[organosurf]

It is postulated that SiO2 facilitates the ionic addition of HBr to an alkene according to Markovnikov’s rule, in the article given at :
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532001000500013
In the article, Scheme  1, PBr3 is used as an indirect hydrobrominating reagent, reacting with H2O ( 3 moles ):

PBr3  +  3H2O  3HBr  +  H3PO3

Now, if anhydrous conditions are used, where is the water coming from ?
Can it be assumed that the water is from the water of crystallization present in SiO2 ?
Or, is the SiO2 “moistened” prior to use ?

SiO2.3H2O   +   PBr3    3HBr  +  H3PO3    ??

Referring to the article, check Reference No 15 that states the “moisture” content of SiO2.
( ca 15% w/w )

Judging by the high quantity of SiO2 used, compared to the quantity of substrate, it appears that the role of SiO2 is 2 fold :

a ) Carrier of H2O ( moistening prior to use or inherent  as water of crystallization ).
b ) Mediation of Hydrobromination ( surface active mechanism )

The Authors of the article state that SiO2 facilitates the addition of HBr to an alkene, by increasing the  rate and yield of reaction, but do not give the exact mechanism of the reaction.

QUESTION 1 : SiO2 appears to favor Markovnikov ionic additions of HBr to an alkene.
                          Will SiO2 also facilitate the free radical addition of HBr ( via Br* free radical  ) to an
                         alkene, according to anti-Markovnikov’s rule, using organic peroxide / UV / Heat ?

QUESTION 2 : To arrive at anti-Markovnikov product, would it be advisable not to use SiO2 ?

QUESTION 3 : Can other salts having water of crystallization also react the same way with PBr3 ?
                          Assuming thay will not react with HBr.

Please let me know the answers, especially to questions 1 & 2.
Thanks.

[Babcock_Hall]

According to Forum Rules, you must show an attempt first, before we can help you.

[orgopete]

Given that the poster is asking me to predict the outcome of a reaction, I can only imagine that I should be wrong.

I have never done a free radical addition of HBr, but I am going to guess that this reaction would work the best with HBr itself. If I am right, then I might think protonation with sulfuric or phosphoric acid might compete with a free radical reaction.

[organosurf]

I didn't understand Babcock_Hall when he said " According to Forum Rules, you must show an attempt first, before we can help you" 
I wouldn't be posting if I knew the answer would I ? Also, I'am familiar with forum rules; I did try to look for an answer and corresponding examples, but couldn't find any; hence my posting of the question.                                      So I don't understand Babcock_Hall at all. 

Orgopete, thanks for your try, but your answer didn't make sense. I'am talking about HBr gas, SiO2, alkene, free radical addition with respect to anti-Markovnikov's rule.
If you read the post carefully, I have not mentioned any sulfuric or phosphoric acid, so the question of competing protonation does not arise. 

[Babcock_Hall]

organosurf,

Attempting a problem does not necessarily imply that you have the correct answer, only that you tried.  There is a red sentence near the top of most pages here that reads: "Forum rules: read this before posting." It is a link that leads to this page:  http://www.chemicalforums.com/index.php?topic=65859.0
Part of the rules page says,
"In short:
don't discuss drugs nor explosives synthesis or preparation,
whenever asking questions show you have already tried to solve them on your own,
whenever helping others, help them solve the questions on their own and don't give the final answers,
don't post crackpottery,
follow netiquette –  be nice, use plain English, pay attention to formatting of your posts, use informative thread subjects."
(bolding mine)

It was not clear from your OP which part was the problem, and which part (if any) was your answer.

[orgopete]

In the article, Scheme  1, PBr3 is used as an indirect hydrobrominating reagent, reacting with H2O ( 3 moles ):

PBr3  +  3H2O  3HBr  +  H3PO3.

@orgosurf, I thought you would recognize the presence of phosphoric acid. I thought this may result in more Marknikov addition.