The four isomers of alcohol C4H10O are butan-1-ol, butan-2-ol, 2-methylpropan-1-ol and 2-methylpropan-2-ol. Isomers are compounds that contain the same number of atoms but have a different spatial arrangement. In the case of butanol, each carbon atom has four bonds (valency 4), each oxygen atom has two bonds (valency 2) and each hydrogen atom has one bond (valency 1).
Butanol isomers, also known as n-butanol, sec-butanol, isobutanol and tert-butanol, have different melting and boiling points. The isomers are soluble because they contain a hydroxyl group, which is an oxygen atom bonded covalently to a hydrogen atom that dissolves in water, whereas the carbon chain resists solubility. This conflict makes n-butanol moderately soluble, while other alcohols, such as methanol, ethanol and propanol, are completely soluble.
Although overexposure to its fumes can be toxic, butanol is safe enough to be used in cosmetics. Butanol is also used as a solvent in paint thinners, and it is added to hydraulic and brake fluids. Sec-butanol has a pleasant fragrance and is used in perfumes. Isobutanol has a variety of industrial applications as an additive. Tert-butanol, which is more stable than the other isomers, is used as a solvent. Butanol was first produced from bacteria in 1861 by Louis Pasteur.