Piperine is an alkaloid responsible for pungency of black pepper. It is a liphophillic amide that is soluble in ethanol (ca. 1 g/15 mL) and isopropyl alcohol. It forms needle-like shaped monoclinic crystals with m. p. 130 °C. Ethanolic solutions of the compound have a sharp taste whereas the crystalline compound is tasteless. Piperine acts as a very weak base forming salt only with strong minerals acids such as hydrochloric acid (B•HCl) or hexachloroplatinic acid (B•H2PtCl6). Dihydrochloride is unstable and spontaneously decomposes. Piperine can be hydrolyzed with sodium hydroxide to another volatile base – piperidine. The acidic hydrolysis yields piperic acid thus it is confirmed that piperine is the piperidine amide of piperic acid. Piperine can be extracted from P. nigrum (black pepper) and also from P. longum (white pepper) and P. clusii (Aschanti). The piperine content in black pepper varies from 6-9%.
Structure of piperine
A 150 mL soxhlet extractor was filled with approximately 27 g of fine grounded black pepper. Isopropyl alcohol (100 mL) was used as a solvent for the extraction. A condenser was fitted to the soxhlet extractor and the extraction process was carried out for two hours. Volume of the solution was then reduced to 15 mL by a simple distillation. Dark brown liquid was treated with 10 mL of potassium hydroixde solution in isopropyl alcohol. A resin that formed immediately after the addition was filtered off and 50 mL of ice cold water was added dropwise into the solution. The product precipitated in a form of light yellow powder. A beaker with the product was let to crystallize for another 12 hours in refrigerator. The powder was filtrated off and dried in the air. Yield: 1.25 g (ca. 4.6 w %).