Reaction CXI.—Action of Dehydrating Agents on a Free Acid

Reaction CXI. Action of Dehydrating Agents on a Free Acid. (B., 34, 

2074 A., 226, 8.)—This is a usual method of preparing the anhydrides of acids, the chlorides of which are not readily available. Acetic anhydride is very frequently used—acetyl chloride can also be employed. 

Preparation 219.—Cinnamic Anhydride [Anhydride of Z-phenyl-2-propen acid], 

50 gms. (2 mols.) of dry finely powdered cinnamic acid and 250 gms. (excess) of acetic anhydride are refluxed together for 8 hours, and distilled to 146°. The cold residue is extracted with ether, the extract filtered, and ether removed on a water bath. The residue is recrystallised from alcohol. 

Preparation 220.—Succinic Anhydride [Anhydride of butan-diadd]. 

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