Diphenyl Ether (13-12-9) Physical and Chemical Properties
Diphenyl Ether
A non-polar aromatic ether commonly used as a solvent and synthetic intermediate in industrial organic chemistry and fragrance ingredient production.
| CAS Number | 13-12-9 |
| Family | Aromatic ethers |
| Typical Form | Colorless crystalline solid or liquid |
| Common Grades | BP, EP, FCC, JP, Reagent Grade, USP |
Diphenyl ether is an aromatic diaryl ether (molecular formula \(\ce{C12H10O}\)) consisting of two phenyl rings connected through an ether oxygen (IUPAC name: phenoxybenzene). Structurally it is a symmetrical, nonpolar to weakly polar molecule in which the oxygen atom links two sp2-hybridized aromatic systems; the oxygen lone pairs are partially delocalized into the adjacent rings, reducing the basicity of the oxygen and minimizing classical hydrogen-bond donor interactions. The molecule presents low topological polar surface area (TPSA = 9.2) and no hydrogen-bond donors, consistent with limited water solubility and pronounced lipophilicity.
Acid–base behaviour is negligible in the neutral form (formal charge 0); protonation of the oxygen is possible under strongly acidic conditions (reported \(\mathrm{p}K_{\mathrm{(BH^+)}} = 5.79\) at 25 °C for the protonated base descriptor). Physicochemical characteristics — high boiling point, low vapor pressure and log K_OW near 4 — reflect strong van der Waals stabilization between aromatic rings and a tendency to partition into organic phases rather than aqueous media. Hydrolysis is not relevant under typical environmental conditions because the ether linkage is relatively resistant to spontaneous cleavage; oxidative or strongly acidic conditions (or specific enzymatic/biodegradation pathways) are needed to cleave the C–O bond.
Commercially and industrially, diphenyl ether is important as a heat-transfer fluid component (commonly used as a eutectic component in heat-transfer mixtures), as a fragrance/flavour ingredient in perfumery and soap formulations, and as a chemical intermediate for electrophilic substitutions (halogenation, acylation, alkylation) and processing aids for polymer production. Common commercial grades reported for this substance include: BP, EP, FCC, JP, Reagent Grade, USP.
Basic Physical Properties
Density
Reported liquid/solid densities cluster around values slightly greater than water, consistent with aromatic, relatively high-molecular-weight organics. Representative reported values include 1.0661 \(\mathrm{g}\,\mathrm{cm}^{-3}\) at 30 °C; a relative density (water = 1) of 1.08; and a range 1.071–1.075 (no single-certified standard density given). The density being >1 means bulk material at typical conditions may sink in water; solid-state packing (polymorphism) can affect measured solid densities.
Melting Point
Multiple experimental melting/freezing points have been reported: 80.3 °F; 26.865 °C; 28 °C; 37–39 °C; and 82 °F. These differing values are consistent with polymorphic solid forms and melting-point measurement conditions; crystalline samples typically exist below ≈82 °F and melt to an oily liquid above that temperature. Polymorphism and crystal packing (reported C–H···π interactions in different crystal forms) account for modest variation in the melting point.
Boiling Point
Diphenyl ether has a high normal boiling point consistent with two aromatic rings and low volatility: reported values include 258 °C and 496–498 °F at 760 mmHg (reported ranges 258.00–259.00 °C at 760.00 mm Hg). The high boiling point under atmospheric pressure explains its use in high-temperature heat-transfer applications.
Vapor Pressure
Low vapor pressures are reported, reflecting low volatility at ambient temperature: typical values include 0.0213–0.0225 \(\mathrm{mmHg}\) at 25 °C and 0.02 \(\mathrm{mmHg}\) at 77 °F. The low vapor pressure results in slow evaporation and low airborne concentration under normal conditions.
Flash Point
Closed-cup flash-point values reported cluster at 115 °C (239 °F); an open-cup value of 96.11 °C is also reported. These flash points place diphenyl ether in the class of combustible liquids that require preheating for ignition, and imply fire control measures appropriate for combustible organic liquids.
Chemical Properties
Solubility and Phase Behavior
Water solubility is very low: reported aqueous solubility values include 18 mg·L−1 at 25 °C (0.018 mg·mL−1), and tabulated as “insoluble / very poor” in water in many sources. The compound is readily soluble in common organic solvents (ethanol, diethyl ether, benzene, acetic acid) and is only slightly soluble in chloroform in some reports. Phase behavior: diphenyl ether is typically a colorless crystalline solid below its melting point and an oily/colorless liquid above it, often described as having a geranium-like or floral odor in fragrance applications.
Reactivity and Stability
Diphenyl ether is generally stable under normal storage conditions but will react vigorously with strong oxidizing agents; contact with strong acids such as chlorosulfuric acid can produce vigorous reactions. When heated to decomposition it emits carbon oxides and acrid, irritating fumes. The ether linkage is resistant to hydrolysis under neutral to mildly acidic/basic aqueous conditions; oxidative biotransformation and specialized catalytic or microbial pathways can yield hydroxylated and ring‑cleavage products.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
Experimental thermochemical values reported include a heat of combustion of −1466.63 kcal·mol−1 (at 25 °C) and a heat (enthalpy) of vaporization reported as 15.99 kcal·mol−1 at 25 °C. A heat of fusion value of 4.115 kcal·mol−1 is also reported. No comprehensive standard molar heat-capacity function is provided in the current data context. These values indicate the substantial energy required for phase changes and combustion consistent with a substituted aromatic hydrocarbon.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \(\ce{C12H10O}\)
- Molecular weight: 170.21 (as reported)
- Exact/monoisotopic mass: 170.073164938
LogP and Polarity
Lipophilicity is high: reported partition coefficients include XLogP = 4.2 and log K_OW ≈ 4.21. Low polarity (TPSA = 9.2) and zero hydrogen-bond donor count with a single hydrogen-bond acceptor (the ether oxygen) result in strong partitioning into organic phases and propensity for bioaccumulation relative to small polar organics.
Structural Features
Diphenyl ether is an asymmetric-conjugated diaryl ether in which rotation about the aryl–O bonds is possible but delocalization and steric interactions constrain free rotation; rotatable-bond count is reported as 2. The oxygen atom provides a single hydrogen-bond acceptor site but, due to resonance with the rings, the ether oxygen is a weak base. Electronic features include conjugated π-systems on each phenyl ring, which influence UV absorption and stabilize substituted derivatives. The low TPSA and absence of polar functional groups underlie poor aqueous solubility and relatively high octanol partitioning.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS (provided identifier field): 13-12-9
- EC number / EINECS: 202-981-2
- UNII: 3O695R5M1U
- FEMA Number: 3667
- RTECS: KN8970000
- Additional registry identifiers and index codes exist in source collections (not listed exhaustively here).
Also available from structural descriptors:
- SMILES: C1=CC=C(C=C1)OC2=CC=CC=C2
- InChI: InChI=1S/C12H10O/c1-3-7-11(8-4-1)13-12-9-5-2-6-10-12/h1-10H
- InChIKey: USIUVYZYUHIAEV-UHFFFAOYSA-N
(IUPAC name reported as phenoxybenzene.)
Synonyms and Structural Names
Common synonyms recorded for the compound include: phenoxybenzene; diphenyl oxide; phenyl ether; benzene, 1,1'-oxybis-; oxybisbenzene; biphenyl oxide; phenyl oxide; 1,1'-oxydibenzene. Additional vendor and historical names exist for specific commercial preparations and isotope-labelled variants.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Diphenyl ether is used primarily as a component in heat-transfer fluid formulations (often as a eutectic mixture with biphenyl), accounting for the largest industrial demand. Secondary uses include application as a fragrance/flavour ingredient in soaps, detergents and personal-care formulations, as a dye carrier and processing aid in polymer and polyester manufacture, and as an intermediate for electrophilic aromatic reactions (halogenation, acylation, alkylation). It is also a precursor for halogenated diphenyl ether derivatives employed in flame-retardant materials.
Role in Synthesis or Formulations
Diphenyl ether can be manufactured by nucleophilic aromatic substitution routes (e.g., heating phenoxide salts with chlorobenzene or bromobenzene) and is generated as a byproduct in some phenol production processes. In formulation contexts it serves as a solvent or carrier for nonpolar ingredients and as a fragrance fixative; grades offered include technical, perfume, and industrial qualities suitable for the intended downstream application.
Safety and Handling Overview
Acute and Occupational Toxicity
Acute oral toxicity values reported include an LD50 for rats in the low grams-per-kilogram range (examples: 2830 mg·kg−1 and ~3.99 g·kg−1 in separate reports). Inhalation and dermal routes can produce irritation of eyes, skin and the respiratory tract; occupational exposures above odor thresholds may cause nausea. Repeated or prolonged skin contact may cause dermatitis; experimentally observed target-organ toxicity includes liver and kidney effects in high-dose animal studies. Reported occupational exposure limits: PEL/REL/TLV values near 1 ppm (7 mg·m−3) as an 8‑hr TWA, with a STEL of 2 ppm in some guidance. IDLH values have been reported in the range of 100 ppm, but site- and regulator-specific criteria should be consulted when planning emergency response.
First-aid measures: remove affected persons from exposure, flush eyes and skin with water, and seek medical evaluation if symptoms persist; do not induce vomiting following ingestion and provide supportive care as clinically indicated.
Storage and Handling Considerations
Handle diphenyl ether with standard industrial controls for combustible aromatic organics: use local exhaust ventilation to limit airborne concentrations, prevent skin and eye contact with appropriate PPE (safety glasses/face shield, chemical-resistant gloves and protective clothing), and control ignition sources because the substance is combustible and has defined flammability/flammable limits when vaporized or heated. Store in a cool, well-ventilated area protected from strong oxidizers and segregated from incompatible materials. Containers should be tightly closed and stored to prevent environmental release; spills should be contained and collected for disposal without allowing entry into drains or waterways.
For firefighting, appropriate media include dry chemical, carbon dioxide, or alcohol-resistant foam; when heated or involved in fire, containers should be cooled from a safe distance and personnel should use self‑contained breathing apparatus as necessary. Decomposition products may include irritating and toxic fumes (carbon oxides and other combustion products).
For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
