Phenol
Aromatic compound essential for plastics, drugs, and explosives.
Phenol, also known as carbolic acid, phenolic acid, or benzenol, is an aromatic organic compound with the molecular formula C6H5OH. It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group bonded to a hydroxy group, is mildly acidic, and requires careful handling because it can cause chemical burns. It is acutely toxic and considered a health hazard. Phenol was first extracted from coal tar, but today is produced on a large scale (about 7 million tonnes a year) from petroleum-derived feedstocks. It is an important industrial commodity as a precursor to many materials and useful compounds, and is a liquid when manufactured.
- field
- Organic chemistry, industrial chemistry
- known_for
- Precursor to plastics, explosives, pharmaceuticals; cumene process production
- molecular_formula
- C6H5OH
- annual_production
- ~7 million tonnes
- primary_use
- Synthesis of plastics and related materials
Lore & Background
Phenol is a weak acid with a pH range of 5 to 6. In aqueous solution in the pH range ca. 8–12 it is in equilibrium with the phenolate anion. Its enhanced acidity compared to aliphatic alcohols is attributed to resonance stabilization of the phenolate anion, though an alternative explanation involves induction from sp2 hybridised carbons. Phenol exhibits keto-enol tautomerism with its unstable keto tautomer cyclohexadienone, but the equilibrium constant for enolisation is approximately 10−13, meaning only one in every ten trillion molecules is in the keto form at any moment. Phenol therefore exists essentially entirely in the enol form.
Reader's Guide
Phenol is highly reactive toward electrophilic aromatic substitution, with enhanced nucleophilicity attributed to donation of pi electron density from oxygen into the ring. It is so strongly activated that bromination and chlorination lead readily to polysubstitution. Phenol reacts with dilute nitric acid at room temperature to give a mixture of 2-nitrophenol and 4-nitrophenol, while with concentrated nitric acid, additional nitro groups are introduced, e.g., to give 2,4,6-trinitrophenol. Because of phenol's commercial importance, many methods have been developed for its production, but the cumene process is the dominant technology, accounting for 95% of production. This process involves the partial oxidation of cumene via the Hock rearrangement, using mild conditions and inexpensive raw materials. For the process to be economical, both phenol and the acetone by-product must be in demand. Phenol is primarily used to synthesize plastics and related materials, and its chemical derivatives are essential for production of polycarbonates, epoxies, explosives such as picric acid, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides, and numerous pharmaceutical drugs.
Did You Know?
- Phenol is a combustible solid with an NFPA rating of 2, and when heated produces flammable vapors explosive at concentrations of 3 to 10% in air.
- Phenol gives a positive result with the Ceric Ammonium Nitrate (CAN) test, producing a dark brownish precipitate, unlike standard aliphatic alcohols which typically give a pink or red color.
- The cumene process accounts for 95% of phenol production and also yields acetone as a by-product.
Frequently Asked Questions
Who is Phenol?
Phenol is an aromatic organic compound (C6H5OH) that appears as a white, volatile crystalline solid. It goes by several aliases in the chemical world, including carbolic acid, phenolic acid, and benzenol. Its structure pairs a phenyl ring with a hydroxyl group, giving it mild acidity.
What are Phenol's powers and role?
Phenol serves as a critical building block for manufacturing plastics, pharmaceuticals, and explosive materials. It is one of the most heavily traded industrial chemicals, with roughly seven million tonnes produced each year.
How does Phenol's story end?
In modern industry, Phenol's ongoing narrative is told through the cumene process, where it is synthesized at scale from petroleum-derived feedstocks. It remains a foundational feedstock rather than a finished consumer product, so its story continues as long as downstream manufacturing demands it.
Why is Phenol important?
Without Phenol, large-scale production of resins, certain medications, and energetic materials would be severely limited. Its position as a hub molecule in organic synthesis makes it indispensable across multiple industries simultaneously.
What is Phenol's origin story?
Phenol was originally isolated from coal tar during the early industrial era. Today, however, the vast majority is manufactured synthetically from petrochemical feedstocks, shifting its backstory from a natural extract to a large-scale engineered product.
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