Decarboxylation of Benzoic Acid Derivatives

Author: Cheng-Hsia Wang

Abstract：

Twenty-four aromatic acids were prepared or collected and they were individually heated in boiling dimethyl sulfoxide.
Phthalic acids carrying four chloro, four bromo, or one 3-nitro groups underwent decarboxylation to form, respectively, tetrach-lorobenzoic acid, tetrabromobenzoic acid, or m-nitrobenzoic acid.
Nitroterephthalic acid gave a yellow solid product, mp above 220 . This product contains no nitrogen or sulfur and its infrared spectrum shows a carbonyl band.
2-Chloro-3, 5-dinitrobenzoic acid also yielded a yellow crystal-line product obtained by ether extraction. This also had a carbonyl band in the infrared spectrum.
Other carboxylic acids employed were stable to the treatment. Requirements for decarboxylation were discussed.
1,8-Naphthalic anhydride and 3-nitro-1 , 8-naphthalic anhydride did not react with dimethyl sulfoxide to form the methylthionethyl es-ters in the manner tetrachlorophthalic anhydride did. The corresponding acids changed to the anhydrides in refluxing dimethyl sul-f oxide.

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