Isopropyl alcohol

Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable, organic compound with a pungent odor.

Isopropyl alcohol, an organic polar molecule, is miscible in water, ethanol, and chloroform, demonstrating its ability to dissolve a wide range of substances including ethyl cellulose, polyvinyl butyral, oils, alkaloids, and natural resins. Notably, it is not miscible with salt solutions and can be separated by adding sodium chloride in a process known as salting out. It forms an azeotrope with water, resulting in a boiling point of 80.37 °C and is characterized by its slightly bitter taste. Isopropyl alcohol becomes viscous at lower temperatures, freezing at −89.5 °C, and has significant ultraviolet-visible absorbance at 205 nm. Chemically, it can be oxidized to acetone or undergo various reactions to form compounds such as isopropoxides, e.g. aluminium isopropoxide. As an isopropyl group linked to a hydroxyl group (chemical formula (CH₃)₂CHOH) it is the simplest example of a secondary alcohol, where the alcohol carbon atom is attached to two other carbon atoms. It is a structural isomer of propan-1-ol and ethyl methyl ether, all of which share the formula C₃H₈O.

It was first synthesized in 1853 by Alexander William Williamson and later produced for cordite preparation. It is produced through hydration of propene or hydrogenation of acetone, with modern processes achieving anhydrous alcohol through azeotropic distillation.

Isopropyl alcohol serves in medical settings as a rubbing alcohol and hand sanitizer, and in industrial and household applications as a solvent. It is a common ingredient in products such as antiseptics, disinfectants, and detergents. More than a million tonnes are produced worldwide annually. Isopropyl alcohol poses safety risks due to its flammability and potential for peroxide formation. Its ingestion or absorption leads to toxic effects including central nervous system depression and coma.

Isopropyl alcohol is miscible in water, ethanol, and chloroform, as it is an organic polar molecule. It dissolves ethyl cellulose, polyvinyl butyral, many oils, alkaloids, and natural resins. Unlike ethanol or methanol, isopropyl alcohol is not miscible with salt solutions and can be separated from aqueous solutions by adding a salt such as sodium chloride. The process is colloquially called salting out, and causes concentrated isopropyl alcohol to separate into a distinct layer.

Isopropyl alcohol forms an azeotrope with water, which gives a boiling point of 80.37 °C (176.67 °F) and a composition of 87.7% by mass (91% by volume) isopropyl alcohol. It has a slightly bitter taste, and is toxic when ingested.

Isopropyl alcohol becomes increasingly viscous with decreasing temperature and freezes at −89.5 °C (−129.1 °F). Mixtures with water have higher freezing points: 99% at −89.5 °C (−129.1 °F), 91% (the azeotrope) at −75.5 °C (−103.9 °F), and 70% at −61.7 °C (−79.1 °F).

Isopropyl alcohol has a maximal absorbance at 205 nm in an ultraviolet-visible spectrum.