5314-03-4Relevant academic research and scientific papers
Experimental and computational determination of Bronsted coefficients for equilibrium transfer of the O,O-dimethyl phosphorothioyl group between oxyanion nucleophiles
Edwards, David R.,Maxwell, Christopher I.,Harkness, Robert W.,Neverov, Alexei A.,Mosey, Nicholas J.,Stan Brown
supporting information; scheme or table, p. 258 - 266 (2012/06/30)
An experimental determination of the βEq value for equilibrium transfer of the O,O-dimethyl phosphorothioyl group between oxyanion nucleophiles in water and methanol at 25 °C is presented. The respective βEq values in the two solvents are experimentally the same at -1.45 ± 0.08 and -1.39 ± 0.12. Based on the observation that the Bronsted correlation for the nucleophilic reaction of phenoxides in water with substrate 1d (dimethyl 4-nitrophenyl phosphorothioate, pKa HOAr of 7.14) is linear over the entire range of phenoxides employed (5.53 ≤ pKaNu ≤12.38), the reaction for phenoxide nucleophiles displacing phenoxide leaving groups is probably concerted. The obtained data allow one to calculate, for a symmetrical transition state involving 2,4,5-trichlorophenoxide as a nucleophile and leaving group, an approximately 60% P-OAr cleavage and about 40% P-Nuc bond formation. A computational method is presented for the rapid prediction of the βEq values for such processes in water and methanol, and the results are compared with known values from the literature. Copyright
Mechanisms of abiotic degradation and soil-water interactions of pesticides and other hydrophobic organic compounds. Part 3. Nucleophilic displacement at the phosphorus centre of the pesticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate] by oxygen nucleophil...
Omakor, John E.,Onyido, Ikenna,vanLoon, Gary W.,Buncel, Erwin
, p. 324 - 330 (2007/10/03)
Rate constants for the reaction of the title compound, 1, with a number of oxygen nucleophiles, including structurally related phenoxides and oxygen-based α-nucleophiles, have been measured in aqueous solution at 25 deg C. A significant α-effect was observed, confirming participation of the nucleophile in the rate-limiting step of the reaction as well as indicating different transition states (TS) for the reaction of α-nucleophiles compared to normal ones. The Broensted-type correlation of log kNu vs. pKa of nucleophiles shows a linear plot for the series of structurally related phenoxides in the pKa range 5.4-10.0, straddling the pKa of the leaving group (3-methyl-4-nitrophenoxide, pKa 7.20), but is curved in the highly basic region corresponding to CF3CH2O- and HO- as nucleophiles. The slope of the linear portion of the plot (βNu) is 0.49 (R2 0.988). The linearity of the plot for the series of structurally related phenoxides is consistent with a concerted mechanism for nucleophilic attack at the P center of the substrate. A value of β1g -0.39 (R2 0.973) is measured for the reaction of PhO- with substituted phenyl dimethyl phosphorothioate esters. Combining the values of βNu and β1g gives βeq = 0.88; these parameters when considered together with the effective charge distribution in the TS, demonstrate that the TS for the symmetrical reaction (in which nucleophile = leaving group = 3-methyl-4-nitrophenoxide) has no significant phosphorylium ion character. The Leffler index points to a concerted reaction in which bond formation is slightly ahead of bound rupture in the TS. Data from the present study are compared with literature data for (thio)phosphoryl group transfer. We propose that, unless special structural and/or environmental features prevail, (thio)phosphoryl transfers between phenoxides are more likely to occur via a concerted mechanism. It is shown that the TS for the concerted transfer of (EtO)2P=O between two PhO- moieties shows more pentacoordiante intermediate character than the symmetrical reaction of 1 due to differences in (i) basicity of PhO- versus 3-CH3,4-NO2PhO-, and (ii) abilities of O and S in the P=X (X = O, S) moiety to stabilize the incoming negative charge.
