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Objectives of the Unit

• Naming Alcohols, Phenols and Ethers

  • Master the IUPAC nomenclature system for these compounds.

• Preparation Reactions

  • Understand how to prepare alcohols from alkenes, aldehydes, ketones, and carboxylic acids.

  • Discuss preparation of phenols from haloarenes, benzene sulphonic acids, diazonium salts, and cumene.

  • Understand preparation of ethers from alcohols and alkyl halides using sodium alkoxides/aryloxides.

• Physical Properties

  • Correlate the physical properties of alcohols, phenols, and ethers with their chemical structures.

• Chemical Reactions

  • Analyze the chemical reactions of these compounds based on their functional groups.

Importance of Alcohols, Phenols, and Ethers

• Serve as basic compounds in the manufacturing of detergents, antiseptics, and fragrances.

• Substitution of hydrogen in hydrocarbons with -OH creates alcohols and phenols, leading to various applications (e.g., ethanol in spirit for polishing furniture).

• Composed of hydroxyl (-OH) groups, which impact properties and functionalities in everyday compounds like sugars and papers.

Classification of Alcohols and Related Compounds

• Alcohols

  • Contain one or more hydroxyl (-OH) groups attached to carbon in an aliphatic structure (e.g., CH3OH).

  • Types of alcohols:

    • Monohydric: One -OH group

    • Dihydric: Two -OH groups

    • Trihydric: Three -OH groups

    • Polyhydric: Multiple -OH groups

• Phenols

  • Hydroxyl group is attached directly to carbon in an aromatic system (e.g., C6H5OH).

• Ethers

  • Formed when a hydrogen atom in alcohol or phenol is replaced with an alkoxy or aryloxy group (e.g., CH3OCH3).

Types of Alcohols

• Hybridization

  • sp3 Alcohols: Hydroxyl group attached to sp3 hybridized carbon (Primary, Secondary, Tertiary).

  • Allylic: Hydroxyl group attached to a sp3 carbon adjacent to a double bond.

  • Benzylic: Hydroxyl group attached to a sp3 carbon adjacent to an aromatic ring.

  • Vinylic: Hydroxyl group bonded to a vinylic carbon (C=C).

Nomenclature of Alcohols and Phenols

• IUPAC Naming for Alcohols:

  • Replace the 'e' in alkane with 'ol'. Indicate -OH positions with numbers (e.g., propan-1-ol).

  • Polyhydric alcohols keep 'e' and add 'ol' with prefixes (di, tri, etc.) for -OH count.

• Phenols:

  • Common and IUPAC names often retain phenol (e.g., -methylphenols for various substituted phenols).

Preparation of Alcohols

1. From Alkenes:

   • Hydration reactions using acid as catalyst.

   • Hydroboration-oxidation method for producing alcohols in high yield.

2. From Carbonyl Compounds:

   • Reduction of aldehydes and ketones to their alcohol equivalents (using hydrogen or reducing agents like LiAlH4).

   • Carboxylic acids converted into primary alcohols via LiAlH4 reduction.

3. From Grignard Reagents:

   • Reaction with aldehydes and ketones to yield corresponding alcohols.

Preparation of Phenols

1. From Haloarenes:

   • React chlorobenzene with NaOH at high temperature and pressure.

2. From Benzene Sulphonic Acid:

   • Convert sulfonic acid to sodium phenoxide, then acidify to yield phenol.

3. From Diazonium Salts:

   • Hydrolysis of diazonium salts to yield phenols.

4. From Cumene:

   • Oxidize cumene to cumene hydroperoxide, then acidify to yield phenol and acetone.

Physical Properties of Alcohols and Phenols

• Boiling Points:

  • Higher boiling points compared to hydrocarbons of similar molecular weight due to hydrogen bonding.

  • Boiling point increases with molecular mass, but decreases with branching.

• Solubility:

  • Soluble in water due to ability to form hydrogen bonds; solubility reduces with larger hydrophobic groups.

Chemical Properties of Alcohols and Phenols

1. Acidity:

   • Alcohols and phenols can donate protons, with phenols being more acidic due to resonance effects.

2. Reactions involving O-H cleaving:

   • Reaction with metals and sodium hydroxide to form alkoxides/phenoxides.

3. Dehydration of Alcohols:

   • Produces alkenes when treated with acids.

4. Oxidation:

   • Primary alcohols to aldehydes or carboxylic acids, secondary alcohols to ketones, tertiary alcohols resistant to oxidation.

5. Electrophilic Aromatic Substitution in Phenols:

   • Phenols are activated to undergo substitutions at ortho and para positions due to -OH resonance effects.

Preparation of Ethers

• Methods:

  • Dehydration of alcohols under specific conditions;

  • Williamson synthesis using alkyl halides and sodium alkoxides.

  • Consideration of primary alkyl halides for effective SN2 mechanism to ensure ether production.

Chemical Reactions of Ethers

• Ethers exhibit limited reactivity, generally undergoing cleavage only under harsh conditions with hydrogen halides.

• Ethers can be protonated, leading to hydrolysis.

• Similar reactions observed in phenyl-alkyl ethers and aromatic compounds.