Heptanoic acid, 1,1'-anhydride

To a flask containing 15.8 gm (0.2 mole) of dry pyridine and 25 ml of dry benzene is rapidly added with stirring 14.8 gm (0.1 mole) of heptanoyl chloride. The reaction is only slightly exothermic and then 13.0 gm (0.1 mole) of heptanoic acid is added dropwise (5 min) causing the temperature to rise to 60-65°C. After stirring for 10 min, the solid (pyridinium hydrochloride) is quickly filtered, washed twice with 25 ml portions of dry benzene, the benzene washings concentrated under reduced pressure, and the residue distilled to afford 19-20 gm (78-83%), b.p. 155-162°C (12 mm Hg), or 170-173°C (15 min).