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

The reduction of [¹¹C]carbon dioxide to [¹¹C]methanol with lithium aluminium hydride (LiAlH₄) and subsequent conversion into [¹¹C]methyl iodide is a standard way of producing the latter precursor for radiolabelling. However, it suffers from appreciable losses by incomplete reduction giving [¹¹C]formate. We show that samarium diiodide (SmI₂) can be used to improve the yield of [¹¹C]methanol by its ability to efficiently reduce [¹¹C]formate to [¹¹C]methanol. This can be done either by making [¹¹C]formate intentionally and treating it with SmI₂ or by treating the LiAlH₄‐reduced [¹¹C]CO₂ with SmI₂. In the latter approach, sodium thiosulphate has a similar effect as SmI₂. Hydriodic acid was also shown to exert some reducing action on [¹¹C]formate too. [¹¹C]Carbonate is reduced to a small extent by SmI₂ under the mild conditions employed. In contrast to the very easy [¹¹C]formate reduction, SmI₂ had little effect on [¹¹C]acetate and practically no [¹¹C]ethanol could be produced. Copyright © 2006 John Wiley & Sons, Ltd.