To make N-acyl cysteine octanoyl chloride surfactant, I have to dissolve cysteine in water/NaOH (to trap formed HCl) which hydrolysis octanoyl chloride. This hydrolysis decreases the surfactant yield.
We CANNOT stop hydrolysis of an acyl chloride in aqueous solution because the acid chloride is highly reactive with water. You can prepare N-acyl cysteine octanoyl chloride from N-acyl cysteine octanoic acid by refluxing the latter with thionyl chloride SOCl2 . If there is need to trap HCl, this can be done by various ways (other than aq.NaOH) such as using pyridine , triethylamine... etc. " just a weak base".
You can try to do the reaction in THF. Add TEA as base to your amino acid in THF. Allow to stir for a while (30 min) and then add your stoichiometric amount of your octanoyl chloride followed by a catalytic amount of DMAP. Then reflux for 18 hours. I have used this method for the synthesis of N-acyl compounds of phenylalanine and tyrosine and it works.
Dear Nizar,
I did the experiment as per your suggestion but couldn't get the compound. Seems that weak bases are not strong enough to trap the formed HCl and also aminolysis reaction is an exothermic reaction so heating the solution with refluxing is a barrier to get the product.
Dear Nausheen
Carefully doing the experiment, I've found that octanoyl chloride is more reactive with TEA than cysteine, which has a very low solubility in THF. So this reaction just gives octanoyl TEA surfactant white precipitate which is soluble in acidic pHs while octanoyl cysteine should precipate out at acidic pHs!
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