7558-79-4/Disodium phosphate

Preparation

Dibasic sodium phosphate is prepared by treating phosphoric acid with a slight excess of sodium carbonate. The solution is boiled to expel carbon dioxide. Upon cooling dodecahydrate crystallizes out. Heating dodecahydrate at 100°C forms the anhydrous salt. H3PO4 + Na2CO3 → Na2HPO4 + CO2 + H2O Dibasic sodium phosphate also is prepared by reacting dibasic calcium phosphate with sodium carbonate. The product calcium carbonate precipitates leaving dibasic sodium salt in the solution. The solution on cooling yields crystals of hydrated product. CaHPO4 + Na2CO3 → CaCO3 + Na2HPO4

Flammability and Explosibility

Nonflammable

Biochem/physiol Actions

Sodium phosphate dibasic is an important component of running buffer of denaturing gel electrophoresis. It induces glomerular calcification as well as other nephrotic syndrome in Sprague-Dawley rats.

Safety Profile

Poison by intravenous route. Moderately toxic by intraperitoneal, subcutaneous, and intramuscular routes. Mildly toxic by ingestion. A skin and eye irritant. When heated to decomposition it emits toxic fumes of POx and Na2O. See also PHOSPHATES.

Purification Methods

Crystallise the salt twice from warm water, by cooling. Dry in air, then in an oven overnight at 130o. It should be dried before use as it is slightly hygroscopic. It forms di-, hepta-and deca-hydrates.

Physical Characteristics

Appears as a colorless to white crystalline solid. Soluble in water. Disodium hydrogen phosphate is used in various industries including fertilizer, pharmaceuticals, food processing, and others.

Crystallization Properties

Crystallizes as the dodecahydrate (Na2HPO4鈰?12H2O) in frozen solution.
Primary drying results in ice sublimation and the disappearance of the dodecahydrate peaks.

Corrosion Inhibition

Disodium hydrogen phosphate and other phosphate compounds are used as environmentally-friendly inorganic inhibitors due to low toxicity and cost.
Can retard the anodic dissolution and migration of metal ions, acting as an inhibitor for tin when used in proper concentration.

Role in Electrochemical Migration (ECM) Inhibition

The addition of Disodium hydrogen phosphate can react with metallic tin or tin ions to form a protective film on the anode surface, increasing the pitting potential. Slows down the rate of anodic dissolution and retards the ECM of tin. Fractal-like dendrites formed during ECM tests consist mainly of tin elements.

Use in Magnesium Potassium Phosphate Cement (MKPC)

Used in combination with potassium dihydrogen phosphate to produce MKPC.
Increases the pH value of MKPC paste, resulting in endothermic reactions and cooling of the paste.
Delays early hydration, improves fluidity and increases setting times of MKPC paste.
Although early compressive strength may be slightly lower, long-term strength development is higher due to better crystallization and more stable hydration products.

Physical properties

The anhydrous compound is white crystalline powder; hygroscopic; density 1.70 g/cm3; converts to sodium pyrophosphate at 240°C; soluble in water;insoluble in alcohol.The dihydrate is a crystalline powder or granular solid; density 2.066 g/cm3 at 15°C; loses water of crystallization at 92.5°C.The heptahydrate is a powdered or granular crystalline solid; density 1.679 g/cm3; loses five molecules of water at 48°C.The dodecahydrate is made up of translucent crystals or granules; density 1.524 g/cm3; readily loses five water molecules on exposure to air at ambient temperature; melts at 35°C when the salt contains all water of crystallization; loses all water at 100°C.All the hydrates are soluble in water and insoluble in alcohol.

General Description

Sodium phosphate dibasic in combination with sodium phosphate monobasic is used in the preparation of oral sodium phosphate solution (OSPS), which is a purgative used for bowel cleansing before colonoscopy.