Crystal structure of a diaryl carbonate: 1,3-phenylene bis(phenyl carbonate)

The whole molecule of the title diarylcarbonate is generated by mirror symmetry, the mirror bisecting the central benzene ring, and the carbonate groups adopt an s-cis-s-cis conformation. In the crystal, there are only weak C—H⋯O hydrogen bonds and offset π–π interactions present.


Chemical context
Organic carbonates have a wide range of applications as polymers, surfactants, fuel additives, solvents for complex industrial syntheses and extractions, and even medical agents, dyes, and foodstuff (Shukla & Srivastava, 2017). They are commonly synthesized by treating alcohols with phosgene, a rather toxic reagent. Alternative preparatory methods include the reaction of alcohols and carbon monoxide in the presence of a catalyst, direct condensation of alcohols and carbon dioxide (Joe et al., 2012;Zhang et al. 2012;Zhao et al., 2009), or the alcoholysis of urea (Ball et al., 1980;Bhanage et al., 2003;Zhang et al., 2016;Mote & Ranade, 2017).
The bis(phenyl carbonate) structure reported herein was identified as an unexpected side product from the attempted recrystallization of 1-(m-phenol)-3-phenylurea from ethanol. We surmise this compound formed through a combination of intermolecular 'self-alcoholysis' reactions leading to a carbamate intermediate (Mote & Ranade, 2017), which subsequently over time yields the title compound, 1,3-phenylene bis(phenyl carbonate). Compared to the one-dimensional hydrogen-bonded chain motif so frequently seen in diarylurea crystals (Solomos et al., 2017;Capacci-Daniel et al., 2010, 2015, diaryl carbonates lack the ability to associate via strong intermolecular hydrogen bonds. Analysis of the relatively limited number of diaryl carbonate structures previously reported shows that the title compound shares some of the same structural features.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1 Groom et al., 2016). The aromatic rings are both s-cis to the carbonate group with C7-O1-C1-C6 and C7-O2-C8-C10 torsion angles of 58.7 (2) and 116.32 (15) , respectively. The 1,3-substitution of the central aromatic ring imparts the molecule with a bent or 'U-shape' conformation and a significant net dipole moment.

Figure 1
Molecular structure of the title compound, with atom labeling. Displacement ellipsoids are drawn at the 50% probability level. Unlabeled atoms are related to the labeled atoms by mirror symmetry (symmetry operation: x, Ày + 1 2 , z).

Synthesis and crystallization
Equimolar amounts of 3-aminophenol and phenyl isocyanate were added to benzene under nitrogen and stirred for 24 h. A white precipitate identified as 1-(m-phenol)-3-phenylurea was filtered, dried, and recrystallized in assorted organic solvents (ethanol, methanol, acetone, ethyl acetate, benzene, toluene, acetone:hexanes, acetonitrile). Slow evaporation of an ethanolic solution in a 1 dram vial, capped with pierced lids, yielded large colorless plates of 1,3-phenylene bis(phenyl carbonate). Needle-like crystals identified within the same vials corresponded to 1-(m-phenol)-3-phenylurea. The appearance of 1,3-phenylene bis(phenyl carbonate) crystals was not consistent across multiple recrystallization experiments, suggesting that select impurities and/or longer, delayed evaporation methods that favor non-equilibrium products may be needed to obtain this material.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were included as riding idealized contributors with C-H = 0.95 Å and U iso (H) = 1.2U eq (C).  Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2014); data reduction: SAINT (Bruker, 2014) and XPREP (Bruker, 2014); program(s) used to solve structure: SHELXT2014/4 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/6 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: XCIF (Bruker, 2014) and publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.22 e Å −3 Δρ min = −0.28 e Å −3 sup-2 Acta Cryst. (2017). E73, 1942-1945 Special details Experimental. One distinct cell was identified using APEX2 (Bruker, 2014). Four frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2014) then corrected for absorption by integration using SAINT/SADABS v2014/2 (Bruker, 2014) to sort, merge, and scale the combined data. No decay correction was applied. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Structure was phased by direct methods (Sheldrick, 2015). Systematic conditions suggested the ambiguous space group. The space group choice was confirmed by successful convergence of the full-matrix least-squares refinement on F 2 . The final map had no other significant features. A final analysis of variance between observed and calculated structure factors showed some dependence on amplitude and little dependence on resolution.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )