Organic Chemistry - Ethers, Thiols, and Sulfides

Introduction to Ethers

• Ether Definition: Compounds with the general formula (R-O-R′), where R and R′ can be alkyl, aryl, vinyl, or allyl groups.
• Specific Compound: Diethyl ether (CH₃CH₂OCH₂CH₃) is often referred to as ether in informal contexts.
• Terminology Clarity: In this course, "ether" refers to the class of compounds, while "diethyl ether" specifies CH₃CH₂OCH₂CH₃. The term "ethyl ether" is avoided to minimize confusion.

Ether Structures and Properties

• General Characteristics:

  • Ethers contain an sp³ hybridized oxygen atom between two carbon groups.
  • Aliphatic ethers lack aryl groups directly connected to the ether oxygen.
  • Aromatic ethers have at least one aryl ring attached to the ether oxygen, affecting their properties significantly due to conjugation.

• Boiling Points Comparison:

  • Ethers generally have higher boiling points than alkanes due to dipole interactions but lower than alcohols because they lack hydrogen bonding.
  • Example comparison:
  • Diethyl ether (74 g/mol, bp = 35°C) vs. Ethyl alcohol (46 g/mol, bp = 78°C) due to the absence of an -OH group in ethers.

Solubility in Water

• Ethers can engage in hydrogen bonding with water, leading to solubilities comparable to alcohols.
  • Example: Dimethyl ether and ethanol are fully soluble, while diethyl ether and 1-butanol show lower solubility (8 g/100 mL).

Peroxide Formation

• Ethers can react with oxygen to form hazardous peroxide compounds via autoxidation, necessitating careful storage.
  • Recommend avoiding prolonged storage and distillation to prevent concentration of peroxides.

Naming Ethers

• Common Naming:
  • No other functional groups mean the names are derived from substituents in alphabetical order + "ether".
  • In the case of complexity or multiple functional groups, IUPAC naming should be utilized.
• Alkoxy Group Naming: (Replacement of -yl with -oxy)
• Examples of Alkoxy Names:
  • Methyl (CH₃–) -> Methoxy (CH₃O–)
  • Ethyl (CH₃CH₂–) -> Ethoxy (CH₃CH₂O–)

Cyclic Ethers

• Defined as heterocycles containing oxygen; commonly found in biological molecules.
  • Examples include dioxane and tetrahydrofuran, notable for their inertness and utility as solvents.

Synthesis of Ethers

• Williamson Ether Synthesis:
  • Utilizes alkoxide nucleophiles reacting with alkyl halides, typically favoring primary halides to avoid elimination reactions.
• Alkoxymercuration-Demercuration:
  • Converting alkenes into ethers involves treating alkenes with peroxy acids in aqueous conditions to yield epoxides or ethers.

Reactions of Ethers

• Ethers may cleave under acidic conditions to yield alcohols and alkyl halides via S⁴ or E1 mechanisms, depending on the structure of the ether.
  • Important to distinguish reactivity between aryl and aliphatic ethers.

Claisen Rearrangement

• A process involving the rearrangement of allyl phenyl ethers to 2-allylphenol under heat.
  • Key mechansism involves the migration of the allyl group to give a stable phenols.

Epoxides

• Definition: Three-membered cyclic ethers targeted in organic synthesis due to their strain and reactivity.
  • Industrially produced by catalytic oxidation of ethylene, functioning as key intermediates in chemical synthesis.