Sciencemadness Discussion Board - Photoreaction of Br2 and Benzoyl peroxide?

Photoreaction of Br2 and Benzoyl peroxide?

swintarka - 20-1-2014 at 10:50

Hi everyone!

I was wondering if mixture of Br2 and benzoyl peroxide would yield benzoyl bromide and oxygen upon irradiation with visible light? If no, then what products would be formed?

This is a purely theoretical question, that has been bothering me from some time.

I am acutely conscious that this reaction could be potentially very dangerous and result in sudden explosion and spreading of highly toxic gases and should not be attempted without appropriate shielding and other precautions.

Thanks for any help.

[Edited on 20-1-2014 by swintarka]

Nicodem - 20-1-2014 at 11:15

Quote: Originally posted by swintarka

I was wondering if mixture of Br2 and benzoyl peroxide would yield benzoyl bromide and oxygen upon irradiation with visible light?

I don't see any mechanism for such a decomposition. What references do you have for suggesting it that way?
The most likely pathway is via the benzoyl peroxide homolysis which would yield bromobenzene and CO₂ as the prevalent products (and probably a few others). For example, the thermal reaction between Bz₂O₂ and I₂ in benzene gives a mixture of iodobenzene, phenyl benzoate (probably via the reaction with the solvent) and benzoic acid (see DOI: 10.1039/P29830000711). With an inert solvent solvent, the iodobenzene would probably be the major product. The thermal decomposition of Bz₂O₂ proceeds homolytically just like the photochemical one, so it should make little difference.

Welcome to the forum and please read the forum guidelines. Also, open topics without references and other beginner's questions only in the Beginnings section.

swintarka - 21-1-2014 at 11:59

Thanks!
I should've thought about radical decarboxylation.

chornedsnorkack - 23-1-2014 at 06:38

So what would the mechanism be?
1)C6H5-CO-O-O-CO-C6H5 ->2 C6H5-CO-O. because the weak bond is O-O bond, not the C-OO bond, so no benzoyl radical should be formed;
(x2) C6H5-CO-O. + Br2 - no reaction, right? Hypobromite anhydride should be an unfavourable reaction product
2) C6H5-CO-O. -> C6H5. + CO2... somehow a favourable reaction
3) C6H5. + Br2 -> C6H5Br+Br.
What next? Does Br atom remain stable till another phenyl radical forms, or is it active enough to attack benzoyl peroxide by radical substitution or addition?