title: Use of 11C as a tracer for studying the synthesis of [11C]urea from [11C]cyanide.
abstract: The use of reversed-phase liquid chromatography and radiochemical detection with carbon-11 (t1/2 = 20.4 min) as a tracer allowed the study of the preparation of [11C]urea from [11C]cyanide at no-carrier-added concentrations. [11C]cyanate was readily prepared by permanganate oxidation of [11C]cyanide at 75 degrees C. The conversion of NH4O11CN (approximately 0.03 mM) to [11C]urea in the presence of excess ammonium ions (0.28 M) was found to best fit pseudo first order reaction kinetics with a rate constant of 0.065 +/- 0.008 min-1 at 75 degrees C. Heating at higher temperatures (180-200 degrees C) revealed that the conversion of NH4O11CN to [11C]urea occurred in high yield in less than 3 min. The hydrolysis of [11C]cyanate to [11C]carbonate, a possible side reaction, was found to proceed at a rate of 0.010 +/- 0.001 min-1 at 113 degrees C.
mesh_terms: D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D003486:Cyanides / Q000378:metabolism*; D014508:Urea / Q000138:chemical synthesis*
chemical_list: D002250:Carbon Radioisotopes; D003486:Cyanides; D014508:Urea