Halogenation of C5 - C10 saturated keto mono-carboxy acids or their acidogenic derivatives with elemental halogen in the presence of certain catalysts to yield olefinic halogenated compounds (e.g. acids and lactones) containing at least four halogen atoms per molecule is disclosed. The catalyst selected depends upon the particular end product desired. Halogenated products of the process are useful as insecticides, plant growth control agents and defoliants. Particularly useful products are those olefinic polychlorinated derivatives of 4-keto-pentanoic acid which contain at least four chlorine atoms per molecule such as, for example, 2,3,5,5,5-pentachloro-4-keto pentenoic acid.
