What Is Isooctanoic Acid?
A Complete Industrial Buyer's Guide
Chemical identity · Key properties · Metal driers · PVC stabilisers · Lubricant additives · Sourcing guide
🔗 View Isooctanoic Acid Product Page📋 Table of Contents
- Chemical Identity: Names, CAS Numbers & Formula
- What Makes Isooctanoic Acid Industrially Important?
- Key Physical & Chemical Properties
- Principal Industrial Applications
- Metal Isooctanoates: The Core Derivatives
- Isooctanoic Acid vs Isononanoic Acid vs 2-Ethylhexanoic Acid
- Commercial Grades & Specifications
- Sourcing & Supply Chain Overview
- Frequently Asked Questions
🏷️ 1. Chemical Identity: Names, CAS Numbers & Formula
"Isooctanoic acid" is a commercial trade name for a branched-chain C8 (eight-carbon) fatty acid. Understanding its identity requires care, because the term is used in industry to refer to either a single pure isomer or a commercial mixture of branched C8 acids - and the CAS number varies accordingly.
🔬 Chemical Identity - Isooctanoic Acid
| Common trade name | Isooctanoic acid |
| CAS (mixture) | 25637-84-7 |
| CAS (pure 2-ethylhexanoic acid) | 149-57-5 |
| EC Number | 247-180-8 |
| Synonyms | 2-Ethylhexanoic acid; isooctylenic acid; isooctoic acid; isocaprylic acid |
| Molecular formula | C₈H₁₆O₂ |
| Molecular weight | 144.21 g/mol |
| Functional group | Carboxylic acid (–COOH) |
| Carbon chain | C8 branched (iso-) |
| SMILES (2-EHA) | CCCCC(CC)C(=O)O |
| Physical form | Clear, pale yellow liquid |
| Odour | Characteristic fatty/rancid odour |
| Water solubility | Very slightly soluble (~0.1 g/L) |
| Primary use | Metal salt (drier/stabiliser) precursor |
| HS Code | 2915.90 (saturated monocarboxylic acids) |
💡 CAS number clarification - important for procurement: Commercial isooctanoic acid (CAS 25637-84-7) is typically a mixture of branched C8 fatty acid isomers in which 2-ethylhexanoic acid (CAS 149-57-5) is the predominant component (usually ≥85–95%). When ordering, always specify by trade name and CAS number. For regulatory filings (REACH SDS, TSCA certification), confirm with your supplier which CAS applies to their specific product - some suppliers register under 149-57-5 (pure 2-EHA), others under 25637-84-7 (isooctanoic acid mixture). Both are commercially acceptable for most industrial applications.
Structural Formula - 2-Ethylhexanoic Acid (predominant isomer)
⚙️ 2. What Makes Isooctanoic Acid Industrially Important?
Isooctanoic acid is not an end-product in most supply chains - it is a functional intermediate whose value lies entirely in the metal salts it forms when reacted with metal oxides, hydroxides, or carbonates. These metal isooctanoates are the commercially important species, and they cover a remarkable range of industrial functions.
🔗 Isooctanoic Acid Value Chain
The key to isooctanoic acid's industrial success is the combination of properties that its branched C8 structure imparts to derived metal salts: oil solubility (the branched hydrocarbon chain dissolves readily in mineral spirits, aromatic solvents, and resin systems), appropriate metal loading (the C8 chain length strikes the right balance between metal content and solubility), and controlled reactivity (the branched carboxylate ligand provides thermally stable coordination to metal centres). Linear fatty acid salts (e.g., octoates from n-octanoic acid) can be more crystalline and less soluble in organic solvents; highly branched or very long-chain acids give poor metal loading per unit mass.
Cobalt, Mn, Zr, Ca driers catalyse oxidative crosslinking of alkyd and linseed oil coatings
Ca/Zn isooctanoates are key components in liquid Ca/Zn one-pack PVC heat stabiliser systems
Metal soaps and ester derivatives provide extreme-pressure, anti-wear, and corrosion-inhibiting functions
Precursor to Ti, Zr, Al, and rare-earth isooctanoates for catalysis and specialty chemistry
Calcium, zinc, and bismuth isooctanoates used as cure accelerators and water-repellents in concrete chemistry
⚗️ 3. Key Physical & Chemical Properties
The properties below reflect commercial isooctanoic acid (predominantly 2-ethylhexanoic acid). Values may vary slightly depending on isomer composition - always verify against the supplier's COA.
| Property | Value | Significance |
|---|---|---|
| Boiling point | 227–229 °C (at 760 mmHg) | High BP; low volatility in formulations; can be processed at elevated temperatures |
| Melting point | −59 °C | Liquid at all normal temperatures; no heating required for handling |
| Density (20 °C) | 0.902–0.910 g/cm³ | Lighter than water; floats; relevant for spill containment and tank calculations |
| Flash point | 113–130 °C (closed cup) | Combustible liquid (GHS Cat. 4); not flammable at room temperature; Class II/III storage |
| Viscosity (25 °C) | ~7–10 mPa·s | Low viscosity; easily pumpable at ambient temperature; good wetting of metal oxides |
| Refractive index (20 °C) | 1.424–1.430 | Identity QC parameter; verify on COA with Abbe refractometer |
| Acid value | 375–395 mg KOH/g | Key QC parameter; used to calculate stoichiometric metal salt conversion; equivalent weight ~145 g/eq |
| Water solubility (25 °C) | < 0.1 g/100 mL | Very slightly water-soluble; hydrophobic; soluble in mineral spirits, aromatic solvents, alcohols |
| Vapour pressure (20 °C) | < 0.1 mmHg | Very low VP; negligible inhalation risk at room temperature during cold handling |
| pKa | ~4.85 | Weak carboxylic acid; reacts with metal bases to form metal soaps; weaker than shorter-chain fatty acids |
| GHS hazard class | Combustible liquid; skin/eye irritant | Moderate hazard; standard industrial chemical; not CMR; GHS signal word WARNING |
🏭 4. Principal Industrial Applications
Isooctanoic acid's applications span several distinct industries, united by the common requirement for a branched-chain carboxylate ligand that confers oil solubility and appropriate reactivity to metal cations. Each application sector uses the acid in a different way, but all exploit the same fundamental chemical character.
The largest single application for isooctanoic acid. Cobalt isooctanoate (6% Co, 12% Co solutions in mineral spirits) is the most important primary drier for alkyd paints, printing inks, and linseed-oil-based coatings - it catalyses oxidative crosslinking (autoxidation) of the unsaturated fatty acid chains in the binder, dramatically accelerating drying time. Manganese isooctanoate (6% Mn) acts as a through-drier. Calcium, zirconium, and bismuth isooctanoates serve as secondary auxiliary driers and cobalt-replacement candidates in formulations seeking to reduce cobalt content under evolving EU regulations. The global drier market is the primary demand driver for isooctanoic acid.
Calcium isooctanoate and zinc isooctanoate are essential components of liquid calcium-zinc (Ca/Zn) heat stabiliser systems for PVC, which are the dominant replacement technology for lead-based PVC stabilisers banned in Europe and increasingly restricted globally. In a Ca/Zn stabiliser, zinc isooctanoate reacts with nascent HCl liberated from PVC during processing to prevent chain degradation and yellowing; calcium isooctanoate replenishes the zinc and acts as a co-stabiliser. The liquid form of these metal salts (in oil) facilitates incorporation into liquid stabiliser one-packs. Used in PVC profiles, cables, flexible film, and flooring.
Isooctanoic acid and its metal soap derivatives contribute corrosion inhibition, extreme-pressure (EP) performance, and lubricity in metalworking fluids, gear oils, and industrial lubricants. Molybdenum and antimony isooctanoates serve as EP additives; zinc isooctanoate provides both corrosion inhibition and lubricity at metal surfaces. The branched chain structure of isooctanoic acid gives lower crystallisation tendency versus linear octanoic acid, providing better cold-flow properties in lubricant applications.
Titanium, zirconium, aluminium, bismuth, and rare-earth isooctanoates are used as precursors in sol-gel chemistry, catalyst preparation, and specialty organometallic applications. Bismuth isooctanoate is of growing interest as a non-toxic replacement for organotin catalysts in PU sealant and foam cure systems. Zirconium isooctanoate is used as a crosslinking catalyst for waterborne coatings. The isooctanoate ligand provides the oil solubility and controlled hydrolysis rate that these metal centre precursors require.
🔬 5. Metal Isooctanoates: The Core Derivatives
Because isooctanoic acid's industrial value is realised through its metal salts, understanding the key derivatives helps buyers and formulators communicate requirements clearly along the supply chain.
| Metal Salt | Metal % | Key Function | Application System | Notes |
|---|---|---|---|---|
| Cobalt isooctanoate | 6% / 10% / 12% | Primary drier; surface drying catalyst | Alkyd paints, printing inks, varnishes | CMR2 under EU CLP - growing pressure to reduce; blue-purple liquid |
| Manganese isooctanoate | 6% / 8% | Through-drier; Co partial replacement | Alkyd coatings, printing inks | Good Co substitute for through-dry; brown liquid |
| Zirconium isooctanoate | 12% / 18% | Auxiliary drier; crosslinking catalyst | Waterborne coatings; alkyd coatings | Co-free drier systems; non-CMR; colourless liquid |
| Calcium isooctanoate | 4% / 5% / 10% | PVC co-stabiliser; auxiliary drier | PVC Ca/Zn systems; alkyd coatings | Non-toxic; colourless to pale yellow; widely used |
| Zinc isooctanoate | 8% / 10% / 18% | PVC stabiliser; auxiliary drier; anti-corrosion | PVC stabiliser systems; lubricants; coatings | Key Ca/Zn component; white to pale yellow liquid |
| Bismuth isooctanoate | 8% / 15% / 24% | Non-toxic organotin replacement; PU catalyst | PU sealants, foams, coatings | Growing demand; non-CMR; replaces DBTDL in some systems |
| Rare-earth isooctanoates (Ce, La, Nd) | Variable | Co-replacement driers; specialty catalysts | Co-free coating drier systems; electronics | Emerging segment; higher cost; growing interest in Co-free formulations |
⚖️ 6. Isooctanoic Acid vs Isononanoic Acid vs 2-Ethylhexanoic Acid
Three closely related branched-chain fatty acids are used in overlapping applications and are frequently confused by buyers and formulators. Understanding the distinctions is essential for correct specification. For a detailed technical comparison, see Isooctanoic vs Isononanoic vs 2-Ethylhexanoic Acid: Key Differences.
| Property | Isooctanoic Acid ⭐ | Isononanoic Acid | 2-Ethylhexanoic Acid (pure) |
|---|---|---|---|
| Carbon chain | C8 (branched) | C9 (branched) | C8 (specific isomer) |
| CAS | 25637-84-7 (mixture) | 26896-18-4 | 149-57-5 |
| MW (g/mol) | 144.21 | 158.24 | 144.21 |
| Acid value (mg KOH/g) | ~385 | ~354 | ~389 |
| Metal content in salt (per gram acid) | Higher | Lower (longer chain) | Same as IOA |
| Composition | Mixture of C8 isomers | Mixture of C9 isomers | Single isomer (pure) |
| Primary use | Metal driers, PVC stabilisers | Metallic soaps, lubricants, polyester | Same as IOA (purer grade) |
| Relative cost | Medium | Medium (similar) | Medium to Medium-High |
| Interchangeable? | Often - in drier/stabiliser formulations | Often - with adjustment for acid value/metal content | Yes - IOA is essentially commercial 2-EHA |
📋 7. Commercial Grades & Specifications
Commercial isooctanoic acid is supplied in a single primary quality tier (technical/industrial grade) suitable for metal soap synthesis, coating drier production, and PVC stabiliser manufacturing. There is no separate cosmetic grade, as isooctanoic acid itself is not a cosmetic ingredient.
| Parameter | Typical Specification | Test Method | Application Significance |
|---|---|---|---|
| Acid value | 375–395 mg KOH/g | ASTM D 974 / potentiometric | Most critical spec; determines stoichiometry in metal salt synthesis |
| Colour (APHA) | ≤ 50 | ASTM D 1209 | Affects colour of derived metal soaps; lighter IOA gives paler drier solutions |
| Water content | ≤ 0.1% | Karl Fischer | Excess water causes foaming and side reactions in metal salt synthesis |
| Saponification value | 375–395 mg KOH/g | ASTM D 464 | Confirms absence of esters; should equal acid value for pure free acid |
| Density (20 °C) | 0.902–0.910 g/cm³ | ASTM D 891 | Identity parameter; confirm on COA |
| Refractive index (20 °C) | 1.424–1.430 | Abbe refractometer | Fast incoming QC identity check |
| GC purity (as 2-EHA content) | ≥ 90% (commercial); ≥ 98% (high-purity) | GC-FID | Higher 2-EHA content generally preferred for high-performance drier synthesis; standard commercial grade adequate for PVC stabiliser |
💡 Acid value is the critical quality parameter for isooctanoic acid. When formulating metal soaps, you need to calculate the exact mass of metal oxide or hydroxide required to neutralise the carboxylic acid. A batch with acid value 380 requires a different metal oxide charge than a batch with acid value 390 - this affects the final metal content of your drier or stabiliser solution. Always obtain the actual acid value from the COA of each batch and recalculate your recipe accordingly rather than assuming a fixed value.
🌐 8. Sourcing & Supply Chain Overview
Isooctanoic acid is produced via the Koch reaction (carbonylation of C7 olefins, primarily from propylene trimerisation) or via oxo synthesis / Guerbet reaction routes. Major Western producers include ExxonMobil (Exxal acids), BASF (Versatic acids - though these are tertiary, related), and specialty fatty acid manufacturers in Europe. Chinese producers manufacture isooctanoic acid at competitive prices via modified oxo and oxidation routes, supplying both the domestic market and export markets in Asia, the Middle East, and increasingly Europe.
- 200 L steel drums (~180–185 kg net): most common packaging for small-medium orders
- IBC (1,000 L) (~900–920 kg net): cost-effective for >1 MT orders
- ISO tank (~18–20 MT): bulk; lowest per-MT cost; requires bulk unloading facilities
- IMDG classification: Class 8 (corrosive), Packing Group III - isooctanoic acid is a DG for sea freight; requires DGD and DG-capable booking
Unlike MPD or isononanoic acid, isooctanoic acid (as a carboxylic acid with pKa ~4.85) is classified as a Class 8 corrosive material under IMDG for sea freight. This means: a Dangerous Goods Declaration (DGD) is required; DG surcharges apply from shipping lines; containers must be properly labelled; and not all shipping lines and vessels accept Class 8 goods. Confirm DG classification with your freight forwarder - the exact UN number and packing group should be specified on the SDS from your supplier.
- Certificate of Analysis (COA) - per batch; must include acid value, colour, water content, and density
- Safety Data Sheet (SDS) - 16-section GHS format; confirm UN number and DG class
- Certificate of Origin - for import duty purposes
- REACH registration/OR letter (EU buyers)
- TSCA positive certification (US buyers)
🔗 Explore More in This Article Series
❓ 9. Frequently Asked Questions
Q1: What is the difference between isooctanoic acid and 2-ethylhexanoic acid?
In commercial practice, the two names refer to the same product family. 2-Ethylhexanoic acid (CAS 149-57-5) is a specific single isomer of a branched C8 fatty acid - the 2-ethyl substituted hexanoic acid. Isooctanoic acid (CAS 25637-84-7) is the commercial designation for a mixture of branched C8 acid isomers in which 2-ethylhexanoic acid is typically the dominant component (85–95%+). For the vast majority of industrial applications - metal drier synthesis, PVC stabiliser production, lubricant additives - these two designations are functionally interchangeable. The more precise CAS 149-57-5 designation is sometimes preferred in regulatory filings, pharmaceutical intermediates, and research applications where isomeric purity matters.
Q2: Why is cobalt isooctanoate used as a paint drier, and are there alternatives?
Cobalt's unique redox chemistry - the ability to cycle between Co(II) and Co(III) oxidation states at mild temperatures - makes it exceptionally effective at catalysing the oxidative crosslinking (autoxidation) of unsaturated fatty acid groups in alkyd resin binders. A small amount of cobalt isooctanoate (0.03–0.06% Co on binder) can reduce drying time from days to hours. The isooctanoate ligand provides the oil solubility needed for cobalt to disperse uniformly in the coating binder. Alternatives are actively sought because cobalt is classified as a suspected CMR substance (Category 1B reproductive toxicant) in the EU, driving regulatory pressure on cobalt drier use. Current alternatives include manganese isooctanoate (good through-drier, weaker surface drier), zirconium isooctanoate (auxiliary), bismuth isooctanoate (moderate drier activity), and iron/vanadium systems - but none matches cobalt's surface drying efficacy across all alkyd systems.
Q3: How do I calculate how much isooctanoic acid I need to make a cobalt drier solution at 10% Co?
The calculation uses the acid value of your IOA batch and the stoichiometry of the cobalt salt. Cobalt isooctanoate is Co(C₈H₁₅O₂)₂ - one Co²⁺ ion neutralises two carboxylic acid groups. MW of Co = 58.93 g/mol; MW of 2-EHA = 144.21 g/mol; MW of Co(isooctanoate)₂ = 58.93 + 2 × 144.21 = 347.35 g/mol. For a 10% Co solution: 100 g solution contains 10 g Co → requires 10/58.93 × 347.35 = 58.97 g Co(isooctanoate)₂. This requires 58.97 × (2 × 144.21/347.35) = 48.99 g IOA per 100 g final solution. In practice, use the specific acid value from your COA to calculate the exact IOA charge; make up with mineral spirits to target density and metal content; verify final Co% by atomic absorption or ICP.
Q4: Is isooctanoic acid hazardous for sea freight?
Yes - isooctanoic acid is classified as a dangerous good under the IMDG Code for sea freight, typically as UN 3265, Class 8 (Corrosive liquid, acidic, organic, n.o.s.), Packing Group III. This means a Dangerous Goods Declaration (DGD) is required for sea shipments; DG surcharges apply; proper container labelling and Class 8 hazard placards are mandatory; and not all shipping lines accept Class 8 in all ship types. Buyers should factor DG logistics costs into the landed cost comparison. This is an important difference from isononanoic acid (which may be classified differently) and from diol products like MPD - isooctanoic acid's carboxylic acid functionality and low pH drive the Class 8 classification. Always confirm the exact UN number and packing group with your supplier's SDS before booking freight.
Q5: What is the acid value of isooctanoic acid and why does it matter?
The acid value (AV) of commercial isooctanoic acid is typically 375–395 mg KOH/g, corresponding to a neutralisation equivalent weight of approximately 142–150 g/mol - consistent with a C8 fatty acid (theoretical AV for pure 2-EHA = 389 mg KOH/g). The acid value is the most critical quality parameter for any buyer using IOA as a metal soap precursor, because it determines exactly how much metal oxide, hydroxide, or carbonate is needed to prepare a metal isooctanoate of the target metal content. A batch arriving at 380 mg KOH/g requires 2.4% more metal oxide than a batch at 390 mg KOH/g for the same final metal concentration - a difference that matters for production batch consistency and yield. Always request the batch-specific AV from your supplier's COA and base your recipe calculations on that figure.
Q6: Where is isooctanoic acid produced and can it be sourced from China?
Isooctanoic acid is produced globally in both Western and Asian manufacturing bases. Western producers (including ExxonMobil's Exxal™ acids range) are well-established, but their pricing reflects Western production costs. Chinese producers now manufacture isooctanoic acid via oxidative and oxo synthesis routes at competitive prices, and Chinese-origin IOA is widely used across Asia, the Middle East, and increasingly Europe for metal drier and PVC stabiliser applications. Sinolook Chemical exports isooctanoic acid from China to customers in 50+ countries with full COA documentation, GHS SDS, and REACH OR support for EU buyers. Contact us via WhatsApp (0086 18150362095), WeChat/Tel (0086 13400715622), or email (sales@sinolookchem.com) for a quotation.
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