The present invention relates to a new stable crystalline polymorph of 2-(2-chloro-4-mesyl-benzoyl)-cyclohexane-1,3-dione and to a process for preparing the same. More particularly, it relates to compositions having said polymorph for controlling unwanted plants. The process for preparing crystalline polymorph of 2-(2-chloro-4-mesyl-benzoyl)-cyclohexane-1,3-dione comprising the following steps of: 1) preparation of 4-sulfomethyl-2-chloro benzoyl chloride 2)preparation of enol ester derivative 3)rearrangement of enol ester derivative to 2-(2-chloro-4-mesyl-benzoyl)-cyclohexane-1,3-dione and 4) purification of 2-(2-chloro-4-mesyl-benzoyl)-cyclohexane-1,3-dione. The polymorphic structure is assessed using infra-red and Raman spectra and X-ray crystallography data. The polymorph has a powder X-Ray diffraction spectrum with characteristic peaks at 2? = 17.2°, 17.6°, 19.1°, 21.0°, 26.0° and 28.7°. A stable formulation of the above mentioned polymorph is used as herbicide.
