Synthesis Of Compounds Bearing Urea And Thiourea Moieties In Water Media

Environmentally friendly chemical process is the vital part of the current chemical research and development. Organic reactions in water media have attracted more and more attention from chemists because there are many potential advantages and benefits in terms of cost, safety, environmental concerns, efficiency, and selectivity when the common organic solvents are replaced by water in organic reactions. Furthermore, due to the polarity of water molecule, organic reactions in water media can be accelerated by means of microwave irradiation, phase transfer catalysts.N,N'-Disubstituted ureas and thioureas are important subunits present in a number of naturally occurring compounds and have found numerous applications as dyes, antioxidants, pesticides, corrosion inhibitors, intermediates for the preparation of pharmaceuticals, and agricultural chemicals. Urea derivatives bearing hydrazine, carbohydrazide and thiocarbohydrazide moieties may be good active compounds.In this thesis, we designed and synthesized three series of urea derivatives by reactions of substituted primary amines with (thio)urea using microwave irradiation, phase transfer catalyst in water.Chapter 1: N,N'-Disubstituted ureas were efficiently synthesized by reactions of urea with a variety of amines in water medium under microwave irradiation using CeCl₃.7H₂O-KI as catalyst. This protocol has advantages of no use of toxic phosgene and hazardous organic solvents, high reaction rate, high yield and a simple work-up procedure.Chapter 2: An environmentally benign method for the synthesis of symmetrical N,N'-disubstituted thioureas in water medium using poly(ethylene glycol)-400 (PEG-400) as catalyst and microwave as heating source is described. Diaryl- and dialkyl-thioureas are efficiently synthesized by reactions of thiourea with a variety of amines. This protocol has advantages of no use of hazardous reagents and volatile organic solvents, rapid reaction rate, high yield and simple work-up procedure.Chapters 3, 4, 5: 1,2-bis(N-substituted carbamoyl)hydrazines, 1,5-bis(N-substitut -ed carbamoyl)carbohydrazides, 1,5-bis(N-substituted carbamoyl)thiocarbohydrazides are efficiently synthesized by reactions of N-substituted ureas with hydrazine, carbohydrazide and thiocarbohydrazide in water media using PEG-400 as catalyst and microwave as heating source. This protocol has advantages of no use of hazardous reagents and volatile organic solvents, rapid reaction rate, high yield and simple work-up procedure.The structures of all compounds were confirmed by elemental analyes, IR and ¹HNMR.