579516-44-2Relevant articles and documents
Kinetic study of the phenolysis of O-methyl and O-phenyl O-2,4-dinitrophenyl thiocarbonates and O-ethyl 2,4-dinitrophenyl dithiocarbonate
Castro, Enrique A.,Arellano, David,Pavez, Paulina,Santos, Jose G.
, p. 6192 - 6196 (2007/10/03)
The reactions of a series of phenols with O-methyl O-2,4-dinitrophenyl thiocarbonate (MDNPTOC), O-phenyl O-2,4-dinitrophenyl thiocarbonate (PDNPTOC), and O-ethyl 2,4-dinitrophenyl dithiocarbonate (EDNPDTC) are studied kinetically in water, at 25.0 °C and an ionic strength of 0.2 M (KCl). All reactions show pseudo-first-order kinetics under an excess of phenol over the substrate, and are first order in phenoxide anion. The reactions of EDNPDTC show a linear Bronsted-type plot of slope β = 0.67, suggesting a concerted mechanism. On the other hand, the phenolyses of MDNPTOC and PDNPTOC exhibit linear Bronsted-type plots of slopes β = 0.27 and 0.28, respectively, consistent with stepwise mechanisms where the formation of an anionic tetrahedral intermediate (T-) is rate determining. By comparison of the kinetics and mechanisms of the reactions under investigation with similar reactions, the following conclusions arise: (i) Substitution of S- by O- in the intermediate T- destabilizes this species. (ii) The change of DNPO in T- to DNPS also destabilizes this intermediate. (iii) Substitution of MeO by PhO as the nonleaving group of the substrate does not affect the kinetics, probably by a compensation of electronic and steric effects. (iv) The change of an amino group in a tetrahedral intermediate to a phenoxy group destabilizes the intermediate.
