Lophine (2,4,5-triphenyl-1H-imidazole)

Diana Yanover; Menahem Kaftory

doi:10.1107/S1600536809006552

. 2009 Mar 6;65(Pt 4):o711. doi: 10.1107/S1600536809006552

Lophine (2,4,5-triphenyl-1H-imidazole)

Diana Yanover ^a, Menahem Kaftory ^a,^*

PMCID: PMC2968781 PMID: 21582448

Abstract

The title compound, C₂₁H₁₆N₂, has been known since 1877. Although the crystal structure of 36 derivatives of lophine are known, the structure of parent compound has remained unknown until now. The three phenyl rings bonded to the imidazole core are not coplanar with the latter, with dihedral angles of 21.4 (3), 24.7 (3), and 39.0 (3)°, respectively, between the phenyl ring planes in the 2-, 4- and 5-positions of the imidazole ring. The molecules are packed in layers running perpendicular to the b axis. Although there are acceptor and donor atoms for hydrogen bonds, no such interactions are detected in the crystal in contrast to other lophine derivatives.

Related literature

For background on lophine and its derivatives, see: Fridman et al. (2008 ▶); Fridman, Kaftory & Speiser (2007 ▶); Fridman, Kaftory, Eichen & Speiser (2007 ▶); Kamidate et al. (1989 ▶); Liu et al. (2005 ▶); Nakashima (2003 ▶); Nakashima et al. (1995 ▶); Radziszewski (1877 ▶); Seethalakshmi et al. (2006 ▶); Thiruvalluvar et al. (2007 ▶); Thuer et al. (2004 ▶). For information about the Cambridge Database, see: Allen (2002 ▶). For related literature, see: Inouye & Sakaino (2000 ▶); Kaftory et al. (1998 ▶); Santos et al. (2001 ▶).

Experimental

Crystal data

C₂₁H₁₆N₂
M _r = 296.36
Orthorhombic,
a = 20.218 (4) Å
b = 7.538 (2) Å
c = 20.699 (4) Å
V = 3154.6 (12) Å³
Z = 8
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 293 K
0.50 × 0.10 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: none
22192 measured reflections
2747 independent reflections
1036 reflections with I > 2σ(I)
R _int = 0.143

Refinement

R[F ² > 2σ(F ²)] = 0.088
wR(F ²) = 0.245
S = 1.09
2747 reflections
209 parameters
H-atom parameters constrained
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.30 e Å⁻³

Data collection: COLLECT (Nonius, 2006); cell refinement: DENZO HKL-2000 (Otwinowski & Minor, 1997 ▶); data reduction: DENZO HKL-2000; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1999 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809006552/hb2915sup1.cif

e-65-0o711-sup1.cif^{(18.4KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809006552/hb2915Isup2.hkl

e-65-0o711-Isup2.hkl^{(135KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Comment

Recently, heterocyclic imidazole derivatives have attracted considerable attention because of their unique optical properties (Santos et al., 1996). These compounds play a very important role in chemistry as multipurpose analytical tools (Nakashima et al., 1995 & Nakashima, 2003 & Kamidate et al., 1989). Lophine (2,4,5-triphenyl-1H-imidazole) (I) is an attractive fluorescence and chemiluminescence compound. The chemiluminescence properties of this synthetic organic compound was reported for the first time by Radziszewski (1877). He showed that lophine emits a yellow light when it reacts with oxygen in the presence of a strong base. Since then many lophine derivatives have been synthesized and studied with regards to their optical properties. Lophine was chosen as the molecule of the week (December 15, 2008) by the American Chemical Society with the following summary "Lophine (2,4,5-triphenyl-1H-imidazole) exhibits lemon yellow chemiluminescence in solution and is one of the few long-lasting chemiluminescence molecules. It forms dimmers that have piezochromic and photochromic properties. It has been proposed as an analytical reagent for trace metal ion detection." The crystal structure of 36 different lophine derivatives have been deposited at the Cambridge Crystallographic Data Center (Allen, 2002). It is interesting to note, however, that the crystal structure of the parent lophine compound was never published. We undertook a search for new lophine derivatives that will show thermo- and photochromic properties (Fridman et al., 2007, Fridman et al., 2007, Fridman et al., 2008).

During our investigation we have succeeded to identify crystals of neat lophine. Here we describe its crystal structure. The molecular structure of lophine depicted in Figure 1, may be described by the rotation of three phenyl rings about their bonds to the imidazole ring. The rotation angles of the phenyl rings plane are 21.4, 24.7, and 39.0° at the 2, 4 and 5 positions of the imidazole ring respectively. Although the imidazole ring bearing H-donor and H-acceptor N atoms, they do not participate in hydrogen bonding as found in five other lophine derivatives (Seethalakshmi et al., 2006, Ynouye & Sakaino, 1986, Thuer et al., 2004, Liu et al., 2005, Thiruvalluvar et al., 2007) where the lophine derivative molecules packed in chains made up of hydrogen bonded molecules of N—H···N type. All other lophine derivatives form hydrogen bonds through the N—H or the N atoms either with molecules of the same kind or with solvent molecules. The absent of strong intermolecular forces might be the reason for the lack of published crystal structure of neat lophine because it is difficult to crystallize it.

Experimental

Lophine synthesis: benzil (1 mmol), suitable benzaldehyde (1 mmol), and ammonium acetate (1.2 g) were dissolved in boiling glacial acetic acid (16 ml) and refluxed for 5–24 h. The reaction progress was monitored by TLC. After the reaction completion, the reaction mixture was poured into ice-water, washed with NaHCO₃ and then washed several times with EtOAc. The combined extracts were dried over MgSO₄. The purification was done by flash column chromatography. The compound was obtained in 46% yield. Colourless plates of (I) were recrystallised from DMSO.