Efficient 16O-18O isotope exchange reactions of carbonyl compounds in aqueous organic solvents catalyzed by acidic resin

A facile preparative method for stable isotope labeled molecules is widely demanded in analytical standard chemicals, biochemical science and medical applications. A rapid 16O-18O isotope exchange reaction of carbonyl group to attain a high isotopic purity has been demonstrated using a capillary column reactor packed with Dowex 50WX4 resin as a solid acid catalyst. Thus, carbonyl-18O compounds such as benzaldehyde-18O, 3-/4-nitrobenzaldehydes-18O, 1-naphthaldehyde-18O and acetophenone-18O were produced with more than 95 at.% purity under the stable flow operation at a moderate temperature within a residence time of 51 s, when the acetonitrile solutions of carbonyl-16O compounds were injected to the reactor with 100 eq. mol of H218O. The maximal product isotopic ratio, zmax, has been formularized as zmax = (x0y + z0)/(y + 1), where x0 and z0 are isotopic ratio of H2O and carbonyl group as reactants, respectively, and y is the molar ratio [H2O]/[carbonyl group]. The achievement ratio of the actual isotopic ratio (z) to theoretical zmax has reached 0.98 or higher.