Thermodynamic Properties And Application Of Sulfonylurea Herbicides

Sulfonylureas are widely used in the field of medicine.G.Levitt of Du Pont reported the herbicidal activity of sulfonylureas in 1978,and he developed the herbicide chlorsulfuron with low toxicity,broad spectrum and high herbicidal activity in 1982.After continuous development,sulfonylureas have corresponding applicable categories for different crop varieties,becoming one of the herbicides with rich varieties and wide application range in the world,marking that the field of weed control has entered a super-efficient era.With the development of environmental protection,it is imperative to reduce the harm of herbicides and other pesticides,but the lack of thermochemical data of herbicides and corresponding intermediates seriously restricts the development of new herbicides and new dosage forms.The research results of this paper are as follows:1.Differential scanning calorimetry（DSC）was used to measure the heat capacities of five herbicides,including pyrisulfuron,nianysulfuron,clopyrisulfuron,bensulfuron and sulfone.By fitting the heat capacity data of samples in the experimental temperature region,the thermodynamic functions such as enthalpy and entropy were obtained.The enthalpy of fusion and melting entropy of samples were obtained by DSC melting point curve.The enthalpy of fusion of the above samples are 81.22KJ·mol^-1,67.31KJ·mol^-1,103.40KJ·mol^-1,89.14KJ·mol^-1,90.65KJ·mol^-1,respectively.The melting entropy of the above samples are117.89J·K^-1·mol^-1,148.38J·K^-1·mol^-1,226.73J·K^-1·mol^-1,195.66J·K^-1·mol^-1,198.40J·K^-1·mol^-1.2.The thermal decomposition processes of the samples at different heating rates of5K·min^-1,10K·min^-1,15K·min^-1,20K·min^-1and 25K·min^-1was measured by thermogravimetry（TG）.Kinetic triplet（A,E,f（a））was calculated by single heating rate method and multiple heating rate method.The preexponential factor lg A of the above five samples are 12.08,12.21,8.24,15.53 and 8.61,respectively.Apparent activation energies E are 71.81k J·mol^-1,69.16k J·mol^-1,75.84k J·mol^-1,78.24k J·mol^-1,74.15k J·mol^-1,respectively.3.The low temperature heat capacities of two drug intermediates,nicosulfuron and metsulfuron-methyl,were measured by a Quantum Design Physical Property Measurement System（PPMS）in the temperature range of 1.9-303K.The Debye-Einstein low temperature heat capacity function model was established to fit the experimental heat capacity of samples.In the range of 1.9-10K,the relative errors of the above models are 1.95%and 1.20%,respectively,which are better than 13.24%and 6.42%of T³model based on Debye’s theory.The relative errors of the new model in the 10-40k are 1.32%and 1.35%,respectively.Considering other energy contributions,the relative errors of heat capacity are 0.47%and0.32%in the temperature range of 40-303K,respectively.