Linear free energy relationship and deuterium kinetic isotope effect observed on phospho and thiophosphoryl transfer reactions in some organophosphorous compounds

2014 International Conference on Science & Engineering in Mathematics, Chemistry and Physics

数学;化学;物理学

Lumbiny, B.J.^1 ; Hui, Z.^2 ; Islam, M.A.^1 ; Quader, M.A.^3 ; Rahman, M.^1

Department of Chemistry, University of Rajshahi, Rajshahi 6205, Bangladesh^1

Department of Chemistry, Inha University, Incheon 402-751, Korea, Republic of^2

Department of Chemistry, University of Dhaka, Dhaka 1000, Bangladesh^3

关键词: Deuterium kinetic isotope effect;    Environmental systems;    Linear free energy relationships;    Nucleophilic substitution reactions;    Organophosphorous compounds;    Partial deprotonation;    Second-order rate constants;    Thiophosphoryl transfer reactions;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/495/1/012004/pdf
DOI  :  10.1088/1742-6596/495/1/012004

来源: IOP

【 摘 要 】

Tetracoordinated organophosphorous compounds were synthesized, characterized and nucleophilic substitution reaction were investigated by varying substituents around phosphorous centre or in nucleophile considering its utility in biological and environmental system. The reactivity is expressed in terms of second-order rate constant, k2and measured conductometrically. Linear Free Energy Relationship (LFER) tools mainly Hammett (ρ), Bronsted (β) LFER coefficients and deuterium kinetic isotope effects (KIEs) being determined for the pyridinolysis of 4-chlorophenyl 4-methoxy phenyl chlorophosphate, 1 in acetonitrile at 5.0 °C. The experimental data's were compared with those of structurally similar organophosphorous compounds reported earlier in quest for the mechanistic information. Nice linear correlation being found for Hammett (logk2vs σx), having negative value of the ρX= -5.85 and Bronsted (logk2vs pKa(x)) plots having large positive value for βX= 1.18 for 1 can be interpreted as SN2process with greater extent of bond formation in transition state (TS) of 1. The observed kH/kDvalues of 1 is 1.00 ± 0.05 and net KIE, 1.32 suggests the primary KIE and indicates frontside nucleophilic attack through the partial deprotonation of pyridine occurs by the hydrogen bonding in the rate-determining step.