2-Hydroxy-N-(4-methoxybenzyl)-4-nitroanilinium chloride

The crystal structure of the title compound, C14H15N2O4 +·Cl−, can be described as being composed of layers containing both cations and anions that are staggered along [010]. Two types of the hydrogen bonds are observed, viz. cation–anion and cation–cation. The chloride anions are acceptors of the strong hydrogen bonds donated by the secondary amine and the hydroxy groups. The packing is also stabilized by weak C—H⋯O intermolecular hydrogen bonds. An intramolecular N—H⋯O interaction also occurs.


Comment
Amines are one of the most important classes of biologically active compounds of natural origin. They are also widely used in the chemical industry as basic intermediates for preparation of e.g. fine chemicals, pharmaceuticals and agrochemicals (Seayad et al., 2002).
Due to their biological properties, amines have played important role in chemotherapeutic treatment of different diseases (Bergeron et al., 1997).
Alkylation of the secondary amines with alkyl halides is the most straightforward method for the synthesis of the tertiary amines (Salvatore et al., 2002). Reductive amination of aldehydes andketones is a powerful tool for the synthesis of amines.
This approach is extensively used for rapid access to diverse sets of amines (Sato et al., 2004;Baxter et al., 2002;Apodaca et al., 2001).
The synthetic route we envisioned for preparation of the title compounds consists of a one-step reductive amination of aromatic aldehydes with primary amine at acid conditions (pH = 4-5). We found that this could be efficiently conducted in methanol at room temperature using the excess of reductive agent (NaBH 3 CN). Under these conditions 2-(4-methoxybenzylamino)-5-nitrophenol was cleanly obtained in very good chemical yield (85%). The layers staggered along the b axis can be discerned in the crystal structure ( Fig. 2). Each layer contains dimers composed of the cations and Cl -. These dimers are situated about the crystallographic two-fold axes. The dimers form the motifs R 2 4 (14) (Etter et al., 1990) with a pair of chains O1-H1···Cl1···H10a-N10-C1-C9 (Fig. 3). Moreover, the dimers are interconnected with those in the adjacent layer by another pair of the hydrogen bonds Cl1···H10b-N10-H10a with the graph set motif R 2 4 (8) (Fig. 3). The latter motifs are situated about the crystallographic inversion centres. The packing is also stabilized by weak N-H···O (intramolecular) and C-H···O (intermolecular) interactions (Fig. 4, Tab. 1). Fig. 5 shows the projection of the structure along the a axis.

Experimental
To the solution of 4-methoxybenzaldehyde (2 mmol) in dry methanol (10 ml) 5-nitro-2-aminophenol (2 mmol) was added and acidified by concentrated HCl until pH = 6. After vigorous stirring for 2 h at room temperature, NaBH 3 CN (6 sup-2 mmol) was added. On completion of the reaction, as indicated by thin layer chromatography (ethyl acetate/hexane: 1/3 as eluent), the excess of the hydride was carefully destroyed by slow addition of 20 ml of cold water. The mixture was left for several hours and the resulting precipitate was filtered off, washed with water, then with ethanol and with hexane. 2-(4methoxybenzylamino)-5-nitrophenol was identified by IR, 1 H and 13 C NMR spectroscopies. Colourless prismatic crystals (0.06×0.12×0.18 mm) of the title structure were obtained by slow crystallization from the aqueous solution with pH = 5.5.

Refinement
Approximate positions for all the H atoms were first obtained from the difference electron density map. However, the H atoms were situated into idealized positions and the H-atoms have been refined within the riding atom approximation. The applied constraints were as follow: C aryl -H aryl = 0.95 Å; C methyl -H methyl = 0.98 Å; C methylene -H methylene = 0.99Å and N sec.amine -H sec.amine = 0.84 Å. The idealized methyl group was allowed to rotate about the C-C bond during the refinement by application of the command AFIX 137 in SHELXL97 (Sheldrick, 2008). U iso (H methyl / hydroxy ) = 1.5U eq (C methyl / O hydroxy ) or U iso (H aryl / methylene / sec. amine ) = 1.2U eq (C aryl /C methylene /N sec. amine ). Fig. 1. The title molecule (Farrugia, 1997) with the atomic labelling scheme. The displacement parameters are drawn at the 50% probability level.