Iodine
[CAS# 7553-56-2]

Identification

• Classification: API >> Hormone and endocrine-regulating drugs >> Thyroid hormone and antithyroid drugs
• Name: Iodine
• Molecular Formula: I₂
• Molecular Weight: 253.81
• CAS Registry Number: 7553-56-2
• EC Number: 231-442-4
• SMILES: II

Properties

• Density: 4.93
• Melting point: 114 °C
• Boiling point: 184 °C
• Water solubility: 0.3 g/L (20 °C)

Safety Data

• Hazard Symbols: GHS07;GHS08;GHS09 Danger
• Risk Statements: H302+H312+H332-H302-H312-H315-H319-H332-H335-H372-H400-H410
• Safety Statements: P260-P261-P264-P264+P265-P270-P271-P273-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P391-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H312
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H302
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Serious eye damage	Eye Dam.	1	H318
Skin corrosion	Skin Corr.	1A	H314
Skin sensitization	Skin Sens.	1A	H317
Skin corrosion	Skin Corr.	1B	H314
Skin sensitization	Skin Sens.	1	H317
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Skin corrosion	Skin Corr.	1C	H314

• Transport Information: UN 1759; UN 1760

Discovery and Applications

Iodine is a non-metallic element with the chemical symbol I and atomic number 53 that plays a vital role in various biological, industrial and medical applications. Iodine was discovered by French chemist Bernard Courtois in 1811. While extracting sodium carbonate from seaweed ash, Courtois accidentally discovered a purple vapor, which turned out to be iodine. This was the first discovery of a new element since ancient times. The name iodine is derived from the Greek word iodes, which means purple.

Iodine is a shiny purple-black solid at room temperature and sublimates into a purple-pink gas when heated. It is slightly soluble in water and soluble in organic solvents such as ethanol and chloroform. The melting point is 113.7°C and the boiling point is 184.3°C.

Iodine is mainly extracted from natural sources such as seaweed, which accumulates iodine from seawater. It can also be obtained as a byproduct of sodium iodide production or through chemical reactions involving reducing agents such as iodate and sulfur dioxide.

Iodine is required for the production of thyroid hormones. It is added to salt (iodized salt) and used in health products to prevent iodine deficiency disorders such as goiter and cretinism. Radioactive isotopes of iodine (I-123, I-125, I-131) are used in nuclear medicine for diagnostic imaging and thyroid function testing.

Iodine compounds (such as potassium iodide) are used in a variety of chemical processes, including organic synthesis and pharmaceutical manufacturing. Silver iodide is a component of photographic emulsions and is essential for image display in traditional and digital photography.

Iodine is used as a disinfectant in water purification tablets and solutions, effectively killing bacteria, viruses, and protozoa in emergency situations and outdoor settings.

Iodine is used as a titrant in analytical chemistry to determine the concentration of reducing agents by iodometric and iodine titration.

While small amounts of iodine are essential to human health, excessive exposure can be harmful. It can cause thyroid dysfunction and other health problems. Proper handling and dosage are essential to prevent adverse effects in medical, industrial, and laboratory settings.

Research continues on the use of iodine in medicine, environmental science, and materials science. Efforts are focused on improving iodine-based technologies, exploring new compounds, and addressing the environmental and health challenges associated with iodine use.

References

2025. Preventive and therapeutic effects of molecular iodine in a model of diabetes mellitus induced by streptozotocin. The Journal of Nutritional Biochemistry, 139.
DOI: 10.1016/j.jnutbio.2024.109783

2024. Investigating environmental and geographical factors affecting iodine concentrations in Australian wheat (Triticum aestivum L.) grain. The Science of the total environment, 953.
DOI: 10.1016/j.scitotenv.2024.177160

2024. Iodine identification in major edible seaweed Kappaphycus alvarezii and establishment of an iodine reduction method for its protein extract for utilization as a protein source. Food Chemistry, 463.
DOI: 10.1016/j.foodchem.2024.140723