4′-Methylpropiophenone bromination to 2-bromo-4'-methylpropiophenone. Large scale.

[Shehry]

Hi friends, I have preceded the reaction with 60 ml of 4 Methyl propiophenone and rational quantities of HBr and H2O2. however the RM remained red after using half the Qty of H2O2. I, then added the rest of H2O2 and later observed the formation of solids product. I let the RM to rest over night and observed green color in the next morning. I vacuum filtered the RM and got 36 g of product with green tint. i found some green liquid (about 40 ml) at the bottom of filter flask, under the aqueous phase. kindly guide me what the green liquid is, why it is formed, why I have got less product and where I was wrong when conducting the process. Thanks to all.

 

[w2x3f5]

Write the exact amounts of substances that were used in reaction, that is, for hydrogen peroxide, you need to specify the volume and its concentration, as well as for HBr acid. It is also important to know the reaction temperature and other conditions. The more precisely you write what you did, the more precisely you will receive the answer.

 

[Shehry]

Dear Bro, thanks a lot for kind response. I had used 60 ml of 4-Methylpropiophenone mixed with 46 ml of HBr (48 %). took 26 ml of H2O2 (35 %) and added drop wise. However, RM color remained red after adding about 15 ml of H2O2. Even then I had added the rest of per oxide. During initial addition of H2O2,temp. of RM raised too high that made hard to touch the flask, then it was controlled by putting ice cooled water around the flask. after some time, white fluffy solid formed and whole RM was allowed to rest whole night. next morning, green liquid (about 40 ml) was found with the solid product and this liquid was resting at bottom, means it was not soluble in aqueous solution. hopping this info will serve the purpose.

 

[w2x3f5]

Most likely, you ran out of free acid in the reaction and only had bromine, and the acid is known to be a bromination catalyst (stable enolization of the ketone is required throughout the entire bromination). I recommend using additional sulfuric acid to continuously enolize the ketone, the bromine color should disappear quickly during the reaction.

 

[Shehry]

Thanks bro, I will take care next time...once again thanks a lot.

 

[TheVacuumGuy]

This is such a breeze compared to the Br2 route in DCM/Toluene

 

[WillD]

It is strange that it turned out to be granules. But sometimes this happens. If the structure is more crystalline, then the final product will be easier to crystallize.

 

[TheVacuumGuy]

Well, I did not follow the procedure 100% which could clarify. I just set it up, adding dropwise and go to sleep. Next morning it was way to hot and I reduced addition. Then 8 hours later noticed that addition has stopped while the mixture was full of crystals and I opened the valve, which added all remaining h2o2 causing vigorous bromine release and heat. I considered it wasted but kept stirring. Eventually turned out all good. I even like the granules since it's easier transferring them, causing less exposure to lachrymatory for me . At least I know it takes a lot to fail this, and that makes it a killer recipe

 

[TheVacuumGuy]

how to get it crystallized? When creating a saturated solution in isopropanol, and letting it stand, the entire content will "crystallize" (with multiple wet inner parts)?

 

[TucoSalamanca.]

Hydrobromic acid 47% I was able to find 47% of this reagent, okay?​

 

[TucoSalamanca.]

how many ml of hydrobromic acid 47% usable

 

[WillD]

You can use about the same amount. The purity of products (4-methylpropiophenone) is not always 99%+, so small errors are possible.
4mp - 1000g
HBr47% - ~800mL (~1100g)
H2O2 - ~300mL (~330g)

It is better to start with such quantities, and do not use excess of reagents, more problems with purifying than you get an additional percentage of an intermediate product.

 

[ifeelsorry]

What if i want to scale it down to 100 or 200ml? How much chemical should i use?

 

[WillD]

change the proportions

 

[Youngchemicals09]

Hello, I tried to make a synthesis according to the method described here, I have a lot of questions. The first time I tried to make a synthesis, the final product came out white almost like in the video. However, with other approaches the final product comes out yellow, I will add that the temperature was kept around 85 degrees Celsius. Does the yellow color indicate that the final product is contaminated? What is the purity of the product from this synthesis? and is recrystallization necessary? If so, what and how to do it? Is final purification of the product necessary? or is the product suitable for further processing without it.

 

[WillD]

At high temperatures, bromine can move to another position. You can get byproducts. Otherwise, recrystallization is not required in this synthesis.

 

[TheVacuumGuy]

Second attempt after the first one which yielded granules.

Best recipe . Just do it in a cold water bath against overheating.

 

[dex]

Yes $!$ , although not for everyone.

 

[TheVacuumGuy]

Yes $!$ , although not for everyone.