Preparation And Application Of Substituted Thiourea Derivatives

Different synthetic methods and applications of symmetric and unsymmetric thioureas were studied in this dissertation. The applications contained two aspects, one is preparation of corresponding carbodiimides from symmetrical and unsymmetrical thioureas via dehydrosul--furisation using HTIB; the other is synthsis of benazolin-ethyl with 1-(2-Chlorophenyl)-2-thiourea as raw material.Symmetrical and unsymmetrical thioureas were synthesized by three methods. Reaction of amine and carbon disulfide using DMAP as catalyst gave 7 symmetrical thioureas, the optimized conditions (aniline as the substrate) is refluxing with molar ratio of amine and carbon disulfide 1:1.6 in the presence of 2.5mmol DMAP. Under these conditions the yields of 7 symmetrical thioureas were at the range of 60% to 96%; Reaction of amine with isothiocyanates at room temperature for 2.5 hours with molar ratio of amine and isothiocyanates 1.05:1, gave symmetric and unsymmetric thioureas. The yields were between 74% and 100%; Reaction of amine and N,N'-diphenyl thiourea under reflux for 3 hours with molar ratio of amine and N,N'-diphenyl thiourea 1.2:1, gave 6 unsymmetric thioureas in yields of 60%-98%.Reaction of amine and isothiocyanates in ionic liquids, [Bmim][BF4], at room temperature for 15 minutes with molar ratio of amine and isothiocyanates 1:1 gave symmetric and unsymmetric thioureas. With phenylisothiocyanate and p-toluidine as the substrates the yields of thioureas were 89% to 99%; the yield of the products was up to 87% after recycling ionic liquids 4 times. Reaction of amine and carbon disulfide in ionic liquids, [Bmim][BF4], at 55℃for 3 hours with molar ratio of amine and carbon disulfide 1.2:1, gave symmetric thioureas in more than 85%yields. The yield of the products was 70% after recycling ionic liquids 5 times.Dehydrosulfurisation of symmetrical and unsymmetrical thioureas using HTIB gave corresponding carbodiimides. Under optimized conditions the yields of symmetrical and unsymmetrical carbodiimides were between 63% and 90%.Benazolin-ethyl was synthesized by using 1-(2-Chlorophenyl)-2-thiourea as raw material via intermediates of 2-amino-4-chlorbenzothiazole and 2-hydroxy-4-chlorbenzothiazole. The overall yield of the product was 43%.