Reaction of phosphonic acids with dicyclohexylcarbodiimide yields pyrophosphonic acids,[RPO (OH)] 20, which with alcohols or phenol furnish the respective alkyl or phenyl hydrogen phosphonate esters. These in turn with dicyclohexylcarbodiimide give diaIkyl pyrophosphonates,[RPO (OR) J20, which react with amines [to render alkyl N-substituted phosphonamidates. The monoesters and ester-amidates of p-aminophenylphosphonic ...