5292-77-3Relevant academic research and scientific papers
Reactions of O-aryl S-aryl dithiocarbonates with secondary alicyclic amines in aqueous ethanol. Kinetics and mechanism
Castro, Enrique A.,Gazitua, Marcela,Santos, Jose G.
supporting information; scheme or table, p. 466 - 473 (2012/01/19)
The reactions of O-(4-methylphenyl) S-(4-nitrophenyl), O-(4-chlorophenyl) (4-nitrophenyl), O-(4-chlorophenyl) S-phenyl, and O-(4-methylphenyl) S-phenyl dithiocarbonates (1, 2, 3, and 4, respectively) with a series of secondary alicyclic (SA) amines are subjected to a kinetic investigation in 44 wt% ethanol-water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically. Under amine excess, pseudo-first-order rate coefficients (kobs) are found. For some of the reactions, plots of kobs vs. free amine concentration at constant pH are linear but others are nonlinear upwards. This kinetic behavior is in accordance with a stepwise mechanism with two tetrahedral intermediates, one zwitterionic (T ±) and the other anionic (T-). In some cases, there is a kinetically significant proton transfer from T± to an amine to yield T-. Values of the rate micro constants k1 (amine attack to form T±), k-1 (its back step), k2 (nucleofuge expulsion from T±), and k 3 (proton transfer from T± to the amine) are determined for some reactions. The Bronsted plots for k1 are linear with slopes β1 = 0.2-0.4 in accordance with the slope values found when T± formation is the rate-determining step. The sensitivity of log k1 and log k-1 to the pK a of the amine, leaving and non-leaving groups are determined by a multiparametric equation. For the reactions of 1-4 with 1-formylpiperazine and those of 3 and 4 with morpholine the k2 and k3 steps are rate determining. Copyright
