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An unusual parabolic dependence of rate on acidity in the fischer indole reaction
Author(s) -
Hughes David L.
Publication year - 1994
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610071106
Subject(s) - chemistry , deprotonation , tautomer , kinetic isotope effect , indole test , reaction rate constant , rate determining step , hydrazine (antidepressant) , inorganic chemistry , reaction rate , medicinal chemistry , ion , kinetics , organic chemistry , catalysis , deuterium , chromatography , physics , quantum mechanics
Over the H 0 acidity range from + 2 to −8, four different mechanistic variations occur in the Fischer indole reaction, leading to an unusual parabolic dependence of the rate constants on the acidity of the medium. In strongly acidic media kinetic isotope effects indicate that the rate‐determining step is deprotonation to form the ene–hydrazine tautomer, whereas in weakly acidic media the tautomerization is so rapid that [3,3]‐rearrangement becomes rate limiting. At an intermediate acidity, the deprotonation is rate determining, with the rate being strongly dependent on the concentration of the anionic counter ion.