18: Ethers and Epoxides; Thiols and Sulfides
- Page ID
- 448736
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- fulfill all of the detailed objectives listed under each individual section.
- design a multi-step synthesis using one or more of the reactions introduced in this chapter, along with any number of the reactions you have studied to date.
- solve “road-map” problems that may require a knowledge of the chemistry of ethers, epoxides, thiols and sulfides, in addition to any of the material you have studied up to this point in organic chemistry.
- define, and use in context, the key terms introduced in this chapter.
We shall begin in a very traditional manner, with a discussion of the nomenclature of ethers. We will then describe how ethers may be prepared in the laboratory, and discuss the relative inertness of these compounds. A discussion of the chemistry of cyclic ethers follows, with particular emphasis on the preparation and reactions of epoxides (cyclic ethers containing a three-membered ring). We will then introduce crown ethers—compounds that consist of large rings containing several oxygen atoms and the spectroscopic properties of ethers. The unit will close with a description of the chemistry of thiols and sulfides, the sulfur-containing analogues of alcohols and ethers.
- 18.0: Why This Chapter?
- This chapter finishes the coverage of functional groups with C–O and C–S single bonds that was begun in the chapter on Alcohols and Phenols. We’ll focus primarily on ethers and take only a brief look at thiols and sulfides before going on to an extensive coverage of compounds with C=O double bonds in latter chapters.
- 18.1: Names and Properties of Ethers
- Ethers are relatively stable and unreactive in many respects, but some ethers react slowly with the oxygen in air to give peroxides, compounds that contain an O–O bond. The peroxides from low-molecular-weight ethers such as diisopropyl ether and tetrahydrofuran are explosive and extremely dangerous, even in small amounts. Ethers are very useful as solvents in the laboratory, but they must always be used cautiously and should not be stored for long periods of time.
- 18.2: Preparing Ethers
- There are several methods for preparing ethers and the two most popular are the Williamson ether synthesis and the alkoxymercuration-demercuration. The Williamson synthesis involves reacting an alkoxide ion with a primary alkyl halide, resulting in ether formation. Alkoxymercuration-demercuration provides an alternative route by using alcohols with alkenes and mercuric acetate. Both methods are commonly used to produce ethers, which serve as solvents or intermediates in reactions.
- 18.3: Reactions of Ethers - Acidic Cleavage
- Under acidic conditions, ethers can be cleaved into alkyl halides and alcohols using hydrogen halides (HX). The process involves protonating the ether oxygen, making it a better leaving group. Different reaction mechanisms occur depending on whether the ether is primary, secondary, or tertiary. For primary and secondary ethers, an SN2 reaction takes place, while for tertiary ethers, an SN1 mechanism is more common.
- 18.4: Cyclic Ethers - Epoxides
- Cyclic ethers, particularly epoxides, which are three-membered ring ethers known for their high reactivity due to ring strain. It explains the methods of preparing epoxides, such as from alkenes using peroxy acids or via halohydrin formation followed by intramolecular cyclization. The reactivity of epoxides is highlighted, including nucleophilic ring-opening reactions that can lead to various products based on the reaction conditions.
- 18.5: Reactions of Epoxides - Ring-opening
- The reactions of epoxides often focus on ring-opening processes. Epoxides, due to their strained three-membered ring structure, are highly reactive. They undergo nucleophilic ring-opening reactions, which can occur under either acidic or basic conditions. In acidic conditions, the nucleophile attacks the more substituted carbon, while in basic conditions, it attacks the less substituted carbon. These reactions are widely used in organic synthesis to produce a variety of compounds.
- 18.6: Crown Ethers
- Crown ethers are cyclic compounds that consist of a ring containing several ether groups. These ethers can trap metal cations inside their ring structure, forming complexes that are useful in both organic synthesis and analytical chemistry. Crown ethers can selectively bind specific ions based on the size of the ether ring, making them valuable in separating and transporting ions across membranes. They also play a role in phase-transfer catalysis.
- 18.7: Thiols and Sulfides
- Thiols and sulfides are sulfur-containing organic compounds analogous to alcohols and ethers. Thiols (-SH group) are notable for their strong odors and form disulfides, crucial in proteins. Sulfides contain sulfur bonded to two carbons and can oxidize to sulfoxides or sulfones. These compounds are important in both biological processes and organic chemistry.
- 18.8: Spectroscopy of Ethers
- The spectroscopy of ethers focuses on identifying and analyzing ether compounds using techniques such as Infrared (IR), Nuclear Magnetic Resonance (NMR), and Mass Spectrometry (MS). IR spectra display C-O stretches, while NMR helps differentiate hydrogen atoms based on their environment. Ethers typically show distinct peaks in these methods, allowing chemists to determine structural details and verify compound identity.
- 18.9: Chemistry Matters—Epoxy Resins and Adhesives
- Epoxy resins, formed from epoxides, exhibit strong adhesion and resistance to environmental factors. They are widely used in coatings, adhesives, and composite materials due to their durability and versatility. The chemistry of these materials allows for customization in various industrial applications.
- 18.11: Summary
- This chapter has finished the coverage of functional groups with C–O and C–S single bonds, focusing primarily on ethers, epoxides, thiols, and sulfides. Ethers are compounds that have two organic groups bonded to the same oxygen atom, ROR′. The organic groups can be alkyl, vinylic, or aryl, and the oxygen atom can be in a ring or in an open chain. Ethers are prepared by either Williamson ether synthesis or the alkoxymercuration reaction.
- 18.12: Summary of Reactions
- This section summarizes the key reactions involving ethers, epoxides, thiols, and sulfides. It outlines the formation and cleavage of ethers, as well as the reactivity of epoxides in nucleophilic attacks. Additionally, it discusses the reactions of thiols and sulfides, including oxidation and formation of disulfides. The importance of these compounds in organic synthesis and their functional roles in various chemical reactions is emphasized.
- 18.14: Preview of Carbonyl Chemistry
- This section introduces carbonyl chemistry, focusing on the properties and reactivity of carbonyl compounds, which include aldehydes and ketones. These compounds are significant in organic chemistry due to their role in various reactions, such as nucleophilic addition. Understanding their structure and behavior is essential for exploring more complex organic reactions.