[sayantan dutta]

NBS always have some trace amount of HBr present it. During the reaction Alkene+ NBS+H2O... BrOH form which reacted with double bond to give bromohydrin and succinimide as the product.....my question is the trace amount of HBr present in NBS what role does it have in this reaction ?? will it stay unreactive in polar solvent or not? if not what will it do and it's outcome?

[rolnor]

What do you think?

[sayantan dutta]

as fas as I can understand HBr role.is.very important in allylic bromination using NBS....the trace amount of HBr helps to maintain steady but low concentration of Br2 supply so that reaction occurs at allylic position not at double bond.
In polar solvent like water NBS gets dissolved and form.plenty.of BrOH that is why reaction takes place across double bond actually
But I can't understand what happened to the trace amount of HBr present with NBS???  I don't think HBr don't react with NBS in polar media otherwise again low concentration Br2 will form and reaction at double bond will become difficult ..this is as fas I can.think.but.i really don't.know the fate of HBr packed with NBS in polar.solvent..

[rolnor]

Maybe the level of BrOH is very high compared to HBr?

[sayantan dutta]

ok so if the solvent in H2O ..then it is in plenty hence NBS interact with water and form BrOH ..trace amount of HBr is not getting any chance to interact with NBS to form Br2 ..moreover in polar solvent hbr breaks and gets solvated trapped by the water molecule ..hence it can't interact with NBS...can this be a probable logical cause ?

[rolnor]

Its really not easy to know what happens but the reaction gives addition of BrOH mainly. Maybe its possible to design a set of experiments that could explain why any present HBr does not interfere?