PIPERINE, C17H19NO3, an alkaloid found in the fruits of Piper nigrum and P. longum. It forms white prisms, which melt at 128°-219°. It is almost insoluble in water, but readily soluble in alcohol and ether. It is a very weak base, salts being only formed with mineral acids, and these are dissociated by water. Alcoholic potash decomposes it into piperidine, C5H11N, and piperic acid, C12H10O4. The constitution of piperic acid was elucidated by R. Fittig and his pupils (Ann., vols. 152, 159, 168, 216, 227) and shown to be (1). Piperine consequently is (2).
Oxidation with potassium permanganate converts piperic acid into pilperonal, C8H6O3, and piperonylic acid, C8H6O4. The latter when heated with hydrochloric acid to 170°, or water to 200°, separates carbon with the formation of protocatechuic acid, 1⋅2-dioxy-3-benzoic acid, C6H3(OH)2COOH. Conversely, by heating protocatechuic acid with potash and methylene iodide, piperonylic acid was regained. These results show that piperonylic acid is the methylene ether of protocatechuic acid. Piperonal (q.v.) is the corresponding aldehyde. Piperic acid differs from piperonylic acid by the group C4H4, and it was apparent that these carbon atoms must be attached to the carbon atom which appears in the carboxyl group of piperonylic acid, for if they were directly attached to the benzene ring polycarboxylic acids would result in oxidation. The above formula for piperic acid was confirmed by its synthesis by A. Ladenburg and M. Scholtz (Ber., 1894, 27, p. 2958) from piperonyl acrolein (the condensation product of piperonal and acetaldehyde) and acetic acid. The synthesis of piperine follows from the interaction of piperyl chloride (formed from piperic acid and phosphorus pentachloride) and piperidine (L. Rugheimer, Ber., 1882, 15, p. 1390).