Abstract
The syntheses of dialkyl N-phosphonophosphoramidates by the reaction of higher dialkyl phosphoramidate with phosphorus pentachloride were investigated. The alkyl groups were amyl, heptyl, hexyl, and octyl.
Unfavourably, the cleavage of C-O-P or P-N bonding took place owing to the large amount of hydrogen chloride liberated during the reaction. Therefore, the reaction mixture must be kept at a low temperature such as from 5 to 10°C and the reaction time must be shortened. On the hydrolysis, although two chlorine atoms out of three chlorine atoms combined with the phosphorous atom of the intermediate were released readily, it was difficult to release one remained chlorine completely and to remove the liberated hydrogen chloride from the product completely. It was found that the convenient hydrogen chloride scavenger in this synthesis is propylene oxide. Use of large exess of propylene oxide resulted to form the addition product of propylene oxide.
Mono-and di-potassium salts of dialkyl N-phosphonophosphoramidates indicated excellent surface activities to give the lowest value of surface tension in aqueous solutions, as low as 26 dyne/cm.
These compounds were found to possess the superior rust-preventive power against mild steel and aluminium in aqueous solutions in the range from pH 3 to 10.
