Modification of the Directive Influence of Substituents in Certain Benzene Derivatives

Bromination of vanillin, 3-methoxy-4-hydroxybenzaldehyde, gives a yield of 88-90 per cent of the 5-bromo compound which indicates that the chief directive influence is exerted by hydroxyl. If the hydroxyl radical is first acylated and the resulting acetyl or benzoyl vanillin is brominated, an equally high yield of the 6-bromo derivative is obtained, and no other product can be isolated. Vanillic acid and methyl vanillate likewise give good yields of the corresponding 5-bromo compounds, while the acylated derivatives give the 6-bromo substitution products only. These results indicate that acylation of hydroxyl suppresses its orienting effect and the entrance of bromine into position 6 shows that the methoxy radical then exercises the chief directive influence