Oleum (Fuming Sulfuric Acid)

Oleum, also known as fuming sulfuric acid, is a highly corrosive, fuming, oily liquid composed of sulfur trioxide dissolved in sulfuric acid. It is commonly represented by the formulas H₂S₂O₇ or H₂SO₄·xSO₃. Oleum is a critical intermediate in the industrial manufacture of sulfuric acid and is widely used in sulfonation reactions, as well as in the production of explosives, dyes, and fertilizers.

Key Details:

Chemical Formula: H₂S₂O₇ (disulfuric acid) or H₂SO₄·xSO₃

Description: Colorless to brown, viscous, oily, and strongly fuming liquid with a pungent odor. Oleum releases toxic sulfur trioxide fumes upon exposure to air and is highly hygroscopic.

Key Property: Essentially an “oversaturated” form of sulfuric acid, containing approximately 15–30% or more free SO₃ dissolved in 100% sulfuric acid.

Common Uses:

• Sulfuric Acid Production: Used as an intermediate in the contact process to efficiently manufacture sulfuric acid.
• Industrial Processes: Widely used in sulfonation reactions for the production of dyes, explosives, detergents, and chemical intermediates.
• Petrochemical Industry: Used in petroleum refining and processing applications.

Safety Note: Oleum is extremely hazardous. It causes severe chemical burns and releases toxic fumes. Specialized handling, storage, and transport procedures are required to prevent serious injury and environmental damage.

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