Dioctyl phthalate (DOP): properties and applications

Dioctyl phthalate (DOP, di(2-ethylhexyl) phthalate, DEHP, CAS 117-81-7) is a clear, oily liquid with a mild characteristic odour, one of the most widely used and versatile plasticizers in industry. It is an ester of phthalic acid and 2-ethylhexanol which, due to its high compatibility with polyvinyl chloride (PVC) and other polymers, imparts flexibility, low-temperature resistance and processability. DOP occupies a key place in the production of flexible PVC compounds, cable compounds, artificial leather, linoleum and construction materials.

Chemical Nature and Physicochemical Properties

The molecular formula of DOP is C₂₄H₃₈O₄, with a molecular mass of 390.56 g/mol. The boiling point is about 386 °C, and the refractive index at 20 °C is 1.487–1.488. DOP is insoluble in water but miscible with gasoline, mineral oils and most organic solvents. The flash point is about 205 °C. The density at 20 °C is 1.377 g/cm³.

Key properties of DOP determining its applications:

• High plasticizing efficiency: DOP effectively lowers the glass transition temperature of PVC, imparting flexibility and elasticity even at low temperatures.

• Low volatility: thanks to its high boiling point, DOP evaporates slowly, ensuring the durability of plasticized products.

• Good thermal and light stability: DOP does not adversely affect the colour of the polymer composition.

• Polymer compatibility: DOP is well compatible with PVC, rubbers, epoxy resins and cellulose esters.

Regulatory Framework and Grades

Requirements for plasticizers, including DOP, in Russia and CIS countries are regulated by GOST 8728-88 "Plasticizers. Specifications". The standard applies to esters of various alcohols and dicarboxylic acids intended for the plasticization of vinyl resins and other polymers. DOP is produced in highest, first and second grades. The highest grade is intended for transparent, uncoloured and light-resistant PVC materials; the first grade — for light-coloured polymer materials; the second grade — for dark-coloured materials and carbon black-filled products.

In terms of impact on the body, ortho-phthalic acid esters belong to hazard class 2 (GOST 12.1.007-76). The maximum allowable concentration of DOP vapours in the working area air is 1 mg/m³.

Production Technology

The main industrial method for producing DOP is the esterification of phthalic anhydride with 2-ethylhexanol in the presence of a catalyst. The process can be carried out in batch or continuous mode. Catalysts include sulfuric acid, p-toluenesulfonic acid, tetraisopropyl titanate (TPT) and other compounds. A typical product yield is 95% or higher using 2–3% catalyst and 15% excess alcohol.

The process stages include: esterification (at 165–200 °C), neutralization of residual catalyst and unreacted anhydride with an alkaline solution, settling and separation of the aqueous phase, washing, vacuum stripping of excess alcohol and vacuum distillation to obtain the commercial product. Modern technologies are aimed at reducing energy consumption and using heterogeneous catalysts to simplify the purification stage.

Applications

Cable compounds. DOP is used for the production of wire and cable insulation and sheathing, providing flexibility, low-temperature resistance and electrical strength.

Construction materials. DOP is used in the production of linoleum, floor coverings, wall panels, roofing membranes and profiles for windows and doors.

Artificial leather and films. DOP is used for plasticizing PVC in the production of artificial leather, films, packaging materials and upholstery fabrics.

Medical devices. DOP is used for the production of medical tubing, blood bags and other flexible medical products.

Other applications. DOP is used in the production of footwear, toys, adhesives, sealants, paints and rubber technical products.

Safety and Regulatory Status

DOP (DEHP) belongs to hazard class 2 substances. When working with it, personal protective equipment must be used: protective clothing, safety goggles and gloves. Premises must be equipped with supply and exhaust ventilation. In case of fire, DOP is extinguished with finely sprayed water or foam.

In the European Union, DEHP is included in the list of substances subject to authorisation under REACH (Annex XIV) due to its reproductive toxicity and endocrine-disrupting properties. The use of DEHP is restricted in children's toys and childcare articles (Annex XVII). At the same time, DEHP is permitted for use in medical devices subject to authorisation. In North America and Asia, regulation is less stringent, but there is a trend towards switching to alternative plasticizers (DINP, DOTP) in safety-sensitive applications.

Conclusion

Dioctyl phthalate (DOP) remains one of the most in-demand plasticizers in the world due to its high efficiency, availability and wide range of applications. However, tightening environmental and sanitary requirements in developed countries are driving the transition to alternative plasticizers in a number of segments. Organising supplies of DOP, including grade selection (highest, first, second), quality confirmation and logistics, requires an individual approach taking into account the regulatory requirements of the destination country.