HEXANOIC ACID, 2-ETHYL-

Hexanoic acid, 2-ethyl-, better known as 2-ethylhexanoic acid or 2-EHA (CAS No 149-57-5, C8H16O2), is a branched C8 monocarboxylic acid produced from propylene via the oxo process, supplied as a clear, almost colorless liquid and used mainly to make oil-soluble metal 2-ethylhexanoates for paint driers, PVC stabilizers and catalysts, as well as esters for plasticizers and synthetic lubricants and corrosion inhibitors for engine coolants.
2-Ethylhexanoic acid is widely used because its branched ethyl group next to the carboxyl group keeps the acid and its salts liquid and highly soluble in non-polar media, so metals such as cobalt, manganese, zirconium, calcium, zinc and tin can be delivered into oils, resins and solvents in a stable, easy-to-handle form.
2-Ethylhexanoic acid works as a weak organic acid that readily reacts with metal oxides, hydroxides and carbonates to form salts, with alcohols to form esters, and with metal surfaces in aqueous systems to form protective adsorbed layers, which explains its role as an intermediate, ligand and corrosion inhibitor.

CAS No: 149-57-5
EC No: 205-743-6
Molecular formula: C8H16O2
Molecular weight: 144.21 g/mol
Appearance: Clear, colorless to pale yellow liquid
Density: approx. 0.90 g/cm³ (25 °C)
Boiling point: approx. 228 °C
Melting point: approx. −59 °C
Flash point: approx. 114–118 °C (closed cup)
Water solubility: approx. 1.4–2 g/L (20 °C)
pKa: approx. 4.8
EU classification: Repr. 1B, H360D (Danger)

COMMON PRODUCT & CHEMICAL NAMES OF HEXANOIC ACID, 2-ETHYL-:

Hexanoic Acid, 2-Ethyl-, 2-Ethylhexanoic Acid, 2-EHA, 2-Ethylcaproic Acid, α-Ethylcaproic Acid, α-Ethylhexanoic Acid, 2-Ethylhexoic Acid, Ethylhexanoic Acid, Ethylhexoic Acid, Butylethylacetic Acid, 2-Butylbutanoic Acid, 3-Heptanecarboxylic Acid, (±)-2-Ethylhexanoic Acid, 2-Ethylhexansäure, Octoic Acid (trade usage)

Hexanoic acid, 2-ethyl- is the CAS index name of the substance, and 2-ethylhexanoic acid is the preferred IUPAC name. The abbreviation 2-EHA is used throughout the coatings, coolant and metal carboxylate industries. Older names such as 2-ethylcaproic acid, α-ethylcaproic acid and butylethylacetic acid are still found in technical literature. Salts and esters of Hexanoic acid, 2-ethyl- are called 2-ethylhexanoates, in trade, metal 2-ethylhexanoates are often sold as "octoates" (for example cobalt octoate, zinc octoate, tin octoate).
2-Ethylhexanoic acid should not be confused with n-octanoic acid (caprylic acid, CAS 124-07-2), its straight-chain isomer, or with 2-ethylhexanol (CAS 104-76-7), the corresponding alcohol. Valproic acid (2-propylpentanoic acid) is a structurally related branched acid but a different substance. Metal 2-ethylhexanoates and esters such as 2-ethylhexyl or cetearyl ethylhexanoate have their own CAS numbers.

WHAT IS HEXANOIC ACID, 2-ETHYL-?

2-Ethylhexanoic acid is a saturated, branched carboxylic acid with eight carbon atoms. Its structure is a hexanoic acid chain with an ethyl group on carbon 2, directly next to the carboxyl group: CH3(CH2)3CH(C2H5)COOH.
Carbon 2 is a stereocenter, but industrial Hexanoic acid, 2-ethyl- is supplied as the racemic mixture. The substance does not occur naturally in significant amounts, it is a petrochemical product.

Industrial production starts from propylene. Hydroformylation (the oxo process) of propylene gives n-butyraldehyde. Aldol condensation of two molecules of butyraldehyde gives 2-ethylhex-2-enal, which is selectively hydrogenated to 2-ethylhexanal. Oxidation of this aldehyde, usually with air or oxygen, yields Hexanoic acid, 2-ethyl-, which is then purified by distillation. The same oxo chain also produces 2-ethylhexanol, which is why both products are often made at the same sites.
Commercial Hexanoic acid, 2-ethyl- is typically a high-purity product with an assay of about 99 % or more, low water content and low color. It is a clear, slightly viscous liquid with a mild characteristic odor. It is only slightly soluble in water but miscible with alcohols, ethers, ketones, esters, hydrocarbons and oils.

The main industrial value of Hexanoic acid, 2-ethyl- lies in its metal salts. Metal 2-ethylhexanoates dissolve readily in mineral spirits, oils and resins, which makes them the standard way of introducing catalytically active metals into alkyd paints, inks, unsaturated polyester resins, polyurethanes and PVC. Cobalt, manganese and iron 2-ethylhexanoates act as primary driers, zirconium, calcium and zinc salts act as auxiliary driers, tin(II) 2-ethylhexanoate is a well-known catalyst for polyurethanes and for polylactide polymerization, and calcium, zinc and barium salts are components of liquid PVC heat stabilizers.
2-Ethylhexanoic acid is also an important acid component for esters. With polyols such as neopentyl glycol, trimethylolpropane or triethylene glycol it forms esters used as synthetic lubricant base stocks and as plasticizers, for example in PVB interlayers for laminated safety glass.
In water-based systems, Hexanoic acid, 2-ethyl- and its salts are used as corrosion inhibitors. In organic acid technology (OAT) engine coolants, 2-EHA has been one of the classic carboxylate inhibitors protecting aluminum, steel and cast iron. It is also used in metalworking fluids and in sodium and potassium salt form in pharmaceutical salt formation.

For producers, Hexanoic acid, 2-ethyl- is a stable, liquid and easily processed intermediate that gives metal salts and esters with good solubility, low-temperature fluidity and consistent quality.
For end users, products made with Hexanoic acid, 2-ethyl- derivatives can mean faster-drying paints, more heat-stable PVC, efficiently catalyzed polyurethanes and better-protected engine cooling systems.
However, Hexanoic acid, 2-ethyl- and its salts carry a harmonized EU classification as toxic for reproduction (Repr. 1B, H360D). This classification has major consequences for labeling, worker protection and permitted uses, and it is driving substitution in some markets.

CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION OF HEXANOIC ACID, 2-ETHYL-

Product name: Hexanoic acid, 2-ethyl-
Common abbreviation: 2-EHA
Chemical name: 2-Ethylhexanoic acid
CAS No: 149-57-5
EC / EINECS No: 205-743-6
Molecular formula: C8H16O2
Molecular weight: 144.21 g/mol
SMILES: CCCCC(CC)C(=O)O
InChIKey: OBETXYAYXDNJHR-UHFFFAOYSA-N
Chemical class: Branched saturated monocarboxylic acid (C8)
Main functions: Intermediate for metal 2-ethylhexanoates (driers, catalysts, stabilizers), intermediate for esters (plasticizers, lubricants), corrosion inhibitor, chemical intermediate

2-Ethylhexanoic acid has a harmonized classification in Annex VI of the EU CLP Regulation that also covers its salts unless they have their own entry. Since the 18th Adaptation to Technical Progress, 2-EHA and its salts are classified as Repr. 1B, H360D ("May damage the unborn child"), with the generic concentration limit of 0.3 % for mixtures. This classification is legally applicable since late 2023.
2-Ethylhexanoic acid is registered under REACH. Because of its reproductive toxicity classification, it is subject to the REACH Annex XVII restriction on substances classified as toxic for reproduction for supply to the general public, and it is not permitted in cosmetic products in the EU.

CHEMICAL STRUCTURE AND MOLECULAR PROPERTIES OF HEXANOIC ACID, 2-ETHYL-

The branching of Hexanoic acid, 2-ethyl- is the key to its industrial usefulness.

LOW MELTING POINT AND FLUIDITY
The ethyl group at carbon 2 disturbs the regular packing of molecules. As a result, Hexanoic acid, 2-ethyl- melts at about −59 °C, far below its straight-chain isomer octanoic acid, and stays liquid and pumpable in cold conditions.

SOLUBILITY OF METAL SALTS
When Hexanoic acid, 2-ethyl- is converted into metal salts, the branched hydrocarbon parts surround the metal center and make the whole complex lipophilic. Metal 2-ethylhexanoates are therefore highly soluble in non-polar solvents and oils. Structurally they behave more like neutral coordination complexes than classic ionic salts, similar to metal acetates.

ACIDITY AND REACTIVITY
With a pKa of about 4.8, Hexanoic acid, 2-ethyl- is a typical weak carboxylic acid. It neutralizes bases, reacts with metal oxides, hydroxides and carbonates, and esterifies with alcohols. The branching next to the carboxyl group slightly hinders esterification, which also makes its esters relatively resistant to hydrolysis.

THERMAL AND OXIDATIVE STABILITY
The saturated, branched structure gives good thermal stability, which is valuable in lubricant esters and in high-temperature stabilizer applications.

PHYSICAL AND CHEMICAL PROPERTIES OF HEXANOIC ACID, 2-ETHYL-

GENERAL TECHNICAL SPECIFICATIONS:

PHYSICAL APPEARANCE: CLEAR, COLORLESS TO PALE YELLOW LIQUID
Odor: Mild, characteristic
Chemical character: Weak branched carboxylic acid
Molecular formula: C8H16O2
Molecular weight: 144.21 g/mol
CAS No: 149-57-5
EC / EINECS No: 205-743-6
Assay: Typically ≥ 99 %
Density: Approx. 0.903 g/cm³ at 25 °C
Refractive index (n20/D): Approx. 1.425
Melting point: Approx. −59 °C
Boiling point: Approx. 228 °C at 1013 hPa
Flash point: Approx. 114–118 °C (closed cup)
Autoignition temperature: Approx. 370 °C
Explosion limits in air: Approx. 0.9–6.7 % (V/V)
Vapor pressure: Low, below 1 Pa at 25 °C
Viscosity: Approx. 7–8 mPa·s at 20 °C
Water solubility: Approx. 1.4–2 g/L at 20 °C
pH: Approx. 3 (saturated aqueous solution)
pKa: Approx. 4.8
Log Pow: Approx. 2.6
Reactivity: Reacts with bases, metal oxides and hydroxides, and with alcohols under esterification conditions, avoid strong oxidizing agents and reactive metals

Typical sales specifications for Hexanoic acid, 2-ethyl- include assay, acid value, water content, color (APHA/Pt-Co) and sometimes content of related acids and aldehydes. Color and residual aldehydes matter especially when the acid is used to make light-colored driers and stabilizers.
The values above are typical literature and safety data sheet values and are not a binding specification. For the current specification of the supplied Hexanoic acid, 2-ethyl- grade, please contact Ataman Kimya.

HOW DOES HEXANOIC ACID, 2-ETHYL- WORK IN ITS MAIN APPLICATIONS?

AS A LIGAND FOR METAL DRIERS AND CATALYSTS
In metal 2-ethylhexanoates, Hexanoic acid, 2-ethyl- serves as a carrier ligand. It does not take part in the drying or catalytic reaction itself, its role is to make the metal soluble and well distributed in the oil or resin. In alkyd paints, cobalt or manganese ions then catalyze the decomposition of hydroperoxides formed by air oxidation of unsaturated fatty acid chains, starting the crosslinking that dries the paint film. Zirconium, calcium and other auxiliary driers help through-drying and pigment wetting.

AS A COMPONENT OF PVC STABILIZERS
In liquid mixed-metal stabilizers, calcium, zinc and barium 2-ethylhexanoates neutralize hydrogen chloride released during PVC processing and replace labile chlorine atoms, slowing degradation and discoloration.

AS AN ESTER-FORMING ACID
Esterified with polyols, Hexanoic acid, 2-ethyl- gives branched esters with low pour points, good thermal stability and good hydrolytic stability, suitable as synthetic lubricant base oils and plasticizers.

AS A CORROSION INHIBITOR
In aqueous systems such as engine coolants and metalworking fluids, neutralized Hexanoic acid, 2-ethyl- adsorbs on metal surfaces and forms a thin protective layer that reduces corrosion of aluminum, steel and cast iron. It is usually combined with other carboxylates (for example sebacic acid) and azoles.

MAIN FUNCTIONS OF HEXANOIC ACID, 2-ETHYL-:

Intermediate for metal 2-ethylhexanoates (driers, catalysts, stabilizers)
Carrier ligand making metals soluble in oils and solvents
Intermediate for esters used as plasticizers and lubricant base stocks
Carboxylate corrosion inhibitor in coolants and metalworking fluids
Intermediate for alkyd resin modification
Salt-forming agent in pharmaceutical synthesis (as sodium or potassium 2-ethylhexanoate)
General chemical intermediate

METAL 2-ETHYLHEXANOATES: THE MAIN USE OF HEXANOIC ACID, 2-ETHYL-

The largest outlet for Hexanoic acid, 2-ethyl- is the production of metal carboxylates.

Paint and ink driers: Cobalt, manganese and iron 2-ethylhexanoates (primary driers), zirconium, calcium, zinc, strontium and barium 2-ethylhexanoates (auxiliary and through driers).

Polyurethane and polymerization catalysts: Tin(II) 2-ethylhexanoate (stannous octoate) for polyurethane foams and coatings and for ring-opening polymerization of lactide, potassium 2-ethylhexanoate as a trimerization catalyst in polyisocyanurate foams, bismuth and zinc 2-ethylhexanoates as alternative urethane catalysts.

Unsaturated polyester curing: Cobalt 2-ethylhexanoate as an accelerator for peroxide curing.

PVC stabilizers: Calcium, zinc and barium 2-ethylhexanoates in liquid stabilizer systems.

Other uses: Aluminum hydroxy bis(2-ethylhexanoate) as a thickener for oils and inks, nickel and other 2-ethylhexanoates as catalyst precursors and fuel or lubricant additives.

Metal 2-ethylhexanoates are produced by reacting Hexanoic acid, 2-ethyl- with metal oxides, hydroxides or carbonates (direct fusion or solvent processes), or by double decomposition between sodium 2-ethylhexanoate and metal salts. The products are typically supplied as solutions in mineral spirits or other solvents with a defined metal content.
Under the EU CLP harmonization, metal 2-ethylhexanoates are covered by the classification of Hexanoic acid, 2-ethyl- and its salts unless they have their own entry. Mixtures containing 0.3 % or more of 2-EHA or its salts are classified Repr. 1B, H360D. This has encouraged the development of driers and catalysts based on alternative carboxylates such as neodecanoates.

IN WHICH SECTORS IS HEXANOIC ACID, 2-ETHYL- USED?

MAIN AREAS OF USE:

PAINTS, VARNISHES AND PRINTING INKS (DRIERS)
Polyurethane foams, coatings, adhesives and elastomers (catalysts)
Unsaturated polyester and composite resins (accelerators)
PVC processing (heat stabilizers)
Synthetic lubricants and lubricant additives (esters, metal salts)
Plasticizers (for example glycol esters for PVB and other polymers)
Engine coolants and heat transfer fluids (corrosion inhibitors)
Metalworking fluids (corrosion inhibitors)
Alkyd resin production
Pharmaceutical and agrochemical intermediates
Specialty chemical synthesis

Paint and ink producers focus on metal content, solubility and drying performance of the derived driers. PVC stabilizer producers need consistent acid quality and low color. Coolant and metalworking producers evaluate corrosion inhibition performance and, increasingly, the regulatory implications of using 2-EHA.

IS HEXANOIC ACID, 2-ETHYL- USED IN COSMETIC, FOOD, AND PHARMACEUTICAL APPLICATIONS?

Cosmetics: Hexanoic acid, 2-ethyl- and its salts are classified as Repr. 1B in the EU and are therefore not permitted in cosmetic products in the European Union. Esters such as cetearyl ethylhexanoate are separate substances with their own regulatory status and are not the same as the free acid.
Food: Hexanoic acid, 2-ethyl- is not a food additive and has no E number. It can occur as a migrant from certain materials, which is why food contact authorities have set limits or monitor its migration in specific materials.
Pharmaceuticals: Hexanoic acid, 2-ethyl- is not an active ingredient, but sodium and potassium 2-ethylhexanoate are used in the synthesis of salts of β-lactam antibiotics and other active ingredients. In such uses, residual 2-ethylhexanoic acid in the active ingredient is controlled according to pharmacopoeial requirements.

INDUSTRIAL APPLICATIONS OF HEXANOIC ACID, 2-ETHYL-

ENGINE COOLANTS
Purpose: To protect cooling system metals against corrosion over long service intervals.
Role of Hexanoic acid, 2-ethyl-: Carboxylate corrosion inhibitor in OAT and hybrid coolants, usually as a neutralized salt in glycol.
Limitations: Because of the Repr. 1B classification, coolant concentrates containing 2-EHA above 0.3 % must be labeled H360D, and many producers are reformulating with alternative inhibitors.

SYNTHETIC LUBRICANTS
Purpose: To produce ester base stocks with low pour points and good stability.
Role of Hexanoic acid, 2-ethyl-: Acid component for neopentyl glycol, trimethylolpropane and pentaerythritol esters.
Limitations: Ester properties depend on the combination of acids and polyols, residual acidity must be controlled.

PLASTICIZERS
Purpose: To soften polymers such as PVB and PVC.
Role of Hexanoic acid, 2-ethyl-: Acid component of glycol and polyol esters (for example triethylene glycol bis(2-ethylhexanoate)).

ALKYD RESINS
Purpose: To modify alkyd resin properties.
Role of Hexanoic acid, 2-ethyl-: Monofunctional acid that controls molecular weight and improves color and yellowing resistance compared with unsaturated fatty acids.

WHICH PROBLEMS CAN HEXANOIC ACID, 2-ETHYL- HELP SOLVE?

METALS THAT DO NOT DISSOLVE IN OILS AND RESINS
Inorganic metal salts are insoluble in paints and resins. Converting them into 2-ethylhexanoates makes them soluble and catalytically available.

SLOW DRYING OF ALKYD PAINTS
Driers based on Hexanoic acid, 2-ethyl- speed up oxidative drying and through-curing.

THERMAL DEGRADATION OF PVC
Calcium/zinc 2-ethylhexanoate stabilizers help prevent discoloration and degradation during PVC processing.

LUBRICANTS THAT THICKEN IN THE COLD
Branched esters from Hexanoic acid, 2-ethyl- remain fluid at low temperatures.

CORROSION IN AQUEOUS CIRCUITS
Neutralized 2-EHA inhibits corrosion in coolants and metalworking fluids.

At the same time, the reproductive toxicity classification creates new challenges, in many applications, the benefits of 2-EHA-based products must now be weighed against labeling, exposure control and customer acceptance.

THINGS TO CONSIDER WHEN USING HEXANOIC ACID, 2-ETHYL-

The most important consideration with Hexanoic acid, 2-ethyl- today is its regulatory status. Using it without accounting for the Repr. 1B classification of the acid and its salts can lead to incorrect labeling, inadequate worker protection or restricted products.

POINTS TO CONSIDER:

Classify and label mixtures correctly, 2-EHA and its salts are added together for the 0.3 % concentration limit.
Apply strict exposure control: closed systems where possible, local exhaust ventilation, gloves and eye protection.
Inform workers, in particular pregnant workers, about the reproductive hazard.
Do not supply mixtures above the limit to the general public in the EU.
Do not use in cosmetic products in the EU.
Evaluate substitution with alternative carboxylic acids or inhibitors where feasible.
Store in suitable materials (stainless steel, lined steel, compatible plastics), the acid can corrode some metals.
Keep away from strong oxidizing agents and strong bases.
Avoid heating to high temperatures in open systems.

2-Ethylhexanoic acid is a combustible liquid with a flash point around 114–118 °C. Contact with skin and eyes should be avoided, and vapors or mists from heated product should not be inhaled.

INITIAL FORMULATION APPROACHES FOR HEXANOIC ACID, 2-ETHYL-

The examples below are laboratory starting points for evaluating Hexanoic acid, 2-ethyl- and its derivatives. They are not production recipes. All work must take into account the Repr. 1B classification and be carried out with appropriate engineering controls and personal protective equipment.

The percentage compositions added below are illustrative starting charges, not validated production recipes. Each totals 100 % before reaction or processing, water removal and other losses change final composition.

EXAMPLE 1: PREPARATION OF A ZINC 2-ETHYLHEXANOATE SOLUTION

Objective: To prepare a zinc 2-ethylhexanoate solution in mineral spirits and evaluate its metal content and stability as an auxiliary drier or stabilizer component.

INITIAL COMPONENTS:

Hexanoic acid, 2-ethyl-: approx. 2.0–2.1 mol per mol of zinc
Zinc oxide: weighed amount
Mineral spirits or suitable solvent: to the target metal content
Small amount of water as reaction aid (optional)

APPLICATION APPROACH:

Hexanoic acid, 2-ethyl- and part of the solvent are charged to a reactor with stirring and reflux.
Zinc oxide is added in portions, and the mixture is heated until the reaction is complete and the mixture becomes clear.
Water formed in the reaction is removed by azeotropic distillation.
The product is filtered and diluted to the target metal content.
Metal content, acid value, color, clarity and storage stability are measured.
The solution is evaluated in a test alkyd paint or PVC formulation.

ILLUSTRATIVE INITIAL CHARGE (% W/W)
2-Ethylhexanoic acid: 40.00 %
Zinc oxide: 11.01 %
Mineral spirits: 48.99 %
Total: 100.00 %
This represents approximately 2.05 mol acid per mol zinc oxide. Optional added water replaces an equal mass of solvent, final metal content must be measured after reaction and water removal.

EXAMPLE 2: SCREENING 2-EHA IN AN OAT COOLANT INHIBITOR PACKAGE

Objective: To compare corrosion protection of a coolant concentrate with and without Hexanoic acid, 2-ethyl-, and to evaluate possible alternatives.

INITIAL APPROACH:

MONOETHYLENE GLYCOL: BASE FLUID
Hexanoic acid, 2-ethyl-: approx. 0, 1, 2 and 3 % in the concentrate, neutralized with potassium or sodium hydroxide
Sebacic acid or other dicarboxylic acid: constant
Tolyltriazole: constant
Alternative carboxylic acid inhibitor: in a separate series for comparison
pH adjusted to a constant value

APPLICATION APPROACH:

CONCENTRATES ARE PREPARED AND DILUTED WITH STANDARD CORROSIVE WATER.
Glassware corrosion tests are carried out on a standard metal coupon set.
Weight losses of aluminum, steel, cast iron, copper, brass and solder are compared.
Results are evaluated together with the labeling consequences of each formulation.

ILLUSTRATIVE INITIAL COMPOSITION FOR THE 2 % ACID TRIAL (% W/W)
Monoethylene glycol: 93.26 %
2-Ethylhexanoic acid: 2.00 %
Sebacic acid: 0.50 %
Tolyltriazole: 0.05 %
Potassium hydroxide solution (50 %): 1.84 %
Water: 2.35 %
Total: 100.00 %
The alkaline solution amount is an illustrative neutralisation allowance for both acids, establish final pH experimentally. For the 0, 1 and 3 % acid trials, recalculate alkali demand and rebalance glycol or water to 100 %.

EXAMPLE 3: NEOPENTYL GLYCOL DI(2-ETHYLHEXANOATE) LUBRICANT ESTER

Objective: To prepare a branched diester for use as a low-temperature lubricant base stock.

INITIAL APPROACH:

Neopentyl glycol: 1 mol
Hexanoic acid, 2-ethyl-: approx. 2.1–2.2 mol (slight excess)
Esterification catalyst: according to process choice
Azeotropic solvent or vacuum for water removal

APPLICATION APPROACH:

REACTANTS AND CATALYST ARE HEATED UNDER STIRRING, AND WATER IS REMOVED CONTINUOUSLY.
The reaction is followed by acid value until the target conversion is reached.
Excess acid is removed by distillation or neutralization and washing.
Kinematic viscosity, viscosity index, pour point, acid value, flash point and hydrolytic stability of the ester are measured.

ILLUSTRATIVE INITIAL REACTANT CHARGE (% W/W)
Neopentyl glycol: 25.14 %
2-Ethylhexanoic acid: 74.86 %
Total: 100.00 %
This is approximately 1 mol glycol to 2.15 mol acid. Any selected catalyst or azeotropic solvent must be included by renormalising the charge to 100 %, this is not the composition of the purified ester.

HEXANOIC ACID, 2-ETHYL- SIMILAR PRODUCTS AND ALTERNATIVES

Hexanoic acid, 2-ethyl- and neodecanoic acid
Neodecanoic acid is a highly branched C10 acid used for metal neodecanoate driers and catalysts. It is not covered by the 2-EHA harmonized classification, but it has its own hazard profile and is not always a drop-in replacement.

Hexanoic acid, 2-ethyl- and isononanoic acid
Isononanoic acid is a branched C9 acid used for esters, driers and coolant inhibitors. It can replace 2-EHA in some applications, with differences in solubility and performance.

Hexanoic acid, 2-ethyl- and octanoic acid
Linear octanoic acid has a much higher melting point and gives less soluble metal salts.

Hexanoic acid, 2-ethyl- in coolants and alternatives
Sebacic acid, benzoic acid, other branched carboxylic acids and inorganic inhibitors can be combined in coolants as alternatives or complements.

Hexanoic acid, 2-ethyl- driers and alternative drier systems
Cobalt-free manganese or iron complexes and other carboxylate-based driers are being developed as alternatives in alkyd paints.

Any alternative should be tested for performance, compatibility and its own regulatory status.

HOW DOES HEXANOIC ACID, 2-ETHYL- WORK AT THE MOLECULAR LEVEL?
 
Hexanoic Acid, 2-Ethyl-, commonly called 2-ethylhexanoic acid, is an eight-carbon carboxylic acid with an ethyl branch on the carbon next to the carboxyl group. This single branch changes its behaviour compared with straight-chain octanoic acid. It disrupts regular packing of the molecules, keeps the acid liquid over a wide temperature range, increases solubility in non-polar media and shields the carboxyl group sterically. Most industrial uses of the molecule rely on these effects, either in the free acid or, more often, in its metal salts and esters.
 
Acid behaviour and solubility: The carboxyl group can release a proton and form the 2-ethylhexanoate anion. The branched C8 tail is strongly hydrophobic, so the acid dissolves only slightly in water but mixes readily with hydrocarbons, alcohols, esters and oils. When neutralised with metal bases, it forms salts that remain soluble in organic solvents instead of crystallising out, which is the key to many of its applications.
 
Metal carboxylates as oil-soluble metal carriers: In metal 2-ethylhexanoates, often called octoates, the carboxylate binds a metal ion while the branched hydrocarbon tails surround it like a soluble shell. The branching hinders orderly crystal packing, so these salts stay dissolved in paints, inks, resins and fuels. In this form, the acid acts as a vehicle that delivers catalytically or chemically active metals such as cobalt, manganese, zirconium, calcium, zinc, tin or bismuth into organic systems.
 
Paint driers: In alkyd paints and inks, drying occurs by autoxidation of unsaturated fatty acid chains. Cobalt and manganese 2-ethylhexanoates catalyse this process by cycling between oxidation states and breaking down hydroperoxides into free radicals that start crosslinking reactions. Zirconium and calcium carboxylates help the reaction proceed through the whole film thickness and improve hardness and pigment wetting. The organic anion keeps the metal soluble and evenly distributed in the binder.
 
Polymer catalysts and heat stabilisers: Tin(II) 2-ethylhexanoate is a widely used catalyst for ring-opening polymerisation of lactide and caprolactone and for polyurethane reactions; the carboxylate ligands keep the tin soluble and can be exchanged with alcohol groups to start chain growth. In PVC, calcium, zinc and barium 2-ethylhexanoates act as heat stabilisers. They react with hydrogen chloride released from degrading polymer and replace unstable chlorine atoms on the chain, slowing further dehydrochlorination and discolouration.
 
Esters as plasticisers and lubricants: When 2-ethylhexanoic acid is esterified with glycols or polyols, the branched acyl groups give esters with low pour points and good flexibility. In plasticisers, these esters move between polymer chains and increase free volume, making materials softer. In synthetic lubricants, the branching near the ester group sterically protects the carbonyl from attack by water, improving hydrolytic stability, while the irregular shape prevents wax-like crystallisation at low temperatures.
 
Corrosion inhibition in coolants: In organic acid technology engine coolants, the salt form of the acid adsorbs onto metal surfaces where corrosion begins. The carboxylate binds to the metal or oxide surface and the hydrophobic tail forms a thin protective barrier that limits contact with water and dissolved oxygen. This film forms selectively at active sites, so protection can be maintained with relatively low inhibitor levels.
 
Peroxide initiators: Esterification with tert-butyl hydroperoxide gives peroxyesters such as tert-butyl peroxy-2-ethylhexanoate. In these initiators, the acid portion influences the temperature at which the peroxide bond breaks into radicals, allowing controlled radical polymerisation and curing at defined temperatures.
 
Behaviour in living systems: The ethyl branch next to the carboxyl group hinders the normal β-oxidation pathway used to break down straight-chain fatty acids. The molecule is therefore metabolised more slowly through alternative oxidation routes and conjugation. Hexanoic Acid, 2-Ethyl- is classified as a reproductive toxicant, so handling requires suitable protective measures and exposure control.
 
Performance in each application depends on the metal or co-reactant used, concentration, temperature, moisture and the other components of the system. Hexanoic Acid, 2-Ethyl- dosage and process conditions should therefore be confirmed through laboratory trials.

QUALITY CONTROL AND PURCHASING CRITERIA FOR HEXANOIC ACID, 2-ETHYL-

RECOMMENDED INFORMATION TO REVIEW BEFORE PURCHASING:

ASSAY (GC)
Acid value
Water content
Color (APHA / Pt-Co)
Content of related acids and residual aldehydes
Density and refractive index
Technical Data Sheet (TDS)
Safety Data Sheet (SDS) with current CLP classification
Certificate of Analysis (COA)
Batch number and production date
Packaging type (drums, IBC, bulk) and net quantity
Storage conditions and shelf life
REACH registration status
Supply chain communication on the Repr. 1B classification and uses

Because of the reproductive toxicity classification, buyers should make sure that the SDS reflects the current harmonized classification and that exposure scenarios cover their intended use.

STORAGE AND HANDLING OF HEXANOIC ACID, 2-ETHYL-

2-Ethylhexanoic acid should be stored in tightly closed containers in a cool, dry and well-ventilated area, below about 30 °C, away from heat and ignition sources.
Suitable container materials include stainless steel, coated steel and compatible plastics. Contact with reactive metals and storage in unprotected carbon steel should be avoided, as the acid can cause corrosion.
The product should be separated from strong oxidizing agents and strong bases.
Handling should take place in closed systems or with local exhaust ventilation. Access to areas where the product is handled should be limited to trained personnel.
Transport: For the transport classification of Hexanoic acid, 2-ethyl-, please contact Ataman Kimya.
In case of spillage, ignition sources should be removed, the liquid absorbed with inert material such as sand or vermiculite and collected in suitable containers for disposal. Release to drains, soil and surface water must be prevented.

SAFETY INFORMATION OF HEXANOIC ACID, 2-ETHYL-

Hazard classification: Hexanoic acid, 2-ethyl- and its salts have a harmonized EU classification as Repr. 1B, H360D ("May damage the unborn child"), signal word "Danger", pictogram GHS08. Depending on the supplier, safety data sheets may list further hazards such as eye irritation or harm if swallowed.
Reproductive hazard: Exposure should be minimized, and special protection is required for pregnant and breastfeeding workers in accordance with occupational safety legislation.
Eyes: Rinse cautiously with water for several minutes, seek medical advice if irritation persists.
Skin: Remove contaminated clothing, wash skin with soap and plenty of water.
Inhalation: Move to fresh air, seek medical advice if symptoms occur.
Ingestion: Rinse mouth, do not induce vomiting, seek medical advice.
Fire: Combustible liquid. Suitable extinguishing media are foam, dry chemical, carbon dioxide and water spray, containers exposed to fire should be cooled with water. Combustion produces carbon oxides.
Personal protection: Chemical-resistant gloves, safety goggles, protective clothing and respiratory protection where vapors or mists may occur.
Environment: Prevent release to drains and the environment.
Waste: Dispose of as hazardous waste according to local regulations.

WHAT SHOULD BE CONSIDERED WHEN BUYING HEXANOIC ACID, 2-ETHYL-?

BEFORE PURCHASING, THE FOLLOWING INFORMATION SHOULD BE CLARIFIED:

INTENDED USE AND WHETHER IT IS COVERED BY THE SUPPLIER'S REACH REGISTRATION
Required purity and color
Specification limits for water and related impurities
Quantity and packaging
Documentation needs (TDS, SDS, COA, REACH information)
Internal capability to handle a Repr. 1B substance safely
Plans or needs for substitution in the final product

The price of Hexanoic acid, 2-ethyl- depends on propylene and oxo chemistry costs, energy, plant availability, order volume, packaging and logistics.

SUPPLY OF HEXANOIC ACID, 2-ETHYL- FROM ATAMAN KIMYA

2-Ethylhexanoic acid is an important oxo-chemical intermediate for metal carboxylates, esters and corrosion inhibitors. Because of its reproductive toxicity classification, buyers should clearly define their application and safety measures before ordering.
Ataman Kimya can provide information on Hexanoic acid, 2-ethyl- availability, specifications, packaging and price quotations.
Current stock, origin and specification details should be confirmed with Ataman Kimya before ordering.

INFORMATION THAT HELPS PREPARE A QUOTATION:

APPLICATION AND TARGET MARKET
Required specification
Estimated quantity
Packaging preference
Required documents

FREQUENTLY ASKED QUESTIONS ABOUT HEXANOIC ACID, 2-ETHYL-

WHAT IS HEXANOIC ACID, 2-ETHYL-?
2-Ethylhexanoic acid is 2-ethylhexanoic acid (2-EHA), a branched C8 carboxylic acid used mainly to make metal 2-ethylhexanoates, esters and corrosion inhibitors.

WHAT IS THE CAS NUMBER OF HEXANOIC ACID, 2-ETHYL-?
The CAS number is 149-57-5.

WHAT IS THE EC NUMBER OF HEXANOIC ACID, 2-ETHYL-?
The EC number is 205-743-6.

WHAT IS THE CHEMICAL FORMULA OF HEXANOIC ACID, 2-ETHYL-?
The formula is C8H16O2, structure CH3(CH2)3CH(C2H5)COOH, and the molecular weight is 144.21 g/mol.

WHAT ARE 2-ETHYLHEXANOATES OR OCTOATES?
They are salts and esters of Hexanoic acid, 2-ethyl-. Metal 2-ethylhexanoates are often called octoates in trade, for example cobalt octoate or tin octoate.

WHAT IS HEXANOIC ACID, 2-ETHYL- USED FOR?
It is used to make paint and ink driers, polyurethane and polymerization catalysts, PVC stabilizers, lubricant esters, plasticizers and coolant corrosion inhibitors.

HOW IS HEXANOIC ACID, 2-ETHYL- PRODUCED?
From propylene via the oxo process to butyraldehyde, aldol condensation to 2-ethylhexenal, hydrogenation to 2-ethylhexanal and oxidation to the acid.

IS HEXANOIC ACID, 2-ETHYL- SOLUBLE IN WATER?
Only slightly, about 1.4–2 g/L at 20 °C, it is miscible with most organic solvents and oils.

WHAT IS THE BOILING POINT OF HEXANOIC ACID, 2-ETHYL-?
About 228 °C at atmospheric pressure.

WHAT IS THE FLASH POINT OF HEXANOIC ACID, 2-ETHYL-?
About 114–118 °C (closed cup).

IS HEXANOIC ACID, 2-ETHYL- HAZARDOUS?
Yes. In the EU, it and its salts are classified as Repr. 1B, H360D ("May damage the unborn child"), with the signal word "Danger".

SINCE WHEN DOES THE REPR. 1B CLASSIFICATION APPLY?
It was introduced by the 18th ATP to the CLP Regulation and has applied since late 2023.

DOES THE CLASSIFICATION ALSO APPLY TO METAL 2-ETHYLHEXANOATES?
Yes. The harmonized entry covers 2-EHA and its salts unless a salt has its own entry, mixtures with 0.3 % or more are classified.

CAN HEXANOIC ACID, 2-ETHYL- BE USED IN COSMETICS?
No, not in the EU, because of its Repr. 1B classification.

IS HEXANOIC ACID, 2-ETHYL- USED IN ENGINE COOLANTS?
It has been widely used as a corrosion inhibitor in OAT coolants, because of its classification, many producers are moving to alternatives.

WHAT IS THE UN NUMBER OF HEXANOIC ACID, 2-ETHYL-?
For the transport classification, please contact Ataman Kimya.

WHAT ARE ALTERNATIVES TO HEXANOIC ACID, 2-ETHYL-?
Neodecanoic acid, isononanoic acid and other carboxylic acids or inhibitor systems, depending on the application.

HOW SHOULD HEXANOIC ACID, 2-ETHYL- BE STORED?
In tightly closed containers of suitable material, in a cool, well-ventilated place below about 30 °C, away from oxidizers, bases and ignition sources.

WHAT DOCUMENTS SHOULD BE REQUESTED WHEN BUYING HEXANOIC ACID, 2-ETHYL-?
TDS, SDS with current classification, COA and REACH information.

WHICH SPECIFICATIONS ARE IMPORTANT WHEN BUYING HEXANOIC ACID, 2-ETHYL-?
Assay, acid value, water content, color and residual aldehydes or related acids.

HEXANOIC ACID, 2-ETHYL- – TECHNICAL SUMMARY

Hexanoic acid, 2-ethyl- (2-ethylhexanoic acid, 2-EHA, CAS 149-57-5, EC 205-743-6, C8H16O2, 144.21 g/mol) is a clear, colorless liquid with a boiling point of about 228 °C, a melting point of about −59 °C, a flash point of about 114–118 °C and low water solubility.
Its branched structure makes its metal salts and esters highly soluble in organic media and fluid at low temperatures, which explains its use in paint and ink driers, polyurethane and polymerization catalysts, PVC stabilizers, lubricant esters, plasticizers and coolant corrosion inhibitors.
In the EU, Hexanoic acid, 2-ethyl- and its salts are classified as Repr. 1B, H360D, with a 0.3 % generic concentration limit, restrictions on supply to the general public and a ban in cosmetics. Handling requires strict exposure control.
It should not be confused with octanoic acid, 2-ethylhexanol or individual 2-ethylhexanoate salts and esters, which have their own identifiers.
Companies planning to source Hexanoic acid, 2-ethyl- through Ataman Kimya are advised to share their application, specification, quantity and documentation needs to confirm current product, stock, origin, packaging and quotation details.

Hexanoic acid, 2-ethyl- can be sourced from ATAMAN KİMYA. For further information and supply inquiries about Hexanoic acid, 2-ethyl-, please contact ATAMAN KİMYA.