Phenols - Reactions of phenols (Due to -OH group- phenols do not resemble to alcohols)

  • Phenols are aromatic compounds containing a hydroxyl group (-OH) attached to a benzene ring.
  • The presence of the hydroxyl group in phenols gives them unique properties and reactions that are different from alcohols.
  • In this lecture, we will explore the reactions of phenols and understand the reasons behind their distinct behavior.
  • Some of the important reactions of phenols include:
    1. Electrophilic aromatic substitution reactions
    2. Oxidation reactions
    3. Condensation reactions
    4. Reactions with metal ions
    5. Reactions with halogens

Electrophilic Aromatic Substitution Reactions

  • Phenols undergo electrophilic aromatic substitution reactions due to the presence of the electron-donating hydroxyl group.
  • These reactions involve the substitution of a hydrogen atom on the benzene ring with an electrophile.
  • Common electrophilic aromatic substitution reactions of phenols include:
    • Nitration
    • Halogenation
    • Friedel-Crafts acylation
    • Friedel-Crafts alkylation
  • The hydroxyl group in phenols enhances the nucleophilicity of the benzene ring, making it more susceptible to attack by electrophiles.

Oxidation Reactions of Phenols

  • Phenols can be oxidized to quinones, which are important compounds with diverse applications.

  • Oxidation of phenols can be achieved by various oxidizing agents such as:

    • Br₂
    • HNO₃
    • KMnO₄

  • The oxidation of phenols leads to the formation of o- and p-quinones.

  • Quinones are highly reactive and can undergo further reactions like nucleophilic addition or reduction.

Condensation Reactions of Phenols

  • Phenols undergo condensation reactions to form various derivatives.
  • One such important condensation reaction is the formation of ethers.
  • Phenols can be reacted with alkyl halides or alkyl sulfates to produce alkyl aryl ethers.
  • The reaction is catalyzed by a strong base like sodium hydroxide (NaOH).
  • The resulting alkyl aryl ethers have a wide range of applications in pharmaceuticals, fragrances, and solvents.

Reactions of Phenols with Metal Ions

  • Phenols can form complexes with metal ions due to the presence of the hydroxyl group.
  • These complexes are commonly known as phenolates and are formed by the ionization of phenols.
  • The metal ion binds with the oxygen atom of the hydroxyl group, leading to the formation of stable complexes.
  • Phenolates can act as ligands in coordination complexes and exhibit interesting properties such as antioxidant activity.

Reactions of Phenols with Halogens

  • Phenols react with halogens (Cl₂ or Br₂) to form halogenated derivatives.
  • The reaction takes place in the presence of a Lewis acid catalyst such as FeCl₃.
  • Halogenation of phenols occurs at the ortho and para positions of the benzene ring due to the directing effect of the hydroxyl group.
  • The resulting halogenated derivatives have different chemical properties and applications compared to phenols.

These were some of the important reactions of phenols that make them distinct from alcohols. Understanding these reactions will help us appreciate the unique properties of phenols in various chemical processes and applications.

Sure, here are slides 11 to 20 on the topic “Phenols - Reactions of phenols (Due to -OH group- phenols do not resemble to alcohols)”:

Nitration of Phenols

  • Nitration of phenols involves the substitution of a hydrogen atom on the benzene ring with a nitro group (-NO₂).
  • The reaction is carried out by treating phenols with a mixture of concentrated nitric acid (HNO₃) and concentrated sulfuric acid (H₂SO₄).
  • The ortho and para isomers are obtained in appreciable amounts due to the directing effect of the hydroxyl group.
  • Example: Nitration of phenol results in the formation of ortho-nitrophenol, para-nitrophenol, and a small amount of meta-nitrophenol.
  • Equation: C₆H₅OH + HNO₃ → C₆H₄(OH)(NO₂) + H₂O

Halogenation of Phenols

  • Phenols can undergo halogenation reactions in the presence of a Lewis acid catalyst such as FeCl₃ or FeBr₃.
  • The halogenation occurs at the ortho and para positions on the benzene ring.
  • Example: Halogenation of phenol with bromine (Br₂) in the presence of FeBr₃ gives 2-bromophenol as the major product.
  • Equation: C₆H₅OH + Br₂ → C₆H₄BrOH + HBr

Friedel-Crafts Acylation of Phenols

  • Friedel-Crafts acylation is a reaction where an acyl group (-COR) is introduced onto a benzene ring.
  • Phenols can undergo acylation reactions to form acylated derivatives.
  • The reaction is catalyzed by a Lewis acid catalyst such as AlCl₃ or FeCl₃.
  • Example: Acylation of phenol with acetyl chloride (CH₃COCl) in the presence of AlCl₃ results in the formation of acetophenone.
  • Equation: C₆H₅OH + CH₃COCl → C₆H₅COCH₃ + HCl

Friedel-Crafts Alkylation of Phenols

  • Friedel-Crafts alkylation is a reaction where an alkyl group is introduced onto a benzene ring.
  • Phenols can undergo alkylation reactions to form alkylated derivatives.
  • The reaction is catalyzed by a Lewis acid catalyst such as AlCl₃ or FeCl₃.
  • Example: Alkylation of phenol with methyl chloride (CH₃Cl) in the presence of AlCl₃ leads to the formation of o- and p-cresols.
  • Equation: C₆H₅OH + CH₃Cl → C₆H₄(CH₃)OH + HCl

Oxidation of Phenols

  • Phenols can be oxidized to form quinones, which are important compounds with various applications.
  • Oxidation of phenols can be achieved by various oxidizing agents such as Br₂, HNO₃, or KMnO₄.
  • The resulting quinones can undergo further reactions like nucleophilic addition or reduction.
  • Example: Oxidation of phenol with bromine (Br₂) leads to the formation of 1,4-benzoquinone.
  • Equation: 2 C₆H₅OH + Br₂ → C₆H₄(OH)₂ + 2 HBr

Reactions of Phenols with Metal Ions

  • Phenols can form complexes with metal ions due to the presence of the hydroxyl group.
  • These complexes are commonly known as phenolates and are formed by the ionization of phenols.
  • Phenolates can act as ligands in coordination complexes and exhibit interesting properties such as antioxidant activity.
  • Example: Formation of phenolate complex with copper ion (Cu²⁺).
  • Equation: C₆H₅OH + Cu²⁺ → [C₆H₅O]Cu

Reimer-Tiemann Reaction

  • The Reimer-Tiemann reaction is a reaction where a carbonyl group (-CHO) is introduced onto a benzene ring.
  • Phenols can undergo the Reimer-Tiemann reaction using chloroform (CHCl₃) and a strong base such as hydroxide ion (OH⁻).
  • The reaction is useful for the synthesis of salicylaldehyde, which is an important compound used in the production of aspirin.
  • Example: Reimer-Tiemann reaction of phenol with chloroform and sodium hydroxide (NaOH) forms salicylaldehyde.
  • Equation: 2 C₆H₅OH + CHCl₃ + 2 NaOH → 2 C₆H₄OHCHO + 3 H₂O + 2 NaCl

Kolbe-Schmitt Reaction

  • The Kolbe-Schmitt reaction is a reaction where a carboxylate group (-COO⁻) is introduced onto a benzene ring.
  • Phenols can undergo the Kolbe-Schmitt reaction using carbon dioxide (CO₂) and a strong base such as hydroxide ion (OH⁻).
  • This reaction is used to synthesize salicylic acid, which is a precursor to aspirin.
  • Example: Kolbe-Schmitt reaction of phenol with carbon dioxide and sodium hydroxide (NaOH) forms salicylic acid.
  • Equation: 2 C₆H₅OH + 2 NaOH + CO₂ → 2 C₆H₄(OH)COO⁻Na⁺ + 2 H₂O

Esterification of Phenols

  • Phenols can undergo esterification reactions to form esters.
  • The reaction involves the substitution of the hydroxyl group (-OH) with an alkyl or aryl group.
  • Esterification can be carried out by reacting phenols with carboxylic acids or acid derivatives such as acid chloride or acid anhydride.
  • Example: Esterification of phenol with acetic anhydride (CH₃CO)₂O forms phenyl acetate.
  • Equation: C₆H₅OH + (CH₃CO)₂O → C₆H₅OCOCH₃ + CH₃COOH

Claisen Condensation of Phenols

  • Phenols can undergo the Claisen condensation reaction to form β-diketones.
  • The reaction involves the condensation of two molecules of a phenol derivative, resulting in the formation of a new carbon-carbon bond.
  • The reaction is catalyzed by a strong base like potassium hydroxide (KOH).
  • Example: Claisen condensation of phenol with ethyl acetate forms 2-phenyl-1,3-dioxane-2,4-dione.
  • Equation: C₆H₅OH + CH₃COOC₂H₅ → C₆H₅OCOCH₂COC₂H₅ + C₂H₅OH

These slides provide an overview of some key reactions of phenols and highlight their distinct behavior compared to alcohols. Understanding these reactions will help in further exploring the chemistry and applications of phenols. Sure! Here are slides 21 to 30 on the topic “Phenols - Reactions of phenols (Due to -OH group- phenols do not resemble to alcohols)”:

Reduction of Quinones

  • Quinones, which are oxidized derivatives of phenols, can be reduced back to form phenols.
  • Reduction of quinones can be achieved using reducing agents such as hydrazine (N₂H₄) or sodium borohydride (NaBH₄).
  • Example: Reduction of benzoquinone (C₆H₄O₂) using sodium borohydride forms hydroquinone (C₆H₆O₂).
  • Equation: C₆H₄O₂ + 2 NaBH₄ → C₆H₆O₂ + 2 NaBO₂ + 2 H₂

Reaction with Amines

  • Phenols can react with amines to form N-substituted phenols.
  • The reaction involves the substitution of a hydrogen atom on the phenol with an amine group (-NH₂).
  • Example: Reaction of phenol with aniline (C₆H₅NH₂) forms N-phenylphenylamine.
  • Equation: C₆H₅OH + C₆H₅NH₂ → C₆H₅OC₆H₅NH₂ + H₂O

Lassaigne’s Test

  • Lassaigne’s test is a chemical test used to detect the presence of nitrogen or sulfur-containing compounds.
  • Phenols can undergo Lassaigne’s test to form sodium salts of phenylamines.
  • The test involves the fusion of the compound with metallic sodium and subsequent reactions with water and acid.
  • Example: Lassaigne’s test of phenol forms sodium phenoxide and sodium phenylamine.
  • Equation: C₆H₅OH + Na → C₆H₅ONa + ½ H₂↑

Hydroxylation of Phenols

  • Phenols can undergo hydroxylation reactions to introduce additional hydroxyl groups on the benzene ring.
  • The hydroxylation can be achieved using reagents such as peroxides or potassium permanganate (KMnO₄).
  • Example: Hydroxylation of phenol using hydrogen peroxide (H₂O₂) in the presence of a catalyst forms trihydroxybenzene (C₆H₆O₃).
  • Equation: C₆H₅OH + 3 H₂O₂ → C₆H₆O₃ + 3 H₂O

Dehydration of Phenols

  • Phenols can undergo dehydration reactions to lose a molecule of water and form unsaturated compounds.
  • Dehydration of phenols is usually achieved by heating the compound in the presence of a strong acid catalyst.
  • Example: Dehydration of phenol forms benzene.
  • Equation: C₆H₅OH → C₆H₅

Electrophilic Addition of Phenols - Directing Effect

  • Phenols can undergo electrophilic addition reactions due to the presence of the hydroxyl group.
  • The hydroxyl group acts as an activating and directing group, facilitating the addition reaction at specific positions on the benzene ring.
  • Example: Electrophilic addition of phenol with bromine forms 2,4,6-tribromophenol.
  • Equation: C₆H₅OH + 3 Br₂ → C₆H₂Br₃OH + 3 HBr

Ehrlich Test

  • The Ehrlich test is a chemical test used to detect the presence of phenols.
  • The test involves the reaction of phenols with p-dimethylaminobenzaldehyde in the presence of hydrochloric acid.
  • The reaction produces a pink or red color, indicating the presence of phenols.
  • Example: Positive Ehrlich test of phenol forms a pink or red color complex.

Acid-Catalyzed Esterification of Phenols

  • Phenols can undergo esterification reactions with carboxylic acids in the presence of an acid catalyst.
  • The reaction involves the substitution of the hydroxyl group with an ester (-COO-) group.
  • Example: Acid-catalyzed esterification of phenol with acetic acid (CH₃COOH) forms phenyl acetate.
  • Equation: C₆H₅OH + CH₃COOH → C₆H₅OCOCH₃ + H₂O

Baeyer’s Test for Phenols

  • Baeyer’s test is a chemical test used to differentiate between phenols and other classes of compounds.
  • The test involves the reaction of phenols with neutral ferric chloride (FeCl₃) solution.
  • Phenols form colored complexes with ferric chloride while other compounds do not.
  • Example: Positive Baeyer’s test of phenol forms a purple or violet color complex.

Reimer’s Test

  • Reimer’s test is a chemical test used to differentiate between phenols and other classes of compounds.
  • The test involves the reaction of phenols with chloroform (CHCl₃) in the presence of a strong base such as sodium hydroxide (NaOH).
  • Phenols undergo hydroxychlorination to form dichlorocarbene, which further reacts with the phenol to form a colored product.
  • Example: Positive Reimer’s test of phenol forms a violet or purple color solution.

These slides provide additional information on various reactions of phenols and related chemical tests. Understanding these reactions and tests will further enhance our knowledge and help us in the study of chemistry.