Synthesis, fungitoxicity and quantitative structure activity relationship analysis of O-aryl O-ethyl 2-chloroethyl phosphonates

Fifteen new O-aryl O-ethyl 2-chloroethyl phosphonates 4a-o have been synthesized by condensing 2-chloroethyl phosphonyl dichloride 3 with ethyl alcohol followed by substituted phenols. The phosphonates are tested for their fungitoxicity in vitro against two phytopathogenic fungi viz, Sclerotium rolfsi and Rhizoctonia solani. O-Ethyl O-2,4,5-trichlorophenyl 2-chloroethyl phosphonate (4m, ED50 28ppm) and O-ethyl O-pentachlorophenyl 2-chloroethyl phosphonate (40, ED50 2.9 ppm) are the most active compounds against S. rolfsi and R. solani respectively and possess better activity as compared to ediphenphos and O-methyl series (ref.2). The quantitative structure activity relationships on the fungicidal activity has been analysed by means of multiple regression analysis. Physico-chemical parameters of phenyl ring substituents using hydrophobic, electronic and steric properties indicate that hydrophobic and electronic parameters have major contribution in determining the fungitoxicity of phosphonates as compared to position specific steric parameters.