Metal ions and complexes in organic reactions. Part X. Effect of methoxy-substituents on copper-catalysed nucleophilic and reductive replacement of halogen in reactions between sodium methoxide and bromo- or iodo-benzene derivatives

Abstract

Seventeen bromo- and seventeen iodo-benzene derivatives, of general formula C₆H_5–n(OMe)_n Hal, were subjected to reaction with sodium methoxide, catalysed by copper(I) iodide, in 2,4,6-collidine solution. Competition occurred between nucleophilic substitution, giving C₆H_5–n(OMe)_n+1, and reductive substitution, giving C₆H_6–,n(OMe)_n. When neither position ortho to the halogen was occupied by a methoxy-group, reduction was negligible; when one ortho-position was thus occupied, the extent of competitive reduction increased as the number of methoxy-substituents increased; when both ortho-positions were thus occupied, reduction was the dominant reaction. In general, the iodides were more responsive to reduction than the bromides. The efficiency of formation of some polymethoxybenzenes gives the process practical value.