Preparation of Alkyl Bromides From Alcohols

by Drone #342


Much interest has been brewed up by YoursTruly in the use of simple alkyl halides -- methyl iodide, ethyl bromide, propyl bromide, isopropyl bromide, butyl bromide, etc. Though people seem to want to experiment with them badly, and though they aren't suspicious, for whatever reason, people have an aversion to ordering them. So be it!

Here's a simple method of producing ethyl, propyl, isopropyl, and n-butyl bromides at home. Currently, I'm investigating whether MeI can be made in a similar fashion (I have journal ref's describing refluxing MeOH in aqueous HI to produce MeI, but who has MeI, and who knows if making HI from KI would still work for this reaction? I'm still looking; so far, it looks good. If someone wants to test it out, I wouldn't stand in their way.)

All of this should be done in a well-ventilated area, since these alkyl halides aren't good for you, not to mention the HBr fumes.

In a rb flask fitted with a reflux condensor and magnetic stirrer, 0.4 moles of the alcohol of you choice is combined with 0.5 moles of either NaBr or KBr.

In a second flask, cooled in an ice bath, to 30 ml of H2O is SLOWLY added 55 mL of concentrated H2SO4. This will get pretty hot, even with cooling. Stick this in the fridge, and let it chill.

Once the diluted acid is chilled, with magnetic stirring, carefully add the acidic solution to the alcohol/bromide salt mixture. Reflux the solution for 1 h. NOTE: be careful with EtBr, since it has a relatively low B.P., and it won't take much to boil it away; use as cold of water in your condenser as possible.

Carefully distill your solution. With EtBr, collect everything coming over below 70°C. With the rest, collect everything above 60°C and below 140°C. With your crude alkyl halide in hand, separate off the aqueous layer (the top layer), and throw it out. Wash it again with cold water, then with a little 10% baking soda, then with water again. Dry over anhydrous MgSO4, and it should turn from cloudy to clear. Redistill. Yields are quite high.

bp EtBr 38.2°C
bp PrBr 71°C
bp iPrBr 59-60°C
bp nBuBr 101.6°C

Protect your final products from light, they're best stored refrigerated, and keep them nice and dry.