Bromine

Bromine is a halogen element with the chemical symbol Br and atomic number 35, belonging to Group 17 of the periodic table. It is a dark reddish-brown liquid at room temperature, the only non-metallic element existing in liquid form under normal conditions. Highly volatile and reactive, bromine emits a strong, irritating odour and forms dense vapours that are toxic. Despite its hazardous nature, bromine and its compounds are widely used in numerous industrial, agricultural, and everyday applications, owing to their unique chemical versatility and reactivity.

Physical and Chemical Characteristics

Bromine lies between chlorine and iodine in terms of reactivity and electronegativity. It is moderately soluble in water, forming bromine water, a pale yellow solution used as a mild oxidising agent. The element readily forms compounds with most metals and non-metals, primarily in the –1 oxidation state (as bromides), but also in higher oxidation states such as +1, +3, and +5 in certain oxides and oxyacids.
Bromine’s molecular form, Br₂, has a melting point of –7.2°C and a boiling point of 58.8°C, making it liquid over a wide range of temperatures. Its volatility and ability to form a wide variety of organic and inorganic compounds underpin much of its commercial importance.

Occurrence and Extraction

Bromine is not found in its elemental state in nature but occurs abundantly as bromide salts (such as sodium bromide and magnesium bromide) in seawater, salt lakes, and underground brine deposits. The Dead Sea, the Great Salt Lake (USA), and certain Chinese inland brines are major natural sources.
Extraction typically involves oxidising bromide ions with chlorine gas, producing elemental bromine, which is then purified by distillation. Major producers include China, Israel, Jordan, and the United States, with bromine production forming a significant part of their chemical industries.

Everyday and Domestic Applications

Though bromine itself is highly corrosive and rarely encountered in households, several of its compounds are common in daily life.

• Water purification: Bromine-based disinfectants, such as bromine tablets (containing hydantoin bromine compounds), are widely used in swimming pools and spas as alternatives to chlorine. They provide effective microbial control and are less irritating to the skin and eyes.
• Photography: In traditional photographic film, silver bromide (AgBr) is a key light-sensitive compound, although digital imaging has reduced this use.
• Medicinal compounds: Historically, potassium bromide (KBr) was employed as a sedative and anticonvulsant drug, and bromine compounds remain in limited pharmaceutical use for anaesthetics and sedative preparations.
• Dyes and fragrances: Bromine derivatives are used in synthesising organic dyes, perfumes, and flavouring agents, contributing to various cosmetic and consumer products.

Industrial and Technological Applications

The industrial significance of bromine stems from its chemical reactivity and ability to stabilise or modify materials. Its key applications span multiple sectors, including chemicals, energy, and manufacturing.

• Flame retardants: The most extensive industrial use of bromine is in the production of brominated flame retardants (BFRs) such as tetrabromobisphenol A (TBBPA) and decabromodiphenyl ether (DecaBDE). These compounds are incorporated into plastics, textiles, electronic devices, and building materials to reduce fire risk. Although some older BFRs have been restricted due to environmental concerns, safer alternatives continue to dominate the market.
• Oil and gas industry: Bromine compounds, notably calcium bromide (CaBr₂) and zinc bromide (ZnBr₂), are used in drilling fluids and completion brines for oil and gas wells. They help control well pressure, cool drilling bits, and prevent blowouts.
• Water treatment and sanitation: In addition to domestic use, bromine-based biocides are employed in industrial cooling towers and power plants to control algae and bacterial growth.
• Pharmaceutical synthesis: Organic bromine intermediates are used in producing antibiotics, painkillers, and sedatives, as bromine facilitates controlled halogenation reactions essential in fine chemical manufacture.
• Agricultural chemicals: Bromine-derived pesticides and fumigants, such as methyl bromide, were historically used to control soil pests and insects. However, due to their ozone-depleting properties, many such compounds have been phased out under the Montreal Protocol, though limited quarantine uses remain under strict regulation.
• Battery technology: Zinc–bromine flow batteries represent a promising energy storage technology. These batteries offer high energy density and are increasingly explored for renewable energy storage, particularly in solar and wind power systems.
• Rubber and plastics industry: Brominated compounds are used to improve thermal stability and elasticity in rubbers and polymers. Bromobutyl rubber, for example, is essential in manufacturing tyre inner linings, providing airtight and heat-resistant qualities.

Economic Importance and Global Production

Bromine plays a vital role in the global chemical economy, with annual production measured in hundreds of thousands of tonnes. As of recent years, China and Israel have dominated production, followed by Jordan and the United States. The element’s market value fluctuates with demand from sectors such as electronics, energy storage, and flame retardant manufacturing.
Economically, bromine’s significance arises from:

• Its versatility in multiple industrial sectors.
• Continuous innovation in energy and environmental technologies that utilise bromine compounds.
• Its role in the development of advanced materials and renewable energy solutions.

The price of bromine is influenced by both environmental regulation and technological demand. Restrictions on certain brominated compounds in Europe and North America have led to diversification into new bromine-based products with reduced ecological impact.

Environmental and Health Considerations

Bromine and many of its compounds are toxic and corrosive, requiring careful handling. Direct exposure can cause burns, respiratory irritation, and eye damage. In the environment, certain brominated organic compounds are persistent and bioaccumulative, leading to ecological concerns.
The phase-out of methyl bromide due to its ozone-depleting potential and the regulation of polybrominated diphenyl ethers (PBDEs) under international treaties highlight the environmental challenges associated with bromine chemistry. However, modern bromine management practices and the development of eco-friendly alternatives have improved safety and sustainability in industrial use.
Despite these issues, bromine’s role in water disinfection, materials safety, and clean energy technology contributes positively to public health and environmental protection when properly controlled.

Advances and Emerging Applications

Recent scientific advances have revitalised interest in bromine for green chemistry and advanced material applications:

• Energy storage: Zinc–bromine and hydrogen–bromine batteries are being explored for grid-scale renewable energy systems, offering long lifespan and recyclability.
• Pharmaceutical innovation: Brominated organic compounds are used as intermediates in synthesising anti-cancer and antiviral drugs, benefiting from bromine’s reactivity in selective halogenation reactions.
• Photonic and electronic materials: Bromine-containing perovskites are integral in next-generation solar cells and light-emitting diodes (LEDs), enhancing efficiency and stability.
• Environmental catalysis: Bromine-based catalysts are being tested in advanced waste-to-energy and pollution control systems, enabling low-emission industrial processes.

Significance in Modern Society

Bromine stands as one of the most versatile non-metals in the chemical industry, bridging traditional applications and emerging technologies. Its compounds support crucial sectors — from fire safety and pharmaceuticals to energy and environmental management — making it a cornerstone of modern industrial chemistry.