2-(2,5-Dichlorobenzenesulfonamido)-3-methylbutanoic acid

The structure of the title compound, C11H13Cl2NO4S, shows one sulfonamide-O atom to lie almost in the plane of the benzene ring [C—C—S—O = −178.7 (2) °] and the other to one side [C—C—S—O = −49.4 (3)°]. Lying to the other side is the amine residue, which occupies a position almost perpendicular to the plane [C—S—N—C = 70.2 (2)°]; the carboxylic acid group is orientated to lie over the benzene ring. In the crystal, the appearance of an 11-membered {⋯OH⋯OCOH⋯OC2NH} synthon, which features the hydroxy group forming both donor (to a carbonyl-O) and acceptor (from the amine-H) interactions, leads to the formation of a supramolecular chain along the a axis. Chains are connected in the crystal structure by C—H⋯O contacts.

The structure of the title compound, C 11 H 13 Cl 2 NO 4 S, shows one sulfonamide-O atom to lie almost in the plane of the benzene ring [C-C-S-O = À178.7 (2) ] and the other to one side [C-C-S-O = À49.4 (3) ]. Lying to the other side is the amine residue, which occupies a position almost perpendicular to the plane [C-S-N-C = 70.2 (2) ]; the carboxylic acid group is orientated to lie over the benzene ring. In the crystal, the appearance of an 11-membered {Á Á ÁOHÁ Á ÁOCOHÁ Á ÁOC 2 NH} synthon, which features the hydroxy group forming both donor (to a carbonyl-O) and acceptor (from the amine-H) interactions, leads to the formation of a supramolecular chain along the a axis. Chains are connected in the crystal structure by C-HÁ Á ÁO contacts.

Comment
The crystal structure of the title compound, (I), was determined in connection with on-going structural studies of sulfonamides Khan et al., 2010), of interest owing to their biological properties (Korolkovas, 1988;Mandell & Sande, 1992).
In the crystal packing, the hydroxyl-O3 group forms both donor and acceptor interactions, the former to a symmetry related carbonyl-O4 and the latter with a symmetry related amine-N1-H atom, Table 1. These lead to a linear supramolecular chain, Fig. 2, aligned along the a axis and mediated by an 11-membered {···OH···OCOH···OC 2 NH} synthon; the chain is further stabilized by a C7-H7···O1 contact, Table 1. Chains are held in the crystal structure by C-H···O contacts, Fig.   3 and Table 1.

Experimental
To 2-amino-3-methylbutanoic acid (234 mg, 2 mmol) in distilled water (15 ml), was added 2,5-dichlorobenzenesulfonyl chloride (491 mg, 2 mmol) while maintaining the pH of reaction mixture at 8 by using 3% sodium carbonate solution. The consumption of the reactants was confirmed by TLC. The pH of reaction mixture was adjusted to 3 using 3 N HCl. The precipitates were washed with water and crystallized from methanol

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.93-0.98 Å) and refined as riding with U iso (H) = 1.2-1.5U eq (C).  Fig. 1. The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 35% probability level.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.