Phenol Preparation from Cumene, Benzene Sulphonic Acid, Chlorobenzene & Aniline
Preparation of Phenol is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. This concept is a cornerstone of Organic Chemistry, directly connecting to the synthesis of many daily-use chemicals, medicines, and polymers.
What is Preparation of Phenol in Chemistry?
A phenol refers to an aromatic compound where a hydroxyl group (-OH) is directly bonded to a benzene ring. This concept appears in chapters related to alcohols, aromatic hydrocarbons, and phenolic compounds, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of phenol is C6H5OH. It consists of a benzene (aromatic) ring attached to a single hydroxyl group. Phenol is categorized under aromatic alcohols or hydroxybenzenes and is also known as carbolic acid.
Preparation and Synthesis Methods
Phenol can be prepared by both industrial and laboratory methods. The most common routes include the cumene process, Dow’s process (from chlorobenzene), alkaline fusion of benzene sulphonic acid, and hydrolysis of diazonium salts. Each method uses unique reagents and steps suited for large-scale or small-scale synthesis.
Physical Properties of Phenol
Phenol is a white crystalline solid with a sweet, tarry odor. Its melting point is about 40.5°C, and the boiling point is 181.7°C. Phenol is moderately soluble in water, slightly acidic (pKa ≈ 9.95), and has a density of 1.07 g/cm3. It reacts with blue litmus, turning it slightly red, and forms colored complexes with FeCl3.
Preparation of Phenol: Stepwise Methods
The preparation of phenol involves several distinct routes:
- Cumene Process (Industrial):
Isopropylbenzene (cumene) is oxidized by air to form cumene hydroperoxide, which is then treated with dilute acid to yield phenol and acetone as a byproduct.
C6H5CH(CH3)2 + O2 → Cumene hydroperoxide
Cumene hydroperoxide + H+ → C6H5OH + (CH3)2CO - Dow’s Process (from Chlorobenzene):
Chlorobenzene is fused with NaOH at 623K and 320 atm to give sodium phenoxide, which upon acidification with HCl forms phenol.
C6H5Cl + 2NaOH → C6H5ONa + NaCl + H2O
C6H5ONa + HCl → C6H5OH + NaCl - From Benzene Sulphonic Acid:
Benzenesulphonic acid is fused with NaOH to get sodium phenoxide, which gives phenol on acidification.
C6H5SO3H + NaOH → C6H5ONa + Na2SO3 + H2O
C6H5ONa + HCl → C6H5OH + NaCl - From Diazonium Salts:
Benzene diazonium chloride (from aniline) is hydrolyzed by warming with water, yielding phenol.
C6H5N2Cl + H2O → C6H5OH + N2 + HCl
Chemical Properties and Reactions
Phenol is mildly acidic, forms salts with strong bases, and is highly reactive towards electrophilic substitution (such as bromination and nitration). It also forms esters and ethers, and shows color change with iron(III) chloride solution.
Frequent Related Errors
- Mixing up phenol preparation methods and confusing industrial (cumene) with laboratory methods (Dow’s, sulfonic acid).
- Forgetting to acidify sodium phenoxide to get phenol.
- Using the wrong temperature or pressure in Dow’s process.
- Ignoring the byproduct (acetone) in the cumene process.
Uses of Phenol in Real Life
Phenol is widely used in industries for making Bakelite, polycarbonate plastics, detergents, and pharmaceuticals. It acts as a starting material for phenolphthalein (indicator), disinfectants, and has application in DNA extraction and preservatives. Learn more about its applications on Vedantu.
Relation with Other Chemistry Concepts
Preparation of phenol is closely related to concepts like chemical reactions of phenol and benzene chemistry. It helps students understand substitution, oxidation, and laboratory conversion reactions between aromatic compounds.
Step-by-Step Reaction Example
1. Start with chlorobenzene as the substrate.2. React chlorobenzene with sodium hydroxide at 623K under 320 atm pressure.
3. Sodium phenoxide is formed.
4. Acidify the solution with hydrochloric acid.
5. Phenol is obtained as the final product.
Lab or Experimental Tips
Remember to use protective gloves when handling phenol due to its caustic nature. Vedantu educators often demonstrate the color change with FeCl3 as an easy test for phenol. Always cool exothermic reactions and work in a ventilated fume hood for safety.
Try This Yourself
- Write the IUPAC name of phenol.
- Give one equation for the preparation of phenol from benzene sulphonic acid.
- Name a real-life application of phenol in plastics or medicine.
Final Wrap-Up
We explored preparation of phenol—its structure, synthesis methods, reactions, and practical importance. For detailed diagrams and notes, or to clarify doubts about phenol chemistry, explore live and recorded sessions by expert teachers on Vedantu.
Related topics you can read more about: Phenolphthalein, Benzene, Uses of Phenol.
FAQs on Preparation of Phenol: Stepwise Methods and Reactions
1. What are the different methods of preparation of phenol?
Phenol can be prepared by several methods, each with specific reagents and conditions:
- Cumene process (oxidation of cumene followed by acidic hydrolysis)
- From benzene sulphonic acid (alkaline fusion and acidification)
- From chlorobenzene (Dow’s process with NaOH at high temperature and pressure)
- From diazonium salts (hydrolysis of benzene diazonium salt)
- From aniline (conversion to diazonium salt, then hydrolysis)
2. How is phenol prepared from cumene?
The cumene process is the main industrial method for phenol production:
- Oxidation: Cumene (isopropylbenzene) is oxidized with air to form cumene hydroperoxide.
- Acidic Hydrolysis: Cumene hydroperoxide is treated with dilute acid to yield phenol and acetone as a byproduct.
This process is widely used due to its high efficiency and valuable co-product formation.
3. Which reagent is used in Dow’s process for phenol?
The key reagent in Dow’s process is aqueous sodium hydroxide (NaOH):
- Chlorobenzene is heated with fused NaOH (at 623 K and 300 atm of pressure).
- This produces sodium phenoxide, which is then acidified to obtain phenol.
4. How can you prepare phenol from benzene sulphonic acid?
Phenol is obtained from benzene sulphonic acid by two main steps:
- Alkaline Fusion: Benzene sulphonic acid is fused with solid sodium hydroxide (NaOH) at high temperature to form sodium phenoxide.
- Acidification: Sodium phenoxide is treated with dilute acid to yield phenol.
5. Why is the cumene process widely used for industrial phenol production?
The cumene process is preferred in industry for these reasons:
- It uses readily available raw materials (benzene and propene).
- Produces phenol with high purity and efficiency.
- Forms acetone as a valuable byproduct.
- Lower energy consumption compared to older methods.
6. What is the role of diazonium salts in the preparation of phenol?
Benzene diazonium salts are important intermediates for phenol synthesis:
- Aniline is converted to benzene diazonium chloride using sodium nitrite and hydrochloric acid at low temperature.
- Diazonium salt is then hydrolyzed with warm water to produce phenol and nitrogen gas.
7. How does the electronic effect of benzene ring influence phenol synthesis?
The electronic effects of the benzene ring affect both the reaction rate and product yield.
- Electron-donating groups activate the ring, making reactions like halogenation and sulphonation easier, thus facilitating phenol synthesis.
- Electron-withdrawing groups deactivate the ring and may reduce yield or require harsher conditions.
8. What safety precautions should be followed during phenol preparation in the laboratory?
Safety is essential when handling phenol and its precursors:
- Wear gloves, goggles, and lab coats to prevent skin and eye contact.
- Work in a well-ventilated area or under a fume hood due to phenol’s toxic vapors.
- Handle all reagents carefully following laboratory protocols.
9. What are the important uses of phenol?
Phenol has a variety of significant applications:
- Manufacture of plastics (phenol-formaldehyde resin), detergents, and pharmaceuticals.
- Used as an antiseptic and disinfectant.
- Raw material for dyes, explosives, and synthetic fibers.
- Preparation of laboratory indicators such as phenolphthalein.
10. How is phenol obtained from aniline?
Phenol is prepared from aniline by the following steps:
- Convert aniline to benzene diazonium salt by treating it with sodium nitrite and hydrochloric acid at 273–278 K.
- Warm the diazonium salt with water to hydrolyze it, producing phenol and nitrogen gas.
11. What are the main byproducts in industrial phenol manufacturing?
Common byproducts depend on the preparation method used:
- In the cumene process, acetone is formed as a valuable co-product.
- Other methods may generate inorganic salts (e.g., NaCl, Na2SO4) or minor organic compounds.
12. How does the structure of phenol affect its chemical reactivity compared to simple alcohols?
Phenol is more reactive than simple alcohols due to its aromatic structure:
- Hydroxyl group (-OH) is directly attached to an aromatic ring, enabling resonance stabilization of the phenoxide ion.
- Phenol acts as a stronger acid and undergoes electrophilic substitution more easily than aliphatic alcohols.
