plz treat the following as suggestions but not process to your work.
Use proper solvent that suits your reaction(i think any polar solvent)
No need to conduct your expt in N2, your reaction is not air sensitive. further it requires atmospheric oxygen as catalyst if you dont supply it thry h2o2.
Take your starting material in a suitable solvent in an RBF at Room temperature
add some catalytic amount of h202
slowly add hbr( generally available as 48% aqueous soluiton) in to the RM using addition funnel at RT.
Maintain until reaciton completion at RT( as per my knowledge, its a simple reaction. no need to go for higher temperatures.)
check the reaction completion by tlc