Synthesis, Characterization and Fungicidal Activity of Some Dialkyl Alkylphosphonates and Dialkyl Phenylphosphonates

Some dialkyl alkylphosphonates and dialkyl phenylphosphonates were synthesized by the reactions between trialkyl phosphite and alkyl/aryl halide in the presence of benzene. The synthesized compounds were characterized by elemental analysis, thin layer chromatography (TLC), fourier –transform infrared, ( 1 H, 13 C) nuclear magnetic resonance (NMR) spectroscopic techniques. In vitro fungicidal activity of the synthesized compounds against Aspergillus flavus, Aspergillus niger, Fusarium oxysporium, Rhizopus stolonifer, Leveillula taurica and Peronospora tabacina showed that they were fungicidal. The ‘Minimum Inhibitory Concentration’ (MIC) of the synthesized compounds ranged between 1000ppm and 5ppm. While their ‘Inhibitory Concentration at 50% inhibition’ (IC50) ranged between 500ppm and 2ppm. These results showed that the fungicidal activity of the synthesized phosphonates varied from one compound to another. Based on the results obtained from the in-vitro screening, the four most active synthesized compounds (diethyl ethylphosphonate, diisopropyl ethylphosphonate, diethyl p-hydroxyphenylphosphonate and diethyl pmethoxyphenylphosphonate) were subjected to in-vivo screening. The results of the in-vivo screening showed that diethyl p-methoxyphenyl phosphonate gave the highest fungicidal activity against powedery mildew. All the compounds subjected to in-vivo screening were phytotoxic at a concentration greater than 50ppm.