Bis(N-methyl-N-phenylcarbamoyl)disulfane

The title compound, C16H16N2O2S2, has been synthesized by several different high-yield routes, and has been encountered as a co-product in a number of reaction pathways, ever since it became of interest to our research program over 30 years ago. We now confirm the proposed molecular structure in which the molecule exhibits a twofold axis of symmetry through the mid-point of the S—S bond and the two planes defined by the (carbamoyl)sulfenyl moieties are essentially perpendicular to each other [dihedral angle = 81.55 (14)°].

The title compound, C 16 H 16 N 2 O 2 S 2 , has been synthesized by several different high-yield routes, and has been encountered as a co-product in a number of reaction pathways, ever since it became of interest to our research program over 30 years ago. We now confirm the proposed molecular structure in which the molecule exhibits a twofold axis of symmetry through the mid-point of the S-S bond and the two planes defined by the (carbamoyl)sulfenyl moieties are essentially perpendicular to each other [dihedral angle = 81.55 (14) ].

sup-1
Acta Cryst. Bis(N-methyl-N-phenylcarbamoyl)disulfane (C 16 H 16 N 2 O 2 S 2 ) was first reported by Kobayashi et al. (1973). The compound became of interest to our research program over thirty years ago (Barany et al., 1983;Schroll and Barany, 1986) and has been synthesized by several different high-yield routes, as well as encountered as a co-product in a number of reaction pathways (Barany et al., 1983;Schroll and Barany, 1986;Schrader et al., 2011). We now confirm the molecular structure of the title compound by single-crystal X-ray analysis. The disulfane reported herein is the flagship of the homologous series of bis(N-methyl-N-phenylcarbamoyl)polysulfanes, C 16 H 16 N 2 O 2 S n , which have been prepared and structurally characterized for n = 1-6.
The title compound exhibits a twofold axis of symmetry through the center of the S-S bond, and all bond distances and angles are within expected ranges. The N-C bond distance is 1.35 Å, consistent with ~60% double bond character, with the consequence that the (carbamoyl)sulfenyl atoms (S1,C1,O1,N1,C2,C3) are in a plane. The aromatic ring is nearly perpendicular to the (carbamoyl)sulfenyl plane, with a torsion angle of 92.5° (C2-N1-C3-C4). The S-S bond length of 2.03 Å is slightly shorter than the 2.07 Å reported for the S-S bond length in elemental sulfur (S 8 ), suggesting that some partial double bond character extends through the S-S bond due to its adjacency to carbonyl groups on both sides.
Several other reference compounds also have an S-S bond length of 2.01-2.03 Å (Bereman et al., 1983;Rout et al., 1983;Paul and Srikrishnan, 2004;Fun et al., 2001;Raya et al., 2005;Li et al., 2006;Singh et al., 2011). The most noteworthy feature of the title compound is the torsion angle about the disulfane, which is 81.6° and as such is somewhat smaller than the theoretical optimum of 90.0° (Pauling, 1949;Torrico-Vallejos et al., 2010) that has been explained as allowing for minimal mutual repulsion of pπ orbital electron lone pairs in sulfur. A comparable deviation from theory was reported for dibenzoyl disulfide (Rout et al., 1983;Paul & Srikrishnan, 2004), where the torsion angle is 80.8°. Bis(Nmethyl-N-phenylthiocarbamoyl)disulfane, which only differs from the title compound by two thiocarbonyls in place of two carbonyls, has a torsion angle about the disulfane of 89.8° and shows a conformation that is not completely superimposable on the title compound (Fun et al., 2001).
Note regarding nomenclature: The title compound is named in a manner that is consistent with our prior publications.

Experimental
The title compound was prepared in high yield from the reaction of N-methylaniline with bis(chlorocarbonyl)disulfane, and recrystallized from hot carbon tetrachloride/chloroform (3:2) in 60-85% recovery or from hot acetone in 75% recovery (Barany et al., 1983).

Refinement
H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 Å (aromatic) or 0.96 Å (methyl), and U iso (H) = 1.2U eq (C) for aromatic and 1.5U eq (C) for methyl H atoms.

Figure 1
Crystallographic structure of the title compound showing 50% probability displacement ellipsoids and with all nonhydrogen atoms labelled and numbered.

Special details
Refinement. Refinement of F 2 against all reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on all data will be even larger.