Pyrrole(redirected from Pyrrhole)
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a heterocyclic compound; colorless liquid that darkens rapidly upon exposure to air. Melting point, — 23.42°C; boiling point, 130°C; density, 0.9698 g/cm3 at 20°C. Moderately soluble in water. Pyrrole is a very weak acid; it forms a salt with potassium or anhydrous caustic potash. It resinifies under the influence of acids, and it oxidizes readily. It hydrogenates with H2 over Ni at 200°C to pyrrolidine.
Pyrrole was first isolated from coal tar. It is produced commercially
by dry distillation of the ammonia salt of mucic acid or by passing a mixture of furan and NH3 over Al2O3 at 400°–450°C. The pyrrole nucleus is a structural fragment of porphyrin molecules. Pyrrole is used in the production of pyrrolidine and in the synthesis of pharmaceuticals—for example, the antiseptic Iodol (2,3,4,5-tetraiodopyrrole).