Experimental Determination And Quantitative Structure-Activity Relationship Modeling Of Aqueous Reaction Rate Constants Of Typical Pesticides With SO₄^·-

The removal of toxic,harmful and difficult-to-degrade organic pollutants in water has been the focus of environmental research.In recent years,advanced oxidation processes?AOPs?based on sulfate radicals(SO₄^·–)have attracted wide attention in the removal of refractory organic compounds.The kinetic parameters(i.e.the second-order reaction rate constant(k _SO4·–))are important for evaluating the reactivity and removal efficiency of organics in engineering applications,thus it is of great significance to obtain them.However,it seems unrealistic to obtain k _SO4·–values for most chemicals by experimental measurement,due to the large number of chemicals,long time to run experiments and high cost.Thus,it is urgent to develop methods to predict k _SO4·–values of organic compounds.Pesticides,as a class of emerging organic pollutants,have received widespread attention.The traditional water treatment processes show limited removal for pesticides.Therefore,it is of great significance for the prevention and control of pesticides to investigate the reaction rate constant of pesticides with SO₄^·–.In this study,the aqueous k _SO4·–values of 17 typical pesticides under neutral and acidic conditions were determined in the cobalt ion-activated peroxymonosulfate?Co/PMS?system through competitive kinetic methods.Subsequently,one quantitative structural-activity relationships?QSAR?model was constructed to predict k _SO4·–of various organic compounds in accordance with the Organization for Economic Cooperation and Development?OECD?guidelines on the development and validation of QSAR models,based on the measured and collected k _SO4·–values in literatures.The main conclusions are as follows:?1?The aqueous k _SO4·–values of 17 typical pesticides were determined under acidic?p H=4?and neutral?p H=7?conditions.The corresponding k _SO4·–values ranged from 5.7 values of most pesticides was c.a.10⁹M^-1s^-1,indicating that there is no significant difference in the reactivity for different pesticides towards SO₄^·–.?2?The k _SO4·–values for 17 pesticides under two p H conditions were close to each other,suggesting that p H had little effect on the k _SO4·–values of 17 pesticides.Under the same p H condition,the reacivity of the same pesticides towards SO₄^·–was similar,and significant diffenence in k _SO4·–can be observed for different pesticides.This suggested that SO₄^·–has a strong selectivity.?3?Based on the 216 k _SO4·–values determined in this study and collected in literatures,a QSAR model for predicting k _SO4·–values of various organic compounds was constructed by multiple linear regression method.The model had good fitting ability(R²_tr>0.750),0.780).It is revealed that the molecular structure parameters affecting the reactivity of organic compounds with SO₄^·–are ratio of oxygen atoms to carbon atoms?#O:C?,minimum Fukui index on hydrogen atom for nucleophilic attack(f⁺_min,H),number of terminal primary C?sp2?(n _R=Cp),maximum Fukui index of molecules attacked by free radicals(f⁰_max),the highest occupied molecular orbital(E_HOMO),the number of multiple bonds(n _BM),and ring complexity index?RCI?.?4?The constructed model covered a larger dataset and had a wider applicability domain.It can be used to predict the k _SO4·–values of aldehydes,alcohols,carboxylic acids,amino acids,ketones,ethers,aromatic compounds,amides,amines,alkanes,olefins,esters,phenols,pyridines,pyrimidines,imidazoles,antibiotics and pesticides.