My partner and I are doing undergraduate research. Currently, we are trying to double brominate 1,12-dodecanediol to simply have Br substitute both -OH groups. We keep on running the experiment, but based on TLC analysis, there's always a mixture of the monobrominated and dibrominated products. Of course, we tweak some parameters, and our current protocols are as follows.
A quick summary of our procedure:
1. 0.5 g of 1,12-dodecanediol.
2. 3 mL of 8.9M HBr
3. Set it up in a reflux apparatus.
4. High heat.
5 Leave it there for two - three days.
Based on stochiometric ratios, we always put an excess of HBr solution to have both -OH groups substituted. Even with excess HBr, we are still getting a mixture of monobrominated and dibrominated products. Some theories, on to why there a mixture, are that water (solvent) is acting a nucleophile replacing the Br or the temperature is too high. At low temperatures, there is no bromination observed. If you have any suggestions or pointers, it will be much appreciated. Thank you for your time!