[enkay]

Hi !

I'm trying Bromination of 4-Phenyl Butyric acid to get 2(alpha)-Bromo-4-Phenylbutyric acid. 

Is this synthesis possible using Bromine liq. & 4-Phenylbutyric acid with any procedure ? 

Awaiting your replies !




Thanks in advance,
Enkay 

[AWK]

see:
http://www.organic-chemistry.org/namedreactions/hell-volhard-zelinsky-reaction.shtm

[lavoisier]

Try this:

Organic Syntheses, Coll. Vol. 4, p.616 (1963); Vol. 38, p.47 (1958).

available free of charge at www.orgsyn.org

There are loads of similar procedures in orgsyn.

[enkay]

Thanks to both of you !

One more question, (as I also read somewhere using PCl3) can I use PCl3 instead of PBr3 as it is readily available for me..?

[lavoisier]

Yes, you can, and if you look in orgsyn you will find other procedures where PCl3 is used in place of PBr3.

[enkay]

Okay !

I'll try this & let you inform my results soon ! 


 

[enkay]

I started putting this reaction but one more point to be clarified....

As per this ORGSYN process, Br2 has been used in 2 moles eq. making one CH2 to CHBr & also COOH to COBr. But in my case I want only the CHBr, keeping COOH unaffected. So, here what should I do ? taking one mole eq. of Br2 ? 

Besides, PBr3 should be used on catalytic amount or molar eq. ? (in orgsyn eq. amount is used)

Awaiting your reply....



ENKAY

[AWK]

Bromination goes only for an acyl halides. After bromination you should decompose acyl bromide, though, usually this is an intermediate for further synthesis. Decomposition is very easy - add some water.

[enkay]

I made this bromoacid (alpha-bromo-4-phenylbutyric acid) using Br2, 4-Phenylbutyric acid & PBr3 (cat.) using this procedure : http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0115

Here I think, the alpha-bromination goes easily only to COOH according to this route (Not sure).

But here, a big question : Is this bromination procedure can keep the phenyl ring unbrominated ?

What you all think ?

[lavoisier]

I made this bromoacid (alpha-bromo-4-phenylbutyric acid) using Br2, 4-Phenylbutyric acid & PBr3 (cat.) using this procedure : http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0115

Here I think, the alpha-bromination goes easily only to COOH according to this route (Not sure).

First, I guess you mean 'alpha to COOH' and not 'to COOH'. And why aren't you sure?

Concerning your question, very few organic reactions are strictly selective, yielding just one product with absolutely no interference. We usually rely on carefully chosen conditions to prevent side reactions from occurring.

In your case, having PhCH2CH2CH2COOH and Br2 around could make you think of at least two competing reactions:
1 - aromatic electrophylic halogenation (on Ph)
2 - free-radical benzylic halogenation (on the CH2 attached to Ph)
However, for side reaction 1 you would need some Lewis acid to activate the halogen. I think PCl3 or PBr3 are not going to do that, at least not as efficiently as AlBr3, AlCl3...
For side reaction 2 you need atomic bromine, which is generated by the action of UV light on Br2. Maybe you want to avoid exposing your reaction flask to sunlight or to strong artificial light (a good old aluminum foil around it will do the job).

Anyway, I think orgsyn describes some procedures of HVZ bromination on n-phenyl-carboxylic acids. If competing processes mean you get a lower yield, well, either accept it or try a different route...

[cvrlik]

One more question, (as I also read somewhere using PCl3) can I use PCl3 instead of PBr3 as it is readily available for me..?

Just running bromination of caproic acid....
I did not have PCl3 so I used PCl5. What do you think?

[Babcock_Hall]

There is at least one earlier thread on the Hell-Volhard-Zelinski reaction:  http://www.chemicalforums.com/index.php?topic=60541.msg216355#msg216355

[cvrlik]

One more question, (as I also read somewhere using PCl3) can I use PCl3 instead of PBr3 as it is readily available for me..?

Just running bromination of caproic acid....
I did not have PCl3 so I used PCl5. What do you think?

update:
conversion 100%
GC 89% crude product...