[fox]

Hi all, first post, although i've been around for some time.

I'm having a lot of trouble preparing a monohalogenated ring. I use diethoxybenzene and tryed through several workups including NBS and NaBrO3/NaHNO3 for monobromination and also some different workups for monoiodonation such as KI/KIO3 .

None worked, and sometimes no product would even form...

The closest that i got was with a reflux using the KI/KIO3 workup.

Literature reports up to 80% yield in some cases, but i didn't even get the product.

Used 1H and 13C NMR and of course ESI MS

[Dude]

Presumably, you are starting with 1,4-diethoxybenzene (para) and want to make 1,4-diethoxy-2-bromobenzene.  Without any other information, it is assumed that you are likely generating polybrominated product (since ethoxy groups should react quickly towards aromatic electrophilic sub.) but no monobrominated product (are you getting your original product back or has it changed? -the NMR and MS should provide evidence if any bromination occurred).  If polybromination is the case, then reducing the time and/or temperature would be your only variables to minimize halogenation and the yields might still not get anywhere near 80 %.  If you are not reacting at all, then you should switch bromination reagents (Br2 / Fe for example).

[fox]

Yes, i'm sorry for the small information, i am starting from p-diethoxybenzene and trying to get 1,4-dietoxi-2-bromobenzene.

NMR data shows the ethoxy protons with nice integration ratio, and coupling data is also OK.

Most of the time i get my product back, but with some reflux or just with over night stirring at RT i get a nice conversion rate.

The last product that i got, the 1H NMR showed that something had happened to my aromatic protons, meaning that the integration ration was now good and the coupling and splitting of the initial aromatic peak did occour.

Can you elaborate on that Br2/Fe workup?

Oh and thank very much for your quick reply!

[movies]

NBS doesn't work for aromatic bromination, at least not very well.

In our lab, the favored conditions are Br₂ + acetic acid.  A co-worker of mine has had good success with that on similar substrates.  I can't recall whether he was trying to brominate twice though.

[ksr985]

Ive used Br2 in glacial acetic acid for monobromination of acetanilide. I think this is the most suitable reagent for monobromination.

It gives a very high yield.

[fox]

OK, ty very much for your replys, will try the Br2 plus CH3COOH tomorrow!

[fox]

well finally managed to get it.

Just left it through the night with 2eq of NBS and puff, there i got it, a brown oil with clear EI-MS M+ peak and 1H and 13C all OK...

Of course there is some dibromide compound, but it's a dead compound for the next synthesis.

Thank you very much.