Bis(2-ethylhexyl) phosphate
[CAS# 298-07-7]

Identification

• Classification: Organic raw materials >> Inorganic acid ester
• Name: Bis(2-ethylhexyl) phosphate
• Synonyms: Bis(2-ethylhexyl) hydrogen phosphate; Di(2-ethylhexyl) phosphate; DEPHA
• Molecular Formula: C₁₆H₃₅O₄P
• Molecular Weight: 322.42
• CAS Registry Number: 298-07-7
• EC Number: 206-056-4
• SMILES: CCCCC(CC)COP(=O)(O)OCC(CC)CCCC

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*, 0.965 g/mL (Expl.)
• Melting point: -60 ºC (Expl.)
• Boiling point: 393.4±25.0 ºC 760 mmHg (Calc.)^*, 48 ºC (12 mmHg (Expl.)
• Flash point: 191.7±23.2 ºC (Calc.)^*, 130 ºC (Expl.)
• Solubility: water: |slightly soluble (Expl.)
• Index of refraction: 1.449 (Calc.)^*, 1.442 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: Pictogram(s)
• Risk Codes: R21;R34
• Safety Description: S25;S36/37/39;S45

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H312
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Skin corrosion	Skin Corr.	1C	H314
Skin corrosion	Skin Corr.	1B	H314
Skin irritation	Skin Irrit.	2	H315
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Skin corrosion	Skin Corr.	1A	H314
Acute toxicity	Acute Tox.	4	H332
Eye irritation	Eye Irrit.	2	H319
Substances or mixtures corrosive to metals	Met. Corr.	1	H290

• Transport Information: UN 1902

Discovory and Applicatios

Bis(2-ethylhexyl) phosphate, also known as dioctyl phosphate, is an organophosphorus compound widely used in industrial and laboratory applications, particularly as a metal extractant, surfactant, plasticizer, and flame retardant additive. The compound consists of a phosphate group esterified with two 2-ethylhexyl groups, giving it both hydrophilic and lipophilic characteristics. Its molecular formula is C₁₆H₃₅O₄P, and its structure includes a central phosphorus atom double-bonded to an oxygen atom and singly bonded to two alkoxy chains derived from 2-ethylhexanol and one hydroxyl group.

Bis(2-ethylhexyl) phosphate is a viscous, colorless to pale yellow liquid at room temperature with limited solubility in water but good solubility in most organic solvents. It is classified as an acidic organophosphate ester due to the presence of a free hydroxyl group, which imparts weakly acidic properties and facilitates hydrogen bonding or metal ion coordination. These features make it particularly useful in solvent extraction systems and in the formulation of certain specialty surfactants.

The compound is typically synthesized via esterification of phosphorus oxychloride (POCl₃) or phosphorus pentoxide (P₂O₅) with 2-ethylhexanol under controlled conditions. The reaction yields a mixture of mono- and diesters, but purification techniques can be employed to isolate the bis(2-ethylhexyl) phosphate form with high purity. It is also available as various metal salts, including sodium and ammonium salts, which are more water-soluble and used in aqueous systems.

One of the principal applications of bis(2-ethylhexyl) phosphate is in the extraction and separation of metal ions in hydrometallurgical and nuclear processing. As a component of solvent extraction systems, particularly in the form of its sodium salt, it acts as a selective chelating agent for rare earth elements, uranium, thorium, and certain transition metals. It is often used in conjunction with diluents such as kerosene or aliphatic hydrocarbons to create an organic phase capable of partitioning specific metal complexes from aqueous solutions.

In addition to metal ion extraction, bis(2-ethylhexyl) phosphate functions as a surfactant and emulsifier in formulations requiring low-foaming and dispersing properties. It is employed in the production of industrial lubricants, metalworking fluids, and pesticide formulations. Due to its thermal stability and compatibility with polymers, it is also used as a plasticizer and flame retardant additive in the manufacture of polyvinyl chloride (PVC) and other plastics, where it imparts flexibility and reduces flammability.

In analytical chemistry, bis(2-ethylhexyl) phosphate is sometimes used in the preparation of liquid–liquid extraction systems for sample pretreatment, particularly in the determination of trace metals. Its ability to form stable complexes with cations allows for selective enrichment and separation of analytes prior to instrumental analysis.

Toxicologically, bis(2-ethylhexyl) phosphate is considered to have low acute toxicity in animals, though prolonged exposure can cause irritation to skin and eyes. Its environmental impact is under evaluation, particularly with respect to its biodegradability and potential to bioaccumulate. It is subject to handling and disposal guidelines consistent with other organophosphorus compounds.

From a chemical standpoint, the phosphate ester linkage is hydrolyzable under strong acidic or basic conditions, leading to the release of 2-ethylhexanol and phosphoric acid derivatives. The compound is stable under normal storage conditions, provided it is protected from moisture and extreme pH environments.

In summary, bis(2-ethylhexyl) phosphate is a versatile organophosphorus compound valued for its amphiphilic nature and ability to coordinate metal ions. It plays a significant role in solvent extraction chemistry, industrial processing, polymer modification, and surface-active applications.

References

2024. Support Loading Effect on Extraction Chromatography Separation of Ytterbium and Lutetium Using 2-Ethylhexylphosphonic Acid Mono-2-ethylhexyl Ester Based Sorbent. Radiochemistry, 66(5).
DOI: 10.1134/s1066362224050072

2016. Solvent extraction of uranium from leach solutions obtained in processing of Polish low-grade ores. Journal of Radioanalytical and Nuclear Chemistry, 311(1).
DOI: 10.1007/s10967-016-5029-5

2012. Characterization of HDEHP-lanthanide complexes formed in a non-polar organic phase using 31P NMR and ESI-MS. Dalton transactions (Cambridge, England : 2003), 41(2).
DOI: 10.1039/c1dt11534k