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Diazotisation Mechanism of Heteroaromatic Amines. Diazotisation of 2‐aminothiazole as an equilibrium
Author(s) -
Diener Heinz,
Güleç Bilge,
Skrabal Peter,
Zollinger Heinrich
Publication year - 1989
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19890720421
Subject(s) - chemistry , reagent , protonation , aqueous solution , solvent , equilibrium constant , ring (chemistry) , ion , kinetic isotope effect , medicinal chemistry , inorganic chemistry , organic chemistry , deuterium , physics , quantum mechanics
The rate of diazotization of 2‐aminothiazole was measured in 65 to 75% ( w / w ) aqueous H 2 SO 4 . The kinetic solvent isotope effect of the diazotization in 72% D 2 SO 4 /D 2 O was determined ( k H / k D = 5.8 ± 0.2). These data are consistent with a mechanism in which the 2‐aminothiazole, protonated at the ring N‐atom, but not at the NH 2 group, is attacked by the NO + ion. The reaction does not go to completion, but to an equilibrium. The equilibrium concentration of the diazonium ion was determined in 30,50,70, and 90% ( w / w ) H 2 SO 4 at three initial concentration of reagents (0.001,0.01, and 0.1m). The final concentrations of the reagents and the diazonium ion are consistent with a reversible process. This is the first diazotization for which quantitative evidence for equilibration has been found. In the very large range of acidities used ( H o = −1.73 to −9.01), it was not possible to calculate meaningful equilibrium constants that are independent of the acidity.