The Student Room Group
Reply 1
mik1w
When you brominate phenol, how come you don't need electrophilic Br+ ions like you need when brominating benzene?


the second one I forgot :redface:


It's simple.
WHen the OH group is on the ring, the O has 2 lone pairs.One of these long pairs overlaps with the Pi system of the benzene ring and becomes delocalised over the entire thing, increasing the electron density of the ring at the 2 and 4 points.
What happens with the aqueous Bromine is that at these areas, the electron density is suffienent enough to push the electrons in the bromine molecule more to one side, and thus there is an induced dipole on the bromine.
It can now substitute onto the ring easily
(there is a Delta + end which attaches)
dinesh
It's simple.
WHen the OH group is on the ring, the O has 2 lone pairs.One of these long pairs overlaps with the Pi system of the benzene ring and becomes delocalised over the entire thing, increasing the electron density of the ring at the 2 and 4 points.
What happens with the aqueous Bromine is that at these areas, the electron density is suffienent enough to push the electrons in the bromine molecule more to one side, and thus there is an induced dipole on the bromine.
It can now substitute onto the ring easily
(there is a Delta + end which attaches)

Electron density increases and benzene becomes activated at carbon 2, 4 and 6; so you get 2,4,6-tribromophenol.
Reply 3
okay thankyou, that clears that up. I remembered the second one as well!

When you use phenol to make an ester, you have to use the phenate ion because phenol is insoluable? But this is alkaline as the hydrogen is dissociated. When you use concentrated sulphuric acid as a catalyst in the reaction (with the acyl chloride), what stops the load of hydrogen ions reacting with the phenate ion, making the insoluable phenol?