Butanone

Ball-and-stick Stick Space-filling

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13 atoms, 12 bonds.

IUPAC name: butan-2-one
Molar mass: 72.107(11) g/mol
Atoms: 13
Polarity: polar
SMILES: CCC(=O)C
InChIKey: ZWEHNKRNPOVVGH-UHFFFAOYSA-N
PubChem CID: 6569

Made of

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

Methyl ethyl ketone, shortened to MEK, names butanone after the two groups on either side of its C=O: a one-carbon methyl and a two-carbon ethyl. The name from IUPAC, the International Union of Pure and Applied Chemistry, butan-2-one, counts instead: a four-carbon chain with the keto group, the C=O, on carbon 2. NIOSH, the US federal institute for workplace safety and health, lists ethyl methyl ketone and methyl acetone as further synonyms.

Four carbon atoms, eight of hydrogen and one of oxygen give a molar mass of 72.11 g/mol. The colourless liquid boils at 79.59 °C, according to the Hazardous Substances Data Bank (HSDB), and mixes freely with ethanol, ether, acetone, benzene and chloroform. Water takes up less: 29 g in 100 mL at 20 °C, on the International Chemical Safety Cards’ figure. ChEBI (Chemical Entities of Biological Interest), a reference database, calls it a polar solvent and a bacterial metabolite.

Structure and bonding

Butanone’s oxygen hangs from the second of four carbons by the molecule’s only double bond, one of 12 bonds joining 13 atoms. That carbon therefore has unequal arms: one carbon on one side, two on the other. In Ball-and-stick, the model’s angles around it are 122.8° and 121.0° for O=C–C and 116.1° for C–C–C. They add to 360.0°, so the corner is flat.

Turned edge-on, the model shows the four carbons and the oxygen in one plane, zigzagging so that the ethyl arm’s end lies on the oxygen’s side. Only hydrogens leave that plane, six of the eight standing above and below it in pairs. This flat backbone is one computed arrangement: in the real molecule the ethyl arm can turn about its single bonds, as propanol’s chain does.

Stick strips the view to the 12 bonds; Space-filling swells the atoms into one hydrogen-covered body. The drawing matches the real bonding: one C=O double bond, no ring, no charge. The model draws atoms and bonds only, so no view shows the molecule’s polarity; acetone explains the C=O bond.

Where it turns up

Not every molecule of butanone comes from a factory. ATSDR, the US Agency for Toxic Substances and Disease Registry, says some trees make it and some fruits and vegetables hold small amounts. The LOTUS natural-products database records it in Tuber melanosporum and Alpinia chinensis, among other organisms, and bacteria make it too. It also occurs in normal human urine; HSDB allows a dietary origin but considers alpha-methylacetoacetic acid its more probable source.

Car and truck exhausts add it to the air, according to ATSDR. The US Environmental Protection Agency (EPA) notes that it can also form outdoors when light-driven oxidation attacks butane and other hydrocarbon pollutants. Sunlight-driven reactions remove it again: HSDB gives a half-life, the time for half of it to break down, of 5.4 hours in city air. Indoors, it is in household lacquers, varnishes, paint removers and glues, according to EPA.

Why it matters

Nearly half of all butanone goes into paints and other coatings, according to ATSDR, because it evaporates quickly and dissolves many substances. In 1981, HSDB records, 30 per cent of it served as a solvent for vinyl coatings and 18 per cent for adhesives. Its primary use in EPA’s account is dissolving gums, resins, cellulose acetate and cellulose nitrate. Perfume makers react it with citral to obtain methylpseudoionone, and it sterilises surgical and dental instruments against bacterial spores, according to HSDB.

It is made by removing hydrogen from 2-butanol or by oxidising butenes or butane. In December 2005, EPA took MEK off its list of toxic air pollutants under the Clean Air Act. The agency said the change might even benefit public health, as companies switch to it from more toxic or environmentally damaging chemicals. It remains regulated as a volatile organic compound. EPA’s Safer Choice programme marks it best in class and among the safest available for its function, though with some hazard profile issues.

Properties

Properties of butanone Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 6569.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₄H₈O
Molar mass	72.107(11) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	4
Hydrogen atoms	8
Oxygen atoms	1
Bonds	12
Single bonds	11
Double bonds	1
PubChem molecular weight	72.11 g/mol	g/mol	PubChem

Safety

Butanone burns readily as a liquid and as a vapour, and the heavier-than-air vapour can travel along the ground to a distant flame. The European Union’s classification adds serious eye irritation and drowsiness or dizziness; the International Chemical Safety Cards add airway irritation and possible effects on the central nervous system. On skin it dissolves away the fat, and dryness or cracking can follow. Workplace exposure limits exist and appear on the NIOSH Pocket Guide card for 2-butanone; the PubChem Laboratory Chemical Safety Summary is the full sheet.

Questions

What is MEK used for?

Mostly as a solvent. The US Environmental Protection Agency lists vinyl lacquers, acrylics, magnetic tapes, printing inks, and degreasing and cleaning fluids among its uses, and it removes wax from lubricating oils. It also serves the synthetic rubber industry and paraffin wax production, the same agency says. Artificial leather, transparent paper and cleaners for electronic equipment use it, according to the Hazardous Substances Data Bank. The US Food and Drug Administration permits it as a synthetic food flavouring.

Is MEK the same as acetone?

No. They are different ketones, one carbon apart. Acetone, propan-2-one, has a three-carbon chain with a methyl group on each side of its C=O. Butanone, butan-2-one, has four carbons: a methyl group on one side of the C=O and an ethyl group on the other, the pair the name methyl ethyl ketone spells out. NIOSH likens the moderately sharp, fragrant smell of the liquid to mint or acetone.

What happens to butanone in the body?

Ketones as a class pass readily through unbroken skin, according to the Hazardous Substances Data Bank (HSDB), and part of the butanone absorbed leaves again in exhaled breath. It is also reduced in the body, as other ketones are; reduction is the change that turns it into 2-butanol. Guinea pigs given it produced 2,3-butanediol, 2-butanol and 3-hydroxy-2-butanone. The blood clears it rapidly.

Does butanone cause cancer?

Its cancer potential is unsettled. According to ATSDR, the US Environmental Protection Agency found the available data too limited to judge whether butanone can cause cancer in people. People who breathed the vapour in studies had irritation of the nose, throat and eyes, and also headache, tiredness and a feeling of being drunk. ATSDR adds that the levels usually present in the environment are lower than those known to harm health.

Made of the same elements

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.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 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.
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.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single 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.