[curiouscat]

What are the main byproducts of the reaction? That should shed some light on the mechanism.

Benzaldehyde and   seem the major by-products that we see.  Some very little   too. 

There's some stuff that we haven't identified yet.

[magician4]

1,2-dichlorphenylethane clearly speaking for the addition of chlorine to styrene*⁾, benzaldehyde i.m.h.o. doesn't favour any of the mechanisms discussed sofar

beats me how that might be formed from styrene, esp. as I would expect it to become further oxidized towards benzoic acid under those conditions... **⁾

regards

Ingo

*⁾
from the redox-reaction H₂O₂, HCl --> H₂O , Cl₂ discussed previously

**⁾
it would require ozone (or something that behaves like it) to result this product, and I don't see how we should get  this form the setup

[curiouscat]

beats me how that might be formed from styrene, esp. as I would expect it to become further oxidized towards benzoic acid under those conditions... **⁾


**⁾
it would require ozone (or something that behaves like it) to result this product, and I don't see how we should get  this form the setup

I'm not sure myself! Good point.

I remember @opsomath mentioned Benzoic Acid in a related post. May be he has an idea how.

Would Benzoic Acid partition out into the aqueous phase? I have only noticed benzaldehyde as a by-product.

[magician4]

Would Benzoic Acid partition out into the aqueous phase?

benzoic acid is very poorly soluble in neutral / acid waterbased systems (2.9 g/L , 25°C) , though its solubility is acceptable under basic conditions (as the corresponding anion, that is)

hence, depending on your very concentrations, it MIGHT partition out more or less completely, yes


regards

Ingo

[Archer]

I would say that this is the mechanism.

Hypochlorous acid would not be ionised at low pH and is formed in equlibrium with Cl₂ when water and chlorine are mixed.

The same reaction happens if you mix chlorine with an alcohol but, obviously, you make the ether insted of the hydroxyl group.

[opsomath]

I thought the mechanism for the chlorine/alcohol addition was solvolysis of the chloronium ion, not formation of alkyl hypochlorite.

[Archer]

I would think so too on paper but then the alcohol would attack the least hindered carbon. In practice it doesn't, the chlorine is attached to the least hindered carbon.

[Archer]

I have a quote here from March Advanced Organic Chemistry 4th Edition p 815

"The mechanism of HOX addition is electrophillic, with initial attack by the positive halogen end of the HOX dipole. Following Markovnikov's rule, the positive halogen goes to the side of the double bond that has more hydrogens. The resulting carbocation reacts with the OH^- or H₂O to give the product."

[magician4]

@ Archer:

Hypochlorous acid would not be ionised at low pH and is formed in equlibrium with Cl2 when water and chlorine are mixed.

agreed, but...

under acid conditions named equilibrium will be shifted far far towards Cl₂/H2O

additionally , how the relatively weak and at the same time low-concentrated HOCl should win the race vs. Cl₂ with respect to the attack of the doublebond  I don't see

@ opsomath

I thought the mechanism for the chlorine/alcohol addition was solvolysis of the chloronium ion, not formation of alkyl hypochlorite.

...witch opens another pathway to the known product

regards

Ingo

[curiouscat]

under acid conditions named equilibrium will be shifted far far towards Cl₂/H2O

additionally , how the relatively weak and at the same time low-concentrated HOCl should win the race vs. Cl₂ with respect to the attack of the doublebond  I don't see

Exactly what I wondered when I first saw this proposal! But I assure you we get fairly decent selectivity to the halohydrin.

Could it be that the Cl2 does win, the chlorinated product forms, and it subsequently hydrolysed  in situ to the halohydrin by the HCl present?

PS. Thanks all of you for the very interesting discussion BTW. Appreciate your insights! Being an Engineer, the minutiae of mechanisms isn't my forte.

[Archer]

under acid conditions named equilibrium will be shifted far far towards Cl₂/H2O

additionally , how the relatively weak and at the same time low-concentrated HOCl should win the race vs. Cl₂ with respect to the attack of the doublebond  I don't see

To quote March again (same page) "HOCl is often generated in situ by the reaction between water and Cl₂"

Don't forget that Cl₂ has a much weaker dipole than HOCl so in this reaction there would be far less "Cl⁺" with Cl₂ than with HOCl.

I am basing my statements on data I have collected and books that I have read and can reference. 

If you wish to poropose an alternative mechanism which is in contrast to experimental data and published theories then I can't really win a debate so can't offer much more to this discussion.

[Archer]

Could it be that the Cl2 does win, the chlorinated product forms, and it subsequently hydrolysed  in situ to the halohydrin by the HCl present?

This is unlikely as it would be attacking a very hindered carbon to give your product. The primary alcohol would be favoured if this were the case.

[magician4]

Could it be that the Cl2 does win, the chlorinated product forms, and it subsequently hydrolysed  in situ to the halohydrin by the HCl present?

I take it that we should allow for several parallel mechanisms to occur: both the chlorine-pathway (by 1,2 dichlorphenylethane) and the epoxide-pathway  (by the very epoxide being observed) are supported by your findings of by-products, and the addition of HOCl of course is an option, too
question is: which of the possible pathways is the most relevant ?

as part of the chlorine-additon pathway:
for the "Cl₂ wins" - scenario both your addition / hydrolysis mechanism as as (in my opinion more plausible) the direct reaction of the initial chloronium-ion*⁾ with water will lead to your product

so many ways lead to Rome....


regards

Ingo


*⁾
chlorination under these conditions is an electrophilic addition of Cl^δ+-Cl^δ-, and will take place as a 2-step reaction, where in the second step the benzylic cation is attacked by whatever nucleophile wins the race: water or chloride in this case are likely candidates
however, benzylhalogenides (i.e. the chloride-anion is the winner) are known to be moisture-sensitive with respect to an X^- /OH^- replacement, so the hydrolysis-pathway also is plausible

[magician4]

To quote March again (same page) "HOCl is often generated in situ by the reaction between water and Cl2"

I take it that you will agree, that the degree of HOCl formation is highly different if I compare the reaction of chlorine with water (March) to the reaction of chlorine with aqueous hydrochloric acid (our setup)

Don't forget that Cl2 has a much weaker dipole than HOCl so in this reaction there would be far less "Cl+" with Cl2 than with HOCl.

I wouldn't want to derive relative reaction velocities from this single aspect: there's so much more to consider, let alone "concentration"

I am basing my statements on data I have collected and books that I have read and can reference. 

so do all of us, i take it, to the best of their knowledge

If you wish to propose an alternative mechanism which is in contrast to experimental data (...)

the experimental data reported sofar by curiouscat explicitly describes the epoxide and the dichloride as known by-products (which your favoured pathway can't explain at all)
if anything, these products support the alternative mechanisms you so fiercely denote as "in contrast to known data"
again: March is talking about water/chlorine, not HCl/chlorine as matrix!
this IS a big difference!

This is unlikely as it would be attacking a very hindered carbon to give your product. The primary alcohol would be favoured if this were the case.

don't forget that we're talking styrene here: in this system the benzylic position is the more stable to harbour the cation
--> I don't agree with your analysis at this point



regards

Ingo

[Archer]

Fair enough.

I would love the oportunity to test these theories experimentally. I think we all agree that this warrants further investigation.

I love this forum, it's good to be challenged on mechanistic chemistry. I would not get this anywhere else. No one where I work tends to discuss such things and my friends generally switch off as soon as I start talking chemistry