atom or an aliphatic cycloaliphatic or aromatic hydrocarbon group or a heterocyclic group examples of these hydrocarbon groups or heterocyclic groups are given above specific examples of suitable amino radicals are dimethylamino diethylamino dipropylamino dibutylamino monomethylamino monoethylamino monododecylamino mono c 10 14 alkylamino monooctadecylamino anilino p dodecylanilino and n butylanilino alternatively both symbols r and the nitrogen atom to which they are attached can together represent a heterocyclic radical linked to the phosphorus atom through the nitrogen atom examples of such groups are morpholino piperidino tetrahydroquinolino pyrrolidino etc the compounds in which y represents a further piperazino group are of course a special instance of this y can also represent a group of the formula or in which r has the meaning given above examples of such groups are alkoxy such as methoxy ethoxy propoxy butoxy dodecyloxy and octadecyloxy and aryloxy such as phenoxy tolyloxy or benzyloxy any of the above radicals can if desired be substituted the only limitation upon the nature of the substituents is that they should be inert under the conditions of the reaction employed in synthesizing the compound in the groups of the formula str11 r 1 r 2 and r 3 which may be the same or different represent substituents on the piperazine ring here again the only limitation upon the nature of the substituent is that it should be inert under the conditions of the reaction used to synthesize the compound the substituent can for example be one of the groups set out above for y provided that such a group is inert when present it can for example be an alkyl group such as a methyl.