Slide 1

• Topic: Ethers
• Definition: Organic compounds consisting of an oxygen atom bonded to two alkyl or aryl groups
• General formula: R-O-R'
• Also known as: Diethyl ethers or Etheric ethers
• Example: Ethyl ether (CH3CH2OCH2CH3)
• Physical properties: Colorless, volatile, and highly flammable liquid

Slide 2

• Classification of Ethers:
  • Symmetrical ethers: Both alkyl groups attached to the oxygen atom are the same (e.g., dimethyl ether)
  • Unsymmetrical ethers: Alkyl groups attached to the oxygen atom are different (e.g., ethyl methyl ether)
• Ethers can be prepared using:
  • Williamson synthesis: Alkyl halides react with alkoxide ions in the presence of a strong base
  • Dehydration of alcohols: Alcohols react with strong acids to lose a water molecule and form ethers

Slide 3

• Physical properties of Ethers:
  • Low boiling points due to weak intermolecular forces (dipole-dipole interactions)
  • Solubility in water is limited since ethers do not have hydrogen bonding capabilities
  • Ether vapors can form explosive mixtures with air
• Uses of Ethers:
  • As solvents for organic reactions and extractions
  • In anesthesia, as inhalation anesthetics
  • As fuel additives to enhance combustion efficiency

Slide 4

• Chemical reactions of Ethers:
  • Cleavage of ethers by strong acids: Alkyl groups on either side of the oxygen atom are protonated to form alkyl oxonium ions
  • Oxidation of ethers: Ethers can be oxidized to corresponding carbonyl compounds using powerful oxidizing agents such as hot acidic KMnO4 or H2CrO4
• Example equation for cleavage of ethers:
  • R-O-R’ + H+ → R-OH + R’-OH

Slide 5

• Ethers as intermediates in organic reactions:
  • Ethers can undergo nucleophilic substitution reactions
  • Ether cleavage reactions can be utilized in the synthesis of alcohols and other organic compounds
• Example:
  • Cleavage of diethyl ether (symmetrical ether) produces two ethanol molecules
  • R-O-R + 2H+ → 2R-OH

Slide 6

• Safety precautions while handling ethers:
  • Ethers are highly flammable, and precautions should be taken to avoid ignition sources
  • Proper ventilation is required when working with ether vapors
  • Ethers should be stored in tightly sealed containers away from heat and flames
• Storage and disposal of ethers:
  • Store in cool, dry places, away from direct sunlight
  • Avoid storing ethers near oxidizing agents
  • Dispose of ethers according to local regulations and guidelines

Slide 7

• Substitution reactions of ethers:
  • Ethers can undergo nucleophilic substitution reactions where one alkyl group is replaced by another nucleophile
  • Common nucleophiles used are alkoxides, Grignard reagents, and amines
• Example:
  • R-O-R’ + Nu^- → R-O-Nu + R’-OH

Slide 8

• Ether synthesis by Williamson synthesis:
  • Reaction between alkyl halide and an alkoxide ion in the presence of a strong base (usually, sodium or potassium alkoxide)
• Example equation:
  • R-X + R’-OH → R-O-R’ + HX
• An example of Williamson synthesis is the preparation of ethyl propyl ether using ethyl bromide and potassium propoxide

Slide 9

• Ether synthesis by dehydration of alcohols:
  • Reactions carried out in the presence of strong acids, such as concentrated sulfuric acid or phosphoric acid
  • Water molecule is eliminated from two alcohol molecules to form an ether
• Example equation:
  • 2ROH → R-O-R + H2O

Slide 10

• Ether isomers:
  • Ethers can exhibit different isomeric forms:
    • Structural isomers: Differ in the arrangement of atoms within the molecule
    • Stereoisomers: Differ in the spatial arrangement of atoms without any change in the connectivity
• Example:
  • Diethyl ether (symmetrical) and methyl ethyl ether (unsymmetrical) are structural isomers
  • Cis- and trans- isomers of disubstituted ethers are stereo isomers

Slide 11

• Acid-catalyzed cleavage of ethers:
  • Ethers can undergo cleavage reactions in the presence of strong acids like concentrated sulfuric acid or hydroiodic acid
  • Acid-catalyzed cleavage results in the formation of two carbocation intermediates
• Example equation:
  • R-O-R’ + HX → R-X + R’-OH
• In the presence of a nucleophile, the carbocation can undergo substitution to form new compounds

Slide 12

• Cleavage of ethers by HI:
  • Cleavage of ethers with hydroiodic acid (HI) results in the formation of alkyl iodides (RI)
  • The reaction proceeds through an SN2 mechanism, where HI acts as both an acid and a nucleophile
• Example equation:
  • R-O-R’ + 2HI → R-I + R’-I + H2O
• This reaction is an important method for the synthesis of alkyl iodides

Slide 13

• Cleavage of ethers by hot concentrated H2SO4:
  • The reaction between ethers and hot concentrated sulfuric acid (H2SO4) also results in the cleavage of ethers
  • The cleavage products are alcohols and alkyl hydrogen sulfate ions
• Example equation:
  • R-O-R’ + H2SO4 (concentrated, hot) → R-OH + R’-OSO3H
• Alkyl hydrogen sulfate ions can be converted back to alcohols through hydrolysis or other reactions

Slide 14

• Ether oxidation reactions:
  • Ethers can be oxidized to form carbonyl compounds (aldehydes or ketones) using powerful oxidizing agents
  • Common oxidizing agents include hot acidic potassium permanganate (KMnO4) or chromic acid (H2CrO4)
• Example equation:
  • R-O-R’ + 2[O] → R-C(=O)-R’ + H2O
• The reaction proceeds through the breaking of the C-O bond and the formation of a C=O bond

Slide 15

• The Williamson synthesis:
  • A method for the preparation of ethers using the reaction between an alkyl halide and an alkoxide ion in the presence of a strong base
  • The reaction is a nucleophilic substitution where the alkoxide attacks the alkyl halide to form the desired ether
• Example equation:
  • R-X + R’-O^- → R-O-R’ + X
• Sodium or potassium alkoxides are usually used as strong bases in this reaction

Slide 16

• Preparation of symmetrical ethers by Williamson synthesis:
  • Symmetrical ethers can be prepared by using the same alkyl halide and alkoxide ion
  • The reaction can be carried out in an aprotic solvent such as dimethyl sulfoxide (DMSO)
• Example equation:
  • R-Br + R-O^- → R-O-R + Br
• The reaction can be performed at room temperature or under reflux conditions

Slide 17

• Ether synthesis by dehydration of alcohols:
  • Dehydration of alcohols is another method to prepare ethers
  • The reaction involves the elimination of a water molecule from two alcohol molecules to form an ether
• Example equation:
  • R-OH + R’-OH → R-O-R’ + H2O
• This reaction can be performed with the help of strong acids like concentrated sulfuric acid or phosphoric acid as catalysts

Slide 18

• Ether synthesis by alkoxymercuration-demercuration:
  • In this method, alkenes are reacted with mercuric acetate in the presence of an alcohol to form an alcoholate ion
  • Subsequent reaction with sodium borohydride results in the formation of the corresponding ether
• Example equation:
  • RCH=CHR’ + Hg(OAc)2 + ROH → RCH(OR’)CO2Hg(OAc) + H2O
  • RCH(OR’)CO2Hg(OAc) + NaBH4 → R-O-R’ + Hg(OAc)2 + NaBH(OAc)3
• This reaction allows for the conversion of alkenes to ethers with the same carbon skeleton

Slide 19

• Ether synthesis by O-alkylation of phenols:
  • Phenols can be alkylated using alkyl halides in the presence of a base to form ethers
  • This reaction is known as O-alkylation and is a method to introduce alkyl groups onto the oxygen atom of a phenol
• Example equation:
  • Ar-OH + RX + base → Ar-O-R’ + X^- + HX
• Sodium hydroxide or potassium hydroxide is commonly used as the base in this reaction

Slide 20

• Ether synthesis by reduction of carbonyl compounds:
  • Carbonyl compounds such as aldehydes and ketones can be reduced to their corresponding alcohols, which can then be converted to ethers
  • Reduction is typically accomplished using reducing agents like sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4)
• Example equation:
  • R-C(=O)-R’ + 2[H] → R-CH2-O-CH2-R'
• The alcohols obtained from the reduction can be further reacted with an acid and dehydrated to form ethers

Slide 21

• Ether reactions with halogens:
  • Ethers can react with halogens, such as chlorine or bromine, to form alkyl halides
  • The reaction proceeds through nucleophilic substitution where the halogen replaces one of the alkyl groups attached to the oxygen atom
• Example equation:
  • R-O-R’ + X2 → R-X + R’-O-X
  • X = Cl or Br
• This reaction is useful for the conversion of ethers into other functional groups

Slide 22

• Ether reactions with hydrogen halides:
  • Ethers can react with hydrogen halides (HCl, HBr, HI) to form alkyl halides and alcohol
• Example equation:
  • R-O-R’ + HX → R-X + R’-OH
  • X = Cl, Br, or I
• This reaction is another way to cleave ethers and obtain alkyl halides as products

Slide 23

• Ether reactions with metallic sodium:
  • Ethers can react with metallic sodium to form alkoxides and hydrogen gas
  • This reaction is highly exothermic and requires careful handling
• Example equation:
  • R-O-R’ + 2Na → 2R-O^-Na+ + H2
• The formed alkoxide ions can further react with various electrophiles

Slide 24

• Ether reactions with Grignard reagents:
  • Ethers can react with Grignard reagents (organomagnesium compounds) to give alcohols and alkyl magnesium halides
  • The reaction proceeds through nucleophilic addition of the Grignard reagent to the ether, followed by hydrolysis
• Example equation:
  • R-O-R’ + R"-MgX → R-OH + R’-MgX
  • X = Cl, Br, or I
• This reaction is a useful method for the synthesis of alcohols

Slide 25

• Ether reactions with amines:
  • Ethers can react with amines to form ammonium salts and alcohol
  • The reaction proceeds through nucleophilic substitution, where the amine replaces one of the alkyl groups attached to the oxygen atom
• Example equation:
  • R-O-R’ + 2NH3 → R-NH3+R’ + R’-OH
• This reaction is useful for the synthesis of ammonium salts

Slide 26

• Ether reactions with peroxyacids:
  • Ethers can react with peroxyacids, such as peracetic acid, to form respective esters
  • Peroxyacids act as electrophiles and attack the electron-rich oxygen atom of the ether
• Example equation:
  • R-O-R’ + peroxyacid → R-C(=O)-OR’ + H2O
• This reaction is important for the conversion of ethers into esters

Slide 27

• Acid-catalyzed isomerization of ethers:
  • Ethers can undergo isomerization reactions in the presence of strong acids like concentrated sulfuric acid
  • The reaction involves the rearrangement of alkyl groups on the oxygen atom
• Example equation:
  • R-O-R’ + H+ → R’-O-R
• This isomerization can result in the formation of new ethers with different connectivity

Slide 28

• Cleavage of cyclic ethers by epoxides:
  • Epoxides are a specific type of cyclic ethers that are highly reactive due to the strained three-membered ring structure
  • Epoxides can be cleaved by strong nucleophiles to form alcohol
• Example equation:
  • R-O-R’ + Nu^- → R-OH + R’-X
  • Nu = Nucleophile, X = Leaving group
• This reaction is an important method for the synthesis of alcohols

Slide 29

• Reactions of ethers in the presence of Lewis acids:
  • Ethers can undergo reactions with Lewis acids to form complex compounds
  • Lewis acids act as electron pair acceptors and can coordinate with the oxygen atom in the ether
• Example equation:
  • R-O-R’ + Lewis acid → [R-O-R’ • Lewis acid]
• Lewis acid-ether complexes can participate in further reactions or serve as intermediates for further synthesis

Slide 30

• Summary:
  • Ethers are organic compounds consisting of an oxygen atom bonded to two alkyl or aryl groups
  • They can be prepared through Williamson synthesis or dehydration of alcohols
  • Ethers have low boiling points, limited water solubility, and are highly flammable
  • Ethers play important roles in organic synthesis, anesthetics, and as solvents
  • They can undergo various reactions, including cleavage, oxidation, and substitution reactions