2-(3-Oxo-2,3-dihydro-1,2-benzothia-zol-2-yl)acetic acid.

In the title compound, C(9)H(7)NO(3)S, the benzoisothia-zolone ring system is essentially planar, with a maximum deviation of 0.013 (2) Å. In the crystal, mol-ecules are linked via O-H⋯O hydrogen bonds, forming chains along [010]. In addition, weak inter-molecular C-H⋯O hydrogen bonds are present.

Ethyl 3-oxo-2,3-dihydro-1,2-benzothia-zole-2-carboxyl-ate.

The title compound, C(10)H(9)NO(3)S, was synthesized by the reaction of benzo[d]isothia-zol-3(2H)-one with ethyl carbonochloridate in toluol. The benzisothia-zolone ring system is approximately planar, with a maximum deviation from the mean plane of 0.020 (1) Šfor the N atom.

Propyl 3-oxo-2,3-dihydro-1,2-benzothia-zole-2-carboxyl-ate.

The title compound, C(11)H(11)NO(3)S, was synthesized by the reaction of benzo[d]isothia-zol-3(2H)-one with propyl carbono-chloridate in toluene. The benzoisothiazolone ring system is approximately planar with a maximum deviation from the mean plane of 0.0226 (14) Šfor the N atom. Weak inter-molecular C-H⋯O hydrogen bonding occurs in the crystal structure.