Kinetic study of base‐promoted elimination reactions of some 1,1,1‐trihalo‐2,2‐bis(dimethoxyphenyl)ethanes in alcoholic solutions

The base–promoted elimination reactions of 1,1,1‐trichloro‐2,2‐bis(dimethoxyphenyl)ethanes were investigated. The bis(3,4‐dimethoxyphenyl)ethane was found to be more reactive than the bis(2,5‐dimethoxyphenyl)ethane and the latter more reactive than the bis(2,4‐dimethoxyphenyl)ethane. Kinetic data relative to 1,1,1‐trihalo(chloro or bromo)‐2,2‐bis(3,4‐dimethoxyphenyl)ethanes show that the tribromo reacts faster than trichloro derivative and that the reactions are general‐base promoted with Brønsted β values of about 0.6. A kinetic isotope effect, with kH/kDratio ranging from 3.5 to 5.7, for the base‐promoted elimination reaction of 1,1,1‐trichloro‐2,2‐bis(3,4‐dimethoxyphenyl)ethane was found. Tunneling occurs for methoxide and ethoxide ion‐promoted eliminations. Activation parameters for alkoxy‐promoted elimination show a similar trend for chloride and bromide derivatives. The data collected seem to confirm that there is contiguity between E1cBirrand E2 mechanisms. © 1998 John Wiley & Sons, Ltd.