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The use of catalytic hydrogenation for the conversion of α-hydroxyiminophosphonates into α-aminophosphonates (and hence α-aminophosphonic acids) is reviewed. Using the synthesis of α-aminopropanephosphonic acid as a specific example for study, the effects of variation in reaction conditions have been investigated. It has been found that both Raney nickel and palladium on activated carbon are effective catalysts at elevated temperatures and pressures, but that traces of nickel may contaminate the finally isolated aminophosphonic acid if Raney nickel is used. The formation of an aminophosphonate-nickel complex is a possible complication. Yields were found to fall as the reactant concentration was increased although this effect was offset by carrying out the hydrogenation in the presence of liquid ammonia. Optimum yields were in the region of 60-65%. Keywords Hydroxyiminophosphonate • aminophosphonate • aminophosphonic acid • catalytic hydrogenation • nickel • palladium Acknowledgement The financial support of KenoGard AB, Stockholm, is gratefully acknowledged. We also thank Dr. G. Cameron for helpful discussions.

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