in situ HBr in acetic acid

[element109]

If you make in situ HBr in AcOH by reacting KBr and H2SO4, with a small excess of KBr of course, dissolve your olefin in there, 1mol olefin : 2mol HBr, this should brominate it, no?
I'm asking this because I found some contradictionary info about a HBr/AcOH mix cleaving the ether bond. Surely this happens only under increased temperatures?
e109

[Rhodium]

The problem is that HBr cannot be generated by KBr/H2SO4 satisfactorily, some Br2 is formed. UTFSE on the reaction of dillapiole with HBr to find a good method. The Uncle Fester method (found at my page) using HBr dehydrated with dry HCl gas also works.

[PolytheneSam]

How about phosphoric acid and KBr?  If you don't have phosphoric acid maybe you could make it in situ using calcium phosphate and sulfuric acid.
http://www.geocities.com/dritte123/PSPF.html
The hardest thing to explain is the obvious

[element109]

Yes, I noticed that the solution is coloured yellow. Perhaps H3PO4 would be better then?

I did a run on TFSE on dillapiole but didn't found it.



e109

[Rhodium]

This thread;

Post 22772

(Osmium: "Bromosafrole breakthrough?", Serious Chemistry)

[ChemicalSolution]

The DMSO/KBr method is, for sure, easier.. But how do the yields compare?

Has anybee distilled bromosafrole before???  details???

[hsark]

Yes lots and lots of times. The problem is in the end of the distllation you tend to get a volcano of black ash and smoke even if your careful. Ive been wanting to say this for a long while the 33% HBr in AA is the best to use. You can get 90 to 95% yields in 12 to 16 hours. Even though i was told 24. and you can just leave it in the freezer. although an ice chest works just fine.(with lots of ice.)when you distill it just be ready to disconnect it and have something to dump it in. And whatever you do save whats in the recieving side.

[Rhodium]

hsark: Tell us more! How did you prepare the HBr/AA (is that Ac2O or HOAc?), what was the distillation temperature and pressure, properties of the distilled bromosafrole etc?

[hsark]

Manly i used to buy the 33% in AA from a chem suply. But i also used to buy the anh.HBr in cylinders and would make the solution myself. Bolth worked great. The main problem is i dont know how easy it is to get now for some. I dont have that problem. At around 20 torr. The bromo would start distill at 175 to 185. and would continue to rise slowly until it reached 212°. at 212° decomposition. i generally  would stop at 205° but some times it decomposes even if your careful. i suggest be prepared and check for vac. leaks very carefully. it is generaly a reddish-brown transparent very nice, sweat smelling oil.

[Rhodium]

Sweat- or sweet-smelling? I guess the latter. Finally, what proportions of HBr to safrole did you use?

[hsark]

Thats sweet. unless you think sweat is very nice   . J/J the proportions were 1L 33% HBr in acetic acid to 450ml safrole.

[otto]

hi hsark,

your results look very promising. what about the amination step? did you ever run it? otto was very sad when some alpha-methoxy-beta-bromophenylpropane didnt react in methanolic NH3 @110°C for 16 hours (pressure tube).

otto

[Ritter]

I've distilled quite a bit of bromosaf myself, and can tell you that a stronger vacuum will prevent that rapid charcoal-decomposition-volcano from occurring.  The decomposition is occuring because the still pot is getting WAY too hot.  When you only have a few ml's left in the still pot (about 50), cool it down and transfer the remaining liquid to a smaller 100ml flask.  This should allow distillation of the last traces of bromosaf without a problem. 

That charcoal volcano really sucks, I learned about that the hard way.  It actually shot all the way through my vacuum jacketed vigreux and into the condensor and ruined the $350 still

[hsark]

I used to use the "pipe bomb" method for the reaction buy bubling  NH3 in to methanol. Then moved to isopropanol. It seemed to work better. I would run the reaction at 130 deg C for 3 hours. Mybe you cooked it to long ,but im not sure. a,but 110 worked when i didnt pay attention one time. I am now trying to reasearch better methods because the "pipe bomb" yields are just to low. I just finished the alaquat 336 and sncl method and im not real happy with it but i didnt distill the azide so its probably my own fault.But it wasstill beter than the "pipe bomb".
     
Thanks for the info herr Ritter on the over heating. And i have someone looking for the info you gave me the other day. But where im at i dont think i have access to it. I tried to search on the web but all the journals require membership i dont have. Or i just dont know how to do it. Can you help?       

[element109]

From Post No. 23995:

reaction of o-allylphenols (12,15) with HBr-AcOH
      aqueous Hbr (48% .2ml) was added to a solution of the phenol 12 (100mg)
in gl. AcHO (1ml) till the whole mixture became turbid.  The mixture was
warmed on a water bathe for 30-45 min at 50-60 c., diluted with water (10 ml)
and fractionated into phenolic and neutral portions. "

It cleaved the MD bond with light heating, but when kept cool, on the ice-bath, this should be of no concern.

45 saf : 100 33% HBr/AcOH and distilling with high vacuum;
followed by Finkelstein reaction (NaI in acetone) and then methylamine or a Gabriel synth, or even Delepine but I ain't going to mess around with the pipe-bomb, 'cause yields are just too low.


e109

[PrimoPyro]

You do the Finkelstein reaction in acetone?

But sodium iodide bonds with ketones forming large molecular weight insoluble adduct precipitates. This is very peculiar to me.

                                                   PrimoPyro
Vivent Longtemps La Ruche!

[element109]

Huh? Isn't it always performed in acetone? I haven't performed it myself, but I am 99.95% sure that the reaction medium is acetone.

I'll look up the original article.

e109

[Rhodium]

The Finkelstein reaction is always done in acetone, I guess the acetone/NaI complex is soluble in acetone, or that it does not form with low molecular weight ketones. I have wondered about that myself, PP.

[element109]

yes, I remember NaI was being suggested as an alternative for NaHSO3 for MDP2P purification

e109

[PrimoPyro]

I know it bonds with acetone. There is a reference on your site, that cites Vogel as the original reference, and Vogel gives the example as the purification of acetone by crystallization of the adduct of the ketone and sodium iodide, followed by decomposing the adduct with heat.

I would think that for the crystallization, perhaps that is why the ketone is solvated, rather than NaI being added to the crude ketone itself.

                                                    PrimoPyro
Vivent Longtemps La Ruche!