Phenylpropiolic acid

Phenylpropiolic acid, C₆H5CCCO₂H, formed by the action of alcoholic potash on cinnamic acid dibromide, C₆H₅CHBrCHBrCO₂H, crystallizes in long needles or prisms which melt at 136–137 °C. When heated with water to 120 °C, it yields phenylacetylene (C₆H₅CCH). Chromic acid oxidizes it to benzoic acid; zinc and acetic acid reduce it to cinnamic acid, C₆H₅CH=CHCO₂H, whilst sodium amalgam reduces it to hydrocinnamic acid, C₆H₅CH₂CH₂CO₂H. Ortho-nitrophenylpropiolic acid, NO₂C₆H₄CCCO₂H, prepared by the action of alcoholic potash on ortho-nitrocinnamic acid dibromide, crystallizes in needles which decompose when heated to 155–156 °C. It is readily converted into indigo.