Introduction

Sodium borohydride is an unique chemical compound with a wide range of properties, reactions and applications, making it a subject of scientific researches. This odorless white crystalline powder, soluble in water, was first synthesized in the 20th century.

One of the main characteristics of sodium borohydride is its ability to serve as a powerful reducing agent in various chemical reactions. This property has found wide range of applications in the synthesis of organic compounds, leading to increased efficiency and reduced cost of production processes.

This article provides a deep overview of the properties of sodium borohydride, its chemical reactions and applications.

Physical and Chemical Properties of Sodium Borohydride

Sodium borohydride (sodium tetra hydroborate) is an inorganic compound with the chemical formula NaBH₄ and a molecular weight 37.83 g/mol. Appearance: white crystals. It is soluble in water – 56g (in 100g at 25°C), liquid ammonia – 99g (in 100g at -22.5°C), ethanol – 4 g (in 100g at 20°C). Its density is 1.074 g/cm³. The melting point of sodium borohydride is relatively high, around 505°C and boiling point 89-90 °C (at 3.5 Torr).

Synthesis of Sodium Borohydride

Sodium borohydride can be synthesized by various methods. Here are the main methods:

Sodium borohydride can be obtained industrially using the Brown-Schlesinger method by reaction of trimethyl borate with sodium hydride in the temperature range 250-270°C.

Alternatively, this compound can also be prepared by the Bayer method. It is prepared from borates by reacting of borax, sodium metal, hydrogen and silicon dioxide at a temperature 700 °C.

Or use borax, magnesium hydride and sodium carbonate instead of hydrogen and sodium.

It is important to note that the choice of synthesis method depends on factors such as cost-effectiveness and the specific requirements of the intended application.

Chemical Reactions of Sodium Borohydride

Sodium borohydride is a universal reducing agent and its chemical reactions are widely used in various fields. Here are the basic chemical reactions of sodium borohydride.

1. Hydrolysis of Sodium Borohydride

Sodium borohydride reacts with water and alcohols in present of catalysts, with evolution of hydrogen gas and formation of the corresponding borate. Hydrolysis becomes faster in acidic medium and slows down in alkaline medium.

2. Reduction of Carbonyl Compounds

Sodium borohydride is widely used for the reduction of carbonyl compounds, such as aldehydes and ketones, to their corresponding alcohols. The reaction is typically carried out in the presence of a solvent, such as methanol or ethanol.

3. Reduction of Nitro Compounds

Sodium borohydride can be used to reduce nitro groups to amino groups in organic compounds. The reaction is carried out in the presence of catalysts based on copper chloride.

4. Reduction of Imines

Sodium borohydride can be used to reduce imines to amines. Reactions are carried out under the influence of microwave radiation or heating.

Applications of Sodium Borohydride

Sodium borohydride is widely used in various industries and scientific fields.

1. Chemical Synthesis

Sodium borohydride is commonly used to reduce aldehydes and ketones to their corresponding alcohols in organic synthesis.

Sodium borohydride is used in reactions of the reduction of metals oxides to metals.

2. Pharmaceutical Industry

Sodium borohydride is used in the synthesis of pharmaceuticals, in the reduction of functional groups and in the production of intermediates.
This reaction is used in the production of various antibiotics including chloramphenicol and dihydrostreptomycin. Various steroids and vitamin A are prepared using sodium borohydride in at least one step.

3. Paper and Textile Manufacture

Sodium borohydride is used as a bleaching agent for wood pulp. Sodium borohydride is used in the textile industry as a bleach-stabilizing agent, helping to maintain the stability of peroxide-based bleaching agents.

4. Fuel Cells and Hydrogen Storage

Sodium borohydride is being considered as a hydrogen storage material in fuel cells due to its high hydrogen content.

These applications demonstrate the wide applicability of sodium borohydride in a variety of industries, from chemical and pharmaceutical synthesis to environmental science and materials science.

Health Effects of Sodium Borohydride

Sodium borohydride is generally considered less toxic compared to other boron-containing compounds, but it is important to handle it with care and follow proper safety precautions.
Here are some considerations regarding the health effects of sodium borohydride:

1. Inhalation

Inhalation of sodium borohydride dust may irritate the respiratory system. Exposure to high concentrations in the air could lead to respiratory discomfort, coughing or shortness of breath.

2. Skin Contact

Sodium borohydride may cause skin irritation, especially if in contact for an extended period. Prolonged or repeated skin exposure can result in redness, dryness or even dermatitis.

3. Eye Contact

Contact with the eyes can cause irritation, redness and tearing.

4. Ingestion

Ingesting sodium borohydride can result in gastrointestinal irritation. Symptoms may include nausea, vomiting, abdominal pain, and diarrhea.

Safety Precautions

1. Personal Protective Equipment

Wear appropriate protective clothing, including gloves and safety goggles, when handling sodium borohydride.

2. Ventilation

Work in well-ventilated areas or use fume hoods to minimize inhalation exposure.

3. Storage

Keep tightly closed and away from heat or sources of ignition.
Never allow the product to come into contact with water during storage.

Conclusion

In conclusion, sodium borohydride is a valuable chemical compound with a wide range of applications in various industries and scientific disciplines. Its role as a powerful reducing agent in organic synthesis, metallurgy and catalysis has significantly impacted fields such as pharmaceuticals and environmental technology.

The compound’s ability to selectively reduce carbonyl compounds, nitro groups and metal ions has made it important in the synthesis of a variety of organic molecules and the production of functional materials.

Bibliography

One-pot amphetamine synthesis from P2NP with NaBH4/CuCl2 https://bbgate.com/threads/one-pot-amphetamine-synthesis-from-p2np-with-nabh4-cucl2-1kg-scale.70/

A review on hydrogen generation from the hydrolysis of sodium borohydride Hani Nasser Abdelhamid International Journal of Hydrogen Energy Volume 46, Issue 1, 1 January 2021, Pages 726-765 https://doi.org/10.1016/j.ijhydene.2020.09.186

Reduction of Aldehydes, Ketones and Acid Chlorides by Sodium Borohydride Saul W. Chaikin and Weldon G. Brown J. Am. Chem. Soc. 1949, 71, 1, 122–125 https://doi.org/10.1021/ja01169a033

Sodium Borohydride Luca Banfi, Enrica Narisano, Renata Riva, Nikola Stiasni, Martin Hiersemann, Tohru Yamada, Tatsuyuki Tsubo Encyclopedia of Reagents for Organic Synthesis (EROS) 20 October 2014 https://doi.org/10.1002/047084289X.rs052.pub3

Sodium Borohydride, Its Hydrolysis and its Use as a Reducing Agent and in the Generation of Hydrogen H. I. Schlesinger, Herbert C. Brown, A. E. Finholt, James R. Gilbreath, Henry R. Hoekstra, and Earl K. Hyde J. Am. Chem. Soc. 1953, 75, 1, 215–219 https://doi.org/10.1021/ja01097a057