Salting-out phenomenon and 1-octanol/water partition coefficient of metalaxyl pesticide

In this paper, we present the effect of inorganic cations such as Na⁺, K⁺, Ca²⁺, Mg²⁺ on the salting-out phenomenon of metalaxyl from pure water to aqueous salt solutions. Moreover the 1-octanol/water partition coefficient in pure water is presented. To accomplish this, aqueous solubility of metalaxyl was determined in pure water, in different salt solution (NaCl, KCl, CaCl₂ and MgCl₂), and at different concentration level ranging from 0.01 to 1.5 M. The 1-octanol/water partition coefficient was determined using the static shake-flask method. Solubility was determined using dynamic saturation method for pure water in the range of 298.15-325.15 K and at 298.15 K for different salt solutions. The solubility value in pure water for studied interval was found constant (m = 3.118 × 10⁻² mol kg⁻¹).Solubility values were used to calculate the standard molar Gibbs free energy of dissolution (Δ_solG°) and transfer (Δ_trG°) at 298.15 K. The values of Δ_trG° from pure to all studied aqueous salt solutions did not exceed 2 kJ mol⁻¹, the value of Δ_solG° of dissolution is 18.5 ±0.72 kJ mol⁻¹. The 1-octanol/water partition coefficient in pure water log K_o/w is equal to 1.69. The obtained results confirm the classification of the neutral metalaxyl as a slightly hydrophobic molecule.