Boric acid

Absorption

Boric acid is well absorbed from the gastrointestinal tract, open wounds, and serous cavities but displays limited absorption in intact skin . Following intraperitoneal injection in mice, the peak concentration was reached in about 1.0-1.5 hr in the brain whereas the value was 0.5 hr in other tissues .

Toxicity

Acute oral LD50 of orthoboric acid is 2660 mg/kg in rat . Individuals are likely to be exposed to boric acid from industrial manufacturing or processing. Local tissue injury from boric acid exposure is likely due to caustic effects. Systemic effects from boric acid poisoning usually occur from multiple exposures over a period of days and involve gastrointestinal, dermal, CNS, and renal manifestations. Gastrointestinal toxicity include persistent nausea, vomiting, diarrhea, epigastric pain, hematemesis, and blue-green discoloration of the feces and vomit.

Description

Orthoboric acid is a white, amorphous powder orcolorless, crystalline solid. Molecular weight=61.84;Boiling point=300℃ (decomposes: loses 1/2 its H2O);Freezing/Melting point=170.9℃ (decomposes above100℃). Saturated solutions: at 0℃, 2.6% acid; at 100℃,28% acid. Hazard Identification (based on NFPA-704 MRating System): Health 2, Flammability 0, Reactivity 1.Boric acid is soluble in water; solubility=4.7 g/100 mL at20℃.

Chemical properties

Boric acid occurs as a hygroscopic, white crystalline powder, colorless shiny plates, or white crystals.

Physical properties

Orthoboric acid is a colorless, transparent triclinic crystal or white granule or powder; density 1.435 g/cm³; melts at 171°C under normal heating; however, slow heating causes loss of water; sparingly soluble in cold water (4.7% at 20°C); pH of 0.1M solution 5.1; readily dissolves in hot water (19.1% at 80°C and 27.5% at 100°C); also soluble in lower alcohols and moderately soluble in pyridine.

The Uses of Boric acid

Boric acid can be used to study molecular biology, DNA and RNA purification, biological buffers and molecular biology reagents. Boric acid has been used to test the toxic effects of boron on growth and antioxidant system parameters of maize (Zea mays L.) roots. Boric acid has also been used to study the effect of time period after boric acid injection on (10)B absorption in different regions of adult male rat′s brain.

Indications

No FDA- or EMA-approved therapeutic indications on its own.

Background

Boric acid, also known as hydrogen borate, is a weak monobasic Lewis acid of boron with the chemical formula H3BO3. Boric acid is typically utilized in industrial processing and manufacturing, but is also used as an additive in pharmaceutical products, cosmetics, lotions, soaps, mouthwash, toothpaste, astringents, and eyewashes . It is known to exhibit some antibacterial activity against infections such as bacterial vaginosis and candidiasis .

Production Methods

Orthoboric acid occurs naturally as the mineral sassolite. However, the majority of boric acid is produced by reacting inorganic borates with sulfuric acid in an aqueous medium. Sodium borate and partially refined calcium borate (colemanite) are the principal raw materials. When boric acid is made from colemanite, the fineground ore is vigorously stirred with mother liquor and sulfuric acid at about 908℃. The by-product calcium sulfate is removed by filtration, and the boric acid is crystallized by cooling the filtrate.

Preparation

Boric acid is produced from borax, colemanite, or other inorganic borates by reaction with sulfuric acid or hydrochloric acid, and cooling the solution to proper temperature:
Na₂B₄O₇ ·10Η₂Ο + H₂SO₄ → 4H₃BO₃ + Na₂SO₄ + 5H₂O
It also may be prepared by extraction of weak borax brine with a kerosene solution of an aromatic diol, such as 2-ethyl-1,3-hexanediol or 3-chloro- 2-hydroxy-5-(1,1,3,3-tetramethylbutyl)benzyl alcohol. The diol-borate chelate formed separates into a kerosene phase. Treatment with sulfuric acid yields boric acid which partitions into aqueous phase and is purified by recrystallization.

Definition

ChEBI: Boric acid is a member of boric acids. It has a role as an astringent. It is a conjugate acid of a dihydrogenborate.

brand name

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World Health Organization (WHO)

Boric acid and some borates were formerly extensively used as disinfectants and antiinflammatory agents. By the late 1960s an association between the death of many infants and application of high concentrations of boric acid contained in topical preparations used in the treatment of napkin rash had been established. This led to the restriction of the use of boric acid in pharmaceutical preparations by many regulatory authorities. In some countries it is now permitted only as an ingredient in ophthalmological preparations.

General Description

Orthoboric acid is a weak monobasic acid, it accepts OH^- ions, hence is a Lewis acid. In boric acid, B is sp² hybridized, forming a planar triangle structure. The principal oxide of boron, B₂O₃, is obtained as a vitreous solid by dehydration of boric acid at red heat.

Hazard

Toxic via ingestion. Use only weak solu- tions. Irritant to skin in dry form.

Flammability and Explosibility

Non flammable

Pharmaceutical Applications

Orthoboric acid is used as an antimicrobial preservative in eye drops, cosmetic products, ointments, and topical creams. It is also used as an antimicrobial preservative in foods.
Orthoboric acid and borate have good buffering capacity and are used to control pH; they have been used for this purpose in external preparations such as eye drops.
Orthoboric acid has also been used therapeutically in the form of suppositories to treat yeast infections. In dilute concentrations it is used as a mild antiseptic, with weak bacteriostatic and fungistatic properties, although it has generally been superseded by more effective and less toxic disinfectants.

Biochem/physiol Actions

Boric acid has antibacterial and fungicidal properties. It is used in the periodontal therapy as an irrigation solution as it elicits bactericidal effects in microbial biofilms in root canal. Boric acid may favor osteoblastic activity and inhibit bone loss. It inhibits Candida albicans fungal infection and has potential to treat vaginal infection.

Pharmacokinetics

Boric acid exhibits minimal bacteriostatic and antifungal activities . Boric acid is likely to mediate antifungal actions at high concentrations over prolonged exposures .

Safety

Boric acid is a weak bacteriostatic and antimicrobial agent, and has been used in topical preparations such as eye lotions, mouthwashes and gargles. It has also been used in US- and Japanese-approved intravenous products. 

Death has occurred from ingestion of less than 5 g in young children, and of 5–20 g in adults. Fatalities have occurred most frequently in young children after the accidental ingestion of solutions of boric acid, or after the application of boric acid powder to abraded skin.

The permissible exposure limit (PEL) of boric acid is 15 mg/m3total dust, and 5 mg/m3 respirable fraction for nuisance dusts.

LdLo (man, oral): 429 mg/kg

LdLo (woman, oral): 200 mg/kg

LdLo (infant, oral): 934 mg/kg

LdLo (man, skin): 2.43 g/kg

LdLo (infant, skin): 1.20 g/kg

LD50 (mouse, oral): 3.45 g/kg

LD50 (mouse, IV): 1.24 g/kg

LD50 (mouse, SC): 1.74 g/kg

LD50 (rat, oral): 2.660 g/kg

LD50 (rat, IV): 1.33 g/kg

LD50 (rat, SC): 1.4 g/kg

Potential Exposure

Boric acid is a fireproofing agent for wood; a preservative, and an antiseptic. It is used in the manufacture of glass, pottery, enamels, glazes, cosmetics, cements, porcelain, borates, leather, carpets, hats, soaps; artificial gems; in tanning leather; printing, dyeing, painting, and photography.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seekmedical attention immediately. If this chemical contactsthe skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove fromexposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing hasstopped and CPR if heart action has stopped. Transferpromptly to a medical facility. When this chemical hasbeen swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.

Orthoboric acid application

Orthoboric acid is a precursor material for other boron compounds. A dilute water solution of boric acid is usually employed as a mild antiseptic and eyewash. Boric acid is too employed in leather manufacture, electroplating, and cosmetics.

Metabolism

No metabolic pathways reported.

Storage

Boric acid is hygroscopic and should therefore be stored in an airtight, sealed container. The container must be labeled ‘Not for Internal Use’.

Shipping

UN 3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9—Miscellaneous hazardous material, Technical Name Required.

Purification Methods

Crystallise the acid three times from H2O (3mL/g) between 100o and 0o, after filtering through sintered glass.Dry it to constant weight over metaboric acid in a desiccator. It is steam volatile. After two recrystallisations of ACS grade. it had Ag at 0.2 ppm. Its solubility (%) in H2O is 2.66 at 0o, 4.0 at 12o and 24 at 80o. At 100o it loses H2O to form metaboric acid (HBO2). When it is heated to redness or slowly to 200o, or over P2O5 in vacuo, it dehydrates to boric anhydride (B2O3) [1303-82-6] to give a white hard glass or crystals with m ~294o.The glass softens on heating and liquefies at red heat. It is an astringent, a fungicide and an antibacterial. [McCulloch J Am Chem Soc 59 2650 1937, Kelly J Am Chem Soc 63 1137 1941, Taylor & Cole J Chem Soc 70 1926, Conti J Soc Chem Ind 44 343T 1925.]

Incompatibilities

Orthoboric acid is incompatible with water, strong bases and alkali metals. It reacts violently with potassium and acid anhydrides. It also forms a complex with glycerin, which is a stronger acid than boric acid.

Waste Disposal

Boric acids may be recovered from organic process wastes as an alternative to disposal.

Regulatory Status

Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (IV injections; ophthalmic preparations; (auricular) otic solutions; topical preparations). Reported in the EPA TSCA Inventory. In the UK, the use of boric acid in cosmetics and toiletries is restricted. Included in the Canadian List of Acceptable Non-medicinal Ingredients.