N- and O-Heterocyclic carboxylic acids

As in the case of %-amino carboxylic acids, the zwitterions of N- and O-heterocyclic a-carboxylic acids can be decarboxylated thus %-picolinic, thiazole-2-carboxylic, quinaldic, and chelidonic acid afford, respectively, pyridine, thiazole, quinoline, and 4-pyrone. Furan is best prepared by removal of carbon dioxide from pyromucic acid (2-furoic acid) by heat in early work this was effected by heating the acid in a sealed tube or with soda-lime, but Wilson19 has described a convenient method that involves only simple apparatus and affords the very good yields of 72-78%  

However, a still better yield (85-91%) is obtained as follows  

Furan 2-Furoic acid is heated at 170° with high-boiling pyridine bases (about 3.5 parts by weight) containing a little copper oxide. This procedure uses the facts that such decarboxylations are effected particularly smoothly in the presence of high-boiling tertiary bases and are catalysed by copper powder or copper oxide. 

Decarboxylation of carboxylic acids with a cationoid centre at the / -carbon atom 

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