The Research For Novel Synthesis Of Thiourea And Its Use

As an important basic chemical material, thiourea, the encouraging investment field for foreign trades, has been widely used in industry and daily life. So the production of thiourea becomes a hot spot. The conventional innovative methods has been widely studied. The purpose of this thesis is just to search a novel synthesis of thiourea, and to use thiourea in dealing with the waste water from the production of phthalic anhydride, and the application of thiourea in solid-state reactions at low heating temperature was also studied.In this thesis, the fundamental industrial chemical urea and waste gas H₂S were selected to synthesize thiourea. Then thiourea was used as the catalyst in dealing with the waste water, by isomerization of maleic acid, to produce fumaric acid in high yield and high purity.The synthesis of thiourea can be divided into two steps. First, cyanamide was produced by dehydration of urea. Second, cyanamide reacted with Na₂S in water solution, which produce thiourea and NaOH. Na₂S can be reformed by the reaction of hydrogen sulfide and NaOH. The optimum conditions of this reaction were obtained: 100ml distilled water and 7.8g Na₂S in the reaction vessel at 50℃, 2g solid cyanamide was added, then start to ventilate H₂S gas at 20ml/min. After 30min, closing H₂S gas and adding another 2g cyanamide. Continual recurrence until the product appeared in the solution. Cooled the system to room temperature and filtered to obtain the white needle crystals of thiourea. The mother liquid was then utilized in circulation. Melting points IR spectra, UV spectra were used as qualitative study and HPLC was used as quantitative study. The yield can increase from 60-70% to 90% and the purity can reach above 97%.Thiourea was then used as the primary catalyst to making fumaric acid from the waste water of phthalic anhydride. In this thesis, we have systematically studied various influence factors, such as catalyst, reaction time and temperature, purificationetc. The optimum conditions were: using thiourea as primary catalyst(2.5wt%), ZnSC>4 as cocatalyst(0.05wt%), the temperature of the isomerization was at 110°C and for 120min, decolouration reaction with active carbon(2wt%)for 15min. Melting point > IR spectra ^ UV spectra were used as qualitative study and HPLC was used as quantitative study. The yield can increase from 84.4% to 93.7% and the purity of fumaric acid can be achieved above 99%.The application of thiourea in solid-state reactions at low heating temperature was also studied. As a normal ligand in coordination chemistry, thiourea has been scarcely studied in the field of solid-state reactions at low heating temperature. Compared to solvent reactions, solid-state reactions at low heating temperature have many merits ,such as simple> convenient -, no pollution and low cost. In this thesis the solid-state reaction of NiCl2-6H2O and thiourea at low heating temperature was studied for the first time. XRD and DTA were used to investigate its mechanism. DTA result shows surface water of NiCb^FbO are easy to lose, which can start the reaction. XRD result shows reaction is the rate controlling step in this solid state reaction at low heating temperature.