Chemical Properties of Amino Trimethylene Phosphonic Acid (ATMP)

Amino Trimethylene Phosphonic Acid (ATMP) is a polyphosphonic acid characterized by its h3 acidity, excellent chelating ability, high water solubility, and good chemical stability. Its key chemical properties are summarized below.

Identity and Physical Form

Chemical Identity: The CAS number is 6419-19-8, with a molecular formula of C₃H₁₂NO₉P₃ and a molecular weight of approximately 299.

Appearance: It is commonly supplied as a colorless to pale yellow aqueous solution (typically 50%) or as a white crystalline solid. The solid form is hygroscopic and easily soluble in water.

Key Chemical Properties

Acidity and Ionization: The phosphonic acid groups make ATMP a h3 acid. Its 1% aqueous solution has a pH of ≤ 2.0 . In water at pH 7, the molecule is almost fully ionized (predominantly in a five-times ionized state), which contributes to its high solubility and reactivity.

Solubility and Partitioning: It is highly soluble in water (≥ 500 g/L) and has a very low octanol-water partition coefficient (Log Kow ≈ -3.53), indicating a low potential for bioaccumulation .

Chelation: ATMP can form stable complexes with polyvalent metal ions such as calcium, magnesium, iron, copper, and zinc. This chelating property is fundamental to its function as a scale inhibitor.

Stability: It exhibits good chemical stability and is resistant to hydrolysis in water systems . Its thermal stability is notable, maintaining scale inhibition properties even at temperatures up to 200°C.

Vapor Pressure: The vapor pressure is extremely low (estimated at ~1.9 × 10⁻¹⁰ Pa at 25°C), meaning it is essentially non-volatile .

Safety and Environmental Notes

Corrosivity: ATMP is classified as corrosive to metals under EU regulations. It is also acidic and can cause skin and eye irritation, necessitating appropriate protective equipment during handling.

Environmental Fate: It is not readily biodegradable under standard laboratory conditions. However, it binds h3ly to sediments and sewage sludge (high Koc), which limits its mobility. Abiotic degradation (e.g., photolysis in the presence of ferric ions) can occur in the environment.

ATMP's utility in water treatment stems directly from its h3 acid nature, high water solubility, and powerful chelating capability with metal ions, combined with its resistance to hydrolysis and thermal degradation.