Solid–liquid equilibrium solubilities of 2-mercapto-5-methyl-1,3,4-thiadiazole (MMTD) in 12 kinds of monosolvents (i.e., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and amyl acetate) were determined by a gravimetric method with the temperature range from 283.15 to 323.15 K. In alcoholic solvents, the solubility order is ethanol > methanol > n-propanol > i-propanol > n-butanol > i-butanol. In ester solvents, the solubility of MMTD ranking is methyl acetate > ethyl acetate > propyl acetate > butyl acetate > amyl acetate > ethyl formate. The solubility of MMTD increased with increasing temperature. Four thermodynamic models (i.e., the modified Apelblat model, the λh model, the Wilson model, and the Jouyban model) were selected to correlate the solubility data. The RAD and RMSD values were less than 0.0254 and 0.000536, respectively. The Wilson model had the best-fitting effect. The KAT-LSER model and Hansen solubility parameters were used to explain the solvent effect in this work. The Hirshfeld surface, molecular electrostatic potential surface, and free energy of solvation were used to explain the interactions between molecules. Dissolution properties of MMTD were calculated by the Wilson model. The dissolution process of MMTD is endothermic, entropy driven, and spontaneous.
Chen Zhong,He Zhao,Qingzhen Han,Hongbin Cao,Feng Duan,Junyi Shen,Yongbing Xie,Wanqian Guo,Shanshan Sun
As an important raw material and intermediate of widely used antibiotics cefazolin and cefazedone, 2-mecapto-5-methyl-1,3,4-thiadizaole (MMTD) in antibiotic wastewater is hardly decyclized during wastewater treatment, posing great risk to the environment. This work proposed a green “coupling-oxidation” process to enhance ring-opening of MMTD during antibiotic wastewater treatment. In particular, the significant role of humic substances (HS) as pre-coupling reagent was emphasized. Real HS and different model HS, especially quinones, not only efficiently pre-coupled MMTD (>95%) but also promoted the MMTD removal by MnO 2 (from 72.4% to 92.4%). Mass spectrometric analysis indicated that MMTD pre-coupled to HS would be oxidized with ring opening to environmental-friendly sulfonated HS, while direct oxidation of MMTD produced MMTD dimers or sulfonated MMTD that would not undergo ring opening. Theoretical calculations indicated that pre-coupling to HS enabled the ring-opening oxidation by increasing the nucleophilicity and decreasing ring-opening barrier of thiadiazole. Based on the density function theory (DFT), the global nucleophilicity index (Nu) followed the trend of HS-MMTD > MMTD dimer > sulfonated MMTD, while the ring-opening barrier followed the trend of HS-MMTD (274 kJ/mol) < first ring of MMTD dimers (286 kJ/mol) < MMTD (338 kJ/mol). Theoretical calculations further confirmed that the cross-coupled HS-MMTD intermediate was more likely to be decyclized than intermediates from direct oxidation. Moreover, nitrogen, acetaldehyde group, sulfate and CO 2 were the products of thiadiazole ring degradation. Pre-coupling of MMTD with HS provides a new idea and strategy in developing a green and sustainable scheme for wastewater treatment.
危险品化学品经营许可证（带存储）