Material guide: acetaldehyde, 94 suppliers and it boils at room temperature

In short: the most extreme volatile in this library, and simultaneously among the best supplied. What to know before buying is not the odour but the boiling point.

Fields

Field	Value
CAS	75-07-0
EINECS	200-836-8
First synonym	ethylaldehyde
Formula	C2H4O, MW 44.053
Database category	cosmetic and flavor agents
Appearance	colorless clear liquid (exp)
Assay	99.00 to 100.00
Melting point	-125 to -123 C
Boiling point	20-21 C @ 760 mmHg
Flash point	-40.00 C
Vapour pressure	902.0 mmHg @ 25 C
Vapour density	1.5 (air = 1)
logP	-0.30 (est)
Specific gravity	0.775-0.785 @ 25 C
Water solubility	1,000,000 mg/L @ 25 C (exp), miscible
Solubility	acetone; alcohol; ethyl ether; water
Odour type	ethereal
Odour	pungent; ethereal; aldehydic; fruity; fresh; musty
Strength	high, evaluate at 0.10% or less (rank 3)
Substantivity	less than 1 hour (neat)
Shelf life	12 months
Storage	refrigerate in tightly sealed containers
Occurrence	beer 265,926 ppm; white bread 40,221 ppm; apple juice 3,643 ppm; butter 109 ppm; hundreds more
Suppliers	94
Regulatory	JECFA 80, FEMA 2003, CoE 89, FLAVIS 05.001
Structure class	I
GHS	H224 Extremely flammable liquid and vapour; H319 serious eye irritation; H335 respiratory irritation; H351 suspected of causing cancer; H402 harmful to aquatic life
Oral toxicity	rat LD50 661 mg/kg
NOEL	125 mg/kg bw per day
Note	a colorless, flammable liquid used in the manufacture of acetic acid, perfumes and flavors; also an intermediate in the metabolism of alcohol

Three numbers

Boiling point 20-21 C. Most people's room temperature is in or above that range. The neat material boils on your bench.

Flash point -40 C. Among the lowest of the 13,166 library records whose flash point parses in Celsius. Ethanol is 9.44 C.

Vapour pressure 902 mmHg at 25 C. Atmospheric pressure is 760 mmHg.

The material I wrote up last time, phenethyl salicylate, has a vapour pressure of 0.000002 mmHg. The two are 451 million-fold apart, sitting in the same field of the same database.

(Which is why comparing vapour pressures across materials needs care. The span in that field is far wider than most people expect; the corpus's commonly used materials span 83,333-fold, and that is only the commonly-used stretch, as computed in the cap-sniffing article.)

The storage field says refrigerate

The standard storage wording is "store in cool, dry place in tightly sealed containers, protected from heat and light", which accounts for 1,045 of the 1,232 records that carry that field.

This one reads refrigerate in tightly sealed containers.

Correction (2026-08-28): my first version said it was the only one, which is wrong. Of the records carrying that field, 145 (11.8%) ask for refrigeration and another 42 ask for storage under nitrogen. Six of my own material guides cover refrigerated materials: (E)-beta-damascone, gamma-decalactone, ethyl butyrate, geranyl acetate, beta-ionone and alpha-ionone. I compared from memory instead of scanning the library.

What is uncommon is not the refrigeration but its reason: most materials asking for it are guarding against oxidation or polymerisation, while this one boils above room temperature.

The shelf life is also 12 months, where most materials read 24 or more.

Substantivity under 1 hour

The field reads < 1 hour(s) at 100.00%.

In the fixation article I noted that a greater-than sign marks a lower bound. Here it runs the other way: a less-than marks an upper bound, and 1 hour is the shortest increment this library uses.

In practice that means it is not a material for staying in a formula. It is a moment at the very top.

Beer at 265,926 ppm

The occurrence field is long, and the largest figure in it is beer: 265,926 ppm, or 26.6%.

That number needs careful reading. It is a proportion within the volatiles in some analysis, not a proportion of the beer by weight (which would make beer a quarter acetaldehyde). The field does not state its denominator, and I cannot confirm it.

(How unreliable the percentages in that field can be, and how the same plant varies hundreds-fold across origins, is measured in How much does a natural actually vary.)

The more readable line is in the notes field: it is an intermediate in the metabolism of alcohol. Ethanol becomes acetaldehyde in the body and then acetic acid. Hangovers involve this one.

(So its appearance in beer, bread and yoghurt makes sense: that is the other end of the same pathway.)

logP -0.30

It is hydrophilic and miscible with water (1,000,000 mg/L, measured).

That is unusual for an aroma material. Most of the ones I have written up sit between logP 2 and 7; this one is negative.

Practically, it means it will not stay in an oil phase, and it partitions into water in any aqueous system.

What this doesn't establish

• I have not smelled it. This is database fields plus one paper.
• All the properties above are for the neat material. What is usually sold is a 10% or weaker solution in ethanol, and the boiling point, flash point and vapour pressure behave differently.
• My first version's claim that it was the only one asking for refrigeration was wrong; 145 records ask for it. The correction stays above. The lesson: scan the library before writing "the only one".
• I cannot confirm the denominator on the beer figure of 265,926 ppm. The field does not say whether it is a share of volatiles or of total weight.
• The 902 mmHg is measured while phenethyl salicylate's 0.000002 is an estimate. The 451 million-fold is a measurement against an estimate.
• I did not look up the basis for H351. It is the wording in the GHS classification field; I have not read the underlying assessment.
• What I cite Liaw 2007 for is that mixture flash points are predictable from components; that paper did not measure acetaldehyde.
• I did not run corpus statistics. Its frequency in the 954-formula corpus is unchecked.