BARIUM HYDROXIDE (BA (OH) 2): PROPERTIES, RISKS AND USES - CHEMISTRY - 2025

The barium hydroxide is a chemical compound of formula Ba (OH) ₂ (H ₂ O) _x. It is a strong base and can be in anhydrous, monohydrate, or octohydrate form. The monohydrate form, also called barite water, is the most common and commercially used. The structure of the anhydrous and monohydrate compounds is presented in Figure 1.

Barium hydroxide can be prepared by dissolving barium oxide (BaO) in water: BaO + 9H ₂ O → Ba (OH) ₂ · 8H ₂ O. It crystallizes as the octahydrate, which becomes the monohydrate on heating in air. At 100 ° C under vacuum, the monohydrate will produce BaO and water.

Figure 1: structure of anhydrous barium hydroxide (Left) and monohydrate (Right)

The monohydrate adopts a layered structure (figure 2). The Ba ²⁺ centers adopt an octahedral geometry. Each Ba ²⁺ center is linked by two water ligands and six hydroxide ligands, which are respectively double and triple bridged to neighboring Ba ²⁺ centers.

In the octahydrate, the individual Ba ²⁺ centers are again eight coordinates but do not share ligands (Barium Hydroxide, SF).

Figure 2: crystal structure of barium hydroxide.

Barium hydroxide properties

Barium hydroxide is white or transparent octahedral crystals. Lacking odor and with a caustic taste (National Center for Biotechnology Information., 2017). Its appearance is shown in figure 3 (IndiaMART InterMESH Ltd., SF).

Figure 3: appearance of barium hydroxide.

The anhydrous form has a molecular weight of 171.34 g / mol, a density of 2.18 g / ml, a melting point of 407 ° C and a boiling point of 780 ° C (Royal Society of Chemistry, 2015).

The monohydrate form has a molecular weight of 189.355 g / mol, a density of 3.743 g / ml, and a melting point of 300 ° C (Royal Society of Chemistry, 2015).

The octohydrate form has a molecular weight of 315.46 g / mol, a density of 2.18 g / ml, and a melting point of 78 ° C (Royal Society of Chemistry, 2015).

The compound is slightly soluble in water and insoluble in acetone. It is a strong base with a pKa of 0.15 and 0.64 for the first and second OH ^- respectively.

Barium hydroxide reacts similarly to sodium hydroxide (NaOH), but is less soluble in water. It neutralizes acids exothermically to form salts plus water. It can react with aluminum and zinc to form metal oxides or hydroxides and generate hydrogen gas.

It can initiate polymerization reactions in polymerizable organic compounds, especially epoxides.

It can generate flammable and / or toxic gases with ammonium salts, nitrides, halogenated organic compounds, various metals, peroxides and hydroperoxides. Blends with chlorinated gums explode when heated or crushed (BARIUM HYDROXIDE MONOHYDRATE, 2016).

Barium hydroxide decomposes to barium oxide when heated to 800 ° C. Reaction with carbon dioxide produces barium carbonate. Its highly alkaline aqueous solution undergoes neutralization reactions with acids. Thus, it forms barium sulfate and barium phosphate with sulfuric and phosphoric acids, respectively.

H ₂ SO ₄ + Ba (OH) ₂ BaSO ₄ + 2H ₂ O

Reaction with hydrogen sulfide produces barium sulfide. The precipitation of many insoluble, or less soluble, barium salts can result from a double replacement reaction when an aqueous solution of barium hydroxide is mixed with many solutions of other metal salts.

Mixing the solid hydrated barium hydroxide with solid ammonium chloride in a beaker produces an endothermic reaction to produce a liquid, with the evolution of ammonia. The temperature drops drastically to approximately -20ºC (Royal Society of Chemistry, 2017).

Ba (OH) ₂ (s) + 2NH ₄ Cl (s) → BaCl ₂ (aq) + 2NH ₃ (g) + H ₂ O

Figure 4: endothermic reaction between barium hydroxide and ammonium chloride.

Ba (OH) 2 reacts with carbon dioxide to produce barium carbonate. This is expressed by the following chemical reaction:

Ba (OH) 2 + CO2 → BaCO3 + H2O.

Reactivity and hazards

Barium hydroxide is classified as a stable, non-combustible compound that reacts rapidly and exothermically with acids, and is incompatible with carbon dioxide and moisture. The compound is toxic and, as a strong base, is corrosive.

Inhalation, ingestion, or skin contact with material can cause serious injury or death. Contact with the molten substance can cause severe burns to the skin and eyes.

Contact with skin should be avoided. The effects of contact or inhalation may be delayed. Fire can produce irritating, corrosive and / or toxic gases. Fire control wastewater can be corrosive and / or toxic and cause contamination.

Eye contact

If the compound comes into contact with the eyes, the contact lenses should be checked and removed. The eyes should be washed immediately with plenty of water for at least 15 minutes, with cold water.

Skin contact

In case of skin contact, the affected area should be rinsed immediately for at least 15 minutes with plenty of water or a weak acid, such as vinegar, while removing contaminated clothing and shoes. Cover irritated skin with an emollient.

Wash clothing and shoes before reuse. If the contact is severe, wash with a disinfectant soap and cover the contaminated skin with an antibacterial cream.

Inhalation

In case of inhalation, the victim should be moved to a cool place. If not breathing, artificial respiration is given. If breathing is difficult, give oxygen.

Ingestion

If the compound is ingested, vomiting should not be induced. Loosen tight clothing such as a shirt collar, belt, or tie.

In all cases, immediate medical attention should be obtained (Material Safety Data Sheet Barium hydroxide monohydrate, 2013).

Applications

1- Industry

Industrially, barium hydroxide is used as a precursor to other barium compounds. Monohydrate is used to dehydrate and remove sulfate from various products. This application exploits the very low solubility of barium sulfate. This industrial application also applies to laboratory uses.

Barium hydroxide is used as an additive in thermoplastics (such as phenolic resins), scratches, and PVC stabilizers to improve plastic properties. This material is used as a general purpose additive for lubricants and greases.

Other industrial applications of barium hydroxide include sugar manufacturing, manufacturing soaps, fat saponification, silicate melting, and chemical synthesis of other barium compounds and organic compounds (BARIUM HYDROXIDE, SF).

2- Laboratory

Barium hydroxide is used in analytical chemistry for the titration of weak acids, particularly organic acids. Its clear aqueous solution is guaranteed to be carbonate free unlike sodium hydroxide and potassium hydroxide as barium carbonate is insoluble in water.

This allows the use of indicators such as phenolphthalein or thymolphthalein (with alkaline color changes) without the risk of titration errors caused by the presence of carbonate ions, which are much less basic (Mendham, Denney, Barnes, & Thomas, 2000).

Barium hydroxide is occasionally used in organic synthesis as a strong base, for example for the hydrolysis of esters and nitriles:

Barium hydroxide is also used in the decarboxylation of amino acids that release barium carbonate in the process.

It is also used in the preparation of cyclopentanone, diacetone alcohol and gamma-lactone D-Gulonic.

3- Catalyst in the Wittig-Horner reaction

The Wittig-Horner reaction, also known as the Horner-Wadsworth-Emmons reaction (or HWE reaction) is a chemical reaction used in organic chemistry to stabilize carbanions of phosphonates with aldehydes (or ketones) to produce predominantly E-alkenes (trans).

The Wittig-Horner soncochemical reaction is catalyzed by activated barium hydroxide and is carried out under solid-liquid interface conditions.

The soncochemical process takes place at room temperature and with a lower catalyst weight and reaction time than the thermal process. Under these conditions, yields similar to those of the thermal process are obtained.

In the work of (JV Sinisterra, 1987) the influence on the performance of the sonication time, the weight of the catalyst and the solvent is analyzed. Small amounts of water must be added for the reaction to take place.

The nature of the active site of the catalyst acting in the process is analyzed. An ETC mechanism is proposed for the sonochemical process.

4- Other uses

Barium hydroxide has other uses. It is used for a number of purposes, such as:

• The manufacture of alkali.
• Building glass.
• Synthetic rubber vulcanization.
• Corrosion inhibitors.
• Like drilling fluids, pesticides and lubricants.
• For the boiler remedy.
• To refine vegetable and animal oils.
• For fresco painting.
• In water softening.
• As an ingredient in homeopathic remedies.
• To clean up acid spills.
• It is also used in the sugar industry to prepare beet sugar.
• Construction materials.
• Electrical and electronic products.
• Floor coverings.

References

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2. Barium Hydroxide. (SF). Recovered from chemistrylearner: chemistrylearner.com.
3. BARIUM HYDROXIDE. (SF). Recovered from chemicalland21: chemicalland21.com.
4. IndiaMART InterMESH Ltd.. (SF). Barium Hydroxide. Recovered from indiamart: dir.indiamart.com.
5. V. Sinisterra, AF (1987). Ba (OH) 2 as catalyst in organic reactions. 17. Interfacial solid-liquid Wittig-Horner reaction under sonochemical conditions. The Journal of Organic Chemistry 52 (17), 3875-3879. researchgate.net.
6. Material Safety Data Sheet Barium hydroxide monohydrate. (2013, May 21). Retrieved from sciencelab: sciencelab.com/msds.
7. Mendham, J., Denney, RC, Barnes, JD, & Thomas, MJ (2000). Vogel's Quantitative Chemical Analysis (6th ed.). New York: Prentice Hall.
8. National Center for Biotechnology Information. (2017, March 28). PubChem Compound Database; CID = 16211219. Recovered from PubChem: pubchem.ncbi.nlm.nih.gov.
9. Royal Society of Chemistry. (2015). Barium hydroxide. Recovered from chemspider: chemspider.com.
10. Royal Society of Chemistry. (2015). Barium hydroxide hydrate (1: 2: 1). Recovered from chemspider: chemspider.com.
11. Royal Society of Chemistry. (2015). Dihydroxybarium hydrate (1: 1). Recovered from chemspider: chemspider.com.
12. Royal Society of Chemistry. (2017). Endothermic solid-solid reactions. Recovered from: learn-chemistry: rsc.org.