56525-82-7Relevant articles and documents
Structure - reactivity correlation in the reactions of pyrrolidine with O-ethyl S-aryl dithiocarbonates in aqueous ethanol
Castro,Cabrera,Santos
, p. 113 - 117 (2007/10/03)
The reactions of pyrrolidine with O-ethyl S-(X-phenyl) dithiocarbonates (X = 4-methyl, 4-methoxy, H, 4-chloro, 4-nitro, 2,4-dinitro, and 2,4,6-trinitro) are subjected to a kinetic study in 44 wt% aqueous ethanol, 25.0°C, and ionic strength 0.2 M (maintained with KCl). Pseudo-first-order kinetics are found under amine excess. Linear plots of the pseudo-first-order rate coefficient against concentration of free-base pyrrolidine are obtained for all the reactions, nucleophilic rate coefficient (kN) being the slope of such plots. The Bronsted-type plot (log kN vs. pKa for the leaving group) is linear with slope β1g = -0.2, which is consistent with a mechanism through a tetrahedral intermediate (T±) where its formation is rate determining. The β1g value is very similar to that found in the same reactions in water. There is a great difference in the mechanism of the reactions of O-ethyl S-phenyl dithiocarbonate with pyrrolidine (order one in amine) and piperidine (complex order in amine) in aqueous ethanol, and this is attributed to a greater nucleofugality from T± of piperidine rather than pyrrolidine.
Kinetics and Mechanism of the Aminolysis of S-Ethoxycarbonyl O-Ethyl Dithiocarbonate and Related Pyrothiocarbonates
Castro, Enrique A.,Alvarado, Noemi E.,Pena, Sergio A.,Santos, Jose G.
, p. 635 - 642 (2007/10/02)
The reactions of S-ethoxycarbonyl O-ethyl dithiocarbonate (1), bis(ethoxythiocarbonyl) sulphide (4), and bis(ethoxycarbonyl) sulphide (5) with pyrrolidine, piperidine, and morpholine in 95percent aqueous ethanol have been subjected to kinetic study.The rate equation found for all the reactions is kobs = ko + kN, where kobs is the pseudo-first-order rate constant (amines were in excess over the substrates) and N represent the free amine.The rate law accounts for reaction schemes with zwitterionic tetrahedral intermediates, EtOC(S-)(NH+)SCXOEt and EtOC(O-)(NH+)SCXOEt, where X is O or S, formation of which from reactants is the rate-determining step.The intermediates break down to products faster than their deprotonation by the solvent or another amine molecule.This is confirmed by estimation of the rate constants involved in the schemes and evaluation of the pKa value of the intermediates.From the kN values obtained it is deduced that amines attack at the CS group of the substrate faster than at the CO group, although the nature of both the substrate and the amine could change this order of reactivity.Activation parameters are reported for all the reactions, and it was found that ΔS was lower for attack for CO compared with that at CS.This is explained in terms of higher solvation of the transition state for CO attack relative to that for CS attack.
