route to 2-EHA<\/a> runs butanal through 2-ethylhexenal and 2-ethylhexanal to the acid, and that oxo product has been sold under the name “isooctanoic acid” for decades.<\/p>\n\n\n\nA granted patent on isooctanoic-acid preparation states outright that 2-ethylhexanoic acid is “also known as isooctanoic acid,” and it cites no CAS number anywhere. That name-only habit is exactly how the ambiguity spreads.<\/p>\n\n\n\n
The cross-wiring runs in every direction. One supplier catalog pairs the name “2-ethylhexanoic acid” with CAS 25103-52-0; another labels isooctanoic acid a nine-carbon pelargonic acid, which is simply wrong.<\/p>\n\n\n\n
A name that resolves three different ways is not a specification. It is the start of a question.<\/p>\n\n\n\n
How to Tell Which Acid a Spec Actually Means<\/h2>\n\n\n\n
The CAS number and the isomer assay on the COA identify which acid a document means; the trade name does not. Read the CAS first, 149-57-5 for the single isomer and 25103-52-0 for the mixture, then confirm it against the isomer distribution, because bulk properties will not save you.<\/p>\n\n\n\n
The property card is a dead end here. 2-EHA boils at about 228 \u00b0C with a density near 0.90 g\/mL, and the mixed grade’s reported boiling point sits at roughly the same value.<\/p>\n\n\n\n
Those figures carry “(estimate)” flags in the reference databases. Both describe isomers of one C8 acid, so a boiling point or density number cannot tell you which material is in the drum.<\/p>\n\n\n\n
Confirm the CAS and the assay together, not either one alone. Some supplier pages print the wrong CAS beside the right name, so a lone CAS field can mislead as easily as the trade name can.<\/p>\n\n\n\n
For CAS 25103-52-0, the assay should state the isomer distribution, because the commercial grade is a UVCB, a substance of unknown or variable composition rather than a single defined compound.<\/p>\n\n\n\n
A CAS number printed next to a name is a claim, not a guarantee. Check both fields before the material ships.<\/p>\n\n\n\n
When to Specify 2-EHA vs Isooctanoic Acid<\/h2>\n\n\n\n
Applications built on a single defined isomer call for CAS 149-57-5. Metal octoates and 2-ethylhexanoate salts, ester synthesis, and alkyd paint driers all depend on a consistent molecular structure, and the mixed-isomer grade (25103-52-0) fits only where a variable composition is acceptable.<\/p>\n\n\n\n
Cobalt, zirconium, and calcium octoate driers are the clearest case. These salts are built directly on the 2-ethylhexanoate ligand, so a batch-to-batch shift in isomer distribution changes the salt you are making.<\/p>\n\n\n\n
Industrial octoate, ester, and drier specifications call for the defined single isomer. Bastone Petrochem supplies it as 2-ethylhexanoic acid, CAS 149-57-5<\/a> with full COA documentation for exactly these uses.<\/p>\n\n\n\nThe mixed grade earns its place where the process tolerates a spread of isomers, and some heat-stabilizer and general metal-salt uses treat the branched-C8 acid as a class rather than one molecule. If your process was qualified on a defined isomer, substituting the mixture is a re-qualification, not a drop-in.<\/p>\n\n\n\n
Match the isomer definition your application was qualified on, not the name on the invoice.<\/p>\n\n\n\n
The Bottom Line<\/h2>\n\n\n\n
When a document says “isooctanoic acid,” do not assume it means 2-EHA. Read the CAS number, then confirm the isomer assay, before the material is ordered or accepted.<\/p>\n\n\n\n
CAS 149-57-5 and CAS 25103-52-0 are two different branched-C8 acids that share a formula but not a structure. Only one of them, the single defined isomer 149-57-5, is the settled feedstock for octoates, esters, and driers.<\/p>\n\n\n\n
The fix costs nothing: one glance at the CAS field plus one line on the COA closes a gap that a shared formula and a swapped trade name would otherwise leave open in your order.<\/p>\n\n\n\n
![\"Branch-position](\"https:\/\/bastone-petrochem.com\/wp-content\/uploads\/2026\/07\/isooctanoic-acid-vs-2-ethylhexanoic-acid-1.jpg\")
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