PROPIOLIC

ACID  , CH:C•CO2H, acetylene mono-carboxylic acid, an unsaturated organic acid prepared by boiling acetylene dicarboxylic acid (obtained by the action of alcoholic potash on dibromsuccinic acid) or its acid potassium salt with water (E. v . Bandrowski, Ber., 188o, 13, p . 2340) . It forms silky crystals which melt at 6° C., and boil at about 144° C. with decomposition . It is soluble in water and possesses an odour resembling that of acetic acid . Exposure to sunlight converts it into trimesic acid (benzene-1.3.5-tricarboxylic acid) . Bromine converts it into dibromacrylic acid, and it gives with hydrochloric acid 0-chloracrylic acid . It forms a characteristic explosive silver salt on the addition of ammoniacal silver nitrate to its aqueous solution, and an amorphous precipitate which explodes on warming with ammoniacal cuprous chloride . Its ethyl ester condenses with hydrazine to form pyrazolone (R: v . Rothenburg, Ber., 1893, 26, p . 1722) . Phenylpropiolic acid, C6H5C:C•CO2H, formed by the action of alcoholic potash on cinnamic acid dibromide, C6H5CHBr•CHBr•CO2H, crystallizes in long needles or prisms which melt at 136–1370 C .

When heated with water to I2o° C. it yields phenyl acetylene C6H5•C;CH . Chromic acid oxidizes it to benzoic acid;

zinc and acetic acid reduce it to cinnamic acid, C6H5•CH:CH•CO2H, whilst sodium amalgam reduces it to hydrocinnamic acid, C6H5•CH2•CO2H . Ortho-nitrophenylpropiolic acid, NO2•C6H4•C: C•CO2H, prepared by the action of alcoholic potash on ortho-nitrocinnamic acid dibromide (A. v . Baeyer, Ber., 188o, 13, p . 2258), crystallizes in needles which decompose when heated to 155–156° C . It is readily converted into indigo (q.v.) .