Crystal structure of benzyl 2-naphthyl ether, a sensitiser for thermal paper

We report the crystal structure of benzyl 2-naphthyl ether, which is used as a sensitiser for thermal paper. In the crystal, one molecule interacts with six neighbouring molecules via C—H⋯π intermolecular interactions to form a herringbone molecular arrangement.

The title compound [systematic name: 2-(benzyloxy)naphthalene], C 17 H 14 O, which is used as a sensitiser for thermal paper, has a twisted conformation with a dihedral angle of 48.71 (12) between the phenyl ring and the naphthyl ring system. In the crystal, one molecule interacts with six neighbouring molecules via intermolecular C-HÁ Á Á interactions to form a herringbone molecular arrangement.

Chemical context
Thermal printing is a rapid and inexpensive printing technology widely used in commercial applications such as receipts, faxes and tickets (Gregory, 1991;Mendum et al., 2011). Many structural reports are available for thermosensitive dyes and developers (Matsumoto et al., 2010;Kodama et al., 2013;Ohashi et al., 2017). On the other hand, we found only one report on the crystal structure of a compound commonly used as a sensitiser for the thermosensitive layer (Rudolph et al., 2010), which can facilitate the dye coloration process by lowering the melting point of the dye/developer composite on thermal paper (US EPA, 2014). The title compound, benzyl 2-naphthyl ether, 1, is known as another commonly used sensitiser. Herein, we report the crystal structure of 1 as fundamental data for the investigation of its influence on the solid-state physicochemical properties of the thermosensitive layer of the thermal paper.

Supramolecular features
In the crystal, one molecule interacts with six neighbouring molecules via intermolecular C-HÁ Á Á interactions (Table 1; Fig. 2). The molecules are linked by a C-HÁ Á Á interaction between the benzene C1-C6 rings (C3-H3Á Á ÁCg1 i ; symmetry code as in Table 1), forming a zigzag chain along the a-axis direction. The chains are connected into a layer structure parallel to the ab plane via a C-HÁ Á Á interaction between the benzene C4/C5/C7-C10 ring and the methylene hydrogen atom (C11-H11AÁ Á ÁCg2 ii ; Table 1). A weak C-HÁ Á Á interaction between the C12-C17 phenyl rings (C16-H16Á Á ÁCg3 iii ; Table 1) links the layers and thus the molecules form a herringbone arrangement when viewed along the a axis, as shown in Fig. 3.

Figure 1
The molecular structure of the title compound, 1, with displacement ellipsoids drawn at the 50% probability level.

Figure 3
A packing diagram of the title compound, 1, viewed along the a axis, showing a herringbone arrangement. H atoms have been omitted for clarity.
shows packing diagrams for compounds 2-4. In the crystals of 2-4, the molecules form zigzag chains via C-HÁ Á ÁO inter-actions. In 2, the chains are linked byinteractions into a three-dimensional network, whereas C-HÁ Á Á interactions contribute to the arrangement of the chains in 3 and 4.

Synthesis and crystallization
The title compound was purchased from Tokyo Kasei Kogyo Co., Ltd., and used without further purification. X-ray diffraction quality colourless platelets were obtained using a liquid-liquid diffusion method, with combination of chloroform and ethanol at 278 K.

Refinement
The crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically (C-H = 0.93 Å ) and refined using a riding model with U iso (H) = 1.2U eq (C). Packing diagrams of compounds 2 (a), 3 (b) and 4 (c). The dotted lines indicate intermolecular C-HÁ Á ÁO and C-HÁ Á Á interactions.

Special details
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. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 sigma(F 2 ) is used only for calculating Rfactor (gt).