ISSN 0323-4479 • Z. phys. Chemie • Leipzig • 270 (1989) 6 • S. 1177-1184 Chemistry Department, Faculty of Science, Benha University, Benha (Egypt) Solvolysis rates in mixed organic solvents: II. Kinetics of dehydrochlorination of 1,1, l-trichloro-2,2-dipbenyIethane by base in methanol/isopropanol mixed solvents By M. A. Mousa1, E. M. Diefallah, A. F. Shaaban and M. M. Azab With 5 Figures and 2 Tables (Received ISth October 1986; in rev. version 8th September 1987) Abstract The kinetics of dehydrochlorination of l,],l-trichloro-2,2-diphenylethane by methoxide and iso-propoxide ions in methanol-isopropanol solutions have been studied over the temperature range 30 to 50°C. The rate of the reaction is first order with respect to both the l,l,l-trichloro-2,2-diphenylethane and the methoxide or isopropoxide ion concentrations. When the concentration of methanol in the solvent is increased the rate constant of the dehalogenation reaction first increases to a maximum at about 0.1 methanol mole fraction, then decreases. The influence of solvent variation on reaction rate has been examined in terms of changes in the activation parameters. The results do not support any simple correlation between the macroscopic dielectric constant of the medium and the reaction rate constant. Solvent effects on the thermodynamic parameters which characterize the activation process (Aare discussed in terms of the electrostatic theory and on the basis of the change in the solvent structure