The Synthesis Technology Of Thionocarbamate Compounds:The Xanthate-Oxidation And Aminolysis Approach

Thionocarbamates are important flotation collectors for sulfide minerals,and they are commonly synthesized by the xanthateesterification and aminolysis approach which obtains sodium thioglycolate as the by-product.While,sodium thioglycolate exhibits a strong odor and suffers from handling and further processing.Therefore,a novel synthesis technology of thionocarbamate is developed in this paper,which is the xanthate-oxidation and ammonolysis approach and the by-product is sulfur.Compared to sodium thioglycolate,sulfur is easy to be recovered only by filtration separation.In addition,sulfur has the widely commercial application.Using sodium isopropyl xanthate,alkylamine and sodium hypochlorite as raw materials,thionocarbamates were synthesized via the one-step and two-step process.In the one-step process,alkylamine and sodium hypochlorite were added dropwise to the solutions of sodium isopropyl xanthate.In the two-step process,dixanthogens were prepared first,and then dixanthogens reacted with alkylamine in the presence of sodium carbonate to deliver thionocarbamates.The influence of solvent type,raw material proportion,reaction temperature,time,and other preparation parameters on the yield of thionocarbamates and sulfur was evaluated.For the one-step process,the optimal synthesis conditions were:Ethyl acetate and water were used as the mixture solvents;to 1 mol sodium isopropyl xanthate,200 mL water and 300 mL ethyl acetate were adopted;the reaction temperature,time and raw material proportion of alkylamine :NaClO : sodium isopropyl xanthate(mol/mol)were 25 ℃,2 h and 1.40:1.45:1.00,respectively.Under this optimal technology,the yield of Oisopropyl-N-ethyl-thionocarbamate,O-isopropyl-N-propylthionocarbamate,O-isopropyl-N-butyl-thionocarbamate were 89.00%,84.80%,and 88.10%,respectively,and that of the co-product sulfur was over 73.50%.The results of ultraviolet spectra,infrared spectra and nuclear magnetic resonance spectroscopy showed that the as-synthesized products were of thionocarbamates,and their purity were above 98% as-determined by the gas chromatography.For the two-step process,the optimal process conditions of dixanthogen were: To 1 mol sodium isopropyl xanthate,solvent water was 300 mL;the molar ratio of sodium hypochlorite to sodium isopropyl xanthate was of 1.05:1.00;reaction temperature and time were 25 ℃ and 0.5 h.And the yield of isopropyl dixanthogen was around 97.00%.Infrared spectroscopy and nuclear magnetic resonance spectroscopy results confirmed the as-synthesized product was of isopropyl dixanthogen.For preparation of thionocarbamates,the optimal process conditions were: To 0.02 mol dixanthogen,10 mL water and 20 mL n-hexane were used as the solvent mixtures;the reaction temperature,time and raw material proportion of alkylamine : sodium carbonate: dixanthogen(mol/mol)were of 45 ℃,6 h and 1.20:1.10:1.00,respectively.Under the optimal conditions,the yield of O-isopropyl-N-ethylthionocarbamate was 95.96%,and that of sulfur was 90.70%.The results of ultraviolet spectra and nuclear magnetic resonance spectroscopy indicated that the as-prepared product was of O-isopropyl-N-ethylthionocarbamate.