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.

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.

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

Fusel alcohols like isoamyl alcohol are grain fermentation byproducts, and therefore trace amounts of isoamyl are present in many alcoholic beverages.

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

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.

Isoamyl alcohol can be synthesized by condensation of isobutene and formaldehyde which produces isoprenol, then hydrogenation. 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. 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.

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.