6085-66-1Relevant academic research and scientific papers
Phenolysis and aminolysis of 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates in aqueous ethanol
Castro, Enrique A.,Aliaga, Margarita E.,Cepeda, Marjorie,Santos, Jose G.
experimental part, p. 353 - 358 (2011/11/30)
The reactions of S-methyl O-(4-nitrophenyl) thiocarbonate (1) and S-methyl O-(2,4-dinitrophenyl) thiocarbonate (2) with a series of secondary alicyclic (SA) amines and phenols are subjected to a kinetic investigation. Under nucleophile excess, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against the free nucleophile concentration at constant pH are linear with slopes kN. The Brnsted plots (log kN vs. nucleophile pKa) for the reactions are linear with slope (β) values in the 0.5-0.7 range, in accordance with concerted mechanisms. Comparison of the SA aminolysis of 1 with the same one carried out in water shows that the change of solvent from water to aqueous ethanol destabilizes the zwitterionic tetrahedral intermediate, changing the mechanism from stepwise to concerted. This destabilization is greater than that due to the change from SA amines to quinuclidines. For the phenolysis reactions, the kN values in aqueous ethanol are smaller than those for the same reactions in water. Considering that the nucleophile is an anion, this result is unexpected because the anion should be more stabilized in the more polar solvent. This result is explained by the facts that the phenoxide reactant has a negative charge that is delocalized in the aromatic ring and the transition state is highly polar.
Effect of substitution of oxygen by sulfur in the npnleaving group of a carbonate: Kinetics of the phenolysis and benzenethiolysis of 5-methyl aryl thiocarbonates
Castro, Enrique A.,Aliaga, Margarita,Santos, Jose G.
, p. 533 - 538 (2008/02/06)
The phenolysis and benzenethiolysis of S-methyl 4-nitrophenyl thiocarbonate (1) and S-methyl 2,4-dinitrophenyl thiocarbonate (2) in water are studied kinetically. The Brnsted plots (log kN versus nucleophile basicity) are linear for all reactions. The Bronsted slopes for 1 and 2 are, 0.51 and 0.66 (phenolysis) and 0.55 and 0.70 (benzenethiolysis), respectively. These values suggest a concerted mechanism for these reactions, as found in the corresponding carbonates. Namely, substitution of OMe by SMe in the nonleaving group does not change the mechanism. Copyright 2007 John Wiley & Sons, Ltd.
