Cyclobenzaprinium salicylate

In the title molecular salt [systematic name: 3-(5H-dibenzo[a,d]cyclohepten-5-ylidene)-N,N-dimethyl-1-propanaminium 2-hydroxybenzoate], C20H22N+·C7H5O3 −, the benzene rings of the cyclobenzaprinium cation are inclined with a dihedral angle of 61.66 (7)°. An intramolecular O—H⋯O hydrogen bond occurs within the salicylate anion, generating an S(6) ring. In the crystal, the cation and anion are linked by an N—H⋯O interaction.


Comment
Cyclobenzaprine is a muscle relaxant medication used to relieve skeletal muscle spasms and associated pain in acute musculoskeletal conditions. It is the most well studied drug for this application and it also has been used off-label for fibromyalgia treatment. Cyclobenzaprine has been considered structurally related to the first-generation tricyclic antidepressants (Commissiong et al., 1981;Katz & Dube, 1988;Cimolai, 2009). The crystal structures of amitriptylinium picrate (Bindya et al., 2007), benzamidinium salicylate (Kolev et al., 2009), 2-amino-5-chloropyridinium salicylate (Hemamalini & Fun, 2010) and 2-amino-4,6-dimethoxypyrimidinium salicylate (Thanigaimani et al., 2007) have been reported. We now report the crystal structure of the title compound, C 20 H 22 N + .C 7 H 5 O 3 -.
The asymmetric unit of the title compound consists of one cyclobenzaprinium cation and one salicylate anion (Fig. 1). The hydrogen atom of the carboxylic acid COOH group is deprotonated to the N1 atom. The two fused benzene rings of the cation make a dihedral angle of 61.66 (7)° whereas the salicylate anion is almost planar with maximum deviation of 0.063 (1) Å for atom O1. The aminium atom adopts a pyramidal conformation. The cation and anion are interconnected by N1-H1N1···O1 interaction (Table 1). An intramolecular O3-H1O3···O2 hydrogen bond (Table 1) stabilize the molecular structure of the anion molecule generating S(6) ring motif (Bernstein et al., 1995).

Experimental
Cyclobenzaprine (10 g, 0.04 mol) and salicylic acid (5.6 g, 0.04 mol) were dissolved in 50 ml of dichloromethane taken in a 100 ml round bottomed flask. Dichloromethane was distilled off under vacuum and 50 ml of ethyl acetate was added and then the flask was cooled to 278-283 K. The product formed was filtered and re-crystallized from dichloromethane to yield colourless blocks of (I) (M.p.: 415-416 K).

Refinement
The O-bound and N-bound hydrogen atoms were located from difference Fourier map and refined as riding on their parent atom, with U iso (H) = 1.2 or 1.5 U eq (N or O). The rest of the hydrogen atoms were positioned geomatrically [C-H = 0.93-0.97 Å] and refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C).
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound, with 30% probability ellipsoids for non-H atoms. Hydrogen bonds (dashed lines) are shown.