The kinetics and mechanisms of aromatic halogen substitution. Part XXXII. The directive power of the acetoxy-group

Abstract

The rates and products of chlorination of acetoxybenzene, the diacetoxybenzenes, and 4-acetoxyacetanilide by molecular chlorine in acetic acid at 25° have been examined. The results allow calculation of partial rate factors for chlorination directed by the acetoxy-group to the ortho-, meta- and para-positions. The extent to which the observed rates and products for chlorination of the diacetoxybenzenes accord with estimates calculated by using the ‘ additivity principle ’ is discussed. The response of change in rate to change in structure for the chlorination of 4-substituted anilides (4-RC₆H₄NHAc, where R is an electron-withdrawing group) is less than would be expected from the rates of chlorination of monosubstituted benzenes containing electron-releasing groups. Possible reasons for this difference are discussed in terms of factors which may affect the electron-releasing power of activating substituents. Further evidence that molecular chlorination of simple aromatic compounds is accompanied by minor, but significant, contributions from sequences initiated by addition of chlorine is presented. Little indication of contributions from chlorodeacylation has been found under the conditions used in the present investigation.