Preparation And Nucleophilic Activation Of Thiourea Dioxide

Due to its good characteristics of slow decomposition, high reduction potential, safe and convenient, and has sustained reduction, thiourea dioxide widespread studied by researchers at home and abroad. However, thiourea dioxide must be in strong alkaline (pH≥10) and heating (>70℃) before generating sulfoxylate, wich is strong reduction, lead to largely restricted in industrial applications. Such as strong alkaline medium is adversely affect to the reduction reaction activity of Fe(Ⅲ) from kaolin and the high cost of heating.Through a series of experiments, we have optimized the synthesis of thiourea dioxide, explored an effective means of catalytic activation, make thiourea dioxide exhibit high reduction potential under the conditions of room temperature (20℃) and weakly alkaline (pH<9). The specific research:(1) Optimal synthesis process of TD:hydrogen peroxide:thiourea as 2.1:1, a reaction temperature of 4℃, the reaction medium is an aqueous solution of 50% ethanol, and 1.6 times the total amount of solvent for the thiourea, the reaction time of 100 min, cultured crystal time 40min, potassium acetate, acetone, EDTANa and sodium dihydrogen phosphate are added during the reaction, accounted for 2%,3%,0.1% and 0.1% the mass of thiourea. Yield of thiourea dioxide up to 94.69%, purity is more than 97%.(2) Thiourea dioxide does not exhibit a strong reduction performance in aqueous solution at room temperature, at a temperature of 85℃, pH=12 aqueous solution reduction potential will up to -895mV, but will soon decline, and maintain a longer time at about -800mV, so that the reduction potential of an aqueous solution of thiourea dioxide in a temperature of 85℃, pH=12 is about -800mV.(3) Activation of thiourea dioxide by nucleophiles:Under normal temperature conditions, the reduction potential rose rapidly when ethylenediamine, accounted for 8% of the mass of TD, is added to the solution, and after 10 min, the reduction potential can be stabilized at about -750mV, the pH value during the activation reaction process is about 8-9.(4) TD activation using ethylenediamine assisted by ultrasonic wave:Mixed solution of ethylenediamine-TD was placed in an ultrasonic cleaner, ultrasonic frequency 200 kHz, power 500W, stirring slowly, a reaction time of 15min. Reduction potential can be maintained approximately 30 minutes at above-800mV, reach as high as -862mV. Approximately reached the reduction potential of TD solution at temperature of 85℃, pH=12. Achieved the purpose of activation.(5) Evaluation of activated TD:Activated TD is very effective in iron removal from kaolin, when the amount of thiourea dioxide, accounted for 0.3% of kaolin, whiteness is 88.3%, Fe2O3 content dropped to 0.75%(Initial whiteness is 84.5%, Fe2O3 content is 0.85%; the whiteness up to 86.7% and Fe2O3 content is about 0.8% after bleached by hydrosulfite). It is proved by experiments that the activated TD has been far more effective than hydrosulfite in reducing and removing of iron.