Isopropanol

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Isopropanol
Isopropanol bottle and sample.jpg
Isopropanol sample and its original bottle.
Names
IUPAC name
2-Propanol
Systematic IUPAC name
Isopropanol
Other names
Dimethyl carbinol
IPA
iPrOH
Propan-2-ol
Rubbing alcohol
s-Propanol
sec-Propyl alcohol
Identifiers
Jmol-3D images Image
Properties
C3H8O
Molar mass 60.10 g/mol
Appearance Colorless volatile liquid
Odor Alcoholic, harsh
Density 0.786 g/cm3 (at 20 °C)
Melting point −89 °C (−128 °F; 184 K)
Boiling point 82.6 °C (180.7 °F; 355.8 K)
Miscible
Solubility Miscible with acetone, benzene, ethanol, methanol, toluene
Insoluble with saline solution
Acidity (pKa) 16.5
Hazards
Safety data sheet ScienceLab
Flash point Open cup: 11.7 °C (53.1 °F; 284.8 K)
Closed cup: 13 °C (55 °F)
Lethal dose or concentration (LD, LC):
12800 mg/kg (dermal, rabbit)
3600 mg/kg (oral, mouse)
5045 mg/kg (oral, rat)
6410 mg/kg (oral, rabbit)
53000 mg/m3 (inhalation, mouse)
12,000 ppm (rat, 8 hr)
Related compounds
Related compounds
 Propanol
Isobutanol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Isopropanol, or isopropyl alcohol, is a secondary alcohol. It provides the familiar smell of rubbing alcohol, where it is frequently used although this may be ethanol. Isopropanol is the largest carbon chain alcohol to be miscible with water and is a common OTC solvent.

Properties

Chemical

Isopropanol is a generally nonreactive (inorganically speaking) alcohol. It can be dehydrated, and is a common reagent in organic chemistry.

Anhydrous isopropanol is used to neutralise small quantities of sodium or potassium metal, as the reaction with the alcohol is mild compared to with water and removes any reactive metal that may pose a danger if left in the lab. This property allows for the production of metal isopropoxides.

A violent runaway reaction happens when isopropanol comes into contact with a nitration bath. Toxic nitrogen dioxide is produced in a rapid reaction as the isopropanol is not nitrated but oxidised by the acids.

Isopropanol can be reacted with nitrous acid to for isopropyl nitrite and with mixed acids to form isopropyl nitrate.

Peroxide formation

Isopropanol is liable to form peroxides when exposed to oxygen and light. Certain impurities may act as promotors of peroxide formation. There are numerous examples of accidents in the literature. In one case, a severe explosion occured when 500-750 mL of isopropanol, recovered a year ago from an Meerwein–Ponndorf–Verley reduction, was distilled. The residue of 50-100 mL exploded violently, injuring the lab worker severly and shooting shrapnel through windows and bottles. The alcohol tested strongly positive for peroxides.[1] The literature warns especially about mixtures containing acetone as a promotor.[2] Benzophenone has been reported to act as a photosensitizer as well, forming 2-hydroxy-2-propylhydroperoxide and to a lesser extend 2,2'-dihydroperoxy-2,2'-diisopropylperoxide.[3] Other sources also claim the formation of TATP.[4] In june 2023 a picture of the alleged peroxide in crystalline form under isopropanol was posted on twitter, which sparked much discussion, but in the absence of further analysis remained inconclusive.[5]

Physical

Isopropanol is a clear, colorless liquid miscible in water. It's smell is described as closer to acetone than other short chain alcohols like ethanol. It burns on contact with cuts (like ethanol) and it's widely used as an antiseptic. It is a good, cheap solvent.

Availability

Isopropanol is available in concentrations anywhere from 60% to 99% (the rest being water and various stabilizers, additives) for a variety of applications, often cleaning electronics or sold as 'rubbing alcohol'. The most common concentrations are 70% and 91%. These store-bought solutions can be salted out up to a concentration of about 91% using sodium chloride, and nearly all water can be separated by salting out with sodium hydroxide, though this may inadvertently contaminate the isopropanol and produce sodium isopropoxide. Dry isopropanol has the potential to form explosive peroxides when distilled, so it is highly recommended that these distillations are carefully monitored if done at all.

Preparation

Isopropanol is produced by hydrogenation of acetone over a nickel catalyst. It can also be obtained by hydrolysing esters containing an isopropyl group.

Projects

Handling

Safety

Isopropanol is flammable. It has low toxicity and it's much less toxic than methanol or ethylene glycol. Vapours of dry isopropanol can potentially be explosive.

Storage

Isopropanol should be stored in closed bottles, away from any oxidants and fire sources. As it is prone to forming peroxides over long periods of time, a small amount of antioxidant should be added, unless it already has. Most OTC isopropanol already has antioxidants in its composition.

Disposal

Isopropanol can be safely burned. Old bottles that have been exposed to air should be checked for any peroxides and if there are any, they should be neutralized if safely possible.

References

  1. ↑ Th. Wagner-Jauregg, Angew. Chem., 52, 709 (1939), https://doi.org/10.1002/ange.19390525004
  2. ↑ A. L. Wilds, Org. React. 2, 178 (1944), http://library.sciencemadness.org/library/books/organic_reactions_v2.pdf
  3. ↑ G. O. Schenck, H.-D. Becker, Angew. Chem., 70, 16, 504 (1958), https://doi.org/10.1002/ange.19580701613
  4. ↑ C. C. Pye, ACS Chem. Health Saf. 27, 5, 279 (2020), https://doi.org/10.1021/acs.chas.0c00061
  5. ↑ https://twitter.com/naohbartfield/status/1674866422080495624

Relevant Sciencemadness threads

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