Butanol

Butanol (also called butyl alcohol) is a four-carbon alcohol with a formula of C4H9OH, which occurs in five isomeric structures (four structural isomers), from a straight-chain primary alcohol to a branched-chain tertiary alcohol; all are a butyl or isobutyl group linked to a hydroxyl group (sometimes represented as BuOH, n-BuOH, i-BuOH, and t''-BuOH). These are n-butanol, 2 stereoisomers of sec-butanol, isobutanol and tert-butanol. Butanol is primarily used as a solvent and as an intermediate in chemical synthesis, and may be used as a fuel. Biologically produced butanol is called biobutanol, which may be n-butanol or isobutanol. The unmodified term butanol usually refers to the straight chain isomer with the alcohol functional group at the terminal carbon, which is also known as n-butanol or 1-butanol. The straight chain isomer with the alcohol at an internal carbon is sec-butanol or 2-butanol. The branched isomer with the alcohol at a terminal carbon is isobutanol or 2-methyl-1-propanol, and the branched isomer with the alcohol at the internal carbon is tert-butanol or 2-methyl-2-propanol. The butanol isomers have different melting and boiling points. n-butanol and isobutanol have limited solubility, sec-butanol has substantially greater solubility, while tert-butanol is miscible with water. The hydroxyl group makes the molecule polar, promoting solubility in water, while the longer hydrocarbon chain mitigates the polarity and reduces solubility. Butanol exhibits a low order of toxicity in single dose experiments with laboratory animals and is considered safe enough for use in cosmetics. Brief, repeated overexposure with the skin can result in depression of the central nervous system, as with other short-chain alcohols. Exposure may also cause severe eye irritation and moderate skin irritation. The main dangers are from prolonged exposure to the alcohol's vapors. In extreme cases this includes suppression of the central nervous system and even death. Under most circumstances, butanol is quickly metabolized to carbon dioxide.