Carbodiimides. Dehydration of ureas

Water-Binding Solid Scintillators: Synthesis, Emission Properties, and Tests in3H and14C Counting

“…By elimination of H 2 S employing HgO [26] the corresponding carbodiimides 10 were obtained in moderate (10 a) to fair (10 b, 10 c) yields. Elimination of H 2 O from the ureas 8 by various methods [24,27,28] failed.…”

Phosgenation Reactions: Sections 4.5.3–4.8

“…Phosphorus pentoxide Dialkyl-and diarylcarbodiimides bearing cyclohexyl, phenyl, p-chlorophenyl, and p-ethoxyphenyl residues have been synthesized from the corresponding ureas with phosphorus pentoxide in pyridine, charged with sand, under reflux [1255]. DCC has been prepared this way within 2.25 h in 76% yield (see also Section 4.5.3.5, Table 4.48).…”

“…Dicyclohexylcarbodiimide DCC [1255]: A stirred mixture of N,N 0dicyclohexylurea (19.7 g), phosphorus pentoxide (100 g), sand (175 g), and pyridine (700 mL) was refluxed for 2.25 h. Stirring was no longer possible after about 30 min. Dicyclohexylcarbodiimide DCC [1255]: A stirred mixture of N,N 0dicyclohexylurea (19.7 g), phosphorus pentoxide (100 g), sand (175 g), and pyridine (700 mL) was refluxed for 2.25 h. Stirring was no longer possible after about 30 min.…”

“…Other frequent applications are in esterifications and general dehydration reactions, and, more recently, in carbodiimidemediated multicomponent reactions [1251] (see Section 4.5.3.5). Several reagents have been employed in carbodiimide synthesis: phosgene [1252,1253], dimethylphosgeniminium chloride [1254], triphosgene [561,562], phosphorus pentoxide [1255], phosphoryl chloride [1256], triphenylphosphine dibromide [758,[1257][1258][1259][1260][1261], triphenylphosphine/tetrahalomethanes [1262,1263], iminophosphoranes [1264][1265][1266][1267][1268][1269][1270][1271][1272][1273][1274][1275][1276][1277], Mitsunobu reagent [1278,1279], p-tosyl chloride [1280,1281], and CDC [1137]; oxidative additions have also been used [1282][1283][1284]. Thus, compounds with a carboxylic function 1688 can be coupled with a nucleophilic compound 1690 to afford the coupled product 1691 under extremely mild conditions.…”

Ultrasonic-assisted synthesis of carbodiimides from N,N′-disubstituted thioureas and ureas

“…Some examples included thermolysis-decarboxylation of isocyanates [5], dehydration of ureas [6][7][8][9][10][11], dehydrosulfurization of thioureas [8,[12][13][14][15][16][17], rearrangements of amidoximes [18,19], as well as metal-catalyzed direct condensation of an amine with an isonitrile [20,21]. Nevertheless, there are still some limitations associated with some of the existing methods including the use of expensive or highly toxic reagents, long reaction times, harsh reaction conditions, and/or limited substrate scope.…”