Pentanol

Pentanol

An amyl alcohol is any of 8 alcohols with the formula C5H11OH.[1] A mixture of amyl alcohols (also called amyl alcohol) can be obtained from fusel alcohol. Amyl alcohol is used as a solvent and in esterfication, for example in the production of amyl acetate. Amyl alcohol as a distinct chemical compound refers to 1-pentanol.

Eight structural isomers with molecular formula C5H12O and all alcohols are known:

Amyl alcohol isomers
Common Name Structure Type IUPAC Name Boiling Point (°C)[2]
normal amyl alcohol primary Pentan-1-ol 138.5
isobutyl carbinol
or isoamyl alcohol
or isopentyl alcohol
primary 3-Methylbutan-1-ol 131.2
active amyl alcohol
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primary 2-Methylbutan-1-ol 128.7
tertiary butyl carbinol
or neopentyl alcohol
primary 2,2-Dimethylpropan-1-ol 113.1
3-Pentanol secondary Pentan-3-ol 115.3
methyl (n) propyl carbinol secondary Pentan-2-ol 118.8
methyl isopropyl carbinol
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secondary 3-Methylbutan-2-ol 113.6
dimethyl ethyl carbinol
or tertiary amyl alcohol
tertiary 2-Methylbutan-2-ol 102

Three of these alcohols, active amyl alcohol (2-methylbutan-1-ol), methyl (n) propyl carbinol (pentan-2-ol), and methyl isopropyl carbinol (3-methylbutan-2-ol), are optically active, as they contain an asymmetric carbon atom.

The most important is isobutyl carbinol, this being the chief constituent of fermentation amyl alcohol, and consequently a constituent of fusel oil. It can be separated from fusel oil by shaking with strong brine solution, separating the oily layer from the brine layer and distilling it, the portion boiling between 125 and 140 °C. being collected. For further purification it may be shaken with hot limewater, the oily layer separated, dried with calcium chloride and fractionated, the fraction boiling between 128 and 132 °C only being collected. It may 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, easily soluble in organic solvents. It possesses a characteristic strong smell and a sharp burning taste. Amyl alcohol has an oral LD50 of 200 mg/kg (mouse),[3] suggesting that the chemical is significantly more toxic than ethanol. On passing its vapour through a red-hot tube, it decomposes with production of acetylene, ethylene, propylene, and other compounds. It is oxidized by chromic acid to isovaleraldehyde, and it forms crystalline addition compounds with calcium chloride and tin(IV) chloride.

The other amyl alcohols may be obtained synthetically. Of these, tertiary butyl carbinol has been the most difficult to obtain, its synthesis having first been reported in 1891, by L. Tissier [4] by the reduction of a mixture of trimethyl acetic acid and trimethylacetyl chloride with sodium amalgam. It is a solid that melts at 48 to 50 °C and boils at 112.3 °C.

References

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