CONVERSION OF NO-CARRIER-ADDED [C-11] CARBON-DIOXIDE TO [C-11] CARBON-MONOXIDE ON MOLYBDENUM FOR THE SYNTHESIS OF C-11 LABELED AROMATIC KETONES

A new method for the efficient conversion of no-carrier-added [C-11]ca rbon dioxide into [C-11]carbon monoxide is described. [C-11]Carbon dio xide produced by proton bombardment of ultra high purity nitrogen is p re-concentrated in a cryo trap and then passed through a quartz tube f illed with a mesh of thin molybdenum wire heated to 850 degrees C. [C- 11]Carbon dioxide readily reacts with molybdenum to form [C-11]carbon monoxide and molybdenum(IV) oxide. The latter also reduces carbon diox ide to carbon monoxide and helps improve the performance of the conver ter. [C-11]Carbon monoxide is purified from remaining [C-11]carbon dio xide and collected in a small silica trap from which it is eluted into a reaction mixture for the palladium-mediated synthesis of a C-11-lab elled aromatic ketone. Radiochemical yields of up to 81% (decay-correc ted) for [C-11]carbon monoxide were obtained. Radiochemical purity and specific radioactivity of both [C-11]carbon monoxide and the C-11-lab elled ketone are sufficient for nuclear medical studies with PET. (C) 1997 Elsevier Science Ltd.