What is a Toluene Sulfonic Acid (TsOH)?

Toluene Sulfonic Acid (TsOH) is an organic sulfonic acid consisting of a benzene ring derived from toluene with a sulfonic acid group (–SO₃H) attached. The most common isomer is para-toluenesulfonic acid, where the methyl and sulfonic acid groups are positioned opposite each other on the benzene ring. Its chemical formula is CH₃C₆H₄SO₃H. It appears as a white to pale yellow crystalline solid and is highly soluble in water and alcohols. TsOH is known for its strong acidity, making it a widely used acid catalyst in organic synthesis, particularly in reactions like esterification, acetal formation, and dehydration. Its salt forms, such as tosylates (e.g., TsCl), are excellent leaving groups in substitution reactions. While stable and easy to handle, TsOH is irritating to the skin and eyes, so proper protective equipment and good ventilation are essential during use.

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