Isoamyl alcohol

Isoamyl alcohol is a colorless liquid with the formula C
5H
12O, specifically (H3C–)2CH–CH2–CH2–OH. It is one of several isomers of amyl alcohol (pentanol). It is also known as isopentyl alcohol, isopentanol, or (in the IUPAC recommended nomenclature) 3-methyl-butan-1-ol. An obsolete name for it was isobutyl carbinol.[5]

Isoamyl alcohol[1]
Names
Preferred IUPAC name
3-Methylbutan-1-ol
Other names
3-Methyl-1-butanol
Isopentyl alcohol
Isopentanol
Isobutylcarbinol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.004.213
KEGG
UNII
Properties
C5H12O
Molar mass 88.148 g/mol
Appearance Clear, colorless liquid
Density 0.8104 g/cm3 at 20 °C
Melting point −117[2][3] °C (−179 °F; 156 K)
Boiling point 131.1 °C (268.0 °F; 404.2 K)
slightly soluble, 28 g/L
Solubility very soluble in acetone, diethyl ether, ethanol
Vapor pressure 28 mmHg (20°C)[3]
-68.96·10−6 cm3/mol
Viscosity 3.692 mPa·s
Thermochemistry
2.382 J·g−1·K−1
-356.4 kJ·mol−1 (liquid)
-300.7 kJ·mol−1 (gas)
Hazards
Flash point 43 °C (109 °F; 316 K)
350 °C (662 °F; 623 K)
Explosive limits 1.2 – 9%
Lethal dose or concentration (LD, LC):
3438 mg/kg (rabbit, oral)
1300 mg/kg (rat, oral)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 100 ppm (360 mg/m3)[3]
REL (Recommended)
 TWA 100 ppm (360 mg/m3) ST 125 ppm (450 mg/m3)[3]
IDLH (Immediate danger)
 500 ppm[3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Isoamyl alcohol is an ingredient in the production of banana oil, an ester found in nature and also produced as a flavouring in industry. It is a common fusel alcohol, produced as a major by-product of ethanol fermentation.

Occurrence

Isoamyl alcohol is one of the components of the aroma of Tuber melanosporum, the black truffle.

The compound has also been identified as a chemical in the pheromone used by hornets to attract other members of the hive to attack.[6]

Isoamyl acetate is a component of the natural aroma of bananas, especially the Gros Michel variety.

Extraction from fusel oil

Isoamyl alcohol can be separated from fusel oil by either of two methods: shaking with strong brine solution and separating the oily layer from the brine layer; distilling it and collecting the fraction that boils between 125 and 140 °C. Further purification is possible with this procedure: shaking the product with hot limewater, separating the oily layer, drying the product with calcium chloride, and distilling it, collecting the fraction boiling between 128 and 132 °C.[5]

Synthesis

Isoamyl alcohol can be synthesized from isobutanol by conversion into isovaleraldehyde, which is subsequently reduced to isobutyl carbinol by means of sodium amalgam. It is a colourless liquid of density 0.8247 g/cm3 (0 °C), boiling at 131.6 °C, slightly soluble in water, and easily dissolved in organic solvents. It has a characteristic strong smell and a sharp burning taste. Amyl alcohol has an oral LD50 of 200 mg/kg in mice,[7] suggesting that it is significantly more toxic than ethanol. On passing the vapour through a red-hot tube, it decomposes into acetylene, ethylene, propylene, and other compounds. It is oxidized by chromic acid to isovaleraldehyde, and it forms addition compounds crystals with calcium chloride and tin(IV) chloride.[5]

Uses

Besides its use in the synthesis of banana oil, isoamyl alcohol is also an ingredient of Kovac's reagent, used for the bacterial diagnostic indole test.

It is also used as an antifoaming agent in the chloroform isoamyl alcohol reagent.[8]

Isoamyl alcohol is used in a phenol–chloroform extraction mixed with the chloroform to further inhibit RNase activity and prevent solubility of RNAs with long tracts of poly-adenine.[9]

References
  1. Lide, David R., ed. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 3–374, 5–42, 6–188, 8–102, 15–22. ISBN 0-8493-0487-3.
  2. Straka, M.; van Genderen, A.; Růžička, K.; Růžička, V. Heat Capacities in the Solid and in the Liquid Phase of Isomeric Pentanols. J. Chem. Eng. Data 2007, 52, 794-802.
  3. NIOSH Pocket Guide to Chemical Hazards. "#0348". National Institute for Occupational Safety and Health (NIOSH).
  4. "Isoamyl alcohol". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5.  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Amyl Alcohols". Encyclopædia Britannica. 1 (11th ed.). Cambridge University Press. p. 900.
  6. Wilson, Calum & Davies, Noel & Corkrey, Ross & J. Wilson, Annabel & M. Mathews, Alison & C. Westmore, Guy. (2017). Receiver Operating Characteristic curve analysis determines association of individual potato foliage volatiles with onion thrips preference, cultivar and plant age. PLOS ONE. 12. e0181831. 10.1371/journal.pone.0181831.
  7. http://www.sigmaaldrich.com/
  8. Zumbo, P. "Phenol-chloroform Extraction" (PDF). WEILL CORNELL MEDICAL COLLEGE P. ZUMBO LABORATORY OF CHRISTOPHER E. MASON, PH.D. Retrieved 19 June 2014.
  9. Green, Michael; Sambrook, Joseph. "Purification of Nucleic Acids: Extraction with Phenol-Chloroform". Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory Press. ISBN 1936113422.

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