Removing water to form acid anhydrides

This synthesis can produce either a symmetric anhydride (both acids the same) or an asymmetric anhydride (different acids). 

The reaction of sodium salt of carboxylic acid (sodium formate) with acid chloride. 

Adit plus acid chloride plus pyridine 

Acid anhydride formed by the reaction of acid chloride with carboxylic acid inthe presence of pyridine. 

Formation of acid anhydride by the reaction of carboxylic acid with acetic anhydride. 

Acid plus acid chtoride plus pyridine 

---