The aim of this research is to hydroxybrominate and hydroxychlorinate the double bonds of methyl oleate and soybean oil in dense CO2. The hydroxychlorination reactions of vegetable oils in dense CO2 are the first such report in literature. Experiments were performed at the reaction conditions of 8, 25 and 40 degrees C and 60, 100, 120 and 150 bar. Effects of temperature, pressure, reaction time and the reactant amounts on the extent of reaction are studied. Hydroxybromination and hydroxychlorination reactions are conducted using sodium hypobromite (NaOBr) and sodium hypochlorite (NaOCl) solutions, respectively. The polymerization of the product is performed by urethane formation with toluenediisocyanate at 40 degrees C. The products were analyzed by NMR and IR spectrometry. Fifty percent consumption of the double bonds was observed in the hydroxybromination reaction of methyl oleate, but no -OH addition was determined. In hydroxychlorination reactions of methyl oleate the consumption of double bonds ranges from 40 to 95%, and the introduction of -OH groups ranges from 14 to 30%. Best yields were observed when the mole ratio of NaOCl to methyl oleate double bonds is 5 to 1. The consumption of soybean triglyceride double bonds, in the hydroxychlorination reactions, are observed to range from 18 to 75% and the formation of -OH groups ranges from 8 to 33%. The highest conversion for one-step hydroxychlorination of soybean is obtained at 25 degrees C and 120 bar for a reaction time of 6 h, with 10/l ratio of NaOCl to double bonds. Better results were obtained when the product of the reaction was reintroduced to the reactor and retreated with NaOCl and 75% consumption of double bonds and 33% formation of -OH groups were observed. (C) 2005 Elsevier B.V. All rights reserved.