[curiouscat]

What are some conditions, ideas etc. that may allow me to maximize yield of product Y in the scheme below starting from X? Boiling (100 to 120 C) under aq. (acidic, HCl) conditions does work, but a fair bit of undesired product Z is also formed.

Before starting a brute force experimental optimization by varying P, T, time etc. I wanted to see if there are any ideas / heuristics. One idea was reducing the acidity as it may be pushing the X  Y reaction backwards, since I assume that reaction involves elimination of the acid?   Anything else that might be worth a shot?

[discodermolide]

How about adding hypochlorus acid to styrene?

[curiouscat]

How about adding hypochlorus acid to styrene?

Hmm...not sure what you mean. Doing what you describe ends up giving a mix of X & Y .  Which is how I end up with the problem of having to convert the unwanted X (~15%) into Y in the first place.

Unless there was a way to not make any X at all to start with?

[Nikola95]

What regioisomer do you need? 2-phenyl-2-chloroethanol, or 2-chloro-1-phenylethanol? Anyway, your current approach is really bad. I would first cook X in KOH/EtOH solution to get styrene, than do a simple extraction to isolate it(doesn`t have to be particularly pure), then treat this with chlorine water. Yield will be much better.

[discodermolide]

I think you will end up with the chlorohydrin mixture, if you leave it long enough

[discodermolide]

Perhaps you need to check the quality of the bleach?

[curiouscat]

I think you will end up with the chlorohydrin mixture, if you leave it long enough

It's not looking like it. I mean yes, the chlohydrin is indeed the major product but I see ~5-10% of  Z. The longer you wait the more of Z I seem to get. With time, X reduces but both Y & Z increase.

[discodermolide]

Try buffering the reaction at say pH3-4 (guesstimate here).
Have you any info. about pH effects on this system?

[Nikola95]

I think what happens is that in excess of acid, free H⁺ ions protonate your chlorohydrine, then Cl^- attacks it and SN2 takes place, so that`s how you get X back again, as for the Z it`s obvious. What you should do is quench the reaction with some base and ice as soon as that starts to happen. Why don`t you listen to me and go via the styrene path? Also, I think your reaction temperature is way too high, that`s why elimination takes place and yield is lower due to SN2 increased possibility.

[curiouscat]

What regioisomer do you need? 2-phenyl-2-chloroethanol, or 2-chloro-1-phenylethanol?

Either one really. Next step is epoxidation which I think happens equally well from either isomer. But we seem to get mostly the 2-chloro-1-phenyl isomer I think.

Anyway, your current approach is really bad.

Why? Can you elaborate?

I would first cook X in KOH/EtOH solution to get styrene,

X was gotten from Styrene in the first place via haloydration as a byproduct while making Y. You want me to convert X back to Styrene?

than do a simple extraction to isolate it(doesn`t have to be particularly pure), then treat this with chlorine water. Yield will be much better.

Styrene treated with Chlorine Water will give exclusively Y with no X by product?

[curiouscat]

Perhaps you need to check the quality of the bleach?

Ah! Not using bleach. Using H2O2 + HCl

[discodermolide]

How does the pH affect this reaction?

[curiouscat]

Try buffering the reaction at say pH3-4 (guesstimate here).

Will do. Thanks for the tip.

Have you any info. about pH effects on this system?

Not off the top of my head, no. I will look. Mostly there's always free excess HCl at the end. Around 5% so pH was always less than 1  for whatever experiments have been done.

Unless I use a buffer it'd be hard to move pH above 1. So far have never thought of using a buffer.

[Nikola95]

Well, if you had styrene in the first place, there is a much better method for a direct epoxidation with 94 % conversion, and 100 % selectivity. No need to bother with chlorohydrin.

Refer to:

http://www.tandfonline.com/doi/abs/10.1080/15533174.2012.750352#.Uu6x9_ldWT8

[Nikola95]

Styrene treated with Chlorine Water will give exclusively Y with no X by product?

Sure it will give some X, but you can reduce a chance for that happening by adding more water. A stupid idea just came to my mind, don`t believe it would work, but adding some siver(I) salt might increase your yield, so that you don`t have to go through trouble of diluting the mixture... Ag⁺ might catch those free Cl^- ions and increase the probability of H₂O attacking chloronium species.