Electrophilic substitutions p2 & Diazonium Salts Flashcards
What is phenol and what is its molecular formula?
Phenol is an aromatic compound with the molecular formula C₆H₅OH.
It contains a hydroxyl group (-OH) directly bonded to a benzene ring.
What are the physical properties of phenol?
- Appears as a white crystalline solid at room temperature
- Has a distinctive sweet and tarry odor
- Slightly soluble in water, and solubility increases with temperature
Common uses of phenol
- Production of plastics (e.g., Bakelite)
- Manufacturing of resins, dyes, and pharmaceuticals
- Acts as an antiseptic and disinfectant in dilute solutions
What is the industrial method for synthesizing phenol?
Cumene Process (Hock Process):
Alkylation of benzene: Benzene + propylene → cumene (isopropylbenzene)
Oxidation of cumene: Cumene + O₂ → cumene hydroperoxide
Acid-catalyzed cleavage: Cumene hydroperoxide → phenol + acetone
What are the advantages of the Cumene Process?
- Produces both phenol and acetone, which are valuable industrial chemicals
- Utilizes readily available raw materials (benzene and propylene)
Why is phenol acidic and how does it behave as an acid?
- Phenol is a weak acid (more acidic than alcohols, less than carboxylic acids)
- Can donate a proton to form the phenoxide ion: C₆H₅OH → C₆H₅O⁻ + H⁺
What factors contribute to the acidity of phenol?
- Resonance stabilization: Phenoxide ion is stabilized by resonance
- Inductive effect: The electronegative oxygen withdraws electron density, stabilizing the negative charge
How does the hydroxyl group on phenol affect electrophilic aromatic substitution?
- The -OH group is activating via resonance donation
- It is an ortho/para-directing group
What are the common electrophilic substitution reactions of phenol?
Nitration:
- With dilute HNO₃ → ortho- and para-nitrophenol
- With concentrated HNO₃ → 2,4,6-trinitrophenol (picric acid)
Halogenation:
- Phenol + Br₂ → 2,4,6-tribromophenol (white ppt)
Sulfonation:
Phenol + conc. H₂SO₄ →
- Phenol-2-sulfonic acid (low temp)
- Phenol-4-sulfonic acid (high temp)
What is esterification and how does phenol participate in it?
Esterification:
Phenol reacts with acid chlorides or anhydrides → phenyl esters
Example:
C₆H₅OH + RCOCl → C₆H₅OCOR + HCl
How is Williamson ether synthesis carried out using phenol?
- Phenol reacts with alkyl halides in the presence of a base (like NaOH) to form ethers
- Forms phenoxide, which reacts with R-X → anisole (methoxybenzene)
Describe the oxidation of phenol and its biological relevance.
- Phenol is oxidized to benzoquinone using oxidizing agents (e.g., chromic acid)
- Quinones are important in biological electron transport systems
What happens when phenol reacts with a base?
- With NaOH:
C₆H₅OH + NaOH → C₆H₅O⁻Na⁺ + H₂O - Does not react with NaHCO₃ or Na₂CO₃, showing it’s weaker than carboxylic acids
What are two qualitative tests used to detect phenol?
Ferric Chloride Test:
- Violet color from phenolate complex:
C₆H₅OH + FeCl₃ → violet complex + HCl
Libermann’s Test:
- Phenol + NaNO₂ + H₂SO₄ → deep blue/green color
What are the major phenol derivatives and their uses?
Catechol (1,2-dihydroxybenzene):
- Used in photography, fragrances
Resorcinol (1,3-dihydroxybenzene):
- Used in resins, dyes, chemical intermediate
Hydroquinone (1,4-dihydroxybenzene):
- Used as developing agent and in skin lightening
What are the industrial applications of dihydroxybenzenes?
- Synthesized from phenol
- Used in industrial and pharmaceutical applications
What are the safety and environmental concerns associated with phenol?
Toxicity:
Corrosive, can cause burns
Inhalation/ingestion → systemic toxicity
Environmental Impact:
Pollutant, must be handled and disposed of properly
Wastewater must be treated before disposal
Regulations:
Use PPE
Follow SDS and regulatory guidelines
