Isopropyl alcohol is a chemical compound with the molecular formula C3H8O or C3H7OH. It
is a colorless, flammable chemical compound with a strong odor. It is the simplest example
of a secondary alcohol, where the alcohol carbon atom is attached to two other carbon
atoms sometimes shown as2CHOH. It is a structural isomer of propanol. Isopropyl alcohol is denatured
for certain uses.
Properties Isopropyl alcohol is miscible in water, alcohol,
ether and chloroform. It will dissolve ethyl cellulose, polyvinyl butyral, many oils, alkaloids,
gums and natural resins. It is insoluble in salt solutions. 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. Isopropyl alcohol forms an azeotrope with
water, which gives a boiling point of 80.37 °C and a composition of 87.7 wt% isopropyl alcohol.
Water-isopropyl alcohol mixtures have depressed melting points. It has a slightly bitter taste,
and is not safe to drink. Isopropyl alcohol becomes increasingly viscous
with decreasing temperature. At temperatures below −70 °C, isopropyl alcohol resembles
maple syrup in viscosity. Isopropyl alcohol has a maximum absorbance
at 204 nm in an ultraviolet-visible spectrum. Reactions
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)2CHOH →2CO + H2
Isopropyl alcohol is often used as both solvent and hydride source in the Meerwein-Ponndorf-Verley
reduction and other transfer hydrogenation reactions; it is oxidized to acetone. Isopropyl
alcohol may be converted to 2-bromopropane using phosphorus tribromide, or dehydrated
to propene by heating with sulfuric acid. Like most alcohols, isopropyl alcohol reacts
with active metals such as potassium to form alkoxides that can be called isopropoxides.
The reaction with aluminium is used to prepare the catalyst aluminium isopropoxide.
Production In 1994, 1.5 million tonnes of isopropyl alcohol
were produced in the United States, Europe, and Japan. This compound is primarily produced
by combining water and propene in a hydration reaction. It is also produced by hydrogenating
acetone. There are two routes for the hydration process:
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. Indirect hydration
The indirect process reacts propene with sulfuric acid to form a mixture of sulfate esters.
Subsequent hydrolysis of these esters by steam produces isopropyl alcohol, which is distilled.
Diisopropyl ether is a significant by-product of this process; it is recycled back to the
process and hydrolyzed to give the desired product.
Direct hydration Direct hydration reacts propene and water,
either in gas phase or in liquid phase, at high pressures in the presence of solid or
supported acidic catalysts. Higher-purity propylene tends to be required for this type
of process. 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 that is 87.9% by weight isopropyl
alcohol and 12.1% by weight water. Pure isopropyl alcohol is made by azeotropic distillation
of the wet isopropyl alcohol using either diisopropyl ether or cyclohexane as azeotroping
agents. Hydrogenation of acetone
Crude acetone is hydrogenated in the liquid phase over Raney nickel or a mixture of copper
and chromium oxide to give isopropyl alcohol. This process is useful when coupled with excess
acetone production, such as the cumene process. Uses
In 1990, 45 thousand tonnes of isopropyl alcohol were used in the United States. The vast majority
of isopropyl alcohol was used as a solvent for coatings or for industrial processes.
Isopropyl alcohol in particular is popular for pharmaceutical applications, it is presumed
due to the low toxicity of any residues. Some isopropyl alcohol is used as a chemical intermediate.
Isopropyl alcohol may be converted to acetone, but the cumene process is more significant.
In that year, a tiny fraction was consumed for household use and in personal care products.
It is also used as a gasoline additive. Solvent
Isopropyl alcohol dissolves a wide range of non-polar compounds. It also evaporates quickly,
leaves nearly zero oil traces, compared to ethanol, 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 oils. Together with ethanol, n-butanol, and methanol, it belongs
to the group of alcohol solvents, about 6.4 million tonnes of which utilized worldwide
in 2011. Examples of this application include cleaning
electronic devices such as contact pins, magnetic tape and disk heads, the lenses of lasers
in optical disc drives and removing thermal paste from heatsinks and IC packages. 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. It
is commonly used to clean prepared optical fibers just before splicing. It is used to
clean LCD and glass computer monitor screens, and used to give second-hand or worn non-vinyl
phonograph records newer-looking sheen. It is effective at removing Hot-Melt Adhesive
from a large variety of surfaces. 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. In addition,
it can also be used to clean paint or other oil-based products so that they may be reused,
commonly known as "repainting." It is used as a wetting agent in the fountain solution
used in lithographic printing, and often used as a solvent for French polishing shellac
used in cabinet making. Intermediate
Isopropyl alcohol is esterified to give isopropyl acetate, another solvent. It reacts with carbon
disulfide and sodium hydroxide to give sodium isopropylxanthate, a herbicide and an ore
flotation reagent. Isopropyl alcohol reacts with titanium tetrachloride and aluminium
metal to give titanium and aluminium isopropoxides, respectively, the former a catalyst, and the
latter a chemical reagent. This compound may serve as a chemical reagent in itself, by
acting as a dihydrogen donor in transfer hydrogenation. Medical
Disinfecting pads typically contain a 60–70% solution of isopropyl alcohol in water. Water
is required to open up membrane pores of bacteria, which acts as a gateway inside for isopropyl.
A 75% v/v solution in water may be used as a hand sanitizer. Isopropyl alcohol is used
as a water-drying aid for the prevention of otitis externa, better known as swimmer's
ear. Early uses as an anesthetic
Although isopropyl alcohol can be technically used for anesthesia, its many negative drawbacks
prohibit this use. Isopropyl alcohol can also be used similar to ether as a solvent or as
an anesthetic by inhaling the fumes or orally. Early uses included using the solvent as general
anesthetic for small mammals and rodents by scientists and some veterinarians. However,
it was soon discontinued, as many complications arose, including respiratory irritation, internal
bleeding, and visual and hearing problems. In rare cases, respiratory failure leading
to death in animals was observed. Automotive
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. Alcohol 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 windshield de-icer. Isopropyl alcohol
is also used to remove brake fluid traces from hydraulic braking systems, so that the
brake fluid does not contaminate the brake pads, which would result in poor braking.
Laboratory As a biological specimen preservative, isopropyl
alcohol provides a comparatively non-toxic alternative to formaldehyde and other synthetic
preservatives. Isopropyl alcohol solutions of 70–99% are used to preserve specimens.
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. Safety
Isopropyl alcohol vapor is denser than air and is flammable with a combustible range
between 2 and 12.7% in air. It should be kept away from heat and open flame. Isopropyl alcohol
has also been reported to form peroxides, which may explode upon concentration. Isopropyl
alcohol is a skin irritant. Toxicology
Isopropyl alcohol and its metabolite, acetone, act as central nervous system depressants.
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. 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 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. Isopropyl alcohol
is oxidized to form acetone by alcohol dehydrogenase in the liver.
Isopropyl alcohol is denatured for certain uses, in which case the NFPA 704 rating is
changed to 2,3,1. History
In 1920, Standard Oil first produced isopropyl alcohol by hydrating propene. Its major use
at the time was not rubbing alcohol but for oxidation to acetone, whose first major use
was in World War One for the preparation of the smokeless propellant, Cordite.
References
External links CDC – NIOSH Pocket Guide to Chemical Hazards
Environmental Health Criteria 103: 2-Propanol