Orthoboric acid
[CAS# 10043-35-3]

Identification

• Classification: API >> Synthetic anti-infective drugs >> Disinfectant antiseptic
• Name: Orthoboric acid
• Synonyms: Boracic acid; Boron trihydroxide; Boric acid; Entimaden; Flea Prufe; NSC 81726
• Molecular Formula: H₃BO₃
• Molecular Weight: 61.83
• CAS Registry Number: 10043-35-3 (11113-50-1)
• EC Number: 233-139-2
• SMILES: B(O)(O)O

Properties

• Solubility: 49.5 g/L (water, 20 °C), soluble (ethanol, acetone) (Expl.)
• Density: 1.4±0.1 g/cm³, Calc.^*, 1.435 g/mL (Expl.)
• Melting point: 169 °C (decomp.) (Expl.)
• Index of Refraction: 1.385, Calc.^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS08 Danger
• Risk Statements: H360FD
• Safety Statements: P203-P280-P318-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Reproductive toxicity	Repr.	1B	H360
Reproductive toxicity	Repr.	1B	H360FD
Reproductive toxicity	Repr.	1A	H360
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	1	H370
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Acute toxicity	Acute Tox.	4	H332
Specific target organ toxicity - single exposure	STOT SE	3	H335
Specific target organ toxicity - single exposure	STOT SE	3	H336
Reproductive toxicity	Repr.	1B	H360FD

Discovery and Applications

Orthoboric acid, commonly known as boric acid (H₃BO₃), is a weak Lewis acid of boron that has been widely studied and utilized across various industries. It occurs naturally in certain minerals, volcanic waters, and hot springs. It can be synthesized through the reaction of borax (sodium tetraborate) with mineral acids, such as hydrochloric or sulfuric acid, resulting in the precipitation of orthoboric acid in crystalline form. The compound is highly soluble in water and alcohol, with its solubility increasing at higher temperatures.

Orthoboric acid is extensively used in the glass and ceramics industry, where it serves as a flux to lower the melting point of silica-based materials and improve the mechanical strength and thermal resistance of glass and ceramic products. In the production of borosilicate glass, it enhances durability and resistance to thermal expansion, making it a key component in laboratory glassware, cookware, and optical materials.

In agriculture, orthoboric acid is an important source of boron, an essential micronutrient for plant growth. It is incorporated into fertilizers to correct boron deficiencies in soil, which can otherwise lead to poor root development and reduced crop yields. However, excessive application can be toxic to plants, requiring careful dosage control.

Orthoboric acid has been widely employed in the pharmaceutical and medical fields. Due to its mild antiseptic and antifungal properties, it has been used in ophthalmic solutions, skin treatments, and as a preservative in some pharmaceutical formulations. It has also been utilized in medical research to study its potential effects in various biological systems.

In industrial applications, orthoboric acid functions as a lubricant and flame retardant. It is used in metalworking fluids, where it helps reduce friction and wear. In polymer manufacturing, it contributes to flame resistance in plastics, textiles, and other materials by inhibiting combustion and reducing flammability.

Another significant application of orthoboric acid is in pest control. It has been widely used as an insecticide against cockroaches, ants, and termites. Its mechanism of action involves disrupting the digestive system and metabolism of insects, leading to dehydration and death. Since it is relatively low in toxicity to humans and pets when used appropriately, it has been incorporated into household and commercial pest control products.

In nuclear energy applications, orthoboric acid is employed as a neutron absorber in pressurized water reactors (PWRs). The boron content in the acid helps regulate the fission reaction by controlling neutron flux, contributing to reactor safety and efficiency.

Orthoboric acid has been extensively studied for its physicochemical properties and interactions with various substances. It is known to form esters with alcohols and reacts with polyhydroxy compounds to create stable complexes. These chemical properties have been leveraged in laboratory research and chemical synthesis.

Due to its wide range of applications and well-documented properties, orthoboric acid remains an important chemical in numerous fields. Its availability, stability, and functional versatility make it a valuable material in both scientific and industrial contexts.

References

2025. Ratio type nanoprobe with boric acid as recognition unit for imaging intracellular H2O2 with SERS. Talanta, 281.
DOI: 10.1016/j.talanta.2024.127224

2025. Modulating room temperature phosphorescence of acrylamide by stepwise rigidification for its detection in potato crisps. Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 328.
DOI: 10.1016/j.saa.2024.125372