Catechol (benzene-1,2-diol) is a dihydric phenol with two -OH groups attached to adjacent carbon atoms of the benzene ring. Other dihydric phenols include resorcinol (1,3-) and quinol/hydroquinone (1,4-).

Resorcinol is a dihydric phenol with two -OH groups at positions 1 and 3 on the benzene ring. Its IUPAC name is benzene-1,3-diol, indicating the positions of the two hydroxyl groups.

m-Cresol has a methyl group at the meta position (position 3) relative to the -OH group. In IUPAC nomenclature, this is named as 3-methylphenol, where phenol is the parent compound.

The phenoxide ion (C6H5O-) is stabilized by resonance. The negative charge on oxygen is delocalized into the benzene ring through resonance structures, where the charge appears at ortho and para positions. This extensive delocalization makes phenoxide ion more stable.

In phenol, the oxygen atom has a partial double bond character with the benzene ring due to resonance. The lone pair on oxygen overlaps with the pi system of the ring, giving partial double bond character to the C-O bond, making it shorter than the pure single C-O bond in methanol.

The cumene process involves oxidation of cumene (isopropylbenzene) with air to form cumene hydroperoxide, which is then treated with dilute acid to give phenol and acetone. This is the major industrial method: C6H5-CH(CH3)2 + O2 → C6H5OH + (CH3)2CO.

Dow’s process involves the reaction of chlorobenzene with sodium hydroxide at high temperature (623 K) and high pressure (300 atm) to form sodium phenoxide, which on acidification gives phenol: C6H5Cl + 2NaOH → C6H5ONa + NaCl + H2O, then C6H5ONa + HCl → C6H5OH + NaCl.

Benzene sulphonic acid is fused with sodium hydroxide at high temperature (around 573 K) to form sodium phenoxide, which on acidification gives phenol: C6H5SO3H + 3NaOH → C6H5ONa + Na2SO3 + H2O. This is known as alkali fusion.

Benzene diazonium chloride undergoes hydrolysis when warmed with water. The diazonium group (-N2+) is replaced by the hydroxyl group (-OH) to form phenol: C6H5-N2+Cl- + H2O → C6H5OH + N2 + HCl. Nitrogen gas is evolved.

Phenol molecules form strong intermolecular hydrogen bonds due to the presence of the -OH group. These hydrogen bonds require significant energy to break, resulting in a higher boiling point (455 K) compared to toluene (384 K), which only has van der Waals forces.

Phenol can form hydrogen bonds with water molecules through its -OH group, which makes it soluble to some extent. However, the large hydrophobic benzene ring limits its solubility. Phenol is more soluble than benzene but less soluble than alcohols of similar molecular mass.

Phenol is more acidic than ethanol because the phenoxide ion (C6H5O-) formed after loss of H+ is stabilized by resonance with the benzene ring. In ethoxide ion (C2H5O-), no such resonance stabilization is possible. Greater stability of the conjugate base means higher acidity.

Phenol is more acidic than water but less acidic than carboxylic acids. Phenol reacts with NaOH (strong base) to form sodium phenoxide but does not react with weak bases like NaHCO3. The pKa of phenol is around 10, water is 15.7, and carboxylic acids are around 4-5.

Phenol being acidic reacts with sodium hydroxide (a strong base) to form sodium phenoxide and water: C6H5OH + NaOH → C6H5ONa + H2O. This reaction demonstrates the acidic nature of phenol, which is stronger than alcohols but weaker than carboxylic acids.

Phenol is a weak acid (pKa around 10) and can only react with strong bases like NaOH. Sodium bicarbonate is a weak base and cannot deprotonate phenol. Only stronger acids like carboxylic acids (pKa around 4-5) can react with NaHCO3 to liberate CO2.

The -OH group activates the benzene ring through +R (resonance) effect. It donates electron density into the ring, particularly at ortho and para positions through resonance. This makes these positions electron-rich and more reactive toward electrophilic substitution reactions.

Phenol reacts with bromine water without any catalyst to give 2,4,6-tribromophenol as a white precipitate. The -OH group strongly activates the benzene ring, making it highly reactive. All three ortho and para positions get substituted: C6H5OH + 3Br2 → C6H2Br3OH + 3HBr.

Nitration of phenol with dilute HNO3 at room temperature gives a mixture of ortho-nitrophenol and para-nitrophenol. With concentrated HNO3, 2,4,6-trinitrophenol (picric acid) is formed. The -OH group activates the ring and directs the incoming nitro groups to ortho and para positions.

Phenol cannot undergo Friedel-Crafts alkylation under normal conditions with AlCl3 catalyst because phenol reacts with AlCl3 (a Lewis acid) to form a complex. The reaction is better performed by first protecting the -OH group as an ester or ether, or by using phenoxide salt instead of phenol.

Phenol reacts with acetyl chloride (CH3COCl) in the presence of a base like pyridine or NaOH to form phenyl acetate (C6H5OCOCH3). This is an esterification reaction where the -OH group is converted to an ester: C6H5OH + CH3COCl → C6H5OCOCH3 + HCl.

In Kolbe’s reaction, sodium phenoxide is treated with carbon dioxide (CO2) under pressure at 398-400 K, followed by acidification to produce salicylic acid (o-hydroxybenzoic acid). The carboxyl group enters at the ortho position: C6H5ONa + CO2 → C6H4(OH)COONa → C6H4(OH)COOH.

The Reimer-Tiemann reaction involves treating phenol with chloroform (CHCl3) and sodium hydroxide to form salicylaldehyde (o-hydroxybenzaldehyde). The -CHO group enters at the ortho position: C6H5OH + CHCl3 + 3NaOH → C6H4(OH)CHO + 3NaCl + 2H2O.

In Williamson ether synthesis, sodium phenoxide (not free phenol) reacts with alkyl halides to form phenyl alkyl ethers (anisole derivatives). For example: C6H5ONa + CH3I → C6H5OCH3 (anisole) + NaI. This is an SN2 reaction.

Oxidation of phenol with strong oxidizing agents like chromic acid (H2CrO4) or sodium dichromate leads to the formation of benzoquinone (p-benzoquinone or quinone). The reaction involves oxidation at the para position: C6H5OH → C6H4O2 (benzoquinone).

When phenol is heated with zinc dust (a reducing agent), the aromatic ring is reduced to give benzene. The -OH group is removed in the process: C6H5OH + Zn → C6H6 + ZnO. Alternatively, hydrogenation with catalyst can give cyclohexanol.

Catalytic hydrogenation of phenol using Ni or Pt catalyst and H2 gas reduces the benzene ring to a cyclohexane ring while retaining the -OH group, producing cyclohexanol: C6H5OH + 3H2 → C6H11OH (cyclohexanol).

Strong electron-withdrawing groups like -NO2 (nitro group) increase the acidity of phenol by stabilizing the phenoxide ion through -I and -R effects. The nitro group withdraws electron density, making the O-H bond more polar and the phenoxide ion more stable. p-Nitrophenol is more acidic than phenol.

Cresols are methylphenols with three isomers: o-cresol (2-methylphenol), m-cresol (3-methylphenol), and p-cresol (4-methylphenol). They have antiseptic properties and are used in disinfectants. They are more effective antiseptics than phenol.

Carbolic acid is the common name for phenol (C6H5OH). It was historically used as an antiseptic and disinfectant. The term ‘carbolic’ comes from its derivation from coal tar. Phenol was first isolated from coal tar and was one of the earliest antiseptics used in surgery.

Resorcinol (benzene-1,3-diol) is used in medicines, particularly in the treatment of skin disorders like acne, eczema, and psoriasis. It is also used in the manufacture of dyes, pharmaceuticals, and as a chemical intermediate. It has antiseptic and disinfectant properties.