1,4-Phenylenebis(methylene) dicarbamate

The title compound, C10H12N2O4, is a phenyl dicarbamate with crystallographically imposed inversion symmetry. The dihedral angle between the carbamoyloxy plane [i.e. the plane of the N—C(O)—O fragment; r.m.s. deviation = 0.002 (3) Å] and the plane of the aryl ring is 29.2 (1)°. In the crystal, two different centrosymmetric N—H⋯O hydrogen-bond interactions are observed; these are described as R 2 2(8) and R 2 4(8) in graph-set notation. The rings form an alternating sequence, linking the molecules into a sheet structure parallel to (011).

The title compound, C 10 H 12 N 2 O 4 , is a phenyl dicarbamate with crystallographically imposed inversion symmetry. The dihedral angle between the carbamoyloxy plane [i.e. the plane of the N-C(O)-O fragment; r.m.s. deviation = 0.002 (3) Å ] and the plane of the aryl ring is 29.2 (1) . In the crystal, two different centrosymmetric N-HÁ Á ÁO hydrogen-bond interactions are observed; these are described as R 2 2 (8) and R 2 4 (8) in graph-set notation. The rings form an alternating sequence, linking the molecules into a sheet structure parallel to (011).

Experimental
The title compound was synthesized by transesterification of ethyl carbamate with 1,4-phenylenedimethanol (Takeuchi et al. 1971(Takeuchi et al. , 1974 as followed: A solution of 8.9 g (100 mmol) ethyl carbamate and 1.38 g (10 mmol) 1,4-phenylenedimethanol in 25 ml of toluene was heated to reflux in the presence of catalytic amount of zinc chloride for 10 h. After cooling to room temperature, the solvent was evaporated under vacuum. The residue was subjected to flash chromatography and the title compound was obtained as colorless crystal. (1.34 g, Yield: 60%; m.p. 484-486 K). Crystals suitable for single-crystal X-ray analysis were grown by slow evaporation of a DMF solution.

Refinement
H atoms were placed in calculated positions [C-H = 0.93-0.97 Å] and allowed to ride on the parent atoms, with U iso values constrained to be 1.2U eq of the parent atom. The bond length of N1-H1A is 0.88 (2) Å and the bond length of N1 -H1B is 0.93 (2) Å.

Figure 2
Packing diagram for (I). The dashed lines show N-H···O hydrogen bonds between neighboring molecules.

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. 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 > σ(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.