2,5-Bis(4-methylphenyl)-4-oxopentanoic acid

The title compound, C19H20O3, was obtained from 1,4-bis(4-methylphenyl)but-3-yn-2-one in the presence of carbon monoxide by Ni(CN)2 catalysis in a basic aqueous medium. Intermolecular O—H⋯O hydrogen bonds lead to the formation of hydrogen-bonded carboxylic acid dimers [graph-set motif R 2 2(8)]. Weak C—H⋯O hydrogen bonds between neighbouring dimers further extend the structure to give rise to a three-dimensional supramolecular network.

The title compound, C 19 H 20 O 3 , was obtained from 1,4-bis(4methylphenyl)but-3-yn-2-one in the presence of carbon monoxide by Ni(CN) 2 catalysis in a basic aqueous medium. Intermolecular O-HÁ Á ÁO hydrogen bonds lead to the formation of hydrogen-bonded carboxylic acid dimers [graph-set motif R 2 2 (8)]. Weak C-HÁ Á ÁO hydrogen bonds between neighbouring dimers further extend the structure to give rise to a three-dimensional supramolecular network.

Related literature
For general background to transition metal-mediated carbonylation reactions, see: Collins (1999); Arzoumanian et al. (1995). For a similar structure, see: Garcia-Gutierrez et al. (2004). For bond length values, see: Allen et al. (1987). For hydrogen-bonding motifs, see: Bernstein et al. (1995).  Table 1 Hydrogen-bond geometry (Å , ).  (Collins, 1999). Amongst the many metal-mediated syntheses used, catalysis by nickel cyanide in aqueous media under phase transfer conditions has attracted particular attention (Arzoumanian et al., 1995) and numerous lactones and their hydrolysis products have been synthesized using this system. Herein, we chose 1,4-di(4-methylbenzyl)but-3-yn-2-one as a carbonylation substrate to be reacted in the presence of Ni(CN) 2 and carbon monoxide in a biphasic toluene/basic aqueous medium to give the title compound.

D-HÁ
The structure of the title compound is depicted in Fig. 1. The C-C bond lengths show normal values (Allen et al., 1987), and the C-O and C═O bond lengths are comparable to those observed in simliar structures (Garcia-Gutierrez et al., 2004). The molecules form dimers with neighboring molecules through O-H···O hydrogen bonding with an R 2 2 (8) graph set motif (Bernstein et al., 1995). These dimers are further linked by C-H···O hydrogen bonds (Table 1) to form a three-dimensional supramolecular network (Fig. 2).

Experimental
A typical experiment was performed as follows: in a round-bottomed flask toluene (25 ml) and 1 M aqueous NaOH (10 ml) were degassed and saturated with CO under atmospheric pressure before Ni(CN) 2 .4H 2 O (1.0 mmol) and tetrabutylammonium bromide (0.3 mmol) were introduced, and the mixture was kept at room temperature overnight with stirring while CO was slowly (2-3 min) bubbled through the solution. To the yellow two-phase mixture was then added 10 mmol of 1,4-di(4-methylbenzyl)but-3-yn-2-one, and stirring and flow of CO at a flow rate of 3 ml min -1 were maintained for 5 h at 393 K. At the end of the reaction, ethyl ether (2 × 20 ml) was used to eliminate the impurities. The aqueous phase was acidified with diluted HCl at pH = 1. Ethyl ether (2 × 20 ml) was used to extract the product. The organic phase was dried over Na 2 SO 4 and evaporated to obtain a yellow powder. During recrystallization, the yellow block crystals were obtained by slow evaporation of the solvent with a yield of 68%. m.p. 476-478 K; IR (KBr) cm -1 : 3052,2980,2948,1716,1705,1669,1607,1573,1465,1416,1379,1345,1285,1246,1232,1217,1186,1150,1068,1044,995,972,850.

Refinement
All H atoms attached to C and O atoms were fixed geometrically and treated as riding with C-H = 0.93 or 0.96 Å and O-H = 0.82 Å, and U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (O).

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