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 synthe sized by condensing 2-chloroethyl phosphonyl dichloride 3 with ethyl alcoho l followed by substituted phenols. The phosphonates are tested for their fu ngitoxicity in vitro against two phytopathogenic fungi viz, Sclerotium rolf si and Rhizoctonia solani. O-Ethyl O-2,4,5-trichlorophenyl 2-chloroethyl ph osphonate (4m, ED50 28ppm) and O-ethyl O-pentachlorophenyl 2-chloroethyl ph osphonate (40, ED50 2.9 ppm) are the most active compounds against S. rolfs i and R. solani respectively and possess better activity as compared to edi phenphos and O-methyl series (ref.2). The quantitative structure activity r elationships on the fungicidal activity has been analysed by means of multi ple regression analysis. Physico-chemical parameters of phenyl ring substit uents using hydrophobic, electronic and steric properties indicate that hyd rophobic and electronic parameters have major contribution in determining t he fungitoxicity of phosphonates as compared to position specific steric pa rameters.