The utilization of phosphonic esters in the Knoevenagel condensation

A study has been made of the kinetics of the Knoevenagel condensation, wherein phosphonlc esters have been employed as the active methylene compounds. The relative reactivities of each of the active methylene compounds were determined. The reaction, which was catalyzed by piperidine acetate, was shown to follow second-order reaction kinetics. The relative reactivities of the methylene compounds are: CNCH₂COOC₂H₅ (955), CH₂(COOC₂H₅)₂ (20.4), CNCH₂PO(OC₂H₅)₂ (16.7), C₂H₅OCOCH₂PO(OC₂H₅)₂ (2.8) and CH₂[PO(OC₂H₅)₂]₂ (1). The order of decreasing activating ability of the electron attracting group is: -CN, -COOC₂H₅ and -PO(OC₂H₅)₂. The semiquantitative comparison of the activating influence of the phosphonlc ester group, the carboxylic ester group and the nitrile group on the reactive methylene group of the ester component is discussed