1.80 Å) of sulfur larger than that (1.52 Å) of oxygen.
The BBTE crystal seems to include intermolecular π-π interactions of a near vertical type (Deguire & Brisse, 1988). In addition, dipole moments, formed close to the O=C bonds, are either parallel or antiparallel to one another. The dipole-dipole interactions are known to stabilize the crystal structure (Sasanuma & Watanabe, 2006). On the other hand, Figure 2 shows that the C=S bonds of BDTBE do not have such clear orientations, because the small difference in electronegativity between C and S little polarizes the C=S bond. In the BDTBE crystal, instead, C-H···π interactions appear to exist between C8-H8A bond and its neighboring phenyl (Ph) ring, and the H···Ph spacing can be estimated to be 2.65 Å.

Experimental
Benzoyl chloride (19.5 g) was added dropwise into 1,2-ethanedithiol (6.2 g) and pyridine (11 ml) in a four-neck flask equipped with a mechanical stirrer and a reflux condenser, and the mixture was stirred at 0 °C for 30 m and, furthermore, supplementary materials sup-2 at room temperature overnight. The reaction mixture was subjected to extraction with water and ether. The organic layer was washed three times with 8% sodium hydrogen carbonate solution, dried overnight over anhydrous magnesium sulfate, filtrated, and condensed on a rotary evaporator. The residue was recrystallized twice from ethanol and dried under reduced pressure. 1,2-Bis(benzoylthio)ethane (1.5 g) thus prepared, Lawesson's reagent (2.5 g), and toluene (10 ml) were mixed and refluxed for 5 h. The reaction mixture was condensed, dissolved in a mixed solvent (15 ml) of toluene and n-hexane (volume ratio 1:3), and fractionated by a silica-gel column chromatograph. The reddish fraction was collected, condensed, recrystallized twice from ethanol, and dried in vacuo.
Crystals for X-ray diffraction were prepared by slow evaporation of a dimethyl sulfoxide solution. Then, the solution was kept in an open vessel so that water vapor, a poor solvent, would be immixed and hasten the crystallization.

Refinement
All C-H hydrogen atoms were geometrically positioned with C-H = 0.95 and 0.99 Å for the aromatic and methylene groups respectively, and refined as riding by U iso (H) = 1.2U eq (C). Fig. 1. Molecular structure of 1,2-bis(dithiobenzoyl)ethane (BDTBE). Displacement ellipsoids are drawn at the 50% probability level. The asterisk corresponds to symmetry code -x, -y + 1, -z.