Billion-fold Acceleration of the Methanolysis of Paraoxon Promoted by La(OTf)₃ in Methanol

Abstract

The methanolysis of the insecticide paraoxon (2) was investigated in methanol solution containing varying [La(OTf)(3)] (OTf = (-)OS(O)(2)CF(3)) as a function of at 25 degrees C. Plots of the pseudo-first-order rate constants (k(obs)) for methanolysis as a function of [La(OTf)(3)](total) were obtained under buffered conditions from 5.15 to 10.97, and the slopes of the linear parts of these were used to determine the second-order rate constants (k(2)(obs)) for the La(3+)-catalyzed methanolysis of 2. Detailed analysis of the potentiometric titration data of La(OTf)(3) in methanol through fits to a multicomponent equilibrium mixture of dimers of general stoichiometry La(3+)(2)((-)OCH3)n, where n assumes values of 1-5, gives the equilibrium distribution of each as a function of. These data, when fit to a second expression describing k(2)(obs) in terms of a linear combination of individual rate constants k(2)(2:1), k(2)(2:2).k(2)(2:)n for the dimers, allow one to describe the overall catalytic profile in terms of the individual contributions. The most catalytically important species are the three dimers La(3+)(2)((-)OCH3)1, La(3+)(2)((-)OCH3)2, and La(3+)(2)((-)OCH3)3. The catalysis of the methanolysis of 2 is spectacular: a 2 x 10(-3) M solution of [La(3+)](total), at neutral, affords a 10(9)-fold acceleration relative to the base reaction (t(1/2) approximately 20 s at 8.2) with excellent turnover. A mechanism of the catalyzed reaction involving the La(3+)(2)((-)OCH3)2 species is proposed.

Bio-inspired approaches to accelerating metal ion-promoted reactions: enzyme-like rates for metal ion mediated phosphoryl and acyl transfer processes

“…OMe for this process is 2.6 × 10 −3 dm 3 mol −1 s −1 at 25 °C [29,30]. A subsequent study of the kinetics of the cyclization of 6a-g promoted by the dinuclear Zn(II) complex 8 revealed that the general mechanism involves saturation binding of the substrate to the complex followed by unimolecular decomposition of a 8:6 complex to give the corresponding phenoxide products and the cyclic ester 7 [31] as in eq.…”

A mechanistic study of the [La2(OCH3)2]4+- and [(1,5,9-triazacyclodo-decane):Zn:(OCH3)]+-catalyzed methanolysis of carbonates: possible application for the recycling of bisphenol A polycarbonates

“…2 is a plot of log k 2 obs determined for cleavage of 3b promoted by [La (III) dimers] at various s s pH values; these kinetic data are overlayed with the speciation diagram of [La 2 (OCH 3 ) n ] (6−n)+ in methanol that was previously determined by potentiometric titration. 17 The plot has a skewed bell-shape profile maximizing at s s pHϳ8.8, suggesting that the the most active species is the dimer [La(OCH 3 ) 2 ] 4+ , although [La 2 (OCH 3 ) 3 ] 3+ also has good activity that is lessened in accordance with its reduced concentration in solution. Similar experiments were performed for the methanolysis of 3 and 4 promoted by 1 at concentrations between 0.175 and 1.75 mmol dm −3 ; the gradients of the k obs versus [1] plots gave the k 2 obs values that are also in Table 1.…”

“…Plot of the first-order rate constant for the methanolysis of 4-nitrophenyl methyl carbonate (3b) catalyzed by added La(Plots of the speciation for La (III) dimers with one to five attached methoxides as a function of s s pH as computed for [La (III) ] total = 2 × 10 −3 mol dm −3 from fits of potentiometric titration data 17. Superimposed on the plots as circles are the k 2 obs data for the La (III) -catalyzed methanolysis of p-nitrophenyl methyl carbonate (3b) determined at various s s pH values, T = 25°C.…”

Analysis of the chemical composition of the products of La-catalyzed mathanolysis of Russian VX

“…Метод каталитического метано-лиза предложен канадскими исследователями [1] для эффективной и в то же время достаточно бережной обработки загрязненных поверхностей и позволяет сохранить в рабочем состоянии электронные приборы, оптическую и измери-тельную аппаратуру. В работах [2][3][4][5][6] предложена технология деструкции фосфорорганических пестицидов и имитаторов ФОВ в спиртовой среде в присутствии катализаторов, содержащих ионы металлов.…”