701208-43-7Relevant articles and documents
Kinetics and mechanism of the pyridinolysis of diaryl carbonates
Castro, Enrique A.,Acuna, Magdalena,Soto, Claudia,Trujillo, Carolina,Vasquez, Barbara,Santos, Jose G.
, p. 816 - 822 (2008)
The reactions of 4-methylphenyl and 4-chlorophenyf 4-nitrophenyl carbonates (1 and 2, respectively), phenyl, 4-methylphenyl, 4-chlorophenyl, and 4-nitrophenyl 2,4-dinitrophenyl carbonates (3, 4, S, and 6, respectively), and bis(2,4-dinitrophenyl) carbonate (7) with a series of pyridines are studied kinetically at 25.0°C in 44 wt% ethanol-water and an ionic strength of 0.2 M (KCl). The reactions are followed spectrophotometrically and under excess amine pseudo-first-order rate coefficients (kobs) are found. For all these reactions, plots of kobs versus free amine concentration at constant pH are linear, the slope (kN) being independent of pH. The Bronsted-type plots (log kN vs. pKa of the conjugate acids of the pyridines) are all biphasic (linear portions at high and low pK a and a curvature in between). These plots are in accordance with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T ±), and a change in the rate-determining step from formation of T± to its breakdown to products, as the pyridine basicity decreases. Also studied are the effects of the leaving, non-leaving, and electrophilic groups of the substrate, and of the amine nature, on the pK a0 value (value at the center of curvature of the Bronsted-type plots). Copyright
