16323-15-2Relevant 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.
experimental part, p. 604 - 611 (2012/09/08)
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 anilinolysis of aryl 4-nitrophenyl carbonates in aqueous ethanol
Castro, Enrique A.,Gazitua, Marcela,Santos, Jose G.
, p. 8088 - 8092 (2007/10/03)
The reactions of anilines with 4-nitrophenyl, 4-methylphenyl, and 4-chlorophenyl 4-nitrophenyl carbonates (BNPC, MPNPC and ClPNPC, respectively) are studied kinetically in 44 wt % ethanol-water, at 25.0 °C, with an ionic strength of 0.2 M (KCl). Plots of kobsd vs [amine] are linear, with the slopes (kN) independent of pH. The Bronsted-type plots (log kN vs pKa of conjugate acids of anilines) are linear, with slopes β = 0.65, 0.85, and 0.78 for the reactions of anilines with BNPC, MPNPC, and ClPNPC, respectively. The values of the slopes for the two latter reactions are in accordance with those obtained in stepwise mechanism where breakdown to product of a zwitterionic tetrahedral intermediate is the rate-determining step. On the other hand, the β value for the reactions of BNPC is at the upper limit of those found for concerted mechanisms. The kinetic results for the reactions of anilines with BNPC correlates well with those for the concerted reactions of the same amines with 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates: A plot of the calculated log k N values (through a multiple parametric equation) vs the experimental log kN values is linear with unity slope and zero intercept, which confirms the concerted mechanism for the latter three reactions.
Kinetics and mechanism of the aminolysis of 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates in aqueous ethanol
Castro, Enrique A.,Campodonico, Paola,Toro, Alejandra,Santos, Jose G.
, p. 5930 - 5935 (2007/10/03)
The reactions of anilines with 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates (MPDNPC and ClPDNPC, respectively) and the latter substrate with secondary alicyclic (SA) amines are subjected to a kinetic study in 44 wt % ethanol-water solution, at 25.0 °C, and an ionic strength of 0.2 M (KCl). The reactions are studied by following spectrophotometrically (360 nm) the release of 2,4-dinitrophenoxide anion. Under amine excess, pseudo-first-order rate coefficients (kobsd) are found. Plots of kobsd vs [amine] are linear and pH-independent, with slope kN. The Bronsted-type plots (log kN vs pKa of aminium ions) are linear, with slopes β = 0.68 and 0.66 for the reactions of anilines with MPDNPC and ClPDNPC, respectively, and β = 0.44 for the reactions of SA amines with ClPDNPC. The magnitude of the slope for the latter reaction indicates that its mechanism is concerted. The slope values for the reactions of anilines are in the borderline between stepwise and concerted mechanisms. The sensitivity of logkN to the basicity of the nonleaving group (βnlg) is ca. -0.7 for the reactions of anilines, in agreement with that found for the SA reactions (βnlg ca. -0.6). These results suggest that the reactions of anilines are concerted, although it is also possible that both mechanisms (stepwise and concerted) operate simultaneously. By comparison of the reactions under investigation between them and with similar aminolyses, the following conclusions can be drawn: (i) ClPDNPC is more reactive than MPDNPC toward the two amine series. (ii) The change of water to aqueous ethanol destabilizes a zwitterionic tetrahedral intermediate. (iii) The change of the nonleaving group from MeO to 4-methylphenoxy or 4-chlorophenoxy also destabilizes this intermediate.
Nucleophilic substitution reactions of phenyl chloroformates
Yew, Kyoung Han,Koh, Han Joong,Lee, Hai Whang,Lee, Ikchoon
, p. 2263 - 2268 (2007/10/03)
Methanolysis and aminolysis of phenyl chloroformates in acetonitrile have been investigated.The rates are slow due to initial-state stabilization by strong resonance electron donation from the phenoxy group.In both reactions the large positive values of ρY = 0.8-1.6 and low ΔH(excit.) and ΔS(excit.) values show that the transition state is strongly associative with little bond breaking.This mechanism is supported by the relatively large solvent isotope effect, kMeOH/kMeOD = ca. 2.3-2.5, and by the relatively strong inverse secondary kinetic isotope effect, kH/kD =/ca. 0.74-0.94, involving deuteriated aniline nuclephiles, in addition to a negative value of ρXY.The dependence on aniline basicity, βx(βnuc) =/ca. 0.8, and the ρX values of -2.3 are similar to those corresponding values for the reactions of benzoyl chlorides which have been predicted to react by an associative SN2 mechanism.These observations are consistent with a concerted displacement mechanism for the methanolysis and aminolysis of phenyl chloroformates.
