| Abstract: | Thirty-five dialkyl phenyl phosphates analogous to methyl and ethyl paraoxon were synthesized and their insecticidal activity against house fly (Musca nebulo) determined. Gas chromatographic retention indices (GCRI) at 200°C for all the phosphates were determined on OV-101, DB-1701 and DB-WX fused-silica capillary columns. The retention indices on polar and nonpolar columns (DB-1701 and OV-101, DB-WX and OV-101) considered together were shown to be related to the Hansch hydrophobic constant (II). Multiple regression analysis using the least-square method was carried out to establish the linear relationships between insecticidal activity and GCRI along with the Hammett constant, (σ). The multiple correlation coefficients (r) of various parameters obtained using GCRI were found to be as significant as those obtained using II values. It was found that both hydrophobic and electronic effects made a significant contribution to the insecticidal activity of dialkyl phenyl phosphates. It is concluded that GCRI on two columns can be used directly as an indicator for hydrophobicity in QSAR studies provided that a suitable pair of polar and nonpolar columns is used for this purpose. |
