andre178 - 7-5-2010 at 12:28
According to Mann & Saunders, Practical Organic Chemistry, 3rd Ed, you can prepare bromobenzene by adding bromine to benzene and then reflux at
various temperatures using minute amounts of pyridine. Is this true?
To summarize, 0.5 ml pyridine + 34 ml benzene, to which 24 ml of bromine is added in a round flask, heated to 25 deg for 1 hour, then heated to 65 for
45 min. (At this point the solution is deep red - bromine color)
This is then set in a sep. funnel and separated with 10% NaOH. The instructions say that the bottom red layer (bromobenzene) is the heavy once shaken
with excess 10% aq NaOH it will turn clear. This has not happened. I followed it through and through.
Also I have not found any theoretical explanations of using just pyridine catalyst?! to get a halidebenzene.
Reference Link:
Prep of bromobenzene
entropy51 - 7-5-2010 at 14:45
Iron wire works as well as pyridine and is easier to obtain.
I don't advise dumping the Br2 in all at once, although a few preps do say that. Add it very slowly until HBr begins to bubble into a H2O trap with
the tube just touching the H2O surface. In addition to avoiding a runaway, adding the Br2 slowly decreases the amount of dibromobenzene formed.
There is a thread on this, I believe.