Alcohols - Solved Examples
- Example 1:
- Write the IUPAC name of the following compound:
- Solution:
- The IUPAC name of the given compound is “propanol”.
- Example 2:
- Classify the following compounds as primary, secondary, or tertiary alcohols:
- CH3-CH2-OH
- (CH3)2CH-OH
- (CH3)3C-OH
- Solution:
- CH3-CH2-OH is a primary alcohol.
- (CH3)2CH-OH is a secondary alcohol.
- (CH3)3C-OH is a tertiary alcohol.
- Example 3:
- Write the structural formula for the following compounds:
- Solution:
- Ethanol: CH3-CH2-OH
- Isopropanol: (CH3)2CH-OH
- Example 4:
- Classify the following alcohols as primary, secondary, or tertiary:
- Solution:
- 2-butanol is a secondary alcohol.
- Cyclohexanol is a tertiary alcohol.
- Example 5:
- Convert the following alcohol into an alkene:
- Solution:
- By eliminating one molecule of water, CH3-CH=CH2 can be obtained.
Alcohols - Solved Examples
- Example 6:
- Write the balanced chemical equation for the oxidation of a primary alcohol to an aldehyde.
- Solution:
- CH3-CH2-OH + [O] → CH3-CHO + H2O
- Example 7:
- Write the balanced chemical equation for the oxidation of a primary alcohol to a carboxylic acid.
- Solution:
- CH3-CH2-OH + 2[O] → CH3-COOH + H2O
- Example 8:
- Write the balanced chemical equation for the oxidation of a secondary alcohol to a ketone.
- Solution:
- (CH3)2CH-OH + [O] → (CH3)2C=O + H2O
- Example 9:
- Write the balanced chemical equation for the dehydration of an alcohol to form an alkene.
- Solution:
- CH3-CH2-OH → CH2=CH2 + H2O
- Example 10:
- Name the following compound:
- Solution:
- The IUPAC name of the given compound is “butanal”.
Ethers - Introduction
- Definition:
- Ethers are organic compounds that have an oxygen atom bonded to two alkyl or aryl groups.
- General Formula:
- Physical Properties:
- Ethers have a sweet or fruity odor.
- They are less dense than water.
- They have low boiling points compared to alcohols.
- Nomenclature:
- Ethers are named by identifying the two alkyl or aryl groups bonded to the oxygen atom and adding the suffix “-ether”.
Ethers - Preparation Methods
- Preparation Method 1: Williamson Ether Synthesis
- In this method, an alkyl halide reacts with an alkoxide ion to form an ether.
- R-X + R’-O- → R-O-R’ + X-
- Preparation Method 2: Dehydration of Alcohols
- When alcohols are heated with a strong acid catalyst, they undergo dehydration to form ethers.
- 2R-OH → R-O-R’ + H2O
- Preparation Method 3: Alkoxymercuration-Demercuration Reaction
- In this method, an alkene reacts with mercuric acetate and an alcohol to form an ether.
- RCH=CH2 + R’-OH + Hg(OAc)2 → R-O-R’ + Hg(OAc)OH
Ethers - Examples and Uses
- Example: Ethyl Ether
- Molecular Formula: C2H5-O-C2H5
- Common Name: Diethyl Ether
- Uses:
- It is used as a general anesthetic.
- It is used as a solvent in organic synthesis.
- It is used as a starting material for the production of other chemicals.
- Example: Methyl Tert-Butyl Ether (MTBE)
- Molecular Formula: (CH3)3C-O-CH3
- Uses:
- It is used as an octane booster in gasoline.
- It is used as a solvent for paints, varnishes, and adhesives.
- Example: Dimethyl Ether (DME)
- Molecular Formula: CH3-O-CH3
- Uses:
- It is used as a propellant in aerosol products.
- It is used as a clean-burning alternative fuel for diesel engines.
Epoxides - Introduction
- Definition:
- Epoxides, also known as oxiranes, are three-membered cyclic ethers.
- Structure:
- Epoxides have a strained ring structure with an oxygen atom and two carbon atoms.
- Physical Properties:
- Epoxides are highly reactive due to the angle strain in the three-membered ring.
- They have higher boiling points compared to ethers.
- Nomenclature:
- Epoxides are named by identifying the two alkyl or aryl groups attached to the oxygen atom and adding the suffix “-epoxide”.
- Example: Ethylene Oxide
- Molecular Formula: C2H4O
- Uses:
- It is used as a sterilizing agent for medical instruments.
- It is used in the production of various chemicals, including detergents and solvents.
Epoxides - Preparation Methods
- Preparation Method 1: Acid-Catalyzed Epoxidation
- In this method, alkenes react with a peroxy acid, such as peracetic acid, to form epoxides.
- CH2=CH2 + CH3CO3H → CH2OCH2 + CH3COOH
- Preparation Method 2: Base-Catalyzed Epoxidation
- In this method, alkenes react with a peroxide in the presence of a base, such as sodium hydroxide, to form epoxides.
- CH2=CH2 + H2O2 + NaOH → CH2OCH2 + NaOH2
- Preparation Method 3: Oxirane Ring Expansion
- In this method, cyclic ethers are treated with a strong acid or base to form epoxides.
- CH3-CH2-OCH2-CH3 + HBr → CH3-CHOH-CH2-Br
Epoxides - Reactions
- Ring Opening Reactions:
- Epoxides can undergo ring-opening reactions with nucleophiles, such as water or alcohol, to form diols.
- R-O-CH2-R + Nu- → R-OH-CH2-R-Nu
- Acidic Cleavage Reactions:
- Epoxides can be cleaved in the presence of a strong acid to form two carbonyl compounds.
- R-O-CH2-R’ + H3O+ → R-C(O)H + R’-C(O)H
- Oxidation Reactions:
- Epoxides can be oxidized with peracids or mCPBA to form vicinal diols.
- R-O-CH2-R’ + RCO3H → R-OH-CH(OH)-R’ + RCO2H
Summary
- Alcohols:
- Primary alcohols can be oxidized to aldehydes or carboxylic acids.
- Secondary alcohols can be oxidized to ketones.
- Alcohols can be dehydrated to form alkenes.
- Ethers:
- Ethers are named by identifying the two alkyl or aryl groups bonded to the oxygen atom.
- Ethers can be prepared by Williamson Ether Synthesis, dehydration of alcohols, or alkoxymercuration-demercuration reaction.
- Epoxides:
- Epoxides are three-membered cyclic ethers.
- Epoxides can be prepared by acid-catalyzed or base-catalyzed epoxidation, or oxirane ring expansion.
- Reactions:
- Alcohols, ethers, and epoxides can undergo various reactions such as oxidation, ring opening, and cleavage reactions.
Practice Questions
- Identify the type of alcohol in each of the following compounds:
- CH3-CH2-CH2-OH
- (CH3)2CHOH
- (CH3)3COH
- Name the following compounds:
- CH3-O-CH3
- C2H5-OC2H5
- CH3-CH2-O-C2H5
- Write the balanced chemical equations for the following reactions:
- Oxidation of ethanol to form ethanoic acid.
- Dehydration of 1-butanol to form butene.
- Classify the following compounds as ethers or epoxides:
- Predict the product of the following reaction:
(End of Slides 11-20)
Ethers - Physical properties
- Ethers have a sweet or fruity odor.
- They are less dense than water.
- Ethers have low boiling points compared to alcohols.
- They are generally liquid at room temperature.
- Ethers are highly flammable.
Ethers - Reactions
- Ethers undergo substitution reactions with halogens in the presence of a Lewis acid catalyst.
- They can be cleaved by strong acids to form two alkyl halides.
- Ethers can be used as solvents in organic reactions.
- They can react with strong bases to form alcohol and alkoxide ions.
- Ethers can participate in nucleophilic addition reactions.
Ethers - Examples and Uses
- Example: Ethyl Ether
- Molecular Formula: C2H5-O-C2H5
- Common Name: Diethyl Ether
- Uses:
- It is used as a general anesthetic.
- It is used as a solvent in organic synthesis.
- It is used as a starting material for the production of other chemicals.
- Example: Methyl Tert-Butyl Ether (MTBE)
- Molecular Formula: (CH3)3C-O-CH3
- Uses:
- It is used as an octane booster in gasoline.
- It is used as a solvent for paints, varnishes, and adhesives.
- Example: Dimethyl Ether (DME)
- Molecular Formula: CH3-O-CH3
- Uses:
- It is used as a propellant in aerosol products.
- It is used as a clean-burning alternative fuel for diesel engines.
Ethers - Williamson Ether Synthesis
- In Williamson Ether Synthesis, an alkyl halide reacts with an alkoxide ion to form an ether.
- The reaction is usually carried out in the presence of a strong base, such as sodium or potassium hydroxide.
- The alkyl halide is the electrophile and the alkoxide ion is the nucleophile in the reaction.
- The reaction proceeds through an SN2 mechanism.
Ethers - Dehydration of Alcohols
- When alcohols are heated with a strong acid catalyst, they undergo dehydration to form ethers.
- The acid catalyst, such as concentrated sulfuric acid, protonates the hydroxyl group of the alcohol, making it a better leaving group.
- The protonated alcohol then loses a water molecule, resulting in the formation of an alkene.
- The alkene can further react with another alcohol molecule to form an ether.
Epoxides - Introduction
- Definition:
- Epoxides, also known as oxiranes, are three-membered cyclic ethers.
- Structure:
- Epoxides have a strained ring structure with an oxygen atom and two carbon atoms.
- Physical Properties:
- Epoxides are highly reactive due to the angle strain in the three-membered ring.
- They have higher boiling points compared to ethers.
- Nomenclature:
- Epoxides are named by identifying the two alkyl or aryl groups attached to the oxygen atom and adding the suffix “-epoxide”.
Epoxides - Preparation Methods
- Preparation Method 1: Acid-Catalyzed Epoxidation
- In this method, alkenes react with a peroxy acid, such as peracetic acid, to form epoxides.
- The reaction proceeds through an electrophilic addition mechanism.
- Preparation Method 2: Base-Catalyzed Epoxidation
- In this method, alkenes react with a peroxide in the presence of a base, such as sodium hydroxide, to form epoxides.
- The reaction proceeds through a nucleophilic addition mechanism.
- Preparation Method 3: Oxirane Ring Expansion
- In this method, cyclic ethers are treated with a strong acid or base to form epoxides.
- The reaction proceeds by breaking a carbon-oxygen bond and forming a carbon-carbon bond.
Epoxides - Reactions
- Ring Opening Reactions:
- Epoxides can undergo ring-opening reactions with nucleophiles, such as water or alcohol, to form diols.
- The nucleophile attacks one of the carbon atoms in the epoxide ring, resulting in the formation of an alcohol.
- The reaction can proceed through either an SN2 or SN1 mechanism, depending on the nucleophile and reaction conditions.
- Acidic Cleavage Reactions:
- Epoxides can be cleaved in the presence of a strong acid to form two carbonyl compounds.
- The acid protonates one of the oxygen atoms in the epoxide ring, making it a better leaving group.
- The protonated epoxide undergoes nucleophilic attack by water, resulting in the formation of two carbonyl compounds.
- Oxidation Reactions:
- Epoxides can be oxidized with peracids or mCPBA (meta-chloroperoxybenzoic acid) to form vicinal diols.
- The oxygen in the epoxide ring is oxidized to a hydroxyl group, resulting in the formation of a diol.