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Catalysis of aminolysis of p ‐nitrophenyl acetate by 2‐pyridones
Author(s) -
Fischer Christian B.,
Steininger Harald,
Stephenson David S.,
Zipse Hendrik
Publication year - 2005
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.914
Subject(s) - chemistry , aminolysis , amine gas treating , 2 pyridone , butylamine , dimer , catalysis , kinetics , medicinal chemistry , reaction rate constant , computational chemistry , organic chemistry , physics , quantum mechanics
The influence of a series of alkyl‐substituted 3‐cyano‐2‐pyridones on the kinetics of the reaction of p ‐nitrophenyl acetate ( 10 ) with n ‐butylamine ( 9 ) was studied. The reactions were monitored under pseudo‐first‐order conditions using an excess of n ‐butylamine by 1 H NMR spectroscopy at 23°C in CDCl 3 . A non‐linear dependence of the observed rate constants k obs on the pyridone concentration was observed in all cases. The results were analysed using two different kinetic models. The first model is based on the amine‐catalysed background reaction in combination with a pyridone‐catalysed process, whose efficiency is reduced through dimerization of the pyridone catalyst to an inactive dimer. The second model also involves the amine‐catalysed background process, now in combination with a catalysed process proceeding through pre‐equilibrium complexation of the substrate with a 1:1 amine–pyridone complex and a second (rate‐determining) step involving C—N bond formation. In addition to these kinetic studies, the aggregation behaviour of pyridones 2 and 3 was also studied in pure deuteriochloroform solutions and mixtures of n ‐butylamine and deuteriochloroform. While substantial aggregation to dimers occurs for both pyridones in deuteriochloroform, no such dimerization appears to occur in deuteriochloroform solutions containing 250 × 10 −3 mol l −1 n ‐butylamine. This finding strongly supports kinetic model 2 as the more realistic choice. Copyright © 2005 John Wiley & Sons, Ltd.