Hydrolysis Mechanism Analysis And Prediction Models Development Of Several Typical Organic Pollutants

Hydrolysis is an important self-purification process of organic chemicals for aqueous ecosystems.The hydrolysis rate constant is an important indicator to characterize the environmental persistence and ecological risk assessment of organic pollutants.The value of the hydrolysis rate constant of the compound determines the length of its half-life.But the hydrolysis rate which the experimental determined,has problems such as high cost,time-consuming and laborious,relying on standard products.The rate is difficult to satisfy the needs of ecological risk assessment for compounds.In this study,the complete reactions of the hydrolysis reaction of haloalkanes,esters and amides were investigated by the quantum chemical calculation method.On this basis,quantitative structure-property relationship(QSPR)models were further constructed using quantum chemical parameters to predict the hydrolysis rate constants of haloalkanes,esters and amides.The research content and results are as follows:1.The hydrolysis processes of haloalkanes,esters and amides were simulated to explore their dominant reactions and their complete reaction pathways by quantum chemical density functional theory(DFT).The results shows bimolecular nucleophilic substitution(S_N2)reaction is considered to be the main hydrolysis mechanism for haloalkanes under neutral conditions.Both S_N2 and bimolecular elimination(E2)reaction mechanisms exist in the alkaline hydrolysis systems of haloalkanes.Although the E2reaction mechanisms is slightly dominant,the products of the S_N2 pathway reaction are more stable.Both neutral and basic hydrolysis of esters follow the nucleophilic addition elimination reaction mechanism.The alkaline hydrolysis reaction of amides follows the nucleophilic addition elimination mechanism.2.Based on the each reaction path,the rate-determining steps of the hydrolysis of halogenated alkanes,esters and amides were analyzed.The rate-determining steps in the neutral hydrolysis of halogenated alkanes is S_N2.The rate-determining steps in the alkaline hydrolysis of halogenated alkanes withβ-H is E2.Under neutral conditions,the addition of nucleophiles in the ester hydrolysis system is the rate-determining step of the reaction.Under alkaline conditions,the departure of alcohols in the hydrolysis system of esters is the decisive step of the reaction.The rate-determining step in the hydrolysis reaction of the amides is the departure of ammonia.Based on Transition State Theory,the hydrolysis rate constants which of 74 halogenated alkanes,esters and amides under neutral and basic conditions were calculated.3.Based on the descriptors calculated by quantum chemistry and Dragon,QSPR models for hydrolysis rate constants of haloalkanes,esters,and amides were constructed by using multiple linear regression methods.The models have good fitting performance,R~2=0.78(haloalkanes,neutral),0.72(haloalkanes,alkaline),0.89(esters,neutral),0.88(esters,alkaline),0.96(amides,alkaline)and RMSE=0.77(haloalkanes,neutral),1.36(haloalkanes,alkaline)and 0.48(esters,neutral),0.81(esters,alkaline)and 0.96(amides,alkaline).The models indicate that quantum chemical parameters can characterize the hydrolysis rate constants of haloalkanes,esters and amides.The simulated external validation and leave-one-out cross-validation results of models show that all models have good predictive ability and robustness.Therefore,these models can predict the hydrolysis rate constants of other similar compounds and provide basic data for ecological risk assessment.