1-Butanol

C 4
H 10
O 1

Ball-and-stick Stick Space-filling

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15 atoms, 14 single bonds.

IUPAC name: butan-1-ol
Molar mass: 74.123(11) g/mol
Atoms: 15
SMILES: CCCCO
InChIKey: LRHPLDYGYMQRHN-UHFFFAOYSA-N
PubChem CID: 263

Made of

C H O

Structural formula of 1-butanol. Each unlabelled corner is a carbon atom, and the six hydrogens on carbon are not drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

In 1-butanol the oxygen atom ends a straight chain of four carbon atoms; in diethyl ether it sits between two carbons, C–O–C. Yet the two share one molecular formula, C₄H₁₀O, and one molar mass, 74.12 g/mol. In 1-butanol the oxygen also carries a hydrogen, forming a hydroxy group, –OH, on carbon 1. That position is the 1 in its IUPAC (International Union of Pure and Applied Chemistry) name, butan-1-ol. HSDB, the Hazardous Substances Data Bank, puts 1-butanol’s boiling point at 117.6 °C and the ether’s at 34.6 °C.

It is also called n-butanol or n-butyl alcohol. The compound is a colourless liquid that flows easily, with a vinous, or wine-like, odour. HSDB describes the smell as harsh, with a note of banana.

Structure and bonding

The model holds 15 atoms joined by 14 single bonds: three C–C, nine C–H, one C–O and one O–H. In Ball-and-stick the four carbons and the oxygen zig-zag instead of running straight, like the chain of butane. PubChem’s computed model gives about 111.5° at each C–C–C bend, 108.9° at O–C–C and 107.6° at C–O–H. Turned edge-on, the chain is almost flat and fully stretched. Labels marks the oxygen with its single hydrogen at one end and a CH₃ group at the other.

Stick shrinks every atom to a joint, which leaves the bends plain. Space-filling swells the atoms into an elongated body of grey carbon under white hydrogen, capped at one end by the red oxygen. This stretched arrangement is only one of many: turning about any C–C single bond lets a chain bend or curl, as Chem1 notes. Beyond that one frozen shape, the drawing matches the real molecule: every bond single, no ring, no charge. Chem1 puts the acidity of an alcohol below even that of water, so 1-butanol stays a neutral molecule in water, the form drawn.

Where it turns up

Among living things, 1-butanol has been reported in Zea mays and Lucensosergia lucens, according to the LOTUS natural-products collection. It is generally recognised as safe as a flavouring substance in food. Among food additives it also serves as an extraction solvent, a liquid used to dissolve one substance out of a food or raw material. It appears, too, on the US Food and Drug Administration’s 1982 list of inactive ingredients in approved prescription drug products.

In cosmetics it has a history as a solvent for nail care. It now also appears at low concentrations in eye make-up, personal hygiene and shaving products. Nail polish, rubber cement and safety glass contain it too. In microscopy it helps prepare paraffin embedding materials. One commercial form of formaldehyde comes dissolved in n-butanol, with ethanol or urea as the other carriers.

Why it matters

The main commercial route starts from propylene. The Oxo reaction, which uses carbon monoxide, turns it into two aldehydes, n-butyraldehyde and isobutyraldehyde, and adding hydrogen converts each into its alcohol. Either the aldehydes are separated first and hydrogenated one by one, or the mixture is hydrogenated whole and distillation then separates n-butyl from isobutyl alcohol.

Fermentation offers a second route. The organism doing the work is Bacillus butylicus, sometimes helped by Clostridium acetobutyricum. It turns glycerol, starches and sugars in general into 1-butanol.

As a solvent it serves paints, lacquers and varnishes, natural and synthetic resins, gums, vegetable oils, dyes and alkaloids. Much of it becomes other chemicals. In 1984, 30 per cent of its use went to butyl acrylates and methacrylate and 23 per cent to glycol ethers, on HSDB’s figures. Butyl acetate and solvent use took 12.5 per cent each. For 2023, the US Environmental Protection Agency’s Chemical Data Reporting puts national volume at 1 billion to under 2.5 billion pounds.

Properties

Properties of 1-butanol Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 263.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₄H₁₀O
Molar mass	74.123(11) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	4
Hydrogen atoms	10
Oxygen atoms	1
Bonds	14
PubChem molecular weight	74.12 g/mol	g/mol	PubChem

Safety

1-Butanol is a flammable liquid, harmful if swallowed and irritating to the skin and airways, and it can seriously damage the eyes. Under EU Regulation 1272/2008 its signal word is Danger, and in HSDB it is Warning. NITE, a Japanese government body, classes repeated or prolonged exposure as damaging to the central nervous system and hearing. The PubChem Laboratory Chemical Safety Summary gathers these classifications, and the NIOSH (US National Institute for Occupational Safety and Health) card for n-butyl alcohol holds the workplace limits.

Questions

What shape is a 1-butanol molecule?

A zig-zag chain rather than a straight rod. In PubChem's computed model the oxygen and the four carbons lie almost in one plane, fully stretched, and 4.91 Å separates the oxygen from the far methyl carbon. The oxygen, with its one hydrogen, caps one end of the zig-zag and a CH₃ group the other. Diethyl ether, with the same formula, holds its oxygen in the middle of its chain.

Does butanol mix with water?

Only partly. Its solubility is 68 g per litre of water at 25 °C on HSDB's figure, and 7.7 g per 100 mL at 20 °C on the International Chemical Safety Card's. Whatever does not dissolve floats, being less dense than water, CAMEO Chemicals notes. Ethanol and ethyl ether are a different matter: butanol mixes with them in any proportion, and it dissolves very readily in acetone.

What happens to butanol in the body?

It is taken up through the lungs, the gut and the skin. It is eliminated after being metabolised, mainly by enzymes called alcohol and aldehyde dehydrogenases. In rabbit liver, an enzyme labelled isozyme 3a oxidises methyl, propyl and butyl alcohols as well as ethyl alcohol. Butanol can also form in the blood when butyl acetate is hydrolysed, split by reaction with water, but it is then quickly oxidised.

Can butanol be used as a fuel instead of ethanol?

It has been proposed as a biofuel alternative to ethanol, and several microbes used in industry, Escherichia coli among them, have been engineered to make it. Toxicity is the drawback: n-butanol harms these organisms more than ethanol does. Tests with fluorescent dyes found a large rise in reactive oxygen species, reactive forms of oxygen inside the cells, while the microbes were under n-butanol stress.

Made of the same elements

C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₁₀H₂₀O Menthol 31 atoms, 31 single bonds.
C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₃H₁₈O₂ Ibuprofen 33 atoms, 33 bonds.
C₂₀H₁₄O₄ Phenolphthalein 38 atoms, 41 bonds.
C₁₈H₂₄O₂ Estradiol 44 atoms, 47 bonds.
C₁₂H₂₂O₁₁ Lactose 45 atoms, 46 single bonds.
C₁₂H₂₂O₁₁ Sucrose 45 atoms, 46 single bonds.
C₁₉H₂₈O₂ Testosterone 49 atoms, 52 bonds.
C₁₆H₃₂O₂ Palmitic acid 50 atoms, 49 bonds.
C₂₁H₃₀O₂ Progesterone 53 atoms, 56 bonds.
C₁₈H₃₄O₂ Oleic acid 54 atoms, 53 bonds.
C₂₁H₃₀O₅ Cortisol 56 atoms, 59 bonds.
C₂₇H₄₄O Cholecalciferol 72 atoms, 74 bonds.
C₂₇H₄₆O Cholesterol 74 atoms, 77 bonds.