Isopropanol

Isopropanol

Isopropyl alcohol
Identifiers
CAS number 67-63-0 YesY
PubChem 3776
ChemSpider 3644 YesY
UNII ND2M416302 YesY
UN number 1219
KEGG D00137 YesY
ChEBI CHEBI:17824 YesY
RTECS number NT8050000
ATC code AX05
Jmol-3D images Image 1
Properties
Molecular formula C3H8O
Molar mass 60.10 g mol−1
Appearance Colorless liquid
Density 0.786 g/cm3 (20 °C)
Melting point

−89 °C, 184 K, -128 °F

Boiling point

82.6 °C, 356 K, 181 °F

Solubility in water miscible
Solubility miscible in benzene, chloroform, ethanol, ether, glycerin
soluble in acetone
insoluble in salt solutions
Acidity (pKa) 16.5[1]
Refractive index (nD) 1.3776
Viscosity 2.86 cP at 15 °C
1.96 cP at 25 °C[2]
1.77 cP at 30 °C[2]
Dipole moment 1.66 D (gas)
Hazards
MSDS External MSDS
GHS pictograms
GHS signal word Danger
GHS hazard statements H225, H319, H336
GHS precautionary statements P210, P261, P305+351+338
R-phrases R11 R36 R67
S-phrases S7 S16 S24 S25 S26
Main hazards Flammable
NFPA 704
3
1
0
Flash point 11.7 °C (open cup)
13 °C (closed cup)
Autoignition
temperature
399 °C
Explosive limits 2–12.7%
Threshold Limit Value 980 mg/m3 (TWA), 1225 mg/m3 (STEL)
LD50 3600 mg/kg (oral, mouse)
12800 mg/kg (dermal, rabbit)
LC50 = 53000 mg/m3 (inhalation, mouse)
Related compounds
Related alcohols 1-Propanol, ethanol, 2-butanol
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Isopropyl alcohol is a common name for 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 as (CH3)2CHOH. It is a structural isomer of propanol. Isopropyl alcohol is denatured for certain uses, in which case the NFPA 704 rating is changed to 2,3,1.

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.[3] 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.[4]

Isopropyl alcohol forms an azeotrope with water, which gives a boiling point of 80.37 oC and a composition of 87.7 wt% (91 vol%) isopropyl alcohol. Water-isopropyl alcohol mixtures have depressed melting points.[4] It has a slightly bitter taste, and is not safe to drink.[4][5]

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 → (CH3)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 which can be called isopropoxides. The reaction with aluminium (initiated by a trace of mercury) is used to prepare the catalyst aluminium isopropoxide.[6]

Production

In 1994, 1.5 million tonnes of isopropyl alcohol were produced in the United States, Europe, and Japan.[7] This compound is primarily produced by combining water and propene in a hydration reaction. It is also produced by hydrogenating acetone.[7][8]

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.[7]

Direct hydration

Direct hydration reacts propene and water, either in gas or liquid phases, at high pressures in the presence of solid or supported acidic catalysts. Higher purity propylene (> 90%) tends to be required for this type of process.[7]

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.[9] Pure (anhydrous) isopropyl alcohol is made by azeotropic distillation of the wet isopropyl alcohol using either diisopropyl ether or cyclohexane as azeotroping agents.[7]

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.[7]

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,[7] presumably 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 (5.4 tonnes) was consumed for household use and in personal care products. It is also used as a gasoline additive.[7]

Solvent

Isopropyl alcohol 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 oils. Together with ethanol, n-butanol, and methanol, it belongs to the group of alcohol-based solvents, about 6.4 million tonnes of which were utilized worldwide in 2011.[10]

Examples of this application 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 heatsinks and IC packages (such as CPUs[11]). 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 (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 sheen. It is effective at removing Hot-Melt Adhesive from a large variety of surfaces. Isopropyl alcohol should not be used to clean vinyl records as it may leach plasticizer from the vinyl making it more rigid. 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[12] and an ore flotation reagent.[13] 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.[7] 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. A 75% v/v solution in water may be used as a hand sanitizer.[14] Isopropyl alcohol is used as a water-drying aid for the prevention of otitis externa, better known as swimmer's ear.[15]

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. 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 windshield de-icer. 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.

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.[16] Isopropyl alcohol has also been reported to form peroxides, which may explode upon concentration.[17] Isopropyl alcohol is a skin irritant.[16]

Toxicology

Isopropyl alcohol and its metabolite, acetone, act as central nervous system (CNS) 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.[18] However, it is not nearly as toxic as methanol or ethylene glycol. Isopropyl alcohol does not cause an anion gap acidosis (in which a 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.[19] Isopropyl alcohol is oxidized to form acetone by alcohol dehydrogenase in the liver.

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 explosive Cordite.[20]

See also

References

External links

  • MSDS for Isopropyl Alcohol
  • CDC - NIOSH Pocket Guide to Chemical Hazards
  • Lab Manager Article on Working with Isopropyl Alcohol