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Topic: Byproducts for halohydrin formation reaction  (Read 3640 times)

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Offline curiouscat

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Byproducts for halohydrin formation reaction
« on: May 27, 2013, 08:22:24 AM »
I'm investigating an industrial reaction where by reacting   c1ccccc1C=C with H2O2 + HCl (with heating) one makes  c1ccccc1C(O)C[Cl].

In terms of byproducts which may I expect? My expectations (partially based on literature searches ) are c1ccccc1C([Cl])C[Cl] and c1c([Cl])cccc1C=C and c1([Cl])ccccc1C=C.

But is there anything else that might be major competition? Am I missing any?

Any strategies to minimize these undesired by products.

Offline orgopete

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Re: Byproducts for halohydrin formation reaction
« Reply #1 on: May 28, 2013, 12:50:47 PM »
I am surprised that aromatic substitution occurs, but I don't know that it does not. The reactions I might expect are further oxidation of the products, the ketone and perhaps the ester. If the ester forms and continued heating under hydrolytic conditions would give phenol. Phenol would be chlorinated or otherwise oxidized. I don't know any of these will occur, just speculation.
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Offline opsomath

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Re: Byproducts for halohydrin formation reaction
« Reply #2 on: May 28, 2013, 02:22:00 PM »
I'm with orgopete, I'd say that over-oxidation is a likely culprit. Benzoic acid?

Not surprised about the aromatic substitution, I think I've seen chlorides + peroxide as a green-chemical chlorinating reagent before. I think with a copper catalyst? Maybe could reduce this if you made sure everything's clean of transition metals.

One other thing; peroxides make radicals, radicals polymerize styrene, or at least cause anti-Markovnikov addition.

Offline curiouscat

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Re: Byproducts for halohydrin formation reaction
« Reply #3 on: May 28, 2013, 02:32:40 PM »
I'm with orgopete, I'd say that over-oxidation is a likely culprit. Benzoic acid?

On further investigation, it seems benzaldehyde was one significant byproduct especially when something goes wrong.


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Not surprised about the aromatic substitution, I think I've seen chlorides + peroxide as a green-chemical chlorinating reagent before. I think with a copper catalyst? Maybe could reduce this if you made sure everything's clean of transition metals.

Thanks. I'll see what I can do. Our plan was test batches  in a Glass Lined Reactor.

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One other thing; peroxides make radicals, radicals polymerize styrene, or at least cause anti-Markovnikov addition.

Yes, especially at 100 C preventing Styrene from polymerizing is going to be challenging.

Offline curiouscat

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Re: Byproducts for halohydrin formation reaction
« Reply #4 on: May 29, 2013, 02:35:29 AM »
Would adding an inhibitor like tert butyl catechol make sense to reduce the undesired self-polymerization?

Or would that be likely to  inhibit my desired reaction too? Is the inhibitor action  a free radical scavenger? Or....?

Offline opsomath

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Re: Byproducts for halohydrin formation reaction
« Reply #5 on: May 29, 2013, 08:42:16 AM »
I think that BHT or whatever would probably react with your peroxide directly. I definitely remember running an oxidation of hydroquinone in peroxide at like 70°C...but that was with iodine catalyst. So I guess my answer is, yes, it makes sense to try, but it may not stand up to the peroxide.

Offline curiouscat

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Re: Byproducts for halohydrin formation reaction
« Reply #6 on: May 29, 2013, 09:58:17 AM »
I think that BHT or whatever would probably react with your peroxide directly. I definitely remember running an oxidation of hydroquinone in peroxide at like 70°C...but that was with iodine catalyst. So I guess my answer is, yes, it makes sense to try, but it may not stand up to the peroxide.

Thanks. It's a tricky problem.

Normally styrene is stored below 30 C to avoid polymerization. Especially above 65 C the risk of highly exothermic runaway polymerization is high. And my desired halohydrin formation (based on most patents) is carried from 80 - 100 C.

So essentially I'm operating much above the self-polymerization kickoff temperature.

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