Diethylene glycol: uses and the identity risk
Technical article · Eapearl Chemical ·
Diethylene glycol is one of those raw materials that never appears on a finished product’s label and sits underneath a surprising share of them. It is also the substance behind several of the worst pharmaceutical poisoning events on record. Buying it well means understanding both roles.
What it is
Two ethylene glycol units joined through an ether bridge: a colourless, almost odourless, viscous liquid that mixes with water in any proportion and pulls moisture out of the air. Those two properties — water miscibility and hygroscopicity — explain most of what it is used for.
| CAS number | 111-46-6 |
|---|---|
| Molecular formula | C4H10O3 |
| Molecular weight | 106.12 g/mol |
| Also sold as | DEG · digol · 2,2′-oxydiethanol · diglycol |
| Not to be confused with | ethylene glycol (CAS 107-21-1) or triethylene glycol (CAS 112-27-6) |
What diethylene glycol is used for
Unsaturated polyester resins
The largest single outlet. DEG goes in as a diol in the polycondensation step, where it lengthens the chain between the rigid segments and gives the cured resin more flex and better impact behaviour. Formulators trade it against other diols to move the balance between toughness and heat resistance; boat hulls, cultured marble and glass-reinforced panels are all downstream of that choice.
Polyurethanes and plasticisers
As a chain extender and as a building block for polyester polyols, and as a feedstock for plasticiser esters. In both cases it is the molecule’s two reactive hydroxyl ends that do the work.
Natural gas dehydration
Water in a gas stream forms hydrates and corrodes pipe. Glycol contactors strip it out, and DEG is one of the glycols used for that duty — although triethylene glycol is the more common choice where the dew point specification is tight. The glycol is regenerated and recirculated, so purity and thermal stability of the make-up material matter more than the unit price.
Solvent and humectant in industrial formulations
Printing inks, textile auxiliaries, adhesives, cork and glue compositions, and tobacco processing use DEG where a high-boiling, water-miscible, moisture-retaining component is wanted. Its low volatility is the point: it stays in the film or the fibre instead of evaporating.
Brake fluids and heat transfer
Glycol ether chemistry derived from DEG forms part of the brake fluid formulation family, and DEG itself appears in heat transfer and antifreeze applications where its higher boiling point is an advantage over ethylene glycol.
Cement and construction chemistry
As a grinding aid in cement milling, where a small dose changes how the mill behaves and how the finished cement flows.
The part most suppliers leave out
Diethylene glycol has killed people, repeatedly, in the same way each time: it was substituted for glycerine or propylene glycol somewhere in a pharmaceutical supply chain, and nobody tested for it.
The pattern first became infamous in 1937, when a sulfanilamide preparation dissolved in diethylene glycol killed more than a hundred people in the United States and led directly to the 1938 legislation that created modern drug safety review. It has repeated since — in cough syrups and paediatric medicines, most recently in incidents that prompted the World Health Organization to issue medical product alerts and several countries to withdraw products from the market.
The mechanism is not exotic. Diethylene glycol is sweet, viscous, water-miscible and visually indistinguishable from glycerine. It is also considerably cheaper. Where a supply chain has many hands in it and incoming inspection checks appearance and density but not identity, the substitution survives every step until it reaches a patient.
What that means when you buy glycerine or propylene glycol
Pharmacopoeial monographs for glycerine and propylene glycol require a specific limit test for diethylene glycol, per batch, for material intended for pharmaceutical use. The test exists because appearance, refractive index and density do not catch the substitution. If your supplier cannot show you that test on the batch you received, you do not have the assurance you think you have — regardless of what the certificate says elsewhere.
What that means when you buy diethylene glycol itself
Nothing on the hazard side that a competent plant does not already handle. What changes is segregation: DEG should not share a transfer line, a pump or a storage tank with material destined for food or pharmaceutical use, and the receiving plant should be able to demonstrate that it does not. We state the substance identity on our documents against the CAS registry entry rather than against a trade name, which is the same reason we verify identity before publishing a grade.
Classification and handling
As published on our product page, diethylene glycol carries the EU harmonised classification: signal word Warning, hazard statement H302 — harmful if swallowed.
Source: Annex VI to Regulation (EC) No 1272/2008 (CLP), 23rd ATP, harmonised list as of 2026-07-07, as republished on the product page with its index entry.
Two practical notes that the classification alone does not convey. First, the acute hazard on ingestion is kidney injury, and the dose that matters is a swallow, not a splash — which is why the material must never be stored in unlabelled drinking vessels or in food-contact containers, a rule that sounds obvious until you see how many incidents began exactly there. Second, DEG is hygroscopic: an open drum gains water, and water changes both the specification and the behaviour of the downstream reaction.
What to specify when you order
- Purity and the impurity profile that matters to you — for resin production, water content and the content of related glycols; for gas dehydration, thermal stability and chloride.
- Grade and intended use — tell us the process. A grade that is right for cement grinding is not automatically right for a polyol plant.
- Packaging — drums, IBC totes or ISO tank; the formats we hold are listed under logistics and packaging.
- Segregation requirements — if your site also handles food or pharmaceutical grade material, say so at the inquiry stage so that loading and documentation reflect it.
Storage in one paragraph
Closed containers, dry, away from strong oxidising agents, at moderate temperature. The failure mode is water pickup rather than degradation: a drum opened repeatedly over a season will drift on water content and take the reaction stoichiometry with it. For plants that draw slowly, smaller packs beat one large one.
Questions we get asked
Is diethylene glycol the same as ethylene glycol?
No. Different substances, different CAS numbers, different boiling behaviour, and they are not interchangeable in a formulation. Both carry H302.
Can diethylene glycol be used in food or medicine?
No. It is an industrial raw material. Its presence in a medicine has historically been the result of substitution or contamination, never of intended use.
Which glycol should I use for gas dehydration?
Triethylene glycol is the usual choice where the dew point specification is demanding; diethylene glycol is used where the duty is lighter or the existing unit was designed around it. The decision belongs to the process engineer and the existing contactor, not to the price list.
Do you supply pharmaceutical grade?
Not for this substance, and we would treat an inquiry asking for a pharmaceutical grade of diethylene glycol as a reason to ask what the material is for before quoting.