Isopropyl alcohol (also isopropanol, iso, isopro, rubbing alcohol, or the abbreviation IPA) is a common name for propan-2-ol, a colorless, flammable chemical compound with a strong odor. It has the molecular formula C3H8O and is the simplest example of a secondary alcohol, where the alcohol carbon is attached to two other carbons. It is an isomer of propanol.
Isopropyl alcohol is produced by combining water and propene. There are two processes for achieving this: indirect hydration via the sulfuric acid process and direct hydration. The former process, which can use low quality propylene, predominates in the USA while the latter process, which requires high-purity propylene, is more commonly used in Europe. These processes give predominantly isopropyl alcohol rather than propan-1-ol because the addition of water or sulfuric acid to propylene follows Markovnikov's rule.
The indirect process reacts propylene with sulfuric acid to form a mixture of sulfate esters. Subsequent hydrolysis of these esters produces isopropyl alcohol. Direct hydration reacts propylene and water, either in gas or liquid phases, at high pressures in the presence of solid or supported acidic catalysts. Both processes require that the isopropyl alcohol be separated from water and other by-products by distillation. Isopropyl alcohol and water form an azeotrope and simple distillation gives a material which is 87.9% by weight isopropyl alcohol and 12.1% by weight water. Pure (anhydrous) isopropyl alcohol is made by azeotropic distillation of the "wet" isopropyl alcohol using either diisopropyl ether or cyclohexane as azeotroping agents.
As a preservative (for biological specimens) isopropyl alcohol provides a cost-effective (when compared to pure ethanol) and comparatively non-toxic solution to formaldehyde and other synthetic preservatives. When used for the preservation of specimens in solution concentrations of 90-99% are optimal, though concentrations as low as 70% can be used in emergencies.
Isopropanol is a major ingredient in "dry-gas" fuel additive. In significant quantities, water is a problem in fuel tanks as it separates from the gasoline and can freeze in the supply lines at cold temperatures. The isopropanol does not remove the water from the gasoline; rather, the isopropanol solubilizes the water in the gasoline. Once soluble, the water does not pose the same risk as insoluble water as it will no longer accumulate in the supply lines and freeze. Isopropanol is often sold in aerosol cans as a windscreen de-icer.
It can also be used to remove stains from any fabric, wood, cotton, etc.
Being a secondary alcohol, isopropanol can be oxidized to the ketone acetone. This can be achieved using oxidizing agents such as chromic acid, or by dehydrogenation of isopropanol over a heated copper catalyst:
Like most alcohols, isopropyl alcohol reacts with active metals such as potassium to form alkoxides which can be called isopropoxides. The reaction with aluminium (initiated by a trace of mercury) is used to prepare the catalyst aluminium isopropoxide.
Like many organic solvents, long term application to the skin can cause defatting.
Isopropyl alcohol is about twice as toxic as ethanol, though isopropyl alcohol does not cause an anion gap acidosis as do ethanol and methanol. It produces an elevated osmolal gap, but generally no abnormal anion gap (though this may be seen as a result of hypotension and lactic acidosis). Overdoses may cause a fruity odor on the breath as a result of its metabolism to give acetone which is not further metabolized. Isopropyl alcohol is more potent than ethanol as a CNS depressant, and its metabolite, acetone, is a CNS depressant in its own right. While around 15 g of isopropanol can be fatal if left untreated, it is not nearly as toxic as methanol or ethylene glycol.