Tris(aminomethyl)phosphine oxide (6) can be synthesized from octakis(hydroxymethyl)diphosphonium sulfate (1b) in an overall yield of 54.6% via the methyl carbamate derivatives2b,3, and4. On a preparative scale, the last step is complicated by the formation of a cyclic by-product8in amounts up to 20% of the total. The triamine6forms a 1:1 adduct (11) with carbon dioxide, whose structure, established by1H and13C nmr, consists of equimolar amounts of carbamateAand dicarbamateBC. The componentsA,B, andCcan be separated by ion exchange. Thermolysis of11regenerates6smoothly, providing a convenient method for purifying the triamine.