[Richard Jeong]

If tosyl chloride is added to carboxylic acid(or carboxylate salt),
I wonder whether this will happen;
1. sp3-hybridized oxygen on carboxylic acid attacks tosyl sulfur
2. chloride takes off
3. chloride attacks proton on the oxygen
4. final product: hydrochloric acid+"tosylate" ester
5. since HCl and tosylic acid pKa is almost same, equilibrium perhaps?

[rolnor]

I think you are right and if you want to get the mixed anhydride you can add some base like triethylamine, if you run the the reaction in ether the trietylaminehydrochloride would precipitate so you can filter and get the pure mixed anhydride.