Bis(4-hydroxyphenyl) 1,4-phenylenebiscarbamate

The crystal structure of the title compound features a three-dimensional framework resulting from hydrogen bonds formed by the hydroxy and urethane groups.

The title compound, C 20 H 16 N 2 O 6 (systematic name: 4-hydroxyphenyl N-{4-[(4hydroxyphenoxycarbonyl)amino]phenyl}carbamate), contains two urethane groups substituting the central benzene ring in para positions. The molecule is centrosymmetric, and displays a twisted conformation for the three aromatic rings [the dihedral angle between central benzene ring and the urethane group is 33.4 (6) , and that between the latter and the terminal ring is 65.1 (1) ]. In the crystal, a three-dimensional framework is formed through O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds involving the hydroxy and urethane functional groups, respectively.

Structure description
The title compound was obtained by reacting hydroquinone, 1,4-phenylene diisocyanate and triethylamine in dioxane. The resulting bis-urethane derivative crystallizes in the centrosymmetric space group P2 1 /c, with the molecule having crystallographic inversion symmetry (Fig. 1). The urethane group displays the expected nearly planar geometry. This functional group is well represented in the CSD: 5700 hits are retrieved for organic compounds including an acyclic C-NH-(COO)-C fragment (CSD v. 5.43 with two updates, Groom et al., 2016). However, most of these urethane derivatives originate from boc-protected amines, using the tert-butoxycarbonyl (boc) protecting group. In contrast, benzene rings substituted by two urethane groups are less studied by X-ray diffraction. For para-substituted benzene, only five structures have been deposited to date in the CSD. These occurrences include dimethyl 1,4-phenylenebiscarbamate (Stapf et al., 2015), intended for anion complexation, and a dicholesterol derivative (Alegre-Requena et al., 2020), intended for the preparation of supramolecular gels.

data reports
As for dimethyl 1,4-phenylenebiscarbamate, the title molecule is not planar. The dihedral angle between the central benzene ring and the urethane group is 33.4 (6) , hindering the formation of an intramolecular hydrogen bond C3-H3AÁ Á ÁO6, although this could potentially stabilize the molecule through the formation of an S(6) ring motif. The peripheral hydroxybenzene group is also rotated with respect to the urethane group, forming a dihedral angle of 65.1 (1) .
This twisted molecular conformation helps in the formation of two kinds of hydrogen bonds, leading to a three-dimensional supramolecular architecture. First, hydroxy groups behave both as donor and acceptor, linking molecules through O-HÁ Á ÁO hydrogen bonds. The resulting two-dimensional structure is nearly parallel to the (102) plane in the crystal (Table 1, entry 1; Fig. 2). These layers are further interconnected by urethane N-HÁ Á ÁO hydrogen bonds oriented nearly perpendicular to the layers (Table 1, entry 2; Fig. 3). The three-dimensional framework is thermodynamically stable, although no intermolecularinteractions are present in the crystal.

Figure 2
Supramolecular layers formed by O-HÁ Á ÁO hydrogen bonds (see entry 1 in Table 1). Hydrogen bonds are shown as purple dashed lines, and the projection is nearly normal to [001]. Note the hanging contacts (orange dashed lines), corresponding to the hydrogen bonds described in Fig. 3.
Benzene-H atoms are omitted for clarity.

Figure 3
The two-dimensional supramolecular motif formed by N-HÁ Á ÁO hydrogen bonds (see entry 2 in Table 1). Two neighbouring molecules are related by the glide plane of space group P2 1 /c. The projection is nearly normal to [010]. Benzene-H atoms are omitted for clarity.

Figure 1
Molecular structure of the title compound, with displacement ellipsoids shown at the 50% probability level. Non-labelled atoms are generated by symmetry operation 1 À x, Ày, 1 À z.  polymeric materials. On the other hand, some classes of urethane derivatives show diverse biological activity and have been used as fungicides, bactericides or analgesics, among other applications (Lamba et al., 1998;Yagci et al., 2011;Wang et al., 2022).

Synthesis and crystallization
The synthesis was performed in a 100 ml three-mouth flask, sealed with silicone grease and evacuated with argon. In 5 ml of dry dioxane, hydroquinone (0.316 g), triethylamine (0.207 ml) and 1,4-phenylene diisocyanate (0.222 g) were added. The reaction was carried out at 353-363 K, under constant stirring. After a few minutes, it was observed that the reaction medium turned white. After 6 h, the reaction product was purified by column chromatography, using ethyl acetate:hexane (60:40) as the eluant. Once the purified monomer was obtained, it was dried in a furnace at 313 K for 24 h. Single crystals were obtained by evaporation of a saturated solution of the compound in an ethanol/dichloromethane mixture (4:1, v:v).

Special details
Refinement. H atoms bonded to heteroatoms were refined freely, while H atoms of aromatic CH groups were placed in calculated positions and refined as riding to their carrier C atom.