[OMED]

Dear all, I really appreciate to get some advices. I am chlorinating one of the COOH groups of a dicharboxylic acid compound. I need to keep other end as a free COOH. For the chlorination I am using SOCl2, it should be done by using 1:1 molar ratio. But it seems to be impossible, would you advise me with an appropriate way to do it.

Thanks

[clarkstill]

This is fairly tricky: if there isn't much interaction between the two acids then you would expect to obtain a statistical mixture of di-acid, mono-acid and di-acid chloride.  Can you post the structure of the diacid?

[Archer]

It is difficult to be selective with many difunctional compounds.

The major issue you will face is the inevitable reaction of the remaining acid group with the acid chloride formed. If the molecule allows intramolecular cyclysation, then this will be a dominant bi-product. If the molecule does not favour cyclysation then you will form an unstable acid anhydride polymer as one of your products.

You need to consider an alternative route, such as replacing one of the acids with, for example, an aldehyde which can be oxidised after you have reacted your acid chloride

All of this is dependent on your molecule and what your ultimate target molecule is.

[kriggy]

you could probably use solid phase synthesis. You lock the one carboxylic group to derivatized resin, then do your reaction and then you cleave it from the resin. By using exces of your acid you reduce the possibility of it being connected to the resin by both COOH groups and then by using excess of SOCl₂ you can get good yields. It however requires some special equipment, chemicals but it might be the best option you have.

[orgopete]

I am chlorinating one of the COOH groups of a dicharboxylic acid compound...would you advise me with an appropriate way to do it.

Could you post your actual problem (not your solution)? Perhaps someone here can think of an alternate not involving a mono-chlorination.