Diethyl Phthalate (84-66-2) Physical and Chemical Properties
Diethyl Phthalate
Diethyl phthalate is a diethyl ester of phthalic acid used industrially as a plasticizer and formulation solvent in coatings, adhesives and consumer-product manufacturing.
| CAS Number | 84-66-2 |
| Family | Phthalate esters |
| Typical Form | Colorless oily liquid |
| Common Grades | BP, EP, JP, USP |
Diethyl phthalate (DEP) is an aromatic diester of phthalic acid (the diethyl ester of benzene-1,2-dicarboxylic acid) and belongs to the phthalate ester class of plasticizers. Structurally it comprises a benzene ring bearing two ortho-positioned carboxylate ester substituents (–COOCH2CH3). The molecule is overall neutral, features two carbonyl groups conjugated to the aromatic ring, four ester oxygen lone pairs (hydrogen-bond acceptors) and no hydrogen-bond donors. Conformational flexibility arises from the two ethoxycarbonyl side chains and several single bonds (rotatable bond count = 6), while the aromatic core provides a compact, relatively rigid scaffold.
Electronically DEP combines a polar functional group set (two ester carbonyls) with a nonpolar aromatic core and short ethyl chains; this gives moderate overall polarity (topological polar surface area = 52.6 Å^2) and intermediate lipophilicity (XLogP ≈ 2.5; log Kow ≈ 2.47). It is a neutral, non‑ionizable species at typical environmental and process pH, so partitioning between water and organic phases is driven by the balance of solubility and lipophilicity rather than acid–base dissociation. The ester functions are susceptible to hydrolysis under strongly acidic or basic conditions (base-catalysed hydrolysis is typically faster), and atmospheric fate is dominated by gas‑phase oxidation (reaction with OH radicals; estimated atmospheric half‑life on the order of days). In biological and environmental systems DEP is enzymatically hydrolysed to the corresponding monoester and then to phthalic acid and further oxidative metabolites.
As a commercial chemical, DEP is widely used as a plasticizer, solvent and formulation carrier (notably in polymers, coatings, fragrances and cosmetic preparations). Environmental and toxicological considerations—particularly its role as a lower‑molecular‑weight phthalate with potential reproductive and endocrine effects in some studies—affect selection, monitoring and regulatory handling in industrial and consumer applications. Common commercial grades reported for this substance include: BP, EP, JP, USP.
Basic Physical Properties
Density
Reported liquid densities for diethyl phthalate indicate it is denser than water and will sink when released to water:
- \(1.12\) at \(68\,^\circ\mathrm{F}\) (USCG, 1999) — denser than water; will sink
- \(1.120\) at \(25\,^\circ\mathrm{C}/25\,^\circ\mathrm{C}\)
- Relative density (water = 1): \(1.1\)
Multiple measurements cluster near \(1.12\), consistent with typical phthalate‑ester densities and with observed tendency to partition into sediments and organic matrices rather than remain in the aqueous column.
Melting Point
Experimental melting/freezing points are variable across sources and may reflect differences in purity or measurement method:
- \(27\,^\circ\mathrm{F}\) (NTP, 1992)
- \(-40.5\,^\circ\mathrm{C}\)
- range: \(-67\) to \(-44\,^\circ\mathrm{C}\)
- \(-41\,^\circ\mathrm{F}\)
The spread of reported values indicates that low‑temperature phase behavior can be sensitive to sample history and analytical conditions. No single consensus crystalline melting point is uniquely established across all datasets.
Boiling Point
Reported normal‑pressure boiling points:
- \(568\,^\circ\mathrm{F}\) at \(760\) mmHg (NTP, 1992)
- \(295\,^\circ\mathrm{C}\) (multiple reports)
Some datasets also list \(563\)–\(568\,^\circ\mathrm{F}\). These values are consistent with a high boiling, low‑volatility organic ester; distillation or thermal processing should account for the elevated boiling range.
Vapor Pressure
Vapor‑pressure data indicate very low volatility at ambient temperature but rising markedly with temperature:
- \(1\) mmHg at \(227.8\,^\circ\mathrm{F}\); \(5\) mmHg at \(285.3\,^\circ\mathrm{F}\) (NTP, 1992)
- \(0.002\) mmHg (generic report)
- \(2.1X10-3\) mm Hg at \(25\,^\circ\mathrm{C}\) (reported) — typically expressed as \(2.1\times10^{-3}\,\mathrm{mmHg}\) at \(25\,^\circ\mathrm{C}\)
- \(0.002\) mmHg at \(77\,^\circ\mathrm{F}\)
At ambient temperatures DEP exists predominantly in the condensed phase, and vapor concentrations are low under equilibrium conditions.
Flash Point
Reported flash points (method dependent):
- \(284\,^\circ\mathrm{F}\) (NTP, 1992)
- \(161\,^\circ\mathrm{C}\)
- \(322\,^\circ\mathrm{F}\) (\(161\,^\circ\mathrm{C}\)) (Open cup)
- \(117\,^\circ\mathrm{C}\) (closed cup)
DEP is classified as a combustible liquid (flash point well above typical solvent‑grade flammability thresholds); however, vapors formed at elevated temperatures can present ignition hazards.
Chemical Properties
Solubility and Phase Behavior
Solubility and miscibility data show strong preference for organic solvents and limited but non‑negligible water solubility:
- "less than 1 mg/mL at \(66\,^\circ\mathrm{F}\)" (NTP, 1992)
- "In water, \(1{,}080\) mg/L at \(25\,^\circ\mathrm{C}\)" (reported)
- Miscible with ethanol, ethyl ether; soluble in acetone, benzene, carbon tetrachloride; miscible with many organic solvents and vegetable oils; partly miscible with some aliphatic solvents.
The apparently divergent water‑solubility reports reflect differences in measurement technique, temperature reporting and expression units; overall DEP has limited water solubility (on the order of \(10^2\)–\(10^3\) mg·L^{-1}) and strong affinity for organic phases. Given density >1 and low volatility at ambient conditions, DEP tends to partition into sediments and organic material in aquatic systems rather than remain as an aqueous dissolved constituent.
Phase‑behavior implications for industrial use:
- Good solvent/plasticizer compatibility with polar and aromatic polymer matrices and many formulation solvents.
- Moderate log Kow (~2.47–2.5) yields measurable partitioning into lipids and polymer phases while remaining sufficiently water‑miscible for some process applications (e.g., solvent systems and fragrance carriers).
Reactivity and Stability
- DEP is chemically stable under normal ambient conditions and is reported as "stable to light" in storage contexts.
- As an ester, DEP undergoes hydrolysis under acidic or basic conditions to yield the monoester and phthalic acid; base‑catalysed hydrolysis is generally faster. Hydrolysis in neutral aqueous media is comparatively slow (environmental hydrolysis half‑lives can range from days to months depending on pH and catalysis).
- Incompatibilities: strong oxidizing agents, strong acids (may liberate heat/alcohol), caustics (heat generation), selective attack on some plastics; avoid contact with powerful oxidizers and agents able to cleave esters.
- On thermal decomposition or combustion DEP emits irritating and potentially toxic fumes; typical decomposition products include combustion‑derived oxides and organic fragments.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
Available energy data (reported in multiple unit systems):
- Heat of combustion reported as: \(-10{,}920\) BTU/LB = \(-6{,}070\) CAL/G = \(-254X10+5\) J/KG (source formatting retained)
- Heat (enthalpy) of vaporization reported as: \(170\) BTU/LB = \(96\) CAL/G = \(4.0X10+5\) J/KG (source formatting retained)
No experimental constant‑pressure heat capacity (\(C_p\)) value is provided in the available data context. The listed combustion and vaporization enthalpy data indicate substantial energy release on combustion and moderate enthalpy demand for vaporization, consistent with a relatively high‑boiling organic ester.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: C12H14O4
- Molecular weight: \(222.24\) (reported)
- Exact/monoisotopic mass: \(222.08920892\)
LogP and Polarity
- XLogP (computed): \(2.5\)
- log Kow (experimental/reported): \(2.47\)
- Topological polar surface area (TPSA): \(52.6\) Å\(^2\) (reported as 52.6)
- Hydrogen bond donors: 0; hydrogen bond acceptors: 4
These parameters indicate moderate lipophilicity and sufficient polarity to interact with both organic solvents and biological membranes; the absence of donors reduces aqueous hydrogen‑bond network interactions and contributes to preferential partitioning into nonpolar phases.
Structural Features
- SMILES: CCOC(=O)C1=CC=CC=C1C(=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
- InChIKey: FLKPEMZONWLCSK-UHFFFAOYSA-N
- Rotatable bond count: 6; molecular complexity reported: 223; heavy atom count: 16.
The two ortho esters create a sterically compact but conformationally mobile molecule; the ester carbonyls are conjugated to the aromatic ring, influencing UV absorption (phthalate esters commonly show maxima near 225 nm and 275 nm) and susceptibility to hydrolytic and oxidative transformations.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS: 84-66-2
- EC number: 201-550-6
- UNII: UF064M00AF
- ChEBI ID: CHEBI:34698
- ChEMBL ID: CHEMBL388558
- RTECS: TI1050000
- ICSC number: 0258
Also available:
- SMILES: CCOC(=O)C1=CC=CC=C1C(=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
- InChIKey: FLKPEMZONWLCSK-UHFFFAOYSA-N
Synonyms and Structural Names
Common reported synonyms (selected from depositor/supplier lists):
- diethyl phthalate
- phthalic acid diethyl ester
- diethyl benzene-1,2-dicarboxylate
- diethyl 1,2-benzenedicarboxylate
- Diethyl o-phthalate
- DEP
- 1,2-Benzenedicarboxylic acid, diethyl ester
- ethyl phthalate
- phthalic acid, diethyl ester
(Additional trade and analytical names exist in supplier and pharmacopeial listings.)
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Diethyl phthalate is employed primarily as a plasticizer, solvent and formulation vehicle:
- Plasticizer for cellulose ester plastics and other polymers to impart flexibility and low‑temperature performance.
- Solvent for cellulose acetate, nitrocellulose, coatings, varnishes, dopes and certain polymer processing applications.
- Fragrance carrier/fixative and solvent in cosmetic and personal‑care formulations.
- Denaturant for alcohol, component in certain insecticidal preparations and formulation solvent in adhesives and sealants.
DEP has historically been produced and used at large scale across plastics, coatings, fragrance and consumer product industries; production volumes reported in recent aggregated statistics fall within the multi‑million pound/year range.
Role in Synthesis or Formulations
- Manufacturing route: produced by esterification of phthalic anhydride with ethanol followed by purification.
- Formulation role: compatible with polar polymers and many organic solvents; used to modify polymer flexibility, act as a carrier for lipophilic additives (e.g., fragrances), and as a processing solvent in coatings and adhesives. Technical and pharmaceutical reference grades are available; typical technical‑grade material is used for industrial polymer applications while high‑purity grades serve analytical and pharmacopoeial purposes.
Safety and Handling Overview
Acute and Occupational Toxicity
Toxicity metrics and occupational exposure limits reported:
- Oral LD50 (mouse): \(8600\,\mathrm{mg}\,\mathrm{kg}^{-1}\) (reported)
- Oral LD50 (rat): ~\(9200\)–\(9500\,\mathrm{mg}\,\mathrm{kg}^{-1}\) (reported ranges)
- Dermal LD50 (guinea pig): \(>20\) mL/kg (reported)
- Inhalation LC50 (rat, 6 h): \(>4.64\) mg·L^{-1} (reported)
- EPA chronic oral reference dose (RfD): \(8\times10^{-1}\,\mathrm{mg}\,\mathrm{kg}^{-1}\,\mathrm{day}^{-1}\) (reported)
- Recommended occupational exposure limits (NIOSH/TLV): \(5\,\mathrm{mg}\,\mathrm{m}^{-3}\) (8‑hr TWA)
Hazard profile and signs:
- Skin and eye irritant; skin sensitization (allergic contact dermatitis) reported in some individuals.
- Central‑nervous‑system effects (drowsiness, dizziness) and respiratory irritation can occur at elevated exposure levels.
- Reproductive and developmental endpoints have been associated with several phthalate esters in animal studies; DEP undergoes hydrolysis to monoesters and further metabolites in vivo and can produce measurable biological effects that warrant exposure minimization.
- Acute medical measures: remove to fresh air for inhalation exposure; irrigate eyes and rinse skin with water for contact; do not induce emesis for ingestion without professional instruction and seek medical attention.
Storage and Handling Considerations
- Store in tightly closed containers in a cool, well‑ventilated area away from strong oxidizers and heat sources; venting and grounding of metal containers is advised for bulk handling to reduce static‑charge risk.
- Avoid contact with strong oxidizing agents and strong acids/alkalis that can promote vigorous or exothermic reactions.
- Engineering controls: use local exhaust ventilation where vapors or aerosols may be generated; maintain good industrial hygiene practices to limit inhalation and dermal exposure.
- Personal protective equipment: solvent‑resistant gloves, splash goggles or face shield and protective clothing for handling bulk liquid or during processes with potential splashing. Respiratory protection should follow a formal respirator selection program when airborne concentrations exceed recommended limits.
- Spill and release: prevent entry to drains and surface waters; contain and recover liquid where possible, absorb residual using inert sorbents and dispose of in accordance with applicable waste regulations. For disposal or incineration, designed thermal treatment at appropriate temperatures and residence times is commonly used for organic esters.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and applicable local legislation.
