[ 11 C]Methanol production by a fast and mild aqueous‐phase reduction of [ 11 C]formic acid with samarium diiodide

The reduction of [ 11 C]carbon dioxide to [ 11 C]methanol with lithium aluminium hydride (LiAlH 4 ) and subsequent conversion into [ 11 C]methyl iodide is a standard way of producing the latter precursor for radiolabelling. However, it suffers from appreciable losses by incomplete reduction giving [ 11 C]formate. We show that samarium diiodide (SmI 2 ) can be used to improve the yield of [ 11 C]methanol by its ability to efficiently reduce [ 11 C]formate to [ 11 C]methanol. This can be done either by making [ 11 C]formate intentionally and treating it with SmI 2 or by treating the LiAlH 4 ‐reduced [ 11 C]CO 2 with SmI 2 . In the latter approach, sodium thiosulphate has a similar effect as SmI 2 . Hydriodic acid was also shown to exert some reducing action on [ 11 C]formate too. [ 11 C]Carbonate is reduced to a small extent by SmI 2 under the mild conditions employed. In contrast to the very easy [ 11 C]formate reduction, SmI 2 had little effect on [ 11 C]acetate and practically no [ 11 C]ethanol could be produced. Copyright © 2006 John Wiley & Sons, Ltd.