Potassium dihydrogen phosphate
[CAS# 7778-77-0]

Identification

• Classification: API >> Water, electrolyte and acid-base balance regulator >> Acid-base balance regulator
• Name: Potassium dihydrogen phosphate
• Synonyms: Potassium dihydrogen orthophosphate; Potassium phosphate; Monopotassium phosphate
• Molecular Formula: KH₂PO₄
• Molecular Weight: 136.08
• CAS Registry Number: 7778-77-0
• EC Number: 231-913-4
• SMILES: OP(=O)(O)[O-].[K+]

Properties

• Density: 2.338
• Melting point: 252.6 °C
• Water solubility: 222 g/L (20 °C)

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302-H312
• Safety Statements: P270-P280-P301+P312-P302+P352-P403-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Skin corrosion	Skin Corr.	1B	H314
Serious eye damage	Eye Dam.	1	H318
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	4	H302
Skin corrosion	Skin Corr.	1A	H314
Acute toxicity	Acute Tox.	4	H332

Discovery and Applications

Potassium dihydrogen phosphate (KH2PO4), also known as KDP, is a widely used compound that was first synthesized and identified in the early 19th century. It consists of potassium ions (K?) and dihydrogen phosphate ions (H2PO4?) that form a colorless to white crystalline solid that is highly soluble in water. The compound is known for its pH buffering capacity and large, well-defined crystals, which are valuable for crystal growth and optics.

Potassium dihydrogen phosphate is widely used as a water-soluble fertilizer in agriculture. It provides plants with essential nutrients - potassium and phosphates, promoting strong plant growth, increased yields, and increased resistance to disease and stress conditions. Its solubility and rapid uptake by plants make it particularly suitable for fertigation in modern agricultural practices. In the food industry, potassium dihydrogen phosphate is a food additive (E340) used primarily as a buffer and acidity regulator. It stabilizes pH in processed foods, beverages, and dairy products, ensuring product consistency, flavor retention, and shelf life.

Potassium dihydrogen phosphate is well known for its role in the production of large, high-quality crystals used in optical and laser technology. It is a key material in nonlinear optical devices such as frequency doublers, where its unique crystal structure and optical transparency enable efficient frequency conversion processes. In addition to crystal growth, KDP crystals are used in electro-optical devices, including modulators and switches. These devices exploit the electro-optic effect of KDP crystals, where the refractive index changes with an applied electric field, enabling precise control of light modulation and signal processing.

Potassium dihydrogen phosphate is used as a buffer in pharmaceutical formulations to maintain pH stability. It ensures the efficacy, safety, and shelf life of drugs and intravenous solutions by preventing pH changes that could affect drug stability or patient safety.

In analytical chemistry, potassium dihydrogen phosphate is used as a standard buffer solution for pH calibration and measurement. Its precise pH control and compatibility with a variety of analytical methods make it indispensable for accurate chemical analysis in laboratory environments.

References

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DOI: 10.1007/bf00256552

1984. Purification and crystallization of bovine liver phosphorylase. Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 790(3).
DOI: 10.1016/0167-4838(84)90016-5

1979. Biliary cholesterol absorption in normal and L-thyroxin-fed rats. Lipids, 14(5).
DOI: 10.1007/bf02533459