Phosphoramides

Phosphoramides are a class of organophosphorus compounds that feature a phosphorus–nitrogen bond and a phosphoryl group (P=O). In their most common forms, the phosphorus center is bonded to two oxygen-containing substituents and to nitrogen-containing substituents, giving structures such as (RO)2P(=O)NR'2 or (R2N)3P=O. The phosphorus is in the pentavalent state (P(V)) and the N-substituents can be alkyl or aryl groups. The class includes simple dialkyl phosphoramides as well as highly substituted derivatives.

Synthesis of phosphoramides typically involves condensation of phosphoryl chlorides with amines or alcohols, or aminolysis of preformed phosphoramide esters. They can also be prepared by oxidation of phosphorane precursors bearing amine substituents. The resulting P(=O)NR2 motifs are generally stable under normal conditions, though some derivatives are moisture-sensitive or air-sensitive.

Among the best-known members are hexamethylphosphoramide (HMPA), with the formula (Me2N)3P=O, and tetrakis(dimethylamino)phosphoramide (TDMA), (Me2N)4P=O. These compounds are highly polar and often serve as polar aprotic solvents or as ligands in coordination and organometallic chemistry due to their strong Lewis basicity. They tend to have high boiling points and substantial thermal stability, which makes them useful in various synthetic applications.

Safety and environmental considerations are important, as many phosphoramides can be toxic or carcinogenic (notably HMPA). Proper handling in well-ventilated fume hoods, with appropriate protective equipment, is advised, and disposal should follow relevant regulatory guidelines.