Newer developments in the microwave-assisted synthesis of potentially biologically active organophosphorus compounds
The microwave (MW) technique has become an important tool in organophosphorus chemistry. In this paper, the advantages of MWs in different reactions are surveyed allowing green chemical accomplishments. The first case is the MW-assisted direct esterification of phosphinic and phosphonic acids to phosphinates and phosphonates, respectively. These reactions do not take place on conventional heating. The higher enthalpy of activation may be overcome only by MW activation. It was also observed that the esterifications became more efficient in the presence of an ionic liquid catalyst. The phase transfer catalyzed (PTC) O-alkylation of phosphonic acids under MW irradiation is another option for the esterification. The opposite reaction, the acidic hydrolysis of the above mentioned P-esters were carried out under optimized conditions both on conventional heating, and on MW irradiation. Both steps of the hydrolysis of phosphonates were characterized by pseudo first order rate constants. The second step was found to be the rate determining.