# Biphenol
**Biphenol** most commonly refers to 4,4'-biphenol (4,4'-dihydroxybiphenyl, [1,1'-biphenyl]-4,4'-diol), an organic compound with the formula C₁₂H₁₀O₂ consisting of two phenol rings joined by a single carbon–carbon bond with a hydroxyl group para to that bond on each ring[1](https://pubchem.ncbi.nlm.nih.gov/compound/%281%2C1%27-Biphenyl%29-4%2C4%27-diol). The name is also used generically for any dihydroxybiphenyl, including the 2,2'- and 2,4'- isomers[2](https://pubchem.ncbi.nlm.nih.gov/compound/15731) • [3](https://pubchem.ncbi.nlm.nih.gov/compound/2%2C4%27-dihydroxybiphenyl). The 4,4' isomer is used as a raw material for polyesters, polycarbonates, polysulfones, and polyepoxides[4](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025).
| Key fact | Detail |
|---|---|
| Identity | [1,1'-Biphenyl]-4,4'-diol; CAS Registry Number 92-88-6; synonyms include 4,4'-dihydroxybiphenyl, p,p'-biphenol, and Antioxidant DOD[5](https://webbook.nist.gov/cgi/cbook.cgi?ID=C92886&Mask=220D) |
| Formula and mass | C₁₂H₁₀O₂, molecular weight 186.21 g/mol (PubChem CID 7112)[1](https://pubchem.ncbi.nlm.nih.gov/compound/%281%2C1%27-Biphenyl%29-4%2C4%27-diol) |
| Melting point | 278–283 °C[6](https://www.guidechem.com/dictionary/en/92-88-6.html) |
| Principal uses | Raw material for polyesters, polycarbonates, polysulfones, and polyepoxides; also a stabilizer and dyestuff intermediate[7](https://cir.nii.ac.jp/crid/1390001205277585408) • [8](https://patents.google.com/patent/US4723046A/en) |
| Main industrial route | Oxidative coupling of 2,6-di-tert-butylphenol followed by dealkylation of the tetra-tert-butyl product[7](https://cir.nii.ac.jp/crid/1390001205277585408) • [9](https://patents.google.com/patent/US5324868A/en) |
| Alternative routes | Decomposition and dehydrogenation of 4,4-bis(4-hydroxyphenyl)cyclohexanol; nickel-catalyzed coupling of p-iodophenol under ultraviolet light[8](https://patents.google.com/patent/US4723046A/en) • [10](https://eureka.patsnap.com/patent-CN114031484A) |
| Natural occurrence | Reported in the cyanobacterium *Nostoc insulare*[1](https://pubchem.ncbi.nlm.nih.gov/compound/%281%2C1%27-Biphenyl%29-4%2C4%27-diol) |
## Properties and identity
4,4'-Biphenol is a member of the hydroxybiphenyls, defined as biphenyl bearing hydroxy groups at positions 4 and 4'[1](https://pubchem.ncbi.nlm.nih.gov/compound/%281%2C1%27-Biphenyl%29-4%2C4%27-diol). Its two phenolic hydroxyl groups undergo substitution and oxidation reactions, giving access to many derivatives[4](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025). The compound combines thermal stability, chemical resistance, and mechanical strength, properties that follow from its rigid, symmetric, rod-like biphenyl skeleton[4](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025). It is classified as hazardous under the US OSHA Hazard Communication Standard, with a "Warning" signal word on supplier safety data sheets[11](https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AC173671000&productDescription=P+P-BIPHENOL+100GR&vendorId=VN00032119).
## Uses in polymers and specialty materials
The 1991 review by Iwane, Sugawara, and Imanari of Mitsubishi Petrochemical's Tsukuba Research Center describes 4,4'-biphenol derivatives as very useful raw materials for polyesters, polycarbonates, polysulfones, and polyepoxides[7](https://cir.nii.ac.jp/crid/1390001205277585408). A patent background from the same era adds use as a stabilizer and dyestuff intermediate, and notes particular attention as a material for high-temperature resistant resin[8](https://patents.google.com/patent/US4723046A/en).
**Liquid crystalline materials.** The biphenol group's high aspect ratio offers good thermal properties and mesophase stability. Diglycidyl ether of 4,4'-dihydroxybiphenol is a liquid crystalline epoxy, and two liquid crystalline epoxy resins based on the biphenol mesogen (rigid rod-like molecular unit that promotes liquid-crystal behavior) were synthesized and cured with diaminodiphenylsulfone (DDS) and diaminodiphenylester (DDE) to produce highly heat-resistant liquid crystalline networks[12](https://www.sciencedirect.com/science/article/abs/pii/S0032386198001013). Wholly aromatic thermotropic polyesters have been prepared from 4,4'-biphenol and its phenyl-substituted derivatives with aromatic dicarboxylic acids by melt polycondensation[13](https://onlinelibrary.wiley.com/doi/pdf/10.1002/pola.10097). The compound also serves as a modifying monomer in polyurethanes and liquid crystal materials, and in the synthesis of pharmaceuticals and pesticides[4](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025).
## Manufacturing routes
A 1991 review lists the established manufacturing processes for 4,4'-biphenol as the phenol process, the 2,6-di-tert-butylphenol process, the 4-halophenol process, the 4,4'-diisopropylbiphenyl process, the 4,4'-dihalobiphenyl process, the alkaline fusion process, and the 4-hydroxycyclohexanone process[7](https://cir.nii.ac.jp/crid/1390001205277585408). Earlier chemistry included diazo decomposition of benzidine, reported in *Chemische Berichte*, and alkali fusion of sodium 4,4-biphenyldisulfonate, patented in 1942[8](https://patents.google.com/patent/US4723046A/en).
**Oxidative coupling of 2,6-di-tert-butylphenol.** The most widely investigated recent route couples 2,6-di-tert-butylphenol oxidatively to 3,3',5,5'-tetra-tert-butyl-4,4'-biphenol, then removes the tert-butyl groups. A European patent describes preparing high-purity p,p'-biphenol by this oxidative coupling followed by thermal dealkylation and product recovery by distillation[14](https://data.epo.org/publication-server/rest/v1.2/publication-dates/19821201/patents/EP0013436NWB1/document.pdf). A Mitsubishi Chemical method carries the debutylation out continuously in 2 to 5 reactors aligned in series, in an organic solvent such as chlorobenzene, toluene, xylene, or decalin, in the presence of a sulfonic acid or Lewis acid catalyst[9](https://patents.google.com/patent/US5324868A/en). A 2023 Chinese patent specifies the coupling step as 2,6-di-tert-butylphenol with an alkali metal or [alkaline earth metal](https://www.edgepedia.org/alkaline-earth-metal) hydroxide or weakly acidic salt and a catalyst, with oxygen introduced at 100–150 °C for 3–5 h[15](https://patents.google.com/patent/CN115626866A/en). A [University of Glasgow](https://www.edgepedia.org/university-of-glasgow) thesis states that the current manufacturing route to 4,4'-biphenol uses the oxidative coupling of 2,6-di-tert-butylphenol[16](https://theses.gla.ac.uk/71783/1/10391427.pdf).
**Cyclohexanol precursor route.** US Patent 4,723,046 introduces 4,4-bis(4-hydroxyphenyl)cyclohexanol, a novel precursor made by acid-catalyzed condensation of 4-hydroxycyclohexanone with phenol at 30–100 °C, preferably 40–70 °C[8](https://patents.google.com/patent/US4723046A/en). Subjecting this precursor to decomposition and dehydrogenation at 100–400 °C in the presence of a dehydrogenation catalyst, with α-methylstyrene as hydrogen acceptor, gave 4,4'-biphenol of 85.8% purity by liquid chromatography in an example, with p-phenylphenol as the impurity and an 83% yield on a purity basis[8](https://patents.google.com/patent/US4723046A/en).
**Direct coupling routes.** A 2022 Chinese patent describes a one-step synthesis in which a nickel catalyst promotes coupling of p-iodophenol under ultraviolet irradiation, avoiding intermediate separation and simplifying workup[10](https://eureka.patsnap.com/patent-CN114031484A). More broadly, oxidative coupling of phenols, which forms the biaryl C–C bond directly, has been explored with metal catalysts (V, Cr, Co, Fe, Cu), electrochemical methods, and photochemical methods[17](https://www.sciencedirect.com/org/science/article/pii/S1615415024005624). Laboratory examples include regioselective coupling with K₂S₂O₈ in trifluoroacetic acid under ambient conditions[18](https://pubs.rsc.org/en/content/articlelanding/2017/cc/c7cc04829g) and visible-light-driven coupling promoted by di-tert-butyl peroxide under metal-free conditions[19](https://www.sciencedirect.com/org/science/article/abs/pii/S1434193X22083244).
## Supply and purity
Although 4,4'-biphenol is used across multiple industries, a 2026 review from Lanzhou Petrochemical University of Vocational Technology and the Gansu Research Institute of Chemical Industry reports that high-purity (99.5%) product is still entirely dependent on imports in China, and that its synthesis faces significant challenges[4](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025). That review sorts the synthetic approaches into four groups: oxidative coupling of phenols, modifying functional groups while retaining a biphenyl backbone, building the biphenyl framework from 4-hydroxyphenyl starting materials, and approaches using other substrates[4](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025).
## Isomers and related compounds
The term biphenol covers several positional isomers sharing the formula C₁₂H₁₀O₂. 2,2'-Biphenol ([1,1'-biphenyl]-2,2'-diol, PubChem CID 15731) carries hydroxy groups ortho to the ring–ring bond and is a backbone for ligand systems in transition-metal catalysis; 3,3',5,5'-tetramethyl-2,2'-biphenol, made by oxidative homocoupling of 2,4-dimethylphenol, is used in hydroformylation catalysis[2](https://pubchem.ncbi.nlm.nih.gov/compound/15731) • [20](https://pmc.ncbi.nlm.nih.gov/articles/PMC10614056/). 2,4'-Biphenyldiol ([1,1'-biphenyl]-2,4'-diol, CID 123079) is the unsymmetrical isomer[3](https://pubchem.ncbi.nlm.nih.gov/compound/2%2C4%27-dihydroxybiphenyl). The 3,3',5,5'-tetramethyl derivative of 4,4'-biphenol was the subject of a dedicated process developed at Mitsubishi Petrochemical[7](https://cir.nii.ac.jp/crid/1390001205277585408). Oxidative coupling of plain phenol by horseradish peroxidase yields mixtures including o,o'-, p,p'-, and o,p'-biphenol dimers alongside phenoxyphenols[21](https://www.sciencedirect.com/science/article/abs/pii/0045653594900280).
## References
1. [4,4'-Dihydroxybiphenyl, PubChem CID 7112](https://pubchem.ncbi.nlm.nih.gov/compound/%281%2C1%27-Biphenyl%29-4%2C4%27-diol)
2. [(1,1'-Biphenyl)-2,2'-diol, PubChem CID 15731](https://pubchem.ncbi.nlm.nih.gov/compound/15731)
3. [(1,1'-Biphenyl)-2,4'-diol, PubChem CID 123079](https://pubchem.ncbi.nlm.nih.gov/compound/2%2C4%27-dihydroxybiphenyl)
4. [Zhang Huaiyuan et al. Recent Advances in the Synthesis of 4,4′-biphenol. Chinese Journal of Organic Chemistry](https://sioc-journal.cn/Jwk_yjhx/EN/10.6023/cjoc202606025)
5. [[1,1'-Biphenyl]-4,4'-diol, NIST WebBook](https://webbook.nist.gov/cgi/cbook.cgi?ID=C92886&Mask=220D)
6. [4,4'-Biphenol 92-88-6, Guidechem Chemical Dictionary](https://www.guidechem.com/dictionary/en/92-88-6.html)
7. [Iwane H., Sugawara T., Imanari M. Recent Progress in the Manufacturing Process for 4,4'-Biphenol Derivatives. Journal of Synthetic Organic Chemistry, Japan 49 (12), 1119–1126, 1991](https://cir.nii.ac.jp/crid/1390001205277585408)
8. [US4723046A, Process for the preparation of 4,4'-biphenol, Google Patents](https://patents.google.com/patent/US4723046A/en)
9. [US5324868A, Method for preparing 4,4'-biphenol, Mitsubishi Chemical Corp, Google Patents](https://patents.google.com/patent/US5324868A/en)
10. [CN114031484A, Method for synthesizing 4,4'-biphenol, Patsnap Eureka](https://eureka.patsnap.com/patent-CN114031484A)
11. [Safety Data Sheet, 4,4'-Biphenol, Fisher Scientific](https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AC173671000&productDescription=P+P-BIPHENOL+100GR&vendorId=VN00032119)
12. [Lee J.Y. et al. Synthesis and curing of liquid crystalline epoxy resins based on 4,4′-biphenol. Polymer 39 (24), 1998](https://www.sciencedirect.com/science/article/abs/pii/S0032386198001013)
13. [Bhowmik P.K. et al. Thermotropic liquid-crystalline polyesters of 4,4′-biphenol and phenyl-substituted 4,4′-biphenols. Journal of Polymer Science Part A, 2002](https://onlinelibrary.wiley.com/doi/pdf/10.1002/pola.10097)
14. [EP 0013436 B1, Process for preparing p,p'-biphenol of high purity, European Patent Office](https://data.epo.org/publication-server/rest/v1.2/publication-dates/19821201/patents/EP0013436NWB1/document.pdf)
15. [CN115626866A, Industrial synthesis method of high-purity 4,4'-diphenol compound, Google Patents](https://patents.google.com/patent/CN115626866A/en)
16. [University of Glasgow thesis on polyether liquid crystals and 4,4'-biphenol manufacture](https://theses.gla.ac.uk/71783/1/10391427.pdf)
17. [Advances in Exploring Mechanisms of Oxidative Phenolic Coupling Reactions. Advanced Synthesis and Catalysis 366 (21), 2024](https://www.sciencedirect.com/org/science/article/pii/S1615415024005624)
18. [More N.Y., Jeganmohan M. Solvent-controlled selective synthesis of biphenols and quinones via oxidative coupling of phenols. Chem. Commun. 2017, 53, 9616](https://pubs.rsc.org/en/content/articlelanding/2017/cc/c7cc04829g)
19. [Visible-light-driven di-tert-butyl peroxide-promoted oxidative homo- and cross-coupling of phenols. European Journal of Organic Chemistry, 2022](https://www.sciencedirect.com/org/science/article/abs/pii/S1434193X22083244)
20. [Improving the Selectivity of C–C Coupled Product Electrosynthesis Using a Molecularly Imprinted Polymer, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10614056/)
21. [Products of oxidative coupling of phenol by horseradish peroxidase. Chemosphere 28 (10), 1994](https://www.sciencedirect.com/science/article/abs/pii/0045653594900280)
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Alcohols, ethers, and organooxygen groups › Phenols and phenolic compounds › Polyhydric phenols (catechols, resorcinols, pyrogallols) › Polyhydric phenols of larger polycyclic arenes*
*Initially written Sep 17, 2026 · Reviewed: Sep 20, 2026; Oct 15, 2026 · Edited: Sep 20, 2026; Oct 15, 2026; Oct 25, 2026 · Last review: Oct 15, 2026*
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