Transesterification of bis(trifluoroethyl) chloromethyl- and azidomethyl-phosphonates with alcohols in the presence of catalytic quantities of alcoholates gives dialkyl chloromethyl- and azidomethyl-phosphonates in good yield. This process has been used for the synthesis of dibenzyl azido[H-2(2)]methylphosphonate which has been reduced and hydrogenolised to amino[H-2(2)]methylphosphonic acid under neutral conditions.