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Home Isopropyl Alcohol

Isopropyl alcohol

Isopropyl alcohol (also propan-2-ol, 2-propanol or the abbreviation IPA) is a common name for a chemical compound with the molecular formula C3H8O. It is a colorless, flammable chemical compound with a strong odor. It is the simplest example of a secondary alcohol, where the alcohol carbon is attached to two other carbons sometimes shown as (CH3)2CHOH. It is a structural isomer of propanol.

Production

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 propene, predominates in the USA while the latter process, which requires high-purity propene, is more commonly used in Europe. These processes give predominantly isopropyl alcohol rather than 1-propanol because the addition of water or sulfuric acid to propene follows Markovnikov's rule.

The indirect process reacts propene with sulfuric acid to form a mixture of sulfate esters. Subsequent hydrolysis of these esters produces isopropyl alcohol. Direct hydration reacts propene 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.

Uses

Isopropyl alcohol is readily available. Like acetone, it dissolves a wide range of non-polar compounds. It also evaporates quickly and is relatively non-toxic, compared to alternative solvents. Thus it is used widely as a solvent and as a cleaning fluid, especially for dissolving lipophilic contaminants such as oil. Examples include cleaning electronic devices such as contact pins (like those on ROM cartridges), magnetic tape and disk heads (such as those in audio and video tape recorders and floppy disk drives), the lenses of lasers in optical disc drives (e.g. CD, DVD) and removing thermal paste from IC packages (such as CPUs.) It is used to clean LCD and glass computer monitor screens (at some risk to the anti-reflection coating on some screens), and used to give second-hand or worn non-vinyl phonograph records newer-looking sheens. Isopropyl alcohol should not be used to clean vinyl records as it may leach plasticizer from the vinyl making it more rigid). Isopropyl alcohol removes smudges, dirt, and fingerprints from cell phones and PDAs. It is effective at removing residual glue from some sticky labels although some other adhesives used on tapes and paper labels are resistant to it. It can also be used to remove stains from most fabrics, wood, cotton, etc. Isopropyl alcohol is also used to remove brake fluid traces from hydraulic braking systems, so that the brake fluid (usually DOT 3, DOT 4 or mineral oil) does not contaminate the brake pads, which would result in poor braking. In addition it can also be used to clean paintballs or other oil based products so that they may be reused, commonly known as "repainting". As a biological specimen preservative, isopropyl alcohol provides a comparatively non-toxic alternative to formaldehyde and other synthetic preservatives. Isopropyl alcohol solutions of 90-99% are optimal for preserving specimens, although concentrations as low as 70% can be used in emergencies.

Disinfecting pads typically contain a 60–70% solution of isopropyl alcohol in water. Isopropyl alcohol is also commonly used as a cleaner and solvent in industry.

Isopropyl alcohol is a major ingredient in "gas dryer" fuel additives. 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. It does not remove water from gasoline; rather, the alcohol solubilizes water in gasoline. Once soluble, water does not pose the same risk as insoluble water as it will no longer accumulate in the supply lines and freeze. Isopropyl alcohol is often sold in aerosol cans as a windscreen de-icer.

Isopropyl alcohol is used in keyboard, LCD and laptop cleaning, is sold commercially as a whiteboard cleaner, and is a strong but safer alternative to common household cleaning products.

Isopropyl alcohol is often used in DNA extraction. It is added to a DNA solution in order to precipitate the DNA into a 'pellet' after centrifuging the DNA. This is possible because DNA is insoluble in isopropyl alcohol.

Isopropyl alcohol is used as a water-drying aid for the prevention of otitis externa, better known as swimmer's ear.

Chemistry

Unlike ethanol or methanol, isopropyl alcohol can be separated from aqueous solutions by adding a salt such as sodium chloride, sodium sulfate, or any of several other inorganic salts, since the alcohol is much less soluble in saline solutions than in salt-free water. The process is colloquially called salting out, and causes concentrated isopropyl alcohol to separate into a distinct layer.

Being a secondary alcohol, isopropyl alcohol can be oxidized to acetone, which is the corresponding ketone. This can be achieved using oxidizing agents such as chromic acid, or by dehydrogenation of isopropyl alcohol over a heated copper catalyst:

(CH3)2CH-OH → (CH3)2CO + H2

Isopropyl alcohol may be converted to 2-bromopropane using phosphorus tribromide, or dehydrated to propene by heating with sulfuric acid.

Isopropyl alcohol is often used as both solvent and hydride source in the Meerwein-Ponndorf-Verley reduction.

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.

Isopropyl alcohol has a maximum absorbance at 204 nm in an ultraviolet-visible spectrum.

Safety

Isopropyl alcohol vapor is more dense than air and is highly flammable with a very wide combustible range. It should be kept away from heat and open flame. When mixed with air or other oxidizers it can explode through deflagration. Isopropyl alcohol has also been reported to form explosive peroxides.

Like many organic solvents, long term application to the skin can cause defatting.

Toxicology

Isopropyl alcohol is oxidized by the liver into acetone by alcohol dehydrogenase. Symptoms of isopropyl alcohol poisoning include flushing, headache, dizziness, CNS depression, nausea, vomiting, anesthesia, and coma. Poisoning can occur from ingestion, inhalation, or absorption; therefore, well-ventilated areas and protective gloves are recommended.

Isopropyl alcohol and its metabolite, acetone, act as central nervous system (CNS) depressants. Around 15 g of isopropyl alcohol can have a toxic effect on a 70 kg human if left untreated. However, it is not nearly as toxic as methanol or ethylene glycol. Isopropyl alcohol does not cause an anion gap acidosis (in which as lowered blood serum pH causes depletion of bicarbonate anion) unlike ethanol and methanol. Isopropyl alcohol does however, produce an osmolal gap between the calculated and measured osmolalities of serum, as do the other alcohols. Overdoses may cause a fruity odor on the breath as a result of its metabolism to acetone, which is further metabolized to produce the nutrients acetate and glucose.