Material guide: DPG (dipropylene glycol) — the one that appears 445 times in the corpus, and it isn't a fragrance material

Short version: nine tenths of every "10% dilution" you own is this. Its division of labour with TEC is not better or worse; it is polarity.

The fields (against TEC)

Field	DPG	TEC
CAS	25265-71-8	77-93-0
Formula	C6H14O3, MW 134.18	C12H20O7, MW 276.29
Database category	Solvents/diluents for flavor and/or fragrance agents	Same
logP	−0.60 (est)	0.10 (est)
Specific gravity	1.019–1.021 @ 25 °C	1.135–1.139 @ 25 °C
Boiling point	230–231 °C @ 760 mmHg	127 °C @ 1 mmHg
Flash point	118.33 °C	118.33 °C
Water solubility	1.00E+06 mg/L @ 25 °C (exp) = miscible	65,000 mg/L
Vapour pressure	0.0319 mmHg @ 25 °C	0.000175 mmHg @ 25 °C
Odour strength	None	None
Odour description	At 100%: slight alcoholic	At 100%: odorless to mild fruity wine
Substantivity	400 hours	216 hours
Shelf life	24 months	24 months
Suppliers	37	54
Natural occurrence	Not found in nature	Cabbage, white wine
GHS	H302 harmful if swallowed (this line only)	H332 harmful if inhaled
Oral toxicity	Rat LD50 14,850 mg/kg	Rat LD50 5,900 mg/kg
Dermal toxicity	Rabbit LD50 > 20 mL/kg	Rabbit LD50 > 5,000 mg/kg

The corpus says it is the default

Solvents written as standalone entries across 954 published formulas:

Solvent	Appearances
DPG	445
Benzyl benzoate	44
TEC	5
IPM (isopropyl myristate)	4
DPG (other spelling)	2
Propylene glycol	1
Ethanol	1
Diethyl phthalate	1

DPG at 89 times TEC.

That does not mean TEC is little used; it means published formula authors default to DPG. This series made the same point writing TEC in article #84: TEC shows up when the material demands it.

Incidentally, of the corpus's 17,481 material entries, 2,179 (12.5%) carry a percentage in the name — they are dilutions. One entry in eight is a dilution, and what solvent it uses is mostly unrecorded. When a formula says "indole 10%", it usually does not say what the other ninety per cent is.

The division of labour is polarity

logP −0.60 against 0.10.

That 0.7 gap does not sound large, but it is a log scale, and both sit in the narrow band of "barely favours oil or water". The difference is that DPG leans slightly aqueous and TEC slightly oily.

In practice:

What you are dissolving	Which one	Why
Ordinary single chemicals	DPG	Cheap, default, and what everyone's formula says
Resins, concretes, absolutes (orris butter, benzoin, olibanum resinoid)	TEC or benzyl benzoate	Lipophilic large molecules that DPG cannot move
Anything going into an aqueous system	DPG	Miscible with water (TEC is 6.5 g per 100 mL)

The water solubility field is the cleanest evidence: DPG's measured value is 1.00E+06 mg/L, a million milligrams per litre, which is another way of writing "miscible". TEC is 65,000 mg/L — high, but with a ceiling.

This series handled a related misconception in article #39: someone received orris butter at 10% in TEC, found it too thick and assumed TEC was thick. The thick thing was the orris butter (melting at 40–46 °C), and the reason it uses TEC rather than DPG is precisely that it is a lipophilic concrete.

"Strength: none" but the odour description is not none

As with TEC, this field wants careful reading.

The strength field says none, while the odour description field (Luebke, tgsc, 1981) says:

At 100%: slight alcoholic

"Slight" is not "none." Nine tenths of what you smell in a 10% dilution is this, so that slight alcoholic note is in the background of every evaluation you make. There is a reason people keep a solvent-only blank strip.

And the substantivity field gives it 400 hours — sixteen days of substantivity for something classified as a solvent. TEC gets 216. I do not know how either number was measured (how do you measure substantivity for something rated "none" in strength?), and this series flagged the same problem in article #84. The number is there and the method is not.

The vapour pressure field does carry a consistent signal, though: DPG's 0.0319 mmHg is about 180 times TEC's 0.000175, so DPG should evaporate faster — and yet its substantivity value is higher. Those two do not reconcile. Recorded, not explained.

That one sentence in the notes

The database's notes field holds a single sentence:

"Very good fragrance diluent and quencher. But it is synthetic."

"Quencher" is worth pausing on. It refers to the ability to damp down notes that are too sharp or aggressive — not merely lowering the concentration but actually modifying. The database gives no quantification for this and I could not find a source, so all I can do is record that it says so.

And the "but it is synthetic" turn gives away the record's position. It is an industrial product not found in nature, and in a natural perfumery context that is a problem. It is also why vegetable and jojoba oils are preferred as diluents in some circles — not because they dissolve better (they dissolve worse) but because of the label.

Safety

DPG's GHS is one line: H302 harmful if swallowed.

And its oral toxicity is rat LD50 14,850 mg/kg, with another record at 15,000. For context: TEC is 5,900, guaiacol 621, isobutyl quinoline 1,020. DPG is the least toxic material this series has covered.

Dermal toxicity is rabbit LD50 > 20 mL/kg — tested to 20 millilitres per kilogram without a lethal result.

Its cosmetic uses field lists four: fragrance, perfuming agents, solvents, viscosity controlling agents. It has a CosIng entry and is a routine cosmetic ingredient.

What matters in practice is ventilation and not drinking it, and the threshold on the second is very high. That differs from TEC's H332 (harmful if inhaled), which is written for the "bulk dilutions in a small room with spray testing" situation. DPG carries no such line.

That "synthetic" label

The natural occurrence field reads not found in nature.

Worth setting beside TEC, whose natural occurrence field reads "cabbage; white wine". Both are industrially synthesised diluents, but TEC has a natural occurrence record and DPG has none.

This does not affect their performance as diluents, but it affects labelling. If you are making something claiming "natural", this is the field you will be asked about.

Whether to use it

• It is the default. The corpus is 445 to 5; DPG is the common language of published formulas. Use it if you want to line up with other people's work.
• Resins, concretes and absolutes go in TEC or benzyl benzoate. DPG is out of its depth with lipophilic large molecules.
• Anything aqueous goes in DPG. It is miscible with water.
• It is not fully odourless. Keep a solvent-only blank strip when evaluating.
• Toxicity is extremely low (oral rat LD50 14,850 mg/kg), but it is not found in nature, and that field gets asked about on natural-claim products.
• Technical grade is fine. The record lists only "grade: technical".

What this doesn't establish

• I do not know where the 400-hour substantivity comes from. The record does not explain how substantivity is measured for a material rated "none" in strength. And its vapour pressure is 180 times TEC's while its substantivity value is higher, which does not reconcile.
• There is no quantification of "quencher" anywhere. The notes field says it; I found no source and ran no test.
• The corpus count of 445 against 5 counts standalone entries, not actual usage. Most dilutions are written as "material name + 10%" with the solvent unrecorded.
• Neither cited paper is about DPG. They establish the cosolvency framework (solute hydrophobicity sets the degree of solubilisation), shared with this round's beginner article. DPG's own PubMed literature is mostly toxicology and occupational health, unrelated to perfumery.
• The logP values are estimates. Every logP here is the database's (est).
• I have not compared DPG and TEC's actual dissolving performance. The whole piece rests on database fields and corpus statistics.