The reaction was carried out without isolation of intermediates in a one pot synthesis. Toluene (30 ml) and phosgene solution (20% in xylene, 9.1 ml, 17.16 mmol) were charged into a reaction flask. The mixture was cooled to −50° C. A mixture of 2-phenylsulfanylphenylamine (3 g, 14.9 mmol), triethylamine (2.4 ml, 17.1 mmol) and toluene (5 ml) was charged into the reaction flask at −50° C. during 5 min. The mixture was allowed to reach room temperature and it was stirred at room temperature for 1.5 h. Then the reaction mixture was added to another reaction flask at −10-0° C., containing the cooled mixture of 1-[2-(hydroxyethoxy)-ethyl]-piperazine, triethylamine (2.7 ml) and toluene (20 ml). The reaction mixture was stirred at room temperature for 1.5 h. Precipitated triethylamine hydrochloride was filtered off. The resulting toluene solution was washed twice with saturated NaCl-water (10 ml), dried with K2CO3 and evaporated in vacuo. The yield of 4-[2-(2-hydroxyethoxy)-ethyl]-piperazine-carboxylic acid (2-phenylsulfanyl-phenyl)-amide was 4.76 g.
