Butanol (also called butyl alcohol) is a four-carbon

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

with a

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

of C₄ H₉ OH, which occurs in five

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

ic 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 In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

group (sometimes represented as BuOH, ''sec''-BuOH, i-BuOH, and ''t''-BuOH). These are 1-butanol, two stereoisomers of ''sec''-butyl alcohol, isobutanol and ''tert''-butyl alcohol. Butanol is primarily used as a

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

and as an intermediate in

chemical synthesis Chemical synthesis (chemical combination) is the artificial execution of chemical reactions to obtain one or several products. This occurs by physical and chemical manipulations usually involving one or more reactions. In modern laboratory uses ...

, and may be used as a

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

. Biologically produced butanol is called biobutanol, which may be ''n''-butanol or isobutanol.

Isomers

The unmodified term ''butanol'' usually refers to the straight chain isomer with the alcohol

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

at the terminal carbon, which is also known as 1-butanol. The straight chain isomer with the alcohol at an internal carbon is ''sec''-butyl alcohol 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''-butyl alcohol or 2-methyl-2-propanol. The butanol isomers have different melting and boiling points. 1-Butanol and isobutanol have limited solubility, ''sec''-butyl alcohol has substantially greater solubility, whereas ''tert''-butyl alcohol is

miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). Such substances are said to be miscible (etymologically ...

with water. The hydroxyl group makes the molecule polar, promoting solubility in water, while the longer hydrocarbon chain mitigates the polarity and reduces solubility.

Toxicity

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 The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

and even death. Under most circumstances, butanol is quickly metabolized to

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. It has not been shown to damage DNA or cause

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

Uses

Primary uses

Butanol is used as a

for a wide variety of chemical and textile processes, in organic synthesis, and as a chemical intermediate. It is also used as a

paint thinner Paint thinners are diluents — solvents used to adjust the viscosity of paint, as well as similar preparations such as varnish and lacquer, by dilution. For water-based paints, such as acrylic paints, water is the primary solvent, but notably, ...

and a solvent in other coating applications where a relatively slow evaporating latent solvent is preferable, as with lacquers and ambient-cured enamels. It is also used as a component of

hydraulic Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concer ...

and brake fluids. A 50% solution of butanol in water has been used since the 20th century to retard the drying of fresh plaster in

fresco Fresco ( or frescoes) is a technique of mural painting executed upon freshly laid ("wet") lime plaster. Water is used as the vehicle for the dry-powder pigment to merge with the plaster, and with the setting of the plaster, the painting become ...

painting. The solution is usually sprayed on the wet plaster after the plaster has been trowelled smooth and extends the working period during which frescos can be painted up to 18 hours. Butanol is used in the synthesis of 2-butoxyethanol. A major application for butanol is as a reactant with

acrylic acid Acrylic acid (IUPAC: prop-2-enoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has ...

to produce butyl acrylate, a primary ingredient of water based acrylic paint. It is also used as a base for

perfumes Perfume (, ) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agre ...

, but on its own has a highly alcoholic aroma.

Salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

of butanol are chemical intermediates; for example,

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

salts of ''tert''-butanol are ''tert''-butoxides.

Recreational use

2-Methyl-2-butanol is a central nervous system

depressant Depressants, also known as central nervous system depressants, or colloquially known as "downers", are drugs that lower neurotransmission levels, decrease the electrical activity of brain cells, or reduce arousal or stimulation in various ...

with a similar effect upon ingestion to ethanol. Case reports have been documented demonstrating its potential for abuse.

Biobutanol

Butanol (''n''-butanol or isobutanol) is a potential

biofuel Biofuel is a fuel that is produced over a short time span from Biomass (energy), biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricu ...

( butanol fuel). Butanol at 85 percent concentration can be used in cars designed for gasoline (petrol) without any change to the engine (unlike 85% ethanol), and it contains more energy for a given volume than ethanol and almost as much as gasoline, and a vehicle using butanol would return fuel consumption more comparable to gasoline than ethanol. Butanol can also be added to diesel fuel to reduce soot emissions. Photoautotrophic microorganisms, like cyanobacteria, can be engineered to produce 1-butanol indirectly from and water.Liu, X., Miao, R., Lindberg, P., & Lindblad, P. (2019). Modular engineering for efficient photosynthetic biosynthesis of 1-butanol from CO 2 in cyanobacteria. Energy & Environmental Science, 12(9), 2765-2777.

Production

Butanols are normally present in fusel alcohol. Since the 1950s, most butanol in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

is produced commercially from

fossil fuel A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geolog ...

s. The most common process starts with

propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like od ...

(propylene), which is put through a

hydroformylation In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes () from alkenes (). This chemical reaction entails the net addition of a formyl group () and a hydrogen ...

reaction to form butanal, which is then reduced with

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

to 1-butanol and/or 2-butanol. ''tert''-butanol is derived from isobutane as a co-product of

propylene oxide Propylene oxide is an epoxide with the molecular formula C3H6O. This colourless volatile liquid with an odour similar to ether, is produced on a large scale industrially. Its major application is its use for the production of polyether polyols f ...

production. Propen Hydroformylierung zu Butanol

Butanol can also be produced by

fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

by bacteria. Prior to the 1950s, '' Clostridium acetobutylicum'' was used in

industrial fermentation Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity ch ...

to produce ''n''-butanol.

References

*''Merck Index'', 12th Edition, 1575. {{Authority control Alkanols Alcohol solvents Fatty alcohols Biotechnology products Liquid fuels Oxygenates