lactol

Lactol is a chemical compound, specifically a cyclic hemiacetal. Its chemical formula is C5H8O2. It is formed by the intramolecular reaction between the aldehyde and hydroxyl groups of 5-hydroxypentanal. Lactol exists in equilibrium with its open-chain form, 5-hydroxypentanal. This equilibrium is a characteristic of hemiacetals and depends on factors such as solvent and concentration.

In aqueous solution, both the open-chain aldehyde form and the cyclic lactol form are present. The ring structure of lactol is a five-membered ring, often referred to as a tetrahydropyran derivative. The formation and stability of lactol are related to the thermodynamics of ring formation.

Lactol is a colorless liquid and is soluble in water and many organic solvents. It is not a commonly encountered compound in everyday life but can be an intermediate in certain organic synthesis pathways. Its chemical properties are typical of hemiacetals, exhibiting reactivity towards both acidic and basic conditions. Under acidic conditions, it can undergo hydrolysis to regenerate 5-hydroxypentanal or further reactions. Under basic conditions, it may undergo deprotonation and other reactions characteristic of aldehydes and alcohols. The study of lactol and similar cyclic hemiacetals is important in understanding carbohydrate chemistry, as many sugars exist in similar cyclic hemiacetal forms.