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| HS Code | 747410 |
| Productname | Diethyl Phthalate (DEP) |
| Casnumber | 84-66-2 |
| Ecnumber | 201-550-6 |
| Chemicalformula | C12H14O4 |
| Molecularweight | 222.24 g/mol |
| Iupacname | Diethyl benzene-1,2-dicarboxylate |
| Synonyms | DEP; Diethyl phthalate; 1,2-Benzenedicarboxylic acid diethyl ester; Ethyl phthalate |
| Appearance | Colorless oily liquid |
| Odor | Slight aromatic odor |
| Meltingpoint | -40.5 °C |
| Boilingpoint | 295 °C |
| Density | 1.12 g/cm³ at 20 °C |
| Refractiveindex | 1.501–1.505 at 20 °C |
| Vaporpressure | 0.0025 mmHg at 25 °C |
| Flashpoint | 161 °C closed cup |
| Autoignitiontemperature | 457 °C |
| Solubilityinwater | 1.08 g/L at 25 °C |
| Solubilityinorganicsolvents | Soluble in ethanol, ether, acetone, benzene |
| Logp | 2.42 |
| Viscosity | 12.7 mPa·s at 25 °C |
| Smiles | CCOC(=O)c1ccccc1C(=O)OCC |
| Inchi | InChI=1S/C12H14O4/c1-3-15-11(13)9-7-5-6-8-10(9)12(14)16-4-2/h5-8H,3-4H2,1-2H3 |
As an accredited Diethyl Phthalate DEP factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
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Extruded cellulose acetate sheet for display and thermoforming applications is compounded with DEP as a primary internal plasticizer at 15–30 wt% of dry resin. The flake is pre-blended with DEP in a high-intensity ribbon mixer and then dried at 70–80°C for 2–4 h to reduce residual moisture below <0.1%. Insufficient drying leads to hydrolytic degradation and silver streaking. Single-screw extruders with L/D 24:1–30:1 and barrier screws are operated with barrel profiles from 150°C feed to 220°C metering and die temperatures at 190–210°C. At melt temperatures above 230°C, free DEP volatility at the vacuum vent becomes measurable, causing plasticizer loss, gauge drift, and plate-out on polishing rolls. Vent vacuum is maintained at -0.06 to -0.08 MPa, with melt pressure monitored upstream of the screen pack as an indicator of viscosity instability. Sheet gauge is controlled at 0.3–2.0 mm. Melt volume-flow rate is measured under ISO 1133-1:2022 at 210°C/2.16 kg, and tensile properties are checked under ASTM D638-14 after 48 h conditioning at 23°C/50% RH. DEP is selected over dimethyl phthalate because its boiling point of 298°C reduces vent losses, although dimethyl phthalate is slightly more efficient on a weight basis. Operational failure is more often linked to plasticizer exudation during downstream thermoforming than to cellulose acetate degradation; maintaining DEP at 20–25 wt% rather than the upper formulation limit reduces haze increase measured under ASTM D1003-13 after repeated heating cycles.
In nitrocellulose-based furniture lacquers, DEP is formulated as a retained film plasticizer that reduces cold checking and improves adhesion over open-pore wood substrates. A conventional base lacquer contains 1/2-second nitrocellulose, an alcohol-tolerant alkyd resin, and a solvent mixture of n-butyl acetate, ethyl acetate, isopropanol, and toluene. DEP is incorporated at 5–15 phr on NC solids; below this range, films show loss of flexibility under ASTM D522-13 mandrel bend testing, and above this range, drying time and blocking tendency increase under ASTM D4366-16 pendulum hardness. Application is carried out by air-assisted airless spray equipment at fluid pressures of 0.15–0.35 MPa and atomizing air pressures of 0.20–0.40 MPa. Flash-off and oven curing occur at 40–60°C for 10–30 min before sanding and topcoat application. Because DEP is not chemically bound to the nitrocellulose matrix, migration into subsequent polyester or polyurethane topcoats can produce adhesion loss and surface tack; this is assessed after 7 days at 40°C by extraction and gas chromatography. DEP is less volatile than dimethyl phthalate but more volatile than dibutyl phthalate; for high-bake curing above 80°C, free DEP losses can accumulate at the exhaust stack, and formulations for these conditions require pre-compensation or replacement.
Anhydrous fine-fragrance concentrates use DEP as a high-boiling fixative and as a mutual solvent for crystalline aroma chemicals such as coumarin, vanillin, and musk ketone. The ester has a boiling point of 298°C and a density of 1.118 g/cm³ at 20°C. In perfume oil, DEP is typically present at 1–10 wt%; in finished hydroalcoholic fragrances it is usually kept below 2 wt% because higher levels can produce low-temperature turbidity. Clarity is evaluated under ISO 7027:2016 after 7 days at 5°C. The limiting factor is not odor impact—DEP has a faint ester character—but its partition behavior between ethanol, water, and lipophilic fragrance components. In body-spray emulsions, DEP partitions into the oil phase and can destabilize droplet size distribution; this is monitored by laser diffraction according to ISO 13320:2020. Compliance for leave-on cosmetic products is assessed under the EU Cosmetic Regulation (EC) No 1223/2009; IFRA Standards apply to the finished fragrance compound. Production mixing uses closed stainless-steel vessels with low-shear propeller agitation at 20–30°C; high-shear dispersion is not required because DEP is miscible with most fragrance oils. The main process failure in this segment is residual acidity in DEP, which can alter ester exchange reactions with alcohol-based fragrance components; incoming quality control sets acidity below 0.1 mg KOH/g and peroxide value under ISO 3960:2017.
For aqueous tablet film coating of oral solid dosage forms, DEP is used as a plasticizer for methacrylic acid copolymer dispersions and cellulosic polymers. The plasticizer is added at 10–25% based on polymer solids; below 10%, coated tablets show edge cracking and erosion under pan attrition, while above 25%, free plasticizer migration can modify drug-release profiles. Coating is performed on perforated side-vented pans with inlet air temperature 50–70°C, atomization air pressure 0.10–0.25 MPa, and gun-to-bed distance 150–200 mm. The coating dispersion is applied at 8–15% solids and stirred continuously to avoid sedimentation. Dissolution is tested under USP <711>, disintegration under USP <701>, and residual solvent and plasticizer content by gas chromatography under USP <467>. DEP is not a Class 1 solvent, but batch release must meet the finished dosage form monograph. Production-scale failures usually involve nozzle blockage from poorly dispersed plasticizer droplets; pre-emulsifying DEP in water with 0.5–1.0% polysorbate 80 before addition to the polymer dispersion reduces this risk. Long-term stability requires evaluation of plasticizer leaching into packaging, particularly for PVC blisters; published data for this specific configuration is limited, so migration studies under ICH Q1A(R2) conditions are advised.
| Application segment | Primary reference | Test method | Measured parameter |
|---|---|---|---|
| Cellulose acetate sheet | ISO 1133-1:2022 | ASTM D638-14 | Tensile properties after 48 h at 23°C/50% RH |
| Nitrocellulose lacquer | ASTM D522-13 | ASTM D4366-16 | Flexibility and pendulum hardness |
| Fragrance concentrate | EU (EC) No 1223/2009 | ISO 7027:2016 | Clarity after 7 days at 5°C |
| Pharmaceutical film coating | USP <711> | USP <467> | Dissolution and residual solvent |
| Solution adhesive | 21 CFR 175.105 | ASTM D1876-08(2015) | T-peel strength and migration |
| Nitrocellulose gravure ink | ASTM D5264-98(2019) | GC headspace | Rub resistance and free DEP |
Solution adhesives based on cellulose acetate or cellulose acetate butyrate are compounded with DEP to reduce viscosity and extend open time on gravure and roller coating lines. DEP is incorporated at 3–12 wt% of the total wet adhesive; the exact dose is set by Brookfield viscosity at 25°C, spindle 3, 30 rpm. Excessive DEP causes blocking of laminated films and plasticizer migration into polyolefin sealant layers; migration is evaluated after 10 days at 40°C using overall migration conditions under EN 1186-1:2002. Drying ovens operate at 60–90°C with air velocities of 2–5 m/s; residual solvent and free DEP are monitored by headspace gas chromatography. For food-contact laminating adhesives, the formulated adhesive is assessed under 21 CFR 175.105. The main manufacturing variable is batch-to-batch viscosity drift in the cellulose ester solution; operators compensate in 0.5 wt% DEP increments because larger changes reduce T-peel strength measured by ASTM D1876-08(2015). DEP is not suitable for retortable laminates where sustained heat can drive free plasticizer to the sealant interface and compromise bond integrity.
On printing lines running nitrocellulose-based gravure inks for flexible packaging, DEP is incorporated to maintain film flexibility after solvent evaporation and to reduce flaking during high-speed slitting. The plasticizer is added at 2–8 wt% of the finished ink varnish, with the lower band for heavily pigmented inks and the upper band for low-pigment overprint varnishes. Inks are reduced to 18–25 s flow time in a Zahn #2 cup and printed at 80–150 m/min on biaxially oriented polypropylene or polyester. Drying is carried out between print stations at 50–70°C with interstation air impingement. Rub resistance is tested by ASTM D5264-98(2019) Sutherland rub; blocking resistance under pressure is evaluated at 40°C/60% RH for 24 h. Because free DEP is mobile in the ink film, aged prints stored above 35°C can show flexibility loss and surface tack; residual free plasticizer is quantified by solvent extraction and gas chromatography. The main incompatibility occurs with certain high-solids polyurethane overprint varnishes, where DEP can migrate into the top layer and reduce adhesion. Incoming quality control for this segment requires DEP acidity below 0.1 mg KOH/g and water content below <0.1%.
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Diethyl phthalate (DEP, CAS 84-66-2; EC 201-550-6) is a short-chain aromatic ester obtained from phthalic anhydride and ethanol. It is supplied commercially as a single molecular entity rather than as a series of structural models; grade differentiation is instead controlled through analytical windows for technical-grade, low-odor fragrance-grade, and low-water plasticizer-grade material. The molecule has the formula C12H14O4 and a molar mass of 222.24 g mol−1. At 20 °C, the liquid exhibits a density of 1.118–1.122 g cm−3, a refractive index of 1.502–1.506, and a closed-cup flash point of 161 °C. The normal boiling point is 298–299 °C at 101.3 kPa. Principal uses include fragrance fixation, plasticization of cellulose acetate and nitrocellulose lacquers, and solvency adjustment in resin-based coatings. DEP is not a primary plasticizer for flexible poly(vinyl chloride), where higher-molecular-weight esters such as dibutyl phthalate or bis(2-ethylhexyl) phthalate provide greater permanence and compatibility. Among short-chain phthalates, DEP occupies an intermediate volatility and polarity position between dimethyl phthalate and dibutyl phthalate, and that position defines its utility in systems requiring moderate solvency, controlled release, and compatibility with alcohol-containing diluents.
Release criteria vary by supplier and intended end-use, but fragrance-grade DEP typically carries narrower windows than technical-grade material. Acid value is controlled because residual free phthalic acid accelerates ester exchange and discoloration in cellulose ester lacquers. Water content is limited because moisture can promote hydrolysis during heated processing and reduce assay retention. Pt-Co color is monitored to prevent yellowing in clear coatings and alcoholic fragrance bases. The following table consolidates representative acceptance limits and test methods used in industrial quality-control laboratories.
| Property | Typical acceptance limit | Principal test method |
|---|---|---|
| Appearance | Clear oily liquid, free of visible water and suspended matter | Visual inspection |
| Assay as ester | ≥99.5 wt% | GC-FID with internal standard; saponification value permitted as secondary check |
| Acid value | ≤0.05 mg KOH g−1 | ASTM D1045-19 |
| Water content | ≤0.10 wt% | ASTM E203-21 Karl Fischer titration |
| Density at 20 °C | 1.118–1.122 g cm−3 | ASTM D4052-22; ISO 758:1976 |
| Refractive index at 20 °C | 1.502–1.506 | ASTM D1218-21 |
| Pt-Co color | ≤15 | ASTM D1209-05 |
| Flash point, closed cup | 161 °C | ASTM D93-20 |
| Boiling range | 298–299 °C at 101.3 kPa | ASTM D1078-11 or equilibrium distillation data |
In cellulose acetate butyrate and nitrocellulose systems, DEP functions both as a viscosity depressant and as a nonvolatile plasticizer. The aromatic ester functionality improves solvency for cellulose nitrate and cellulose acetate butyrate chains by reducing hydrogen-bonded chain-chain interaction. In high-shear dispersion equipment, such as a cooled horizontal sigma-blade mixer or a vented twin-screw extruder with L/D 44, DEP is introduced at 5–20 phr depending on whether the objective is lacquer-base viscosity reduction or flexible cellulose ester film formation. Production-scale observations indicate that batch-to-batch acid value drift above 0.06 mg KOH g−1 correlates with increased yellowness during barrel residence above 180 °C, presumably because free acid accelerates cellulose ester hydrolysis. Published quantitative kinetic data for this specific configuration are limited; therefore, line-specific validation remains necessary. Rapid addition to a high-solids nitrocellulose chip dispersion can create a localized low-viscosity vortex that reduces distributive mixing in the rotor-stator zone; stepped addition over 10–15 min is standard practice to avoid this processing defect.
Direct substitution among short-chain phthalates is not neutral because molar mass, polarity, and vapour pressure shift evaporation, water extraction, and plasticizer efficiency. Table 2 provides baseline comparative properties. DEP is more volatile than dibutyl phthalate and less volatile than dimethyl phthalate. Its water solubility is lower than that of dimethyl phthalate but substantially higher than that of dibutyl phthalate. These differences create a practical hierarchy: dimethyl phthalate is commonly selected for fast-evaporating cellulose acetate coatings; DEP is chosen when longer open time and lower water leachability are required; dibutyl phthalate is selected for PVC and some nitrocellulose systems where lower volatility and higher plasticizer efficiency outweigh higher odor and oiliness.
| Property | Diethyl phthalate | Dimethyl phthalate | Dibutyl phthalate |
|---|---|---|---|
| Molar mass | 222.24 g mol−1 | 194.18 g mol−1 | 278.34 g mol−1 |
| Boiling point at 101.3 kPa | 298–299 °C | 282 °C | 340 °C |
| Water solubility at 25 °C | 1.08 g L−1 | 4.0 g L−1 | 0.011 g L−1 |
| Closed-cup flash point | 161 °C | 146 °C | 171 °C |
| Primary industrial role | Fragrance fixative; cellulose ester plasticizer | Cellulose acetate plasticizer; fast solvent | PVC plasticizer; lacquer plasticizer |
| PVC compatibility | Limited; not recommended as primary plasticizer | Limited; high volatility restricts permanence | Good at conventional plastisol and dry-blend loadings |
Formulation of nitrocellulose lacquers with DEP requires rebalancing the true solvent, cosolvent, and diluent fractions. In a typical wood-coating lacquer, nitrocellulose is dissolved in ester and ketone solvents, and a plasticizer such as DEP is added at 5–15 wt% of resin solids. Because DEP has a lower molar mass than dibutyl phthalate, equal mass loading gives a higher molar concentration. This can produce greater initial flexibility but also shifts the glass transition temperature of the film downward. Pencil hardness measured by ASTM D3363-20 after 72 h at 23 °C and 50% RH is therefore typically lower with DEP than with dibutyl phthalate at equal plasticizer mass, while retained elongation measured by ISO 527-3:2018 is higher. If lacquers are flash-dried above 60 °C, DEP migration toward the film surface can become measurable as surface tack and reduced print resistance. This behavior arises because DEP vapour pressure allows partial evaporative loss from the surface while leaving a plasticizer-rich boundary layer. The mechanism is distinct from dibutyl phthalate exudation, which is primarily driven by compatibility limits at high addition levels.
The substitution of dibutyl phthalate with DEP in low-odor lacquer systems is not drop-in. Because DEP is more volatile and more water-soluble, the lacquer exhibits faster viscosity rise after thinning and increased sensitivity to high-humidity application. A formulation containing 8 phr dibutyl phthalate may require 9–10 phr DEP to maintain equivalent loop tack and film flexibility. This adjustment increases total ester content and can reduce block resistance if coated parts are stacked within 24 h at 40 °C. Final film properties should be verified with ASTM D1640/D1640M-14 for drying times, ASTM D4366-16 for pendulum hardness, and ISO 2813:2014 for gloss retention. In water-immersion applications, the substitution should be rejected unless the coating is reformulated with hydrophobic resins, because DEP water solubility of 1.08 g L−1 is approximately 98-fold higher than that of dibutyl phthalate and leads to faster extraction from cured films under ASTM D870-15 immersion conditions.
Regulatory controls are substance-specific and jurisdiction-dependent. DEP is outside the scope of REACH Annex XVII entry 51, which restricts dibutyl phthalate, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, and diisobutyl phthalate in toys and childcare articles. It is also not among the four phthalates restricted under RoHS Directive 2011/65/EU Annex II entries 8–11. In the United States, DEP appears in 21 CFR 175.105 as an optional substance in adhesives intended for food contact; compliance is established through end-use extraction testing, and published migration data for specific adhesive configurations are limited. Under the EU Cosmetic Regulation 1223/2009, formulators must consult Annex II and Annex III because phthalate ester entries are substance-specific. No harmonised CMR classification is currently assigned to DEP under Regulation (EC) No 1272/2008, but downstream due-diligence obligations remain. In heated mixing operations, local exhaust ventilation or vapour recovery is recommended; although the boiling point is high, aerosol droplet formation during high-shear mixing is a relevant exposure pathway.
Material handling boundaries require attention to hydrolytic and oxidative incompatibilities. DEP should not be combined with strong oxidizing agents because degradation under fire conditions can generate phthalic acid, carbon oxides, and dense organic vapours. Prolonged heating in the presence of aqueous alkali causes saponification to ethanol and sodium phthalate, reducing plasticizer efficiency. Bulk storage in carbon steel or 316L stainless steel tanks with dry nitrogen padding is preferred over copper-containing alloys because trace acidity can form discolouring metal soaps. Seal materials should be selected from fluoroelastomer or PTFE rather than nitrile or neoprene, since low-molecular-weight esters extract plasticizers from these elastomers and cause seal shrinkage.
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