Reaction CIX.—Action of Heat on certain Dibasic Acids

Reaction CIX.. Action of Heat on certain Dibasic Acids. (B., 10, 326.) —When acids such as phthalic acid or succinic acid, which contain two carboxyl groups attached to adjacent carbons, are heated, they readily lose water and pass into the acid anhydride. 

Dibasic acids with the carboxyl groups not attached to adjacent carbons only form anhydrides with difficulty or not at all. 

Preparation 217.—Phthalic Anhydride Anhydride of 1 2-benzene-dicarboxylic arid). 

20 gins. (1 mol.) of phthalic acid (Preparation 187) are sublimed over a naked flame in the apparatus described on p. 31. Long needles collect on the filter paper and funnel. 

The following reactions, unlike the above, deal mostly with the preparation of anhydrides in which the carboxyl groups belong to different molecules — 

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