What Is 2-Ethylhexanol?
2-Ethylhexanol, usually abbreviated 2-EH, is a branched eight-carbon primary alcohol with the molecular formula C8H18O and the CAS number 104-76-7. It is a colorless liquid with a characteristic mild odor, very low solubility in water, and good miscibility with most organic solvents. Its low volatility and high boiling point make it a valuable solvent and chemical intermediate.
2-EH is produced on a very large scale worldwide because it is the alcohol backbone of most plasticizers used in flexible PVC.
Step 1: Hydroformylation of Propylene
The industrial route to 2-ethylhexanol starts with propylene. In the first step, propylene reacts with synthesis gas, a mixture of carbon monoxide and hydrogen, in the hydroformylation reaction, also called oxo synthesis. With a rhodium or cobalt catalyst, this produces a mixture of n-butyraldehyde and isobutyraldehyde.
After separation, the straight-chain n-butyraldehyde is retained for the next step, while isobutyraldehyde is typically hydrogenated to isobutanol or used for other derivatives.
Step 2: Aldol Condensation
In the second step, two molecules of n-butyraldehyde undergo an aldol condensation in the presence of a base catalyst. The reaction joins the two molecules and eliminates water to form 2-ethylhex-2-enal, an unsaturated aldehyde. This step doubles the carbon chain from four to eight carbon atoms and creates the branched structure of the final product.
Step 3: Hydrogenation and Purification
In the final step, 2-ethylhex-2-enal is hydrogenated with hydrogen gas over a metal catalyst, typically nickel or copper-based, at elevated temperature and pressure. Hydrogenation saturates both the double bond and the aldehyde group to yield 2-ethylhexanol. The crude product is then purified by distillation to the required commercial purity, usually 99 percent or higher.
The complete sequence from propylene to 2-EH is highly integrated in large petrochemical complexes so that byproducts and heat can be reused efficiently.
Main Applications of 2-Ethylhexanol
Plasticizers
About 80 percent of 2-EH output is converted to plasticizers, mainly phthalate esters such as DOP and DINP, and the non-phthalate plasticizer DOTP. These plasticizers soften rigid PVC into flexible films, cables, flooring, coated fabrics and hoses. Because certain phthalates are restricted in toys and food-contact articles, demand for non-phthalate esters made from 2-EH is growing.
Chemical Intermediates
2-EH is esterified to 2-ethylhexyl acrylate, a monomer for acrylic polymers used in paints, adhesives and coatings. It is also used in surfactants, lubricant additives, emulsifiers, dispersants, antioxidants and mineral processing reagents.
Solvent and Specialty Uses
2-EH is used as a low-volatility solvent in coatings and inks, as a defoamer component in latex systems, in paper sizing and textile auxiliaries, and in small volumes in fragrance and cosmetic formulations.
Quality, Safety and Regulatory Considerations.
2-Ethylhexanol is supplied in industrial and higher purity grades, typically at 99 percent assay. Buyers should confirm the certificate of analysis, including assay, water content, acidity and color. The liquid is combustible with a flash point near 85 degrees Celsius, so it requires standard precautions against ignition and proper labeling. It is mildly irritating to skin and eyes, and ventilation is recommended during handling. Products made from 2-EH that enter the EU market must comply with REACH registration and relevant restriction rules.
Frequently Asked Questions
What is 2-ethylhexanol? 2-Ethylhexanol, usually abbreviated 2-EH, is a branched eight-carbon primary alcohol with the molecular formula C8H18O and the CAS number 104-76-7.
How is 2-ethylhexanol produced? In the first step, propylene reacts with synthesis gas, a mixture of carbon monoxide and hydrogen, in the hydroformylation reaction, also called oxo synthesis. In the second step, two molecules of n-butyraldehyde undergo an aldol condensation in the presence of a base catalyst.
What are the main applications of 2-ethylhexanol? 2-EH is produced on a very large scale worldwide because it is the alcohol backbone of most plasticizers used in flexible PVC. Plasticizers About 80 percent of 2-EH output is converted to plasticizers, mainly phthalate esters such as DOP and DINP, and the non-phthalate plasticizer DOTP.
What are the key properties of 2-ethylhexanol? Its low volatility and high boiling point make it a valuable solvent and chemical intermediate. The liquid is combustible with a flash point near 85 degrees Celsius, so it requires standard precautions against ignition and proper labeling.
Is 2-ethylhexanol flammable? The liquid is combustible with a flash point near 85 degrees Celsius, so it requires standard precautions against ignition and proper labeling.