No CMR · Not Repr. 1B · No REACH SVHC · No Annex XIV/XVII · Non-HAP · TSCA Listed - Clean Regulatory Profile vs 2-EHA: Isononanoic acid (CAS 26896-18-4) carries only mild irritant classification under EU CLP (Skin Irrit. 2 H315; Eye Irrit. 2 H319) - no Repr. 1B, no carcinogen, no mutagen. Directly contrasts with 2-ethylhexanoic acid (2-EHA, CAS 149-57-5), which carries Repr. 1B (H360D), US HAP listing, and REACH SVHC candidate status. INA is not on the REACH SVHC Candidate List; not subject to REACH Annex XIV or Annex XVII. Confirmed non-HAP (EPA CompTox), TSCA-listed. Flash point ~105–113°C - Combustible Liquid Class III-B. Sinolook provides EU CLP SDS, REACH registration confirmation, non-HAP declaration, and TSCA letter with every shipment.
Oxo-Derived Branched C9 Carboxylic Acid · Repr. 1B-Free 2-EHA Alternative · Synthetic Ester · Metal Salts · PVC Stabiliser
INA - Isononanoic Acid
(3,5,5-Trimethylhexanoic Acid / iso-C9 Acid / Isononanoic Acid 99.5%)
| CAS No. | 26896-18-4 (Oxo-derived mixed branched C9 acid; primary isomer CAS 3302-10-1) |
| EC Number | 248-191-6 |
| IUPAC Name (dominant isomer) | 3,5,5-trimethylhexanoic acid (C6 principal chain with 3 methyl substituents - not "trimethylheptanoic acid") |
| Molecular Formula / MW | C₉H₁₈O₂ / 158.24 g/mol |
| Production Route | Oxo process: C8 olefin hydroformylation → C9 aldehyde → oxidation → C9 carboxylic acid (branched isomers) |
| EU CLP Classification | Skin Irrit. 2 (H315) Eye Irrit. 2 (H319) ✓ No CMR / No Repr. 1B |
| REACH / SVHC / HAP | ✓ No SVHC ✓ No Annex XIV/XVII ✓ Non-HAP · TSCA listed |
| Key Quality Advantages | Pt-Co ≤15 (actual 3.2 - water-white) C9 acid ≥99.50% (actual 99.93%) Water ≤0.10% (actual 0.01%) |
What Is Isononanoic Acid? The Repr. 1B-Free Alternative to 2-Ethylhexanoic Acid
Isononanoic acid (INA, CAS 26896-18-4) is a high-purity branched-chain C9 carboxylic acid of molecular formula C₉H₁₈O₂ and molecular weight 158.24 g/mol, produced by the Oxo process - hydroformylation of C8 olefins (isooctene or mixed C8 olefin fractions from propylene or butylene oligomerisation) followed by air oxidation of the resulting C9 aldehyde intermediates. The dominant product is 3,5,5-trimethylhexanoic acid (CAS 3302-10-1, structure: (CH₃)₃C–CH₂–CH(CH₃)–COOH), which accounts for ≥99% of the product by GC; commercial CAS 26896-18-4 designates this Oxo-derived mixed branched C9 acid as a whole. INA is a colorless, clear liquid with density 895–905 kg/m³, boiling point ~215–220°C, and an extremely low colour of Pt-Co 3.2 (actual) - essentially water-white.
INA's defining commercial value is its position as a regulatory-clean C8/C9 chain carboxylic acid for ester lubricant synthesis and metal carboxylate salt production - occupying the space that 2-ethylhexanoic acid (2-EHA, CAS 149-57-5) has historically dominated, but without 2-EHA's critical regulatory liabilities: 2-EHA carries Repr. 1B (H360D), US HAP listing, and REACH SVHC candidate status. INA carries none of these. This regulatory separation enables buyers to synthesise metal isononanoate salts (cobalt, zirconium, bismuth, cerium isononanoates), polyol ester lubricants (TMP triisononanoate, PE tetraisononanoate), and Ca-Zn PVC stabiliser components without the Repr. 1B supply chain disclosure and worker safety management obligations that 2-EHA derivatives impose.
INA occupies a precise position in the branched acid series between 2-EHA (C8, AV ~389 mg KOH/g, Repr. 1B) and neodecanoic acid (NDA, C10, AV ~326 mg KOH/g, quaternary alpha carbon). Its acid value of ~354.5 mg KOH/g (theoretical for pure 3,5,5-TMH) gives INA a higher acid charge efficiency than NDA per kilogram in synthesis, while its secondary alpha carbon (vs NDA's quaternary) provides adequate hydrolytic stability for solventborne coating drier and synthetic ester lubricant applications. INA's Pt-Co 3.2 colour (actual) - achieved through high-vacuum distillation and activated carbon purification - produces water-white metal salt drier concentrates and clear ester lubricants without post-reaction decolourisation.
INA Physical Properties & Specifications
| Parameter | Specification | Actual / Typical | Test Method / Note |
|---|---|---|---|
| Appearance | Colorless clear liquid | Colorless, water-white | No turbidity, no suspended matter; characteristic faint fatty acid odour |
| C9 Acid Content | ≥99.50% | 99.9294% | GC; total branched C9 carboxylic acid purity verification |
| 3,5,5-TMH Content | ≥99.00% | 99.9287% | GC; isomeric composition - dual GC verification of both total purity and dominant isomer content |
| Water Content | ≤0.10% | 0.01% | Karl Fischer; GB/T 6283-2008; near-anhydrous; residual water promotes ester hydrolysis in compressor lubricants |
| Color (Pt-Co) | ≤15 | 3.2 | GB/T 3143-1982; water-white; enables premium-colour metal salt driers and water-white ester lubricants |
| Acid Value | ≥340 mg KOH/g | ~352–358 mg KOH/g | GB/T 7304-2014; theoretical for pure 3,5,5-TMH: 354.5 mg KOH/g; use COA value for stoichiometry |
| Density (kg/m³, 20°C) | 895–905 | 898.6 kg/m³ | SH/T 0604-2000; ≈0.895–0.905 g/cm³ |
| Flash Point | ~105–113°C | ~108°C | Combustible Liquid Class III-B; lower than 2-EHA (~116°C) and NDA (~140°C); apply standard combustible storage |
| Boiling Point | ~215–220°C | 217°C | At 760 mmHg; reduced-pressure distillation used in Oxo process purification |
| Refractive Index | ~1.420–1.425 | ~1.422 | n20/D; reported on COA; identity confirmation alongside GC and density |
| EU CLP | No CMR ✓ Mild irritant only | H315 / H319 | Standard nitrile gloves + eye protection adequate; no Repr. 1B; no CMR hazard mixture labelling triggered |
| Packaging | 200 kg galvanised steel drum / 1000 kg IBC | Tank truck available | Avoid copper/aluminium alloy vessels; galvanised steel and HDPE compatible; shelf life 12 months |
INA Applications - Lubricants, Metal Salts, PVC Stabilisers & More
1. Synthetic Ester Lubricant Synthesis - TMP & Pentaerythritol Isononanoate Esters
INA's primary lubricant application is as an acid component in polyol ester base oils - trimethylolpropane (TMP) triisononanoate and pentaerythritol (PE) tetraisononanoate - which are high-performance synthetic ester lubricants for turbine oils, reciprocating and rotary screw compressor lubricants, aviation lubricants, and refrigeration lubricants. The branched C9 isononanoate chain contributes several performance advantages: low pour point (TMP triisononanoate typically below −40°C - superior to straight-chain C9 acid polyol esters); high viscosity index (branched chain provides more gradual thermal thinning); good thermal-oxidative stability; and low volatility (158.24 g/mol molecular contribution per INA unit).
For refrigeration compressor lubricants - where synthetic ester lubricants have largely replaced mineral oils in modern HFC and HFO refrigerant systems - INA-based TMP and PE esters provide excellent miscibility with polar HFC refrigerants (R-134a, R-410A, R-32, R-1234yf), good low-temperature fluidity for cold-start in commercial refrigeration, and hydrolytic stability adequate for hermetically sealed compressor environments. INA's water content of ≤0.10% (actual 0.01%) is directly critical here: residual water in the acid promotes acid-catalysed ester hydrolysis during compressor service, generating free acid that corrodes copper and iron compressor components.
Colour significance for lubricant production: INA's Pt-Co 3.2 (actual) colour enables ester lubricant base oils that meet ASTM colour ≤0.5 (water-white to pale yellow) specifications for premium turbine oil and compressor oil products without post-reaction decolourisation treatment - reducing production cost and avoiding colour reversion during storage.
2. Metal Isononanoate Salt Synthesis - Driers, PU Catalysts & PVC Co-Stabilisers
Metal carboxylate salts of INA - metal isononanoates - are direct structural analogues of the well-established metal 2-ethylhexanoate (octoate) family but with one additional methylene unit (C9 vs C8). This extra carbon provides greater oil solubility in aliphatic hydrocarbon solvents, enabling production of more highly concentrated metal salt solutions (drier concentrates at 6–18% metal) for liquid alkyd and PU coating additives. The C9 isononanoate anion's slightly larger lipophilic volume also improves low-temperature stability of concentrated drier solutions, reducing precipitation in cold-climate storage.
| Metal Salt | Metal % | Primary Function | vs Octoate (C8) Advantage |
|---|---|---|---|
| Cobalt isononanoate | 6–12% Co | Primary through-drier (alkyd coatings) | Higher oil solubility (C9 vs C8) |
| Zirconium isononanoate | 12–18% Zr | Surface/hardening drier; cobalt replacement | Higher oil solubility; hydrolysis stable |
| Zinc isononanoate | 12–18% Zn | Auxiliary drier; PVC co-stabiliser | C9 chain improves formulation compatibility |
| Calcium isononanoate | 4–10% Ca | Through-drier activator; PVC co-stabiliser | C9 chain improves compatibility |
| Bismuth isononanoate | 15–25% Bi | Non-tin, non-cobalt PU catalyst | High Bi% achievable; favourable CMR profile ✓ |
| Cerium isononanoate | ~15% Ce | Cobalt-free UV-stable primary drier | Advanced cobalt-free technology ✓ |
3. PVC Stabilisers, Non-Phthalate Plasticisers, Surfactants & Resin Modifiers
PVC heat stabiliser synthesis: In calcium-zinc PVC heat stabiliser systems, INA contributes the isononanoate anion as part of multi-carboxylate Ca-Zn packages alongside stearate, laurate, and benzoate ligands. The branched C9 isononanoate provides a specific balance of HCl scavenging speed, processing lubricity, and thermal colour stability intermediate between stearate (good lubricity, moderate scavenging) and 2-ethylhexanoate (fast scavenging, lower lubricity). INA's Pt-Co ≤15 colour directly determines the initial colour of the stabiliser concentrate and consequently the colour of the stabilised PVC compound - critical for light-coloured and transparent PVC formulations.
Non-phthalate ester plasticisers: INA is esterified with diols (1,2-propanediol, neopentyl glycol) and triols (trimethylolpropane) to produce isononanoate diester and triester plasticisers for flexible PVC in cable, automotive, and specialty film applications requiring non-phthalate documentation. The branched C9 chain contributes low-temperature flexibility and low migration to these non-CMR ester plasticisers.
Surfactant synthesis: INA undergoes ethoxylation, amide formation, or sulfonation to produce specialty non-ionic and anionic branched-chain surfactants with low CMC, rapid wetting kinetics, low foam profile, and enhanced biodegradability vs linear fatty acid surfactants - for industrial cleaners, agricultural adjuvants, oilfield chemicals, and personal care.
Coatings and adhesive resin modifier: INA incorporated as a branched acid monomer in alkyd resin and saturated polyester resin synthesis reduces crystallinity of the polyester backbone, improves aliphatic solvent solubility, and extends flexibility of cured films - particularly valuable in low-VOC alkyd reformulations. Also used in metalworking fluid concentrates providing boundary lubrication, rust inhibition, and EP film formation in cutting and grinding fluid applications.
INA vs 2-EHA vs NDA - Branched C-Chain Acid Selection Guide
| Property | 2-EHA CAS 149-57-5 |
INA CAS 26896-18-4 |
NDA CAS 26896-20-8 |
|---|---|---|---|
| Carbon Number / Type | C8, branched | C9, branched (Oxo) | C10, neo (Koch) |
| Alpha Carbon | Secondary | Secondary (3-position) | Quaternary ✓ (best hydrolysis) |
| MW (g/mol) | 144.21 | 158.24 | ~172.26 |
| AV (theor., mg KOH/g) | ~389 (highest) | ~354.5 | ~326 (lowest) |
| Flash Point (°C) | ~116 | ~105–113 ⚠ (lowest) | ~140 ✓ (highest) |
| Hydrolysis Resistance | Good (secondary α-C) | Good (secondary α-C) | Exceptional ✓ (quaternary α-C) |
| Metal Salt Oil Solubility | Good (octoate) | Good → Better (C9 > C8) | Excellent ✓ (neodecanoate) |
| EU CLP Repr. 1B | Repr. 1B (H360D) ⚠ | Not classified ✓ | Not classified ✓ |
| US HAP | HAP-listed ⚠ | Not listed ✓ | Not listed ✓ |
| REACH SVHC | Candidate list ⚠ | Not listed ✓ | Not listed ✓ |
| Key Advantage | Lowest cost; widest use; highest AV - but restricted | C9 chain; No Repr. 1B; water-white colour ✓✓ | Best hydrolysis resistance (quaternary α-C) ✓ |
INA Regulatory Status - Repr. 1B-Free, Non-HAP, Non-SVHC
Storage, Handling & Safety
Storage
Store at 5–30°C in sealed galvanised steel drums or HDPE containers. INA remains liquid at all storage temperatures above 0°C. Standard combustible liquid storage area - no explosion-proof electrical equipment required.
Avoid copper and aluminium alloy vessels - INA forms metal soap films with these metals over time. Galvanised steel and HDPE are compatible. Segregate from strong alkalis (rapid saponification), strong oxidising agents, and reactive metals.
Shelf life: 12 months in sealed original packaging at 5–30°C. Retest acid value and colour if stored more than 9 months. Maximum 3-layer drum stacking; IBC tanks single-layer only.
PPE & Handling
GHS hazards: Skin Irrit. 2 (H315) - mild; Eye Irrit. 2 (H319) - mild. Combustible Liquid Class III-B. No CMR, no Repr. 1B, no HAP.
PPE: Chemical-resistant nitrile gloves (≥0.1 mm) + safety goggles for all handling. Good general ventilation adequate at ambient temperature. Local exhaust ventilation for heated processes above 100°C.
First aid: Skin/eye contact - flush with copious water for ≥15 minutes; seek medical advice for eye contact. Inhalation (heated vapour) - move to fresh air.
Spill: Absorb with dry sand or activated carbon; dispose as mildly corrosive organic chemical waste. Occupational safety reference: GESTIS CAS 26896-18-4 ↗
Frequently Asked Questions about Isononanoic Acid
Q: Is isononanoic acid (CAS 26896-18-4) used to make DINP plasticiser?
No - DINP (diisononyl phthalate, CAS 28553-12-0) is produced from isononanol (C9 branched alcohol, CAS 27458-93-1), not from isononanoic acid. Both are Oxo-process products from C8 olefin feedstock but by different routes: hydroformylation followed by hydrogenation of the C9 aldehyde yields isononanol (the alcohol for DINP); hydroformylation followed by oxidation of the C9 aldehyde yields isononanoic acid (this product). INA is esterified with alcohols to produce isononanoate ester lubricants and plasticisers. Buyers seeking the alcohol precursor for DINP synthesis should enquire about isononanol (CAS 27458-93-1).
Q: What is the correct IUPAC name - "3,5,5-trimethylhexanoic acid" or "trimethylheptanoic acid"?
The correct IUPAC name for the principal isomer is 3,5,5-trimethylhexanoic acid - the compound has a six-carbon principal chain (hexanoic acid) with methyl substituents at positions 3, 5, and 5: (CH₃)₃C–CH₂–CH(CH₃)–COOH. The name "trimethylheptanoic acid" (implying a seven-carbon principal chain) that appears in some supplier documents is a systematic naming error. The compound has nine carbons in total (C9) but the longest continuous chain containing the carboxyl group is only six carbons, not seven. In regulatory filings, REACH notifications, and procurement contracts, use "3,5,5-trimethylhexanoic acid" and CAS 3302-10-1 for the pure dominant isomer, or "isononanoic acid" and CAS 26896-18-4 for the commercial Oxo-process mixed isomer product.
Q: How does INA compare to 2-EHA for metal salt synthesis - what stoichiometric adjustments are needed?
INA replaces 2-EHA in cobalt, zirconium, zinc, calcium, bismuth, and manganese carboxylate salt synthesis with straightforward stoichiometric adjustments. The key difference is acid value: INA AV ~354.5 mg KOH/g vs 2-EHA AV ~389 mg KOH/g - approximately 9% more INA by weight is required per mole of metal salt produced. Always use the COA acid value for batch-specific charge calculations. Metal isononanoate salts have slightly higher oil solubility and MW compared to equivalent metal 2-ethylhexanoate (octoate) salts, generally improving compatibility with aliphatic hydrocarbon alkyd solvents and reducing low-temperature precipitation in concentrated drier solutions. The key regulatory benefit: INA has no Repr. 1B or SVHC designation, simplifying EU supply chain documentation for the metal salt derivatives. Sinolook provides acid substitution guidance and stoichiometric conversion tables for customers transitioning from 2-EHA to INA.
Q: Why does INA have such a low colour (Pt-Co 3.2) - and why does it matter?
Sinolook's INA achieves Pt-Co 3.2 (actual) - essentially water-white - through thorough activated carbon decolourisation during purification combined with high-vacuum distillation minimising coloured by-products. INA colour matters directly in two applications: (1) Metal carboxylate salt synthesis: INA's Pt-Co 3.2 produces much paler metal salt drier solutions than a Pt-Co 50–100 acid, enabling premium water-white cobalt, zirconium, and bismuth drier concentrates required by coating customers who insist on water-white drier additives to avoid yellowing in white and pastel alkyd coatings. (2) Polyol ester lubricant synthesis: ester lubricants from INA (Pt-Co ≤15) can meet ASTM colour ≤0.5 (water-white to pale yellow) specifications for premium turbine and compressor oils without additional post-reaction decolourisation - reducing production cost and avoiding colour reversion during storage.
Authoritative Technical & Regulatory References
ECHA substance page for INA: confirming mild irritant-only EU CLP classification, no CMR, no SVHC designation, and REACH registration status.
NCBI PubChem compound record for the dominant isomer (CAS 3302-10-1): molecular structure, physicochemical data, and GHS classification confirming no reproductive toxicant designation.
EPA CompTox Dashboard for CAS 26896-18-4: TSCA inventory listing, non-HAP confirmation under Section 112(b) of the Clean Air Act, and available physicochemical data.
IFA GESTIS substance database for CAS 26896-18-4: occupational exposure classification, physicochemical data, and toxicological summary for isononanoic acid.
ECHA substance page for 2-EHA - carrying Repr. 1B (H360D) and SVHC candidate designation - directly illustrating INA's regulatory advantage as the Repr. 1B-free C9 branched acid alternative.
ECHA substance page for NDA - the C10 Koch neo-acid reference for comparison with INA's C9 Oxo branched acid chain length and hydrolysis resistance characteristics.
Buy Isononanoic Acid from China · ≥99.5% Purity · Pt-Co ≤15 Water-White · No Repr. 1B · 2-EHA Alternative
Request INA Price, Qualification Sample & Regulatory Documentation
Sinolook supplies isononanoic acid (INA, CAS 26896-18-4) at ≥99.5% C9 acid purity (actual 99.93%), ≥99.00% 3,5,5-TMH isomer content, Pt-Co ≤15 (actual 3.2 - water-white), water ≤0.10% (actual 0.01%). Non-Repr. 1B, non-HAP, non-SVHC. Full documentation: EU CLP SDS, REACH registration, non-HAP declaration, TSCA confirmation, comparative INA vs 2-EHA regulatory summary. Qualification samples 0.5–5 kg. Volume from 200 kg drums to ISO tanks. Response within 24 hours.
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