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All 4 posts   Subject: PAA by chlorination of styrene or PhEt   Please login to post   Down

(Wonderful Personality)
11-14-04 00:00
No 541445
      PAA by chlorination of styrene or PhEt     

Thus was dig up by Polverone:

Hydrolysis of chlorinated styrene - a new route for the synthesis of phenylacetic acid and a-ethoxyphenylacetic acid.
Lanchow University, Dep. Chem., Lanchow, Peop. Rep. China. Huaxue Xuebao (1976), 34(4), 295-300. CODEN: HHHPA4 ISSN: 0567-7351. Journal written in Chinese. CAN 88:104848 AN 1978:104848 CAPLUS

Chlorination of styrene in the presence of Bz2O2 at 100-10° gave 12 chlorinated products, which on alk. hydrolysis in alc. gave PhCH2CO2H, PhCH(OEt)CO2H and BzOH in 56-63, 7 and 0.6% yield, resp. Chlorination of PhEt gave similar products, and esterification of the crude acidic products gave 53.4% PhCH2CO2Et.

Can somebody get the article?
Maybee there is a chance to get it translated.

It is not understandable to me how this is going to work. All literature states that styrene is favorably chlorinated at alpha-position by chlorine. I found that HBr and Bz2O2 with a suitable cosolvent yields beta-bromoethylbenzene at 95°C in good yields, but this is told to reacts with bromine to dibromostyrene. frown
But I may have overlooked something.

I am sure the solvent to use is essential, benzene might be suitable.

A question on the hydrolysis:
"Alkaline hydrolysis in alcohol" does this say NaOH/KOH in anhydrous alcohol or NaOH/KOH in water in the presence of alcohol?
The sideproduct PhCH(OEt) makes me think its without water, but hey, I think says I dont know..... smile

Nevertheless, if its possible to get this working, it would provide a quite simple way from styrene to PAA without the stink of hell and the risks of H2S (Ok, chlorine, but thats doable IMHO).


(Hive Bee)
11-14-04 20:45
No 541548
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It is not understandable to me how this is going to work. All literature states that styrene is favorably chlorinated at alpha-position by chlorine.

Perhaps you misinterpreted it with a HCl addition?
A reaction of styrene with Cl2 should proceed mainly like this in the first step:

Ph-CH=CH2 + Cl2  ==>  Ph-CHCl-CH2Cl

Given the presence of a radical initiator and the temperature of 100°C the next step should be a radical chlorination of the side chain:

Ph-CHCl-CH2Cl + Cl2  ==>  Ph-CCl2-CH2Cl + HCl

The hydrolisys of such product should proced like this (in steps):

Ph-CCl2-CH2Cl + OH-  ={-Cl-}=>  [Ph-CCl(OH)-CH2Cl] ={-HCl}=>  Ph-CO-CH2Cl  ={+OH-}=>  Ph-CO-CH2OH + Cl-

"Hydroxyphenacyl" should rearrange to phenylacetic acid if the conditions are favorable (high T in strong base - just like those in hydrolisys):

Ph-CO-CH2OH <==> [Ph-C(OH)=CH2OH]  <==>  Ph-CH(OH)-CHO  ={?}=> Ph-CH2-COOH

I'm unsure about the mechanism of the last step (I would expect the necessity of acidic, not basic conditions here), but all the rest up to here is pretty basic chemistry. There are also other possible mechanisms of hydrolysis which however all lead to the same aldehyde.
It might be an interesting use of styrene. Though, to avoid a whole bunch of ring chlorinated and side chain chlorinated products it would bee much wiser to chlorinate acetophenone to phenacylchloride, which can be done very easily by bubling chlorine trough Ph-CO-Me/AcOH solution. No ring chlorination can happen since the ring iz deactivated and furthermore the hydrolysis should bee higher yielding. But unfortunately acetophenone is not as OTC as styrene.

“The real drug-problem is that we need more and better drugs.” – J. Ott
(Hive Addict)
11-14-04 21:05
No 541552
      An interesting proposition.     

An interesting proposition. My idea was similar, something along the lines of Ph-CHCl-CHCl2 -OH--> Ph-CHOH-CH(OH)2 --> Ph-CH=CH(OH)2 --> Ph-CH2-COOH but it seems pretty much a long shot, with the elimination of an hydroxide and all that. There might be information on such a reaction of phenacyl chloride somewhere.

fear fear hate hate
(Wonderful Personality)
11-14-04 21:29
No 541559

Perhaps you misinterpreted it with a HCl addition?

No, I looked this up in "Reactions of monomeric styrenes" which was posted by Rhodium.
Post 488000 (Rhodium: "Styrene references", Stimulants)

The first addition is almost unavoidably alpha as it is told and produces alpha-chlorostyrene:
Ph-CH=CH3 + Cl ------ Ph-CCl=CH3

The second addition is beta and one ends up with alpha-beta-dichlorostyrene:

Its just what I read.

Thanks for the explanaitions in special on the rearrangement, I was confused by the literature and the fact that ethylbenzene to PAA was always told to need chromylchloride - nasty. A procedure for styrene and ethylbenzene as simple, straightforward and basic in chemistry as this, should have surfaced here already I thought.
Shouldnt it? laugh

Nevertheless, now it has.


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