Reaction between ethylenediamine and aryl phosphorodichloridates yields aryl hydrogen N-(2-aminoethyl)-phosphoramidates and not cyclic phosphorodiamidates as reported earlier. I.r. spectroscopy distinguishes between such acids and true cyclic phosphorodiamidates made from trimethylenediamine. 1,2-, 1,3-, and 1,4-Diaminoalkanes cyclise with phenyl phosphorodichloridothionate. o-Phenylenediamine behaves analogously to ethylenediamine.