Catalytic conversion of 11CO2 and 11CO into synthesis precursors for 11C labelling

The positron emitter carbon-11 (T1/2=20.3 min) is an ideal radio nuclide for tracers in positron emission tomography (PET). In this study catalytic methods for the synthesis of [11C]alcohols have been investigated. The formation of [11C]methanol has been studied on Pd/Al2O3 and Cu/ZnO/Al2O3 catalysts with respect to CO and CO2 carrier addition to the synthesis gas. Carbon monoxide was identified as the precursor of methanol formation on the Pd/Al2O3-catalyst. In contrast on the Cu/ZnO/Al2O3-catalyst methanol was formed on a reaction pathway via an adsorbed CO2-species. A n.c.a.-[11C]methanol synthesis basing on the Cu/ZnO/Al2O3-catalyst has been developed by substitution of the oxygen containing components CO and CO2 in the synthesis gas by N2O. The radiochemical yield, the low selectivity of [11C]methanol production and the rather slow kinetics of this process were arguments against the practical use of this process in the synthesis of 11C-labelling agents. (orig.)