Question

Give reason : phenol with aq bromine gives 246 tribromo phenol but in non polar medium mono substitution takes place

Answer 1

Actually, water is a polar substance and so in bromine water, the phenol gives a strongly stable phenoxide ion. This ion has negative charge on oxygen and that transfers electrons to the benzene ring and that becomes much activated that substitution reaction occurs at three positions and tri-substituted product is obtained.

But, CS2 is less polar solvent so the solvent effect is minimum and the formation of phenoxide ion is not much stable so the activation of ring also does not occur and thus only monosubstituted product is obtained.

When activation of ring occurs, ring het tri substituted and if activation is not occured, ring get mono substituted