Alcohols (Detailed Notes)

Classification of Alcohols

• Primary alcohols: have one alkyl group attached to the carbon atom that bears the -OH group. -Secondary alcohols: have two alkyl groups attached to the carbon atom that bears the -OH group.
• Tertiary alcohols: have three alkyl groups attached to the carbon atom that bears the -OH group.
• Phenols: hydroxyl group is attached to an aromatic ring.

Nomenclature of Alcohols

• IUPAC nomenclature:
• The parent name of an alcohol is derived from the name of the hydrocarbon that corresponds to the longest carbon chain containing the -OH group.
• The suffix “-ol” is added to the parent name to indicate the presence of an alcohol functional group.
• The position of the -OH group is indicated by a number.
• Common names:
• The common name of an alcohol is derived from the name of the alkyl group that is attached to the carbon atom bearing the -OH group.
• The suffix “alcohol” is added to the alkyl group name.

Physical Properties of Alcohols

• Boiling point:
• Alcohols have higher boiling points than alkanes of comparable molecular weight due to hydrogen bonding.
• The boiling point of alcohols increases with increasing molecular weight and with increasing number of -OH groups.
• Melting point:
• Alcohols have lower melting points than alkanes of comparable molecular weight due to hydrogen bonding.
• Density: Alcohols are denser than alkanes of comparable molecular weight due to the presence of the polar -OH group.
• The density of alcohols increases with increasing molecular weight and with increasing number of -OH groups.
• Solubility:
• Alcohols are soluble in water due to hydrogen bonding.
• The solubility of alcohols in water decreases with increasing molecular weight and with increasing number of -OH groups.

Chemical Properties of Alcohols

• Oxidation: Alcohols can be oxidized to aldehydes, ketones, or carboxylic acids.
  • Primary alcohols are oxidized to aldehydes.
  • Secondary alcohols are oxidized to ketones.
  • Tertiary alcohols are oxidized to carboxylic acids.
• Dehydration: Alcohols can be dehydrated to form alkenes.
  • The dehydration of alcohols is a catalyzed reaction.
  • The type of alkene formed depends on the starting alcohol and the reaction conditions.
• Esterification: Alcohols can react with carboxylic acids to form esters.
• The esterification reaction is a catalyzed reaction.
• The product of an esterification reaction is an ester and water.
• Reaction with HX: Alcohols can react with hydrogen halides (HX) to form alkyl halides.
  • The reaction of an alcohol with HX is a substitution reaction.
  • The product of a reaction between an alcohol and HX is an alkyl halide and water.
• Reaction with ROH: Alcohols can react with themselves to form ethers.
  • The reaction of an alcohol with ROH is a condensation reaction.
• The product of a reaction between an alcohol and ROH is an ether and water.

Preparation of Alcohols

• Hydration of alkenes: Alkenes can be hydrated to form alcohols by reacting them with water in the presence of an acid catalyst.
• Hydroboration-oxidation of alkenes: Alkenes can be hydroborated-oxidized to form alcohols by reacting them with diborane followed by hydrogen peroxide and sodium hydroxide.
• Reduction of carbonyl compounds: Carbonyl compounds can be reduced to form alcohols by reacting them with a reducing agent, such as lithium aluminum hydride (LiAlH4) or sodium borohydride (NaBH4).
• Fermentation: Alcohols can be produced by the fermentation of sugars by yeast.

Reactions of Alcohols

• Nucleophilic substitution: Alcohols can undergo nucleophilic substitution reactions with a variety of nucleophiles, such as hydroxide ion, halide ions, and alkoxide ions.
• Elimination: Alcohols can undergo elimination reactions to form alkenes.
  • The elimination of alcohols is a catalyzed reaction.
• The type of alkene formed depends on the starting alcohol and the reaction conditions.
• Oxidation: Alcohols can be oxidized to form aldehydes, ketones, or carboxylic acids.
• The oxidation of alcohols is a catalyzed reaction.
• The type of product formed depends on the starting alcohol and the reaction conditions.
• Esterification: Alcohols can react with carboxylic acids to form esters.
  • The esterification of alcohols is a catalyzed reaction.
  • The product of an esterification reaction is an ester and water.
• Acetylation: Alcohols can react with acetic anhydride to form acetates.
  • The acetylation of alcohols is a catalyzed reaction.
• The product of an acetylation reaction is an acetate and acetic acid.

Uses of Alcohols

• As solvents: Alcohols are used as solvents for a variety of substances, including oils, greases, and paints.
• As fuels: Alcohols can be used as fuels for internal combustion engines.
• In the production of other chemicals: Alcohols are used in the production of a variety of other chemicals, including plastics, detergents, and pharmaceuticals.
• In the food industry: Alcohols are used in the production of alcoholic beverages, flavorings, and preservatives.
• In the pharmaceutical industry: Alcohols are used in the production of a variety of pharmaceuticals, including antibiotics, pain relievers, and antiseptics.
• In the cosmetics industry Alcohols are used in the production of a variety of cosmetics, including perfumes, lotions, and hair products.