469891-30-3Relevant academic research and scientific papers
Reactivity of N-pyridylcarbamates in basic media
Norberto, Fatima,Santos, Susana,Silva, Daniel,Herves, Pablo,Miguel, Ana Sofia,Vilela, Filipe
, p. 1162 - 1165 (2002)
New secondary aryl N-pyridylcarbamates were prepared by reaction of the aminopyridine anion with aryl chloroformates and their hydrolysis was studied over the pH range from 12 to 13.7. The pH-rate profile points to an E1cB mechanism, involving pre-equilibrium deprotonation of the nitrogen atom to form an anion that undergoes rate-limiting decomposition into pyridyl isocyanate and a phenoxide ion. Further reaction of the highly reactive isocyanate with water affords N-pyridylcarbamic acid, which spontaneously decomposes to aminopyridine and carbon dioxide. The absence of significant base catalysis and the isolation of a new product resulting from trapping of the intermediate with the base piperidine are also consistent with an elimination addition mechanism. Finally the observed substituent effect (σ-) gives ρ 2.45 which is in accordance with a rate-determining departure of the phenoxide group from the anion intermediate formed in a pre-equilibrium step. Blocking the E1cb mechanism of the secondary carbamates by introduction of N,N-disubstitution in the substrate led to a rate-limiting decrease of ca. 106.
