[neobenzene]

Hi! In my syllabus, we learn about two kinds of bromination of phenol - one in water medium and the other in CS2 medium.

When you brominate phenol in a water medium, you get 2,4,6-tribromophenol
When you brominate phenol in a CS2 medium, you get o-bromophenol and p-bromophenol?

How does the difference in medium help give you different products? As in, what do water and CS2 do differently to give their respective products?

[discodermolide]

Bromination which which reagent, Br₂? Or something else?

[neobenzene]

Yes, Br2

[discodermolide]

What happens when you mix bromine and water, and can what you get explain the different products observed with different solvents?

[neobenzene]

You get bromine water and HBr

[neobenzene]

I don't understand how I am to proceed.

[discodermolide]

Have a look at this page for the water reaction.
http://www.chemguide.co.uk/organicprops/phenol/ring.html

and
Quote from another source
"in presence of less polar solvent such as CS2,CHCl2,CCl4 etc..and at low temperature monohalophenols are produced
phenol + Br2 (in CS2) ------> 4-bromophenol (major product)+ 2-bromophenol (minor product)
reason
in aqueous solution ,phenol ionizes to form phenoxide ion due to the presence of negative charge ,the oxygen of phenoxide ion donates electron on benzene ring to a large extent as a result the ring gets highly activated and hence trisubstituion occurs on the other hand in non-polar solvents the ionization of phenols is greatly suppressed as a result oxygen of OH group donates electrons to benzene ring only to a small extent consequently the ring is activated only slighlty and hence only mono substitution occurs furthur because of steric hindrance at ortho-position the para substittuion product usually predominates."

[orgopete]

Have a look at this page for the water reaction.
and … from another source
"in presence of less polar solvent such as CS2,CHCl2,CCl4 etc..and at low temperature monohalophenols are produced
phenol + Br2 (in CS2) ------> 4-bromophenol (major product)+ 2-bromophenol (minor product)
reason
in aqueous solution ,phenol ionizes to form phenoxide ion due to the presence of negative charge ,the oxygen of phenoxide ion donates electron on benzene ring to a large extent as a result the ring gets highly activated and hence trisubstituion occurs on the other hand in non-polar solvents the ionization of phenols is greatly suppressed as a result oxygen of OH group donates electrons to benzene ring only to a small extent consequently the ring is activated only slighlty and hence only mono substitution occurs furthur because of steric hindrance at ortho-position the para substittuion product usually predominates."

I would say use this if it works for you. I really doubt that is the correct reason. HBr is the by-product. Dibromophenol is ionizing in HBr? I could understand that water is more polar and that water or HBr itself could activate bromine or hypobromite similar to a Lewis acid for bromination of unactivated aromatic compounds.