Ammonium 2-(3,4-dimethylbenzoyl)benzoate dihydrate

In the anion of the title compound, NH4 +·C16H13O3 −·2H2O, the benzene rings are twisted with respect to each other by 73.56 (10)°. In the crystal, extensive N—H⋯O and O—H⋯O hydrogen bonds link the cations, anions and lattice water molecules into a three dimensional supramolecular structure.


Ming-Hui Zhang, Yue-Lin Yuan and Jun-Feng Kou Comment
Friedel-Crafts acylation provides a fundamentaland useful method for the synthesis of aromatic ketones, which are important intermediates for preparing fine chemicals in the field of pharmaceuticals, agrochemicals, and fragrances.
Typically, these reactions are performed using acyl chloride (for acylation) in the presence of a little more than one equivalent of Lewis acids, such as anhydrous aluminium chloride, titanium chloride and iron chloride (Elofson et al. 1965;Boon et al. 1986;Yeung et al. 2002;Gopalakrishnan et al. 2005;Qiao et al. 2008;Gouda et al. 2010). Herein we report the synthesis and structure of the title compound with aluminium chloride.
The structure of the title compound is shown in Fig. 1, Fig. 2 and hydrogen-bond geometry is given in Table 1. The compound crystallizes in the triclinic space group p-1,and the crystallographic asymmetric unit consists of one crystallo graphically independent anion, one ammonium cation and two water molecules. As shown in Fig.2, the dihedral angle is 73.2 between benzene rings which are not coplane. An interesting part of the structure of title compound is the helical chains formed by the N-H···O and O-H···O. hydrogen-bonding interactions along c axis in this molecule (Table 1 &

Experimental
In a 250 ml dry three-necked round-bottom flask, aluminium chloride (34.8 g, 0.26 mol) was dissolved in dry dichloromethane (150 ml), ortho-xylene (11.2 g, 0.105 mol) was added and then phthalic anhydride portion-wise with formation of an orange liquid in ice bath for 3 h while stirring. The mixture was reacted for 10 h while elevating the temperature of the reactor up to 303 K with formation of a yellow precipitate, then cooled down to room temperature and poured over a mixture of ice (20 g) and concentrated hydrochloric acid (10 ml) with a large amount of gas generated by HCl (Elofson et al., 1965). The organic layer was separated and the aqueous layer was extracted with dichloromethane (3 × 50 ml). The

Figure 1
The molecular structure of the title compound, with atom labels and 30% probability displacement ellipsoids.  Hydrogen bonds are shown as brown dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 > σ(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.