Hydrogen bromide
[CAS# 10035-10-6]

Identification

• Classification: Inorganic chemical industry >> Inorganic acid
• Name: Hydrogen bromide
• Synonyms: Hydrobromic acid
• Molecular Formula: HBr
• Molecular Weight: 80.91
• CAS Registry Number: 10035-10-6
• EC Number: 233-113-0
• SMILES: Br

Properties

• Density: 1.49 g/mL (Expl.)
• Melting point: -87.2 - -86.1 $degree$C (Expl.)
• Boiling point: -67.0$+/-$9.0 $degree$C 760 mmHg (Calc.)^*, -67.2 - -66.1 $degree$C (Expl.)
• Flash point: 65 $degree$C (Expl.)
• Solubility: 48-50 g/100g (Expl.)

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

Safety Data

• Hazard Symbols: GHS04;GHS05;GHS07 Danger
• Risk Statements: H335-H314
• Safety Statements: S26;S45;S7/9

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin corrosion	Skin Corr.	1A	H314
Serious eye damage	Eye Dam.	1	H318
Skin corrosion	Skin Corr.	1B	H314
Gases under pressure (liquid)	Press. Gas (Liq.)		H280
Acute toxicity	Acute Tox.	3	H331
Gases under pressure (compressed)	Press. Gas (Comp.)		H280
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Gases under pressure (refrigerated liquid)	Press. Gas (Ref. Liq.)		H280
Germ cell mutagenicity	Muta.	1B	H340
Specific target organ toxicity - single exposure	STOT SE	3	H371
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Specific target organ toxicity - single exposure	STOT SE	1	H370
Reproductive toxicity	Repr.	1A	H360
Flammable liquids	Flam. Liq.	2	H225

• Transport Information: UN 1788

Discovery and Applications

Hydrogen bromide is a simple inorganic compound composed of hydrogen and bromine, with the molecular formula HBr. It is a colorless gas under standard conditions and forms hydrobromic acid when dissolved in water. Hydrogen bromide has been known since the early development of halogen chemistry in the nineteenth century, when it was prepared through reactions of bromine with hydrogen or by the action of acids on bromide salts. Its strong acidity in aqueous solution and high reactivity have made it an important substance in both laboratory and industrial chemistry.

The molecule consists of a single covalent bond between hydrogen and bromine, with a significant difference in electronegativity between the two atoms. This polarity leads to the formation of a strong acid when the compound dissolves in water, where it dissociates almost completely into hydrogen ions and bromide ions. Compared to other hydrogen halides, hydrogen bromide exhibits acid strength that increases down the group, reflecting the weakening of the hydrogen–halogen bond and greater ease of ionization.

Hydrogen bromide is commonly produced by the direct combination of hydrogen and bromine at elevated temperatures or under catalytic conditions. It can also be generated by the reaction of bromide salts with strong acids such as sulfuric acid, although care must be taken to avoid oxidation side reactions. Industrial production often involves catalytic processes that ensure high yield and purity, allowing the compound to be used in large-scale applications.

One of the most important applications of hydrogen bromide is in organic synthesis, where it is used to introduce bromine into organic molecules. It readily adds across carbon–carbon double bonds in alkenes to form alkyl bromides, following well-established reaction pathways. In the presence of peroxides, the addition can proceed through a radical mechanism, leading to different regioselectivity. This versatility makes hydrogen bromide a valuable reagent for preparing a wide range of brominated compounds used in pharmaceuticals, agrochemicals, and materials.

Hydrogen bromide is also widely used in the preparation of inorganic bromides. It reacts with metals, metal oxides, and hydroxides to form bromide salts, which are important in various industrial and chemical processes. These salts are used in applications ranging from photography and water treatment to the synthesis of other chemical intermediates. The strong acidity of hydrobromic acid makes it effective for dissolving metals and facilitating such reactions.

In addition to its role in synthesis, hydrogen bromide has applications in the semiconductor industry, where it is used in etching processes. Its reactivity with certain materials allows for controlled removal of layers in the fabrication of electronic components. This application requires high-purity hydrogen bromide and carefully controlled conditions to achieve precise results.

Hydrogen bromide is a corrosive and hazardous substance, requiring careful handling and appropriate safety measures. It can cause severe irritation to the respiratory system, skin, and eyes, and its aqueous solutions are strongly acidic. Proper storage and use in well-ventilated environments are essential to minimize risks associated with exposure.

Overall, hydrogen bromide is a fundamental inorganic compound with significant importance in organic synthesis, industrial chemistry, and materials processing. Its strong acidity, reactivity, and versatility have established it as a key reagent in many chemical applications.

References

2025. Recent Advances in Ligand Engineering for Stable Halide Perovskite Light-Emitting Diodes. Electronic Materials Letters.
DOI: 10.1007/s13391-025-00587-3

2025. Bromo- and iodobismuthates of l-proline with a (A+···A+) type dimeric and a new type of tetrameric cations. Structural Chemistry.
DOI: 10.1007/s11224-025-02570-y