Sciencemadness Discussion Board

anit-markovnikov HBr

thirdharmonic - 1-3-2009 at 18:50

say one were attempting a antimarkovnikov addition to an alkene, like styrene(monomer), and regarded BH3 as too pricey . radical HBr addition is often mentioned in texts but as a synthetic route how is it practically done?

is it done in aqueous HBr? what concentrations, temps? what peroxides work best as initiators and what sort of concentrations?

does UV penetrate deep eneough into water to help initiate?

is my hyposthesis that BH3 is pricey correct or have i just been looking in the wrong places....i think going rates ~$300 for like .3L 10% if i remember right

danke, kamsamnida etc.

kclo4 - 1-3-2009 at 19:43

BH3 = Borane.
I don't get what you would be using that for?

Perhaps this may be helpful: http://en.wikipedia.org/wiki/Markovnikov%27s_rule

Also you should be able to find some information about this sort of stuff on the rhodium archives at erowid.

Sauron - 1-3-2009 at 20:10

Are you talking about BH3 in THF?

It's not cheap but neither is in unthinkable.

thirdharmonic - 1-3-2009 at 22:58

yes by bh3 i meant borane /thf stabilized , avg of sources i looked at 1M 1L=$800 or there abouts. seems very expensive relative to radical HBr addition, provided Hbr addition doesnt require "exotic" reaction conditions.

polar aqueous soltions dont seem like they would be supportive of radicals(cuz everything is all charge seperated), so really i was mainly curious if the anti-markinikov reaction happens in Aq HBr or in a less polar solvent

Nicodem - 2-3-2009 at 00:31

There are several examples of radical addition of HBr to styrene in the literature. Why don't you do a literature search first?

PS: I'm moving this thread to Beginnings section due to lack of references.

Sauron - 2-3-2009 at 01:26

I do not know who is quoting you $800/liter.

First of all this is a 1:1 complex of Borane and THF not a solution so molarity is immaterial.

CAS 14044-65-6 Acros 175088000 800 ml <$180 US

See their website

[Edited on 2-3-2009 by Sauron]

gsd - 2-3-2009 at 05:50

Anti Markonikov addition of HBr to alkenes is a free radical reaction in non- aqueous media. It it facilitated by presence of peroxides or UV light ( FR initiators).

eg. When gaseous HBr is bubbled in Allyl Chloride in presence of Benzoyl peroxide, it yields 1-bromo 3-chloro propane, whereas the product expected by Markonikov rule is 2-bromo 1-chloro propane.

gsd

thirdharmonic - 4-3-2009 at 08:58

Quote:
Originally posted by Nicodem
There are several examples of radical addition of HBr to styrene in the literature. Why don't you do a literature search first?

PS: I'm moving this thread to Beginnings section due to lack of references.


aside from google searching , which turned up nothing, and whatever books are in my physical library, i do not have accsess to"the literature", at least not that i know of, but if there is a free online searchable chemistry journal please point it out

thirdharmonic - 4-3-2009 at 09:02

Quote:
Originally posted by Sauron
I do not know who is quoting you $800/liter.

First of all this is a 1:1 complex of Borane and THF not a solution so molarity is immaterial.

CAS 14044-65-6 Acros 175088000 800 ml <$180 US

See their website

[Edited on 2-3-2009 by Sauron]



no, they did mean a 1M solution of borane in thf, (which exists as the complex) i didnt just make that up, so please dont insult my intelligence.