Disodium phosphate is one of the many sodium phosphates and is obtained by treating phosphoric acid with sodium carbonate at high temperature.

The name describes the structure of the molecule:

• Disodium indicates the presence of two sodium ions (Na+) in the compound.
• Phosphate indicates that the compound is a phosphate, i.e. it contains one phosphorus atom bonded to four oxygen atoms (PO₄^3-).

The synthesis process takes place in different steps:

• Preparation of sodium hydroxide and phosphoric acid. Sodium hydroxide (NaOH), also known as caustic soda, is prepared by electrolysis of a sodium chloride solution. Phosphoric acid (H3PO4) is produced by the reaction of sulphuric acid with phosphate rock.
• Neutralisation reaction. Sodium hydroxide is reacted with phosphoric acid. This is a type of acid-base neutralisation reaction, which produces water and a salt, in this case disodium phosphate.

What it is used for and where

It has many applications:

• In medicine to combat lead poisoning and in cases of phosphorus deficiency.
• In the textile industry to make fabrics less flammable.
• In the ceramic glaze industry.
• In the food industry as a buffer and neutralizer.
• In agriculture  as a fertilizer.
• In veterinary medicine, as a laxative.

Cosmetics

Disodium phosphate in cosmetics, it is an acidity regulator, enhances the antioxidant action of other ingredients and prevents the formation of lumps.

• Buffering agent. An ingredient that can bring an alkaline or acid solution to a certain pH level and prevent it from changing. in practice a pH stabiliser.
• Corrosion inibitor
• Fragrance. It plays a very important role in the formulation of cosmetic products as it allows perfume to be enhanced, masked or added to the final product, improving its commercial viability.  The consumer always expects to find a pleasant scent in a cosmetic product.
• pH adjuster. This ingredient tends to restore the pH of a cosmetic formulation to its optimal value. The correct pH value is an essential determinant for lipid synthesis in the stratum corneum. The average physiological pH value of the face ranges between 5.67 and 5.76. The hair fibre has a pH value of 3.67.

Disodium phosphate studies

• Molecular Formula: HNa₂O₄P
• Molecular Weight: 141.957 g/mol
• CAS: 7558-79-4
• EC Number: 231-448-7
• UNIII: 22ADO53M6F
• FEMA Number: 2398

• dibasic sodium phosphate, anhydrous
• phosphoric acid, disodium salt, heptahydrate
• disodium acid phosphate
• phosphoric acid, monosodium salt
• disodium hydrogen phosphate
• phosphoric acid, monosodium salt, anhydrous
• disodium hydrogen phosphate anhydrous
• phosphoric acid, sodium salt
• monosodium dihydrogen phosphate
• phosphoric acid, trisodium salt
• neutral sodium hydrogen phosphate
• phosphoric acid, disodium salt
• phosphoric acid, disodium salt, 32P-labeled
• phosphoric acid, disodium salt, anhydrous
• phosphoric acid, disodium salt, dodecahydrate