4-(Dimethylamino)pyridinium 4-toluenesulfonate

In the title compound, C7H11N2 +·C7H7O3S−, the cation is protonated at the N atom of the heterocyclic ring. The dimethylamino group lies close to the pyridinium ring plane with a dihedral angle between the pyridinium and the dimethylamine CNC planes of 3.82 (17)°. The N—C bond linking the dimethylamino substituent to the pyridinium ring is characteristically short [1.3360 (19) Å], suggesting some delocalization in the cation. In the crystal structure, N—H⋯O hydrogen bonds link individual pairs of cations and anions. The structure is further stabilized by an extensive series of C—H⋯O hydrogen bonds, augmented by π–π [centroid–centroid distance between adjacent pyridinium rings = 3.5807 (10) Å] and C—H⋯π interactions, giving a network structure.

In the title compound, C 7 H 11 N 2 + ÁC 7 H 7 O 3 S À , the cation is protonated at the N atom of the heterocyclic ring. The dimethylamino group lies close to the pyridinium ring plane with a dihedral angle between the pyridinium and the dimethylamine CNC planes of 3.82 (17) . The N-C bond linking the dimethylamino substituent to the pyridinium ring is characteristically short [1.3360 (19) Å ], suggesting some delocalization in the cation. In the crystal structure, N-HÁ Á ÁO hydrogen bonds link individual pairs of cations and anions. The structure is further stabilized by an extensive series of C-HÁ Á ÁO hydrogen bonds, augmented by -[centroid-centroid distance between adjacent pyridinium rings = 3.5807 (10) Å ] and C-HÁ Á Á interactions, giving a network structure.

Comment
The title compound (I) was first reported and characterized as a side product by Haynes and Indorato (1984). However, it is better known under the acronym DPTS following the work of Moore and Stupp (1990) for its role as a convenient provider of stoichiometric quantities of anhydrous p-toluenesulfonic acid (PTSA) and 4-(dimethylamino)pyridine (DMAP) for the catalytic synthesis of polyesters at room temperature. Our interest in the synthesis of organometallic polyesters required the synthesis of DPTS and its structure is reported here, Fig 1. The asymmetric unit of (I), C 7 H 11 N 2 + , C 7 H 7 O 3 S − , consists of a 4-(dimethylamino)pyridinium cation and a 4-toluenesulfonate anion. In common with other DMAPH + cations (Chao et al., 1977;Mayr-Stein & Bolte, 2000;Sluka et al., 2003), protonation is at the N1 atom of the pyridinium ring. Bond distances and angles in both the cation and anion are normal (Allen et al., 1987) and those in the anion are comparable to those in other 4-toluenesulfonate salts (Koshima et al., 2001(Koshima et al., , 2004Biradha & Mahata 2005). The N2-C10 bond linking the dimethylamino substituent to the pyridinium ring is short, 1.3360 (19)Å suggesting some delocalization in the cation. The fact that the dimethylamino group lies close to the plane of the pyridinium ring, with a dihedral between the pyridinium and the dimethylamine C13N2C14 planes of 3.82 (17) (Cg1 & Cg2 are the centroids of the N1, C8···C12 and C1···C6 rings respectively).

Experimental
The title compound was prepared according to the method of Moore and Stupp (1990) with X-ray quality crystals grown from 1,2-dichloroethane.

Refinement
The H1 atom involved in N-H···O hydrogen bonding was located in a difference Fourier map and was freely refined with an isotropic displacement parameter. All H-atoms bound to carbon were refined using a riding model with d(C-H) = 0.95 Å, U iso =1.2U eq (C) for aromatic and 0.98 Å, U iso = 1.5U eq (C) for CH 3 H atoms. The highest residual electron density peak is located at 0.76 Å from H2. Fig. 1. The asymmetric unit of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.

Special details
Experimental. As the crystals were weakly diffracting data was collected using 55 sec exposures per frame. 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 > 2sigma(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.