Nat Phos: How Dibasic Sodium Phosphate Is Made
At a glance
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Chemical name |
Dibasic sodium phosphate |
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Alternative names |
Disodium hydrogen phosphate; disodium phosphate |
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Chemical formula |
Na₂HPO₄ |
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Water solubility |
Freely soluble |
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Natural occurrence |
Rare as the exact compound; commonly manufactured from purified sodium and phosphate sources |
Sodium phosphate minerals occur in nature, but large deposits of the exact pharmaceutical compound Na₂HPO₄ are uncommon. Dibasic sodium phosphate is therefore typically made from purified sodium compounds derived from halite or brine and purified phosphate derived from phosphate rock.
A note on acidity and historical use
Dibasic sodium phosphate is mildly alkaline in ordinary chemical quantities because HPO₄²⁻ can accept H⁺. This chemistry helps explain why sodium phosphate salts have historically been used as buffering ingredients and why Schüessler associated Nat Phos with “acid” complaints such as sour stomach or heartburn.
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Body connection: How the phosphate buffer works When Na₂HPO₄ dissolves, it releases two sodium ions and the hydrogen phosphate ion, HPO₄²⁻. Hydrogen phosphate can accept a hydrogen ion, H⁺, to form dihydrogen phosphate, H₂PO₄⁻. The reaction is reversible: H₂PO₄⁻ ⇌ H⁺ + HPO₄²⁻. If acidity rises, HPO₄²⁻ can bind some H⁺; if conditions become more alkaline, H₂PO₄⁻ can release H⁺. This phosphate pair helps resist sudden pH changes, especially inside cells and in the kidneys. Potassium phosphate can supply the same HPO₄²⁻ ion, so sodium does not make phosphate intrinsically “better” at buffering; the sodium and potassium ions have their own separate physiological distributions. |
Making pharmaceutical-grade Nat Phos
1. Preparing the sodium source
Sodium begins in halite or purified brine. After removal of calcium, magnesium, insoluble matter, and other impurities, the sodium chloride can be converted into reactive compounds such as sodium hydroxide, NaOH, or sodium carbonate, Na₂CO₃.
2. Preparing the phosphate source
Phosphate rock is concentrated and chemically processed to produce purified phosphate material, commonly phosphoric acid, H₃PO₄, as described in the Calc Phos article.
3. Controlled neutralization
The sodium compound and phosphoric acid are combined in the ratio needed to retain one hydrogen on the phosphate ion and produce the dibasic salt.
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2NaOH + H₃PO₄ → Na₂HPO₄ + 2H₂O |
Sodium carbonate may also be used:
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Na₂CO₃ + H₃PO₄ → Na₂HPO₄ + CO₂ + H₂O |
In both reactions, two sodium ions pair with hydrogen phosphate, HPO₄²⁻, to produce Na₂HPO₄.
Crystallization and final purification
Dibasic sodium phosphate is highly soluble, so it generally remains in solution until water is removed or the temperature and concentration are adjusted. Controlled evaporation and cooling produce crystals with the desired form and physical properties.
The crystals are separated, washed if necessary, dried, milled or classified, and tested. The exact hydration state must be specified because sodium phosphate can form hydrates as well as an anhydrous material.
Testing may include identity, sodium and phosphate assay, pH, moisture, hydration state, chloride, sulphate, heavy metals, elemental impurities, and physical appearance.