chemrox - 30-6-2009 at 16:15
Have been working through a published procedure for making phenyl-2-bromopropane from allylbenzene (Carter, HE, J Biol Chem, 108, 619 (1935) via
erowid). It is a Makovnikov hydrohalogenation using HBr/GAA. The procedure had me put the reagents in a bottle and shake every once in awhile.
After 10-12 hrs the "original two layers merged into a clear red solution."
Well after 24 hours its a purple solution with a yellowish one on top of about 1/5 the volume of the purple. I dropped in a stir bar and put it on
the mixer. The only changes I made were to adjust ingredients to 90 g of allylbenzene in place of 100 and a 1000 ml bottle was used instead of a 500
ml. That made 180 g GAA/135g HBr (48%). I combined them cooled with an ice bath and let the bottle rise to room temp after, stoppered as per
process. For now its on the stirrer at least overnight. Any ideas? Experience? Insights?
[Edited on 1-7-2009 by chemrox]
[Edited on 1-7-2009 by chemrox]
stoichiometric_steve - 30-6-2009 at 23:15
Would it be possible that the original procedure used HBr gas in GAA, so the water you added with the 48% HBr would make your product at least
partially immiscible?
Sauron - 1-7-2009 at 00:05
J Biol Chem is free online all the way bacl to the start.
HBr (g) is soluble in GAA to 6N or more. Often used as a peptide reagent.
I obtained the Carter paper from JVC site, indeed as steve surmised it is very clearly HBr (g) 150 g dissolved in 200 g GAA (starting weight) for a
total mass 350 g.
FW HBr 81 so 150 g is 1,8 mols so solution is approx 9 M whoch is reasonable.
Readin the instruction as 150 g HBr in 50 g GAA for total 200 g leads to an absurd molarity of 36.
NOT HBr aq 48% w;/w in GAA.
Fisher sells 33% w/w HBr in GAA at a reasonable price.
But this stoff is a lot stronger.
[Edited on 1-7-2009 by Sauron]
[Edited on 1-7-09 by The_Davster]
The_Davster - 1-7-2009 at 13:22
How about keeping it on topic? Irrelevant crap has been deleted.
chemrox - 1-7-2009 at 15:44
@Sauron- I sure missed that one. I wonder if one could accomplish the conversion to ph-2-Cl-propane by way of commercially available HCl in GAA? At
least HCl is an easy generator to rig up. Entropy: chemrox has zero interest in red neck nose candies. He likes your writing style tho...
Sauron - 1-7-2009 at 18:21
What's the molarity of commercially available HCl in GAA?
Commercial HBr in GAA (Acros) is 33 wt% and so 330 g/ = 4 M and change, you want 9 M. I have not adjusted for density of GAA which is not a numer I
keep on my head. I seem to recall 6 M being available. But you need 9 M.
HBr is not that hard to generate, NaBr and H3PO4 ought to do it with an H2SO4 scrubber for water.
not_important - 1-7-2009 at 21:25
You'll lose some HBr doing that
2HBr + H2SO4 => Br2 + 2 H2O + SO2
the reverse of one process to make HBr(aq)
CaBr2 is used, I believe someone posted a reference that stated only a small amount of halogen exchage happens between CaCl2 and HBr(g). Concentrated
H3PO4 can be used, better H3PO4 on an absorbent such as perlite and heated high enough to generate poly- and even meta- phosphoric acids.
Sauron - 1-7-2009 at 21:33
The loss of HBr in H2SO4 is minimal to nonexistant if the wash bottle is kept cool. He nust needs a few hundred g HB2, after all.
DJF90 - 1-7-2009 at 22:45
It appears from the first post that he only needs 135g of HBr, and so using conc sulfuric acid in a washbottle submersed in ice water will be fine.
85% H3PO4 should be fine for generation of HBr with NaBr or KBr. I seem to recall that the liberation of bromine from H2SO4/HBr only occurs at
~>70*C, and this was experimental data from another thread here on making 48% HBr(aq).
entropy51 - 2-7-2009 at 14:22
Attachment: HBr Patent 2705670.pdf (172kB)
This file has been downloaded 721 times
Sauron - 2-7-2009 at 22:46
Easy to try it.
A reactor with stirrer on a mantle, a thermometer, a trap against suckback and a receiver with either GAA or water amd a gas dispersion tube.
jon - 7-7-2009 at 17:59
do this make the hbr insitu in acetic acid. works great the only quirk is that no, you just leave it be don't try to get it to merge, you are not
staring at two phases just let it be.
reason is
the nahso4 sits in the bottom as a yellow colored salt.
if one were to agitate it it would entrain some of the product.
expirimentation has proven 24-30 hrs in the freeze leave it be.
strive for 40% conc. you see all of the color changes and the sweet aroma don't know what you are brominating, mileage varies.
[Edited on 8-7-2009 by jon]