Ethylene Glycol
Properties
| State | Liquid at room temperature (viscous) |
| Color | Colorless |
| Solubility | Miscible with water |
| Melting Point | -12.9 °C |
| Boiling Point | 197.3 °C |
About Ethylene Glycol
Ethylene glycol is the smallest diol where two adjacent hydroxyls do something genuinely useful — the 1,2-arrangement gives it the bidentate hydrogen-bonding pattern that lowers water's freezing point dramatically, makes it an excellent ligand for cis-diol-protecting acetal chemistry, and makes it the bis-functional monomer that condenses with terephthalic acid to give PET. About 30 million tonnes a year are made by hydrating ethylene oxide, either thermally (high water-to-EO ratios to suppress diethylene and triethylene glycol byproducts) or via the more selective OMEGA process Shell commercialized in 2008, which routes through ethylene carbonate. The freeze-protection chemistry comes from colligative depression: a 50/50 v/v mix with water freezes around -37°C and boils around 108°C at 1 atm, giving the typical green coolant its operating window. The PET application — bottles, polyester fiber, food trays — consumes roughly 60% of global MEG output and is what drives capacity expansion. The other consumer-facing reality is poisoning: the sweet taste and the metabolism to glyoxylic acid and oxalic acid via alcohol dehydrogenase make accidental ingestion (cat or child finding a leaking radiator) a calcium-oxalate kidney emergency, treated with fomepizole or, in a pinch, ethanol.
Where you'll encounter it
If you've ever drained a car radiator in fall and refilled it with the green stuff, that's roughly 4 L of MEG diluted with deionized water and a corrosion inhibitor package. In the polymer plant it's a different scene entirely: tank cars of MEG arrive at PET production sites continuously, fed into esterification reactors at 250–280°C with terephthalic acid, water flashed off the top, and the resulting bis-hydroxyethyl terephthalate polycondensed under vacuum to molten polymer that's spun into fiber or chipped for bottle preforms. In the analytical lab, MEG is the standard mounting medium when you need a clear, viscous, nonvolatile liquid — for example as a heat-transfer fluid in a Dean-Stark setup running above water's boiling point.
Common Uses
- Antifreeze and engine coolant base fluid (50/50 with water + corrosion inhibitors)
- Monomer for PET bottle resin and polyester staple fiber
- Aircraft and runway deicing fluids (Type I and Type II formulations)
- Heat-transfer fluid in geothermal and HVAC closed loops
- Cis-diol-protecting acetal formation in synthesis (with TsOH or BF3)
- Hygroscopic humectant in inks, leather conditioners, and natural-gas dehydration
Safety Information
GHS: H302 harmful if swallowed, H373 may cause damage to kidneys via prolonged exposure. ACGIH TLV-Ceiling 100 mg/m³ aerosol. Oral LD50 in rats ~4700 mg/kg, but in cats and dogs the toxic dose is much lower because feline metabolism handles oxalate poorly — vet ER cases involve doses as small as 1.5 mL/kg. Treatment is fomepizole (Antizol) to inhibit alcohol dehydrogenase, or ethanol IV if fomepizole isn't available. Bittering agents (denatonium benzoate) are mandated in many US states and EU member states to discourage ingestion.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.