105902-71-4Relevant academic research and scientific papers
Concerted aminolysis of diaryl carbonates: Kinetic sensitivity on the basicity of the nucleophile, nonleaving group, and nucleofuge
Castro, Enrique A.,Cubillos, Maria,Iglesias, Rocio,Santos, Jose G.
, p. 604 - 611 (2012)
The kinetics of the reactions of 4-methylphenyl, phenyl, and 4-chlorophenyl 2,4,6-trinitrophenyl carbonates (1, 2, and 3, respectively) with a series of anilines and secondary alicyclic (SA) amines has been carried out spectrophotometrically in 44 wt% ethanol-water, at 25.0°C, ionic strength 0.2 M. The BrAnsted plots (statistically corrected) for the reactions of carbonates 1-3 with anilines and SA amines were linear with slopes (βN) in the range of 0.69-0.78 and 0.45-0.48, respectively, attributed to a concerted mechanism. The negative values found for the sensitivity of log kN to the basicity of the nonleaving (βnlg) and leaving (βlg) groups are discussed. Anilines are more reactive than isobasic SA amines, probably because of the greater steric hindrance offered by the latter.
Kinetics and mechanism of the aminolysis of 4-nitrophenyl and 2,4-dinitrophenyl 4-methylphenyl carbonates in aqueous ethanol
Castro, Enrique A.,Andujar, Monica,Campodonico, Paola,Santos, Jos G.
, p. 309 - 315 (2007/10/03)
The reactions of 4-methylphenyl 4-nitrophenyl carbonate (MPNPC) and 4-methylphenyl 2,4-dinitrophenyl carbonate (MPDNPC) with a series of secondary alicyclic amines are subjected to a kinetic investigation in 44 wt% ethanol-water, at 25.0°C, ionic strength 0.2 M (KCl). Under amine excess over the substrate, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against [amine] are linear, with kN as slopes. A biphasic Broensted-type plot for kN is obtained for the aminolysis of MPNPC, with slopes β1 = 0.2 (high pKa) and 32 = 0.9 (low pKa). This is in accordance with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T±), and a change in the rate-determining step, from formation to breakdown of T± the amine pKa decreases. For the aminolysis of MPDNPC, a slightly curved Broensted-type plot for kN is obtained, with β1 = 0.1 (low pKa) β2 = 0.55 (high pKa). This is consistent with a concerted mechanism.
Structure-reactivity correlations in the aminolysis of aryl chloroformates
Castro, Enrique A.,Ruiz, Mara G.,Santos, Jos G.
, p. 281 - 287 (2007/10/03)
The reactions of a series of secondary alicyclic amines with 4-methylphenyl and 4-methoxyphenyl chloroformates are subjected to a kinetic investigation in water, at 25.0°C, ionic strength 0.2 M (KCI). Under amine excess, pseudo-first-order rate coefficients (kobs) are found for all reactions. Plots of kobs vs [NH] (NH is the free amine) are linear, with the slope (kN) pH independent, except the reactions of l-(2-hydroxyethyl)piperazine with both substrates at pH 6.2-7.3. The Broensted-type plots for the kN values for the aminolysis of both chloroformates are linear, with slopes ca. 0.3, which is consistent with rate-determining formation of a zwitterionic tetrahedral intermediate (T±). With the PKa and log kN data for the present reactions, together with those for the same aminolysis of phenyl and 4-nitrophenyl chloroformates, two dual parametric equations are found for log kN as a function of pKa of the nucleophile, Hammett sigma of the "nonleaving" group, and pKa of the "nonleaving" group, with coefficients βN = 0.3, ρnlg = 0.7, and βnlg = -0.2, respectively.
