Saturated Solubility Determination and Correlation of 2-Methyl-4-Methylamino-6-Methoxy-1,3,5-Triazine in Several Aqueous Cosolvent Systems from 278.15 to 323.15 K

Abstract

2-Methyl-4-methylamino-6-methoxy-1,3,5-triazine is an important intermediate of tribenuron-methyl with poor aqueous solubility. In this study, we have considered five pure solvents as raw materials and formed four sets of mixed solvents according to their pairs by mixing methanol, ethanol, ethylene glycol (EG), and N,N-dimethyl formamide (DMF) in water. Taking 278.15 K as the starting temperature and referring to the principle of the isothermal static state, the temperature was gradually increased at 5 K intervals until it reached 323.15 K. Under normal pressure (101.1 kPa), when the mole fraction of the solute did not change, the value obtained by high-performance liquid chromatography (HPLC) was the equilibrium solubility of 2-methyl-4-methylamino-6-methoxy-1,3,5-triazine. The mole fraction of 2-methyl-4-methylamino-6-methoxy-1,3,5-triazine at 323.15 K obeyed the following descending sequence: DMF (0.4557) > methanol (0.1852) > ethanol (0.1364) > EG (0.05972). From the point of view of temperature, the influence on the solute cannot be ignored. The amount of 2-methyl-4-methylamino-6-methoxy-1,3,5-triazine dissolved increased from a low value to a high value when the temperature increased from low to high. In addition, a difference observed was that the water content of the mixed solvent was repulsive to the dissolution of the solute. When the water content increased from low to high, the mole fraction of 2-methyl-4-methylamino-6-methoxy-1,3,5-triazine decreased from high to low. In any temperature environment, the same proportion of water was added to the four organic solvents. Compared with other solvents, the mixture of DMF and water had an absolute dissolution advantage. We adopted three cosolvency models including the Jouyban–Acree, van’t Hoff–Jouyban–Acree, and modified Apelblat–Jouyban–Acree models to calculate and correlate the saturated solubility data of 2-methyl-4-methylamino-6-methoxy-1,3,5-triazine. The RAD and RMSD values were 8.90 × 10–3 and 6.36 × 10–4, respectively, as obtained from the van’t Hoff–Jouyban–Acree model, and the Jouyban–Acree model demonstrated a better fitting effect. The determination of solubility helps to obtain solubility parameters, which are a measure of intermolecular forces. Solubility is required in the fields of recrystallization and fractional crystallization in the chemical industry, as well as the synthesis and separation of compounds.