Bromination fo 1,4-dimethoxybenzene using Amm. Bromide/H2O2

anime · Fri Apr 22, 2005 10:23 am

Another weird strange dream last night.

I was in the Amazon jungle when I ran into this monkey....
The monkey decided to test out the synthesis posted on the rhodium using H2O2, NH4Br in GAA. 0.5 mole of 1,4-dimethoxybenzene (69g), 0.5mole H2O2 (in a 40% solution) and 0.5mole NH4Br were added to 400ml of Glacial Acetic Acid. The reagents didn't dissolve (1,4-DMB immediately falls out of solution when H2O2 is added). The temperature was raised to 40C and stirred for two hours. During this course the solution turns from a orange juice yellow(0-1h) to a dark deep red (1h40). At 2:30, the solution is removed and allowed to cool to room temp. A 40% solution is added to this, and the solution turns a deep brown color. This is allowed to cool to room temperature.

The solution is extracted with 2x 200ml toluene (maybe the monkey should have used more). The toluene layer was a deep brown color, below it, a frustrating emulsion Mad

layer containing half of the product and finally the aqueous solution. The toluene layer and emulsion were separated from the aqueous layer; a saturated brine solution was mixed with toluene/emulsion layer. This helped clear things a bit, the toluene layer was easy to separate from the emulsion layer. The toluene was removed via distillation and a dark brown oil (60g) was obtained.

The monkey believes the other half was in the emulsion layer and the work up is most likely the cause for the low yield (55% molar).

The monkey has a few questions:
What advice would be given concerning the workup as to improve the yields?
Also what other methods could be used to produce the 1,4-dimethoxybenzene in which the work-up doesn't produce in emulsion layer.

Nicodem · Fri Apr 22, 2005 10:29 pm

Check the post below the one where you got that procedure:
http://12.162.180.114:90/synthetika/hiveboard/chemistrydiscourse/000514641.html

However, skip the heathing to 35°C at the end of the bromination as this only cause some dibromination to occur. Do not skip the the destroyal of the excess of bromine (you can use Na2SO3 instead of ascorbic acid)!

fogged · Sat Apr 23, 2005 5:01 am

On the issue of emulsions, to break one, simply get your sep funnel and run the liquid down a ground glass joint (another sep funnel is best, of course, but an RBF or something is fine, just means you have to pour it back into the original funnel!). What I mean, if it's not clear, is you run the emulsified liquid out of the sep funnel with the end of the outlet touching the inside of the joint so the liquid runs down it. As I understand, the roughness of the joint is enough to break the emulsion. Hope this makes the monkey's life easier! Hate to see an animal suffer!! Smile

anime · Sat Apr 23, 2005 6:02 am

Nicodem, do you still have that chloromethylation proceedure you posted at the hive.

The monkey is interested in performing a bromomethylation on the 1-bromo-2,5-dimethoxybenzene product.

Thx.
The DCM method looks much easier.