INA vs Neodecanoic Acid (NDA) vs 2-EHA: Branched C-Chain Acid Selection Guide
Three branched acids, three different jobs. How alpha-carbon type, hydrolysis resistance, oil solubility and regulatory profile decide which one belongs in your formulation.
💡 Quick answer: Pick 2-EHA (C8) for lowest cost and highest acid value - if you can accept its Repr. 1B / SVHC status. Pick INA (C9) for a clean regulatory profile, water-white colour and good all-round performance. Pick NDA (C10) when maximum hydrolysis resistance is essential - its quaternary alpha carbon is unbeatable for waterborne driers and hydrolytically demanding esters.
These three acids are the workhorses of branched-acid chemistry. If you have already decided 2-EHA has to go for compliance reasons, that specific swap is covered in isononanoic acid vs 2-EHA. This guide is the wider, three-way engineering decision - useful when you are choosing on performance, not only on regulation.
🔬 The One Structural Feature That Decides Everything: The Alpha Carbon
Before the comparison table, understand the single feature that drives most of the differences - the nature of the alpha carbon (the carbon next to the –COOH group). It controls how well the acid, and esters made from it, resist hydrolysis.
🔹 2-EHA - secondary alpha carbon. One branch at the alpha position. Good hydrolytic stability, but the carboxyl is relatively accessible.
🔹 INA - secondary alpha carbon (3-position branch). Similar accessibility to 2-EHA; its main branching sits further along the chain (the 5,5-tert-butyl end). Good, balanced hydrolytic stability.
🔹 NDA - quaternary alpha carbon. A "neo" (Koch) acid: the alpha carbon carries no hydrogen and is fully substituted, sterically shielding the carboxyl. This gives exceptional resistance to hydrolysis - the defining NDA advantage.
Chain length then layers on top: more carbons mean higher oil solubility and molecular weight, but a lower acid value (fewer –COOH groups per kilogram). That trade-off - hydrolysis resistance and solubility rising from C8 → C10, acid charge efficiency falling - is the heart of the decision.
📊 Property-by-Property Comparison
This table compares the three across the properties that shape a formulation decision. (For INA's full certified specification and datasheet values, see the isononanoic acid product page.)
| Property | 2-EHA (C8) | INA (C9) | NDA (C10) |
|---|---|---|---|
| CAS number | 149-57-5 | 26896-18-4 | 26896-20-8 |
| Chain / synthesis | C8, branched (Oxo) | C9, branched (Oxo) | C10, neo (Koch) |
| Alpha carbon | Secondary | Secondary | Quaternary ✅ |
| MW (g/mol) | 144.21 | 158.24 | ~172.26 |
| Acid value (theor., mg KOH/g) | ~389 (highest) ✅ | ~354.5 | ~326 (lowest) |
| Flash point (°C) | ~116 | ~105–113 ⚠️ (lowest) | ~140 ✅ (highest) |
| Hydrolysis resistance | Good | Good | Exceptional ✅ |
| Metal-salt oil solubility | Good | Better (C9 > C8) | Excellent ✅ |
| EU CLP Repr. 1B | Repr. 1B ⚠️ | None ✅ | None ✅ |
| REACH SVHC / US HAP | Both flagged ⚠️ | Neither ✅ | Neither ✅ |
| Relative cost | Lowest ✅ | Mid | Higher |
🧮 How to Read the Trade-Offs
🔹 Acid value (charge efficiency). 2-EHA delivers the most –COOH per kilogram, so you buy less acid per mole of metal salt or ester. Going up in chain length costs charge efficiency: INA needs ~9% more mass than 2-EHA per mole; NDA more still.
🔹 Oil solubility. Rises with chain length. If your metal-salt drier precipitates in cold storage or you need a high-metal concentrate, the C9/C10 acids buy you margin.
🔹 Hydrolysis resistance. NDA's quaternary alpha carbon is in a class of its own - the reason it dominates waterborne alkyd driers, where water contact is constant. INA and 2-EHA are fine for solventborne systems.
🔹 Regulatory profile. INA and NDA are both free of Repr. 1B, SVHC and HAP; 2-EHA carries all three. This increasingly overrides cost for EU-facing supply chains - see the INA regulatory guide for the full picture.
🏭 Which Acid Wins, by Application
Solventborne alkyd driers
INA is the sweet spot: clean profile, water-white colour, good oil solubility. 2-EHA only if cost dominates and regulation permits.
Waterborne alkyd driers
NDA wins - its quaternary alpha carbon resists the hydrolysis that constant water contact would otherwise cause.
Polyol ester lubricants
INA for balanced performance and colour in turbine/compressor oils; NDA where extreme hydrolytic stability is specified.
Bismuth PU catalysts
INA or NDA - both clean-profile; choose on the metal-loading and solubility your catalyst needs.
The drier case for INA is developed in metal isononanoate driers for coatings, the lubricant case in isononanoic acid in synthetic ester lubricants, and the catalyst case in bismuth isononanoate PU catalysts. The batch-to-batch acid-value verification you will need for accurate charge calculations is in the INA quality & COA guide.
💡 Decision shorthand:
✅ Need maximum hydrolysis resistance (waterborne)? → NDA
✅ Need a clean regulatory profile + colour + all-round performance? → INA
✅ Cost is everything and Repr. 1B is acceptable in your market? → 2-EHA
❓ Frequently Asked Questions
🔹 What is the difference between an Oxo acid and a Koch acid?
Oxo acids (2-EHA, INA) are made via hydroformylation then oxidation, giving a secondary alpha carbon. Koch (neo) acids like NDA are made by Koch carbonylation, producing a quaternary alpha carbon that dramatically improves hydrolysis resistance.
🔹 Why does NDA resist hydrolysis so much better than INA?
NDA's alpha carbon is fully substituted (quaternary, no hydrogen), which sterically shields the ester bond from water attack. INA's alpha carbon is secondary, giving good but not exceptional resistance - ideal for solventborne, less so for constant water contact.
🔹 If NDA performs best, why use INA at all?
INA has a higher acid value (better charge efficiency), water-white colour, and lower cost than NDA, while sharing the clean regulatory profile. For solventborne driers and most ester lubricants, that combination makes INA the more economical choice.
🔹 Are all three regulated the same way?
No. INA and NDA carry no Repr. 1B, SVHC or HAP flags; 2-EHA carries all three. That regulatory gap is the main reason formulators migrate away from 2-EHA - see the dedicated substitution guide.
📚 Authoritative References
🔗 Related Articles
The Repr. 1B-free substitution roadmap and stoichiometry. →
INA in Synthetic Ester Lubricants
TMP & pentaerythritol polyol esters, pour point and VI. →
Read acid value, isomer purity, colour and water correctly. →
✅ Not Sure Which Branched Acid Fits? Ask Sinolook
We supply water-white, high-purity isononanoic acid (≥ 99.5% C9, no Repr. 1B) and can advise on where INA, NDA or 2-EHA best suits your driers, esters or catalysts - with samples and full documentation.
