The stability of EDTMPS (Ethylene Diamine Tetra (Methylene Phosphonic Acid) Sodium Salt) as a phosphate compound at different pH values is strongly related to the phosphate group (-PO₄) and amino group (-NH₂) in its molecular structure . In general, the stability of EDTMPS is affected by the following factors:
1. Stability under acidic environment:
The phosphate group of EDTMPS usually remains well stabilized under acidic conditions, but the amino group may be affected by protonation (-NH₂ → -NH₃⁺), resulting in a change in its complexation properties. Acidic conditions may reduce its ability to bind metal ions, making EDTMPS potentially less effective as a corrosion inhibitor or water treatment agent in such environments.
2. Stability in neutral environments:
EDTMPS generally exhibits good stability in the neutral pH (approximately pH 6-8) range. At this time, the functionality of the phosphate and amino groups is more balanced, contributing to its effectiveness in applications such as water treatment and metal corrosion protection. Therefore, a neutral environment is usually the most stable pH range for EDTMPS.
3. Stability in alkaline environments:
In alkaline environments, the amino group (-NH₂) of EDTMPS tends to deprotonate and becomes more susceptible to forming ligand complexes with metal ions. Although the phosphate group is relatively stable under alkaline conditions, high pH may cause certain changes in the molecular structure, such as a weakening of the phosphate group’s ability to complex with water, thus affecting its performance. Therefore, EDTMPS may show some decrease in stability under strong alkaline conditions.
4. Solubility and stability:
In general, the solubility of EDTMPS at different pH values also affects its stability. EDTMPS is more soluble in acidic and neutral environments, but at very high or very low pH conditions, solubility may decrease, thus affecting its stability.
Summary:
EDTMPS is most stable under neutral pH conditions and can effectively complex with metal ions to provide corrosion inhibition. In contrast, its stability may be reduced in strongly acidic or alkaline environments, especially at high pH values which may lead to a decrease in its performance. Therefore, EDTMPS is generally recommended for use in neutral to weakly acidic or alkaline environments, especially in water treatment, corrosion inhibition and other related applications.