Synthesis and quantitative structure activity relationships of aryl 2-chloroethyl methyl phosphate fungicides

Twenty new O-aryl O-2-chloroethyl O-methyl phosphates (3) have been synthesised by reacting 2-chloroethyl phosphoryl dichloride (1) first with methanol and then with respective phenol and are tested for fungitoxicity in vitro against Pyriculuria oryzae, Helminthosporium oryzae, Rhizoctonia solani and Pythium aphanidermatum. O-2-Chloroethyl O-methyl O-pentachlorophenyl phosphate (3t) is the most active compound against all the test fungi and possessed better activity compared to ediphenphos. QSAR study using physico-chemical parameters of phenyl ring substituents for hydrophobic, electronic and steric properties indicate that hydrophobic and electronic parameters have major contribution ill determining the fungitoxicity of compounds against all the fungi. Fungitoxicity increases with increase in hydrophobicity and electron withdrawing nature of the benzene ring substituents. Position specific steric effect of the benzene ring substituents expressed as STERIMOL parameters L, B1 and B4 also contribute towards fungitoxicity.