An electrochemical aromatic chlorination, comparison with electrophilic reaction

The electrophilic and the anodic chlorination of 1,4-dimethoxy-2-tert-butyl benzene appear to involve different mechanistic pathways. The electrophilic chlorination of 1,4-dimethoxy-2-tert-butylbenzene requires Lewis acid cata lysts when carried out in CCl4 but not in CH3CN. It yields 1,4-dimethoxy-2- tert-butyl-5-chlorobenzene as the primary product and in subsequent reactio ns 1,4-dimethoxy-2, 5-dichlorobenzene, 1,4-dimethoxy-2-tert-butyl-dichlorob enzene and 1,4-dimethoxy-2-chlorobenzene. In contrast, anodic chlorination of 1,4-dimethoxy-2-tert-butylbenzene in CH3CN yields 1,4-dimethoxy-2-tert-b utyl-6-chlorobenzene and 1,4-dimethoxy-2-tert-butyI-5-chlorobenzene in abou t equal amounts. Further chlorination is forestalled and replacement of the tert-butyl group is not observed. 1,4-Dimethoxy-2-tert-butyl-6-chlorobenze ne is therefore the main product of the electrochemical route. (C) 2001 Els evier Science B.V. All rights reserved.