Ethylene glycol

Ball-and-stick Stick Space-filling

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10 atoms, 9 single bonds.

IUPAC name: ethane-1,2-diol
Molar mass: 62.0680(72) g/mol
Atoms: 10
SMILES: C(CO)O
InChIKey: LYCAIKOWRPUZTN-UHFFFAOYSA-N
PubChem CID: 174

Made of

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

Car antifreeze often comes dyed a fluorescent yellow-green, but the ethylene glycol inside it is a clear, colourless and odourless liquid that pours like syrup. Its IUPAC name, ethane-1,2-diol, spells out the structure. A chain of two carbon atoms, as in ethane, carries one hydroxyl group, –OH, on each carbon. Two such groups make it a diol, or glycol, and the molar mass is 62.07 g/mol.

HSDB, the Hazardous Substances Data Bank, lists it as miscible with water, meaning the two mix in any proportion. Yet it is practically insoluble in benzene and in chlorinated hydrocarbons. It is also hygroscopic: it pulls moisture out of the air. The liquid boils at 197.3 °C and evaporates slowly, at less than a hundredth of the rate of butyl acetate. Below about −13 °C it freezes into a solid.

Structure and bonding

The model holds ten atoms and nine single bonds. With Labels on, the two C symbols sit in the middle, each holding two H, and an O at each end carries one more hydrogen. In Ball-and-stick, every carbon has four neighbours: the other carbon, two hydrogens and an oxygen. Each carbon is tetrahedrally coordinated, and Chem1 describes carbon chains as tetrahedra joined end-to-end. In the model the O–C–C angle is 109.0° and the H–C–H angle 109.1°.

The drawing and the real bonding agree. Every bond is single, and there is no ring or alternative structure to draw.

Turned to look down the C–C bond, the model shows the two C–O bonds about 61° apart. Both hydroxyl groups therefore sit on one flank, not on opposite sides, and each C–O–H angle is 107.5°. This is one of the ways the molecule can twist about its central bond. Stick view thins the atoms to lines, so the twisted O–C–C–O chain is easy to trace, while Space-filling swells the atoms into one compact lump.

Where it turns up

Ethylene glycol goes into antifreeze and de-icing solutions for cars, aircraft and boats, according to ATSDR, the federal Agency for Toxic Substances and Disease Registry. It also goes into hydraulic brake fluids and into the inks of stamp pads, ballpoint pens and print shops. De-icing solutions for bridges use it too.

Airport run-off, where it de-ices runways and planes, is the main source of ethylene glycol in the environment. In air it breaks down in about 10 days, and in water and soil within several days to a few weeks. As a liquid it soaks easily into soil and can reach groundwater and nearby streams.

Cosmetics use it to dissolve other ingredients, to thin a product or to keep it moist, and the Consumer Product Information Database lists 908 consumer products that contain it. Oil and gas fracturing fluids carry it as a stabiliser and winterising agent. It is a synthetic substance.

Why it matters

Industry makes ethylene glycol from ethylene oxide and water. US output for 2023 was reported to the Environmental Protection Agency (EPA) at between 15 and just under 20 billion pounds. In 1993, on HSDB’s figures, antifreeze took 42 per cent, polyester fibre 27 per cent, and bottles, packaging and film of the plastic PET 18.5 per cent. The EPA also lists it as a monomer, a small molecule joined into chains to make a polymer, and as a humectant, a substance that holds moisture.

Its danger lies in what the body makes from it. In the liver, the enzyme alcohol dehydrogenase oxidises it in steps. On HSDB’s account the major pathway ends in carbon dioxide, while a minor one passes through glycolaldehyde to glycolic, glyoxylic and oxalic acids. Oxalic acid binds calcium into insoluble calcium oxalate crystals, which ATSDR says collect in the kidneys. HSDB attributes tissue injury to those crystals together with glycolic and glyoxylic acids, which upset the body’s acid balance.

Properties

Properties of ethylene glycol Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 174.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₂H₆O₂
Molar mass	62.0680(72) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	2
Hydrogen atoms	6
Oxygen atoms	2
Bonds	9
PubChem molecular weight	62.07 g/mol	g/mol	PubChem

Safety

Ethylene glycol is harmful if swallowed, and 24.8% of GHS (Globally Harmonized System) reports add that it may damage organs after prolonged or repeated exposure. The liquid irritates the eyes and skin and is combustible. NIOSH, the US National Institute for Occupational Safety and Health, keeps a Pocket Guide card for it. That card and the PubChem Laboratory Chemical Safety Summary are the sheets for anyone handling it at work.

Questions

What shape is an ethylene glycol molecule?

It has no one shape word, because the molecule is a chain with four centres, two carbons and two oxygens, and no single central atom. Each carbon carries four single bonds, and Chem1 describes carbons in a chain as tetrahedra joined end-to-end. In PubChem's computed model the O–C–C angle is 109.0°, and the chain is twisted by about 61° around its C–C bond.

Why is ethylene glycol so thick and syrupy?

NIOSH describes the liquid as syrupy, and HSDB gives its viscosity, its resistance to flow, as 16.1 mPa s at 25 °C, thinning to 6.554 mPa s at 50 °C. Each molecule carries two hydroxyl groups. According to Chem1, several hydroxyl groups on one molecule give many chances to form hydrogen bonds, and that raises the viscosity of substances that carry them.

Why is antifreeze dangerous for children?

ATSDR, the federal Agency for Toxic Substances and Disease Registry, says accidental swallowing happens because antifreeze tastes sweet and is brightly coloured, and it asks that such products be kept out of children's reach. Suspected ingestion calls for medical attention as soon as possible. The poisoning can be treated effectively when it is diagnosed early, and tests are needed within a few hours, because ethylene glycol clears from the body fast.

Is breathing ethylene glycol vapour dangerous?

Toxic inhalation is unlikely at room temperature because the liquid has low volatility, though heating, stirring or spraying the liquid can make it possible. Low vapour pressure is also the reason workplace exposure does not bring the kidney damage seen after swallowing. The Hazardous Substances Data Bank (HSDB) reports that the vapour does not irritate the eyes or throat, although the liquid irritates eyes and skin.

Made of the same elements

CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₃H₁₈O₂ Ibuprofen 33 atoms, 33 bonds.
C₁₀H₂₀O Menthol 31 atoms, 31 single 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.