2-Benzenesulfonamido-3-methylbutyric acid

In the crystal structure of the title compound, C11H15NO4S, two independent molecules are present per asymmetric unit; they are dimerized through O—H⋯O hydrogen bonds between their carboxy groups to generate R 2 2(8) loops. An intramolecular N—H⋯O link in one of the molecules closes an S(5) ring. The dimers are linked by N—H⋯O and C—H⋯O hydrogen bonds to form a three-dimensional network. The C atoms of the isopropyl group of one of the molecules are disordered over two orientations in a 3:1 ratio.

In the crystal structure of the title compound, C 11 H 15 NO 4 S, two independent molecules are present per asymmetric unit; they are dimerized through O-HÁ Á ÁO hydrogen bonds between their carboxy groups to generate R 2 2 (8) loops. An intramolecular N-HÁ Á ÁO link in one of the molecules closes an S(5) ring. The dimers are linked by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds to form a three-dimensional network. The C atoms of the isopropyl group of one of the molecules are disordered over two orientations in a 3:1 ratio.
Benzenesulphonyl chloride (0.75 g, 0.043 mmole) added within 3-5 min. The pH was adjusted by sodium carbonate (1M). Disappearance of suspended benzenesulfonyl chloride gave indication of completion of reaction. Then, dilute HCl was added dropwise to result in a pH 2-3. The precipitate was filtered, washed with plenty of water and dried. Colourless prisms were obtained upon recrystalization from methanol solution.

Refinement
All the C-H and H-atoms were positioned with idealized geometry with C-H = 0.93 Å for aromatic, C-H = 0.96 Å for methyl group and C-H = 0.98 Å for tertiary, and were refined using a riding model with U iso (H) = 1.2 U eq (C) for aromatic & tertiary and U iso (H) = 1.5 U eq (C) for methyl carbon atoms.
Reaction does not affect the chirality of product, and the chirality is that of the reactant (L-Valine).

supplementary materials
The atoms C9-C11 were disordered over two positions with the occupancies of 0.75 for C9A-C11A and 0.25 for C9B-C11B. The temperature factors of pairs of atoms were restrained to be identical.

Figure 1
The labelled molecular structure of (I) with 50% displacement ellipsoids, showing intramolecular hydrogen bonding and formation of dimers through carboxylic group using dashed lines.  Unit cell packing showes intermolecular interactions using dashed lines.   (6) 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.