An experience dating back to antiquity and passed on by the great alchemists is that the fumes produ — Physical Chemistry — Thermodynamics Chemistry Question
Theoretical Problem 14
An experience dating back to antiquity and passed on by the great alchemists is that the fumes produced when heating proteins (e.g., slaughterhouse waste) with lime stain an acid-impregnated wooden stick deep red. The compound responsible for this interesting reaction (B) can be produced as follows (several of its typical reactions are indicated as well):
[VISUAL]
A - E are all colorless (white) compounds. B and E are liquids with a characteristic odor.
Draw the structures of A - E.
Model Answer
A: pyroglutamic acid, B: pyrrole, C: potassium pyrrolide, D: 2,3,4,5-tetrabromopyrrole, E: pyrrolidine. [VISUAL]
Explain the stability of B against bases and its rapid decomposition with acids.
Model Answer
The pyrrole anion is aromatic; the pyrrole cation has two conjugated double bonds, and is non aromatic, thus less stable.
Compare the basicity of B and E. Explain.
Model Answer
E is a stronger base having a localized lone pair on the N.
Suggest a reaction scheme for the acidic decomposition of B. Explain why the products are colored.
Model Answer
Polymerization occurs by reaction at the conjugated double bonds. The resulting polymeric compounds have several conjugated π systems.