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(dim ethoxyphenyl) ethanes were investigated. The bis(3,4-dimethoxyphenyl)e thane was found to be more reactive than the bis(2,5-dimethoxyphenyl)e thane and the latter more reactive than the bis(2,4-dimethoxyphenyl)et hane. 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 Bronsted beta values of about 0.6. A kinetic isotope effect, with k(H)/k(D) ratio ranging from 3.5 to 5.7, for the base-promoted elimin ation reaction of 1,1,1-trichloro-2,2-bis(3,4-dimethoxyphenyl)ethane w as found. Tunneling occurs for methoxide and ethoxide ion-promoted eli minations. Activation parameters for alkoxy-promoted elimination show a similar trend for chloride and bromide derivatives. The data collect ed seem to confirm that there is contiguity between E1cB(irr) and E2 m echanisms. (C) 1998 John Wiley & Sons, Ltd.