Pyrrole

Pyrrole, a five-membered heterocycle. Products of addition of two hydrogen atoms to P. are called pyrrolines, and of four atoms—pyrrolidines. P. is a colorless liquid with an odor resembling chloroform; boiling point 130-131°, specific gravity d²]«=0.96694, soluble in alcohol and ether; easily oxidized, difficult to nitrate and sulfonate; a weak base; under the action of acids, it loses part of N as NH₃ and polymerizes into the so-called "red pyrrole." P. in some properties resembles phenol. A pine stick moistened with HCl and dried gives a red coloration with a solution of P. or its homologs. It is obtained synthetically by dry distillation of mucic acid. P. is contained in bone oil, obtained by dry distillation of proteins, and in small quantities in coal tar. As a core entering into the composition of plant (chlorophyll) and animal pigments (hemoglobin, bile), it has great biological interest. The presence of P. establishes a close connection between individual representatives of plant and animal pigments. It is obtained by the decomposition of melanins (see). When phylloporphyrin, hematoporphyrin, hemin, and bilirubin are reduced with hydriodic acid, a mixture of P. homologs and pyrrolecarboxylic acids is obtained (see also Porphyrin). Derivatives of pyrrolidine include the pyrrolidine- and oxypyrrolidine-carboxylic acids that are part of the protein molecule. Some alkaloids are also derivatives of pyrrolidine: hygrine, stachydrine, nicotine, atropine, cocaine. Introduction of P. to a dog and rabbit causes the appearance of methyl-piperidine in the urine. Pyrroblau. A derivative of isatin, an acidic dye, easily soluble in water and alcohol. Used in histological technique as a vital dye for detecting in connective tissue cells of the macrophage type (pyrrole cells). However, for this purpose, it is preferable to use aminoblau or trypanblau.