Sciencemadness Discussion Board

Odd results from 5-bromovanillin synthesis?

mnick12 - 1-10-2010 at 17:54

Well I have a question regarding the bromination of vanillin using elemental bromine, vanillin, and acetic acid.

So I followed this procedure but doubled up on the amounts as I had alot more bromine than expected.
"To vanillin (15.2g, 0.1 mol) in glacial acetic acid (75 ml) is added bromine (17.6g, 0.11 mol). After stirring for 1h, the reaction mixture is diluted with ice/water (200ml), the precipitated solid is filtered, washed with water, and dried to give 5-bromovanillin"

Now like I said I had more bromine than I expected so I doubled up on the amounts used, but I did not have 150ml of acetic acid so I used 110ml. Now once the vanillin had dissolved in the AcOH I placed the mix in an ice bath and slowly added the bromine using an addition funnel. Once the bromine was added the solution turned orange and began to give off large amounts of HBr indicating bromination. But a few minutes later the solution turned cloudy. Now I am not to worried but is the cloudiness a result of using less solvent?
Anyway this is the first time I have conducted a bromination of vanillin so I am not sure what to expect.

If there is anyone who has conducted this procedure before help would appreciated.


Magic Muzzlet - 1-10-2010 at 19:58

It is likely that the product is precipitating from solution. I have not brominated vanillin in AcOH, but have done so in MeOH with other reagents. Regardless of the amount of solvent I use the product ppts slightly. I would say its the same deal here. Once you dilute with water you will see your product ppt as usual, I would expect little if any problem with your reaction from the use of a little less solvent.

mnick12 - 2-10-2010 at 13:01

Ahh well a little update,

So after sitting for an hour I added 200ml of water causing the precipitation of creamy orange crystals. I then vac filtered the mix and washed with 3x20ml of cold water. The wash ended up looking like kool-aid and the crystals took on a creamy orange color. The final yield was 41.82gr of bromovanillin which needs to be washed again it smells kinda like AcOH.

Sergei_Eisenstein - 4-10-2010 at 04:48

It probably is the formed 5-bromovanillin starting to go out of solution. The end product should not be orange though. If I recall correctly, it should be white when pure. I'd suggest to use a little bit of a sodium bisulfite solution instead of just water. I did the bromination in MeOH and diluted the reaction mixture in the end with 5% sodium bisulfite, followed by filtration and washing the end product with water until "odorless" (i.e. only vanillin-like aromas remained). Alternatively, you can also make the 5-bromovanillin precipitate with water and wash with sodium bisulfite.