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Chapter 14
Ethers, Epoxides, and Sulfides

14-01

Title	Structure of Dimethyl Ether
Caption	Figure 14-1 Structure of dimethyl ether.
Notes	The C-O-C angle of ethers is around 110o. There is a dipole along the C-O bond because the oxygen is more electronegative than the carbon.
Keywords	dipole, ether

14-02

Title	Bonding in Alcohols and Ethers
Caption	Figure 14-2 A molecule of water or an alcohol can serve as both a hydrogen bond donor and an acceptor. Ether molecules have no hydroxyl groups, so they are not hydrogen bond donors. If a hydrogen bond donor is present, ethers can serve as hydrogen bond acceptors.
Notes	While molecules of water and alcohol can hydrogen-bond with each other, ethers cannot hydrogen bond with other ether molecules. Molecules that cannot hydrogen-bond intermolecularly have a lower boiling point. Ethers molecules can interact hydrogen bond with water and alcohol molecules.
Keywords	hydrogen bond, hydrogen bond donor, hydrogen bond acceptor

14-03

Title	Solvation of Ions with Ether
Caption	Figure 14-3 An ionic substance such as lithium iodide is moderately soluble in ethers because the small lithium cation is strongly solvated by the ether's lone pairs of electron. Unlike alcohols, ether canot serve as hydrogen bond donors, so they do not solvate small anions well.
Notes	The oxygen of the ether can have a dipole interaction with cations but not with anions so salts will not be very soluble in ether solvents.
Keywords	dipole, solubility

14-04

Title	Grignard-Ether Complex
Caption	Figure 14-4 Complexation of an ether with a Grignard reagent stabilizes the reagent and helps keep it in solution.
Notes	The lone pairs of the oxygen interact with the magnesium. The same thing happens with borane (BH3-THF) complex in which the THF stabilizes the boron.
Keywords	complexation

14-04-03UN1-3

Title	Crown Ether Cmplexes
Caption	Cyclic polyethers are commonly known as crown ethers. These ethers can complex metal cations inside the ring, the size of the cation will determine the size of the ring needed. Complexation by crown ethers often allows polar inorganic salts to dissolve in non-polar organic solvents,
Notes	The name of the crown ether comes from the total number of atoms in the ether and the number of oxygens that it has. For example, 18-crown-6 is a cyclic ether with 18 atoms, six of which are oxygens.
Keywords	crown ethers, complexation

14-04-23UN

Title	Mass Spectrometry: a-Cleavage of Ethers
Caption	The molecular ion of an ether can lose part of an alkyl group by breaking the bond between the alpha and the beta carbon to form an oxonium ion. The oxonium ion is stabilized by resonance.
Notes	Only positively charged species (cations or radical cations) can be observed. The other product of the a-cleavage is a radical so it will not be detected.
Keywords	oxonium ion, resonance

14-04-24UN

Title	Loss of an Alkyl Group
Caption	Another common cleavage is the loss of either of the two alkyl groups to give another oxonium ion or an alkyl cation.
Notes	Only positively charged species (cations or radical cations) can be observed. The other products of the alkyl loss are radicals so they will not be detected.
Keywords	oxonium ion, cleavage, alkyl cation

14-05

Title	Mass Spectrum of Diethyl Ether
Caption	The mass spectrum of diethyl ether shows major peaks for the molecular ion, loss of an ethyl group, a cleavage , and a cleavage combined with the loss of a molecule of ethylene.
Notes	The highest peak (m/z = 31) is the base peak and it is assigned a 100% abundance. The abundance of all other peaks is relative to the base peak.
Keywords	molecular ion,

14-05-03UN

Title	Williamson Ether Synthesis
Caption	The WIlliamson synthesis is the most reliable and verstile ether synthesis. This method involves an SN2 attack of the alkoxide on an unhindered primary halide or tosylate.
Notes	The alkoxide will displace the halide or the tosylate and can be easily prepared by the reaction of an alcohol with Na, K, or NaH.
Keywords	Williamson synthesis, ether, alkoxide

14-05-08UN

Title	Alkoxymercuration-Demercuration Reaction
Caption	The alkoxymercuration-demercuration process adds a molecula of alcohol across the double bond of an alkene producing an ether.
Notes	Analogous to the oxymercuration-demercuration reaction, the alkoxymercuration is carried out using alcohol as a solvent. The addition will follow Markovnikov's rule so the alcohol will be on the most substituted carbon of the double bond.
Keywords	alkoxymercuration-demercuration, oxymercuration-demercuration, Markovnikov's rule

14-05-11UN

Title	Reaction of an Ether with Hydrohalic Acids
Caption	Ethers react with concentrated HBr and HI because these reagents are sufficiently acidic to protonate the ether, while the bromide and iodide are good nucleophiles for the substitution.
Notes	After protonation of the ether molecule the halide will attack either one of the a carbons and displace a molecule of alcohol.
Keywords	substitution

14-05-12UN

Title	Mechanism of Ether Cleavage by HBr
Caption	Mechanism of ether cleavage by HBr.
Notes	After protonation of the ether, the bromide will attack the carbon and displace an alcohol molecule. The alcohol molecule produced can be protonated by HBr and attacked again to produce more alkyl bromide.
Keywords	cleavage

14-05-17UN

Title	Autooxidation of Ethers
Caption	When ethers are stored in the presence of atmospheric oxygen, they slowly oxidize to produce hydroperoxides and dialkyl peroxides, both of which are explosive. Such a spontaneous oxidation by atmospheric oxygen is called autooxidation.
Notes	Distillation of ethers should be carried out using peroxide-free ether.
Keywords	autooxidation, peroxide, hydroperoxide

14-05-20UN

Title	Thioether Synthesis
Caption	Thiolates are easily synthesized by the Williamson ether synthesis, using dithiolate a the nuclephile.
Notes	The reaction is SN2 but secondary halides will give good yields of substitution.
Keywords	thiolate, thioether, Williamson synthesis

14-05-24UN

Title	Sulfides as Reducing Agents
Caption	Because sulfides are easily oxidized, they are often used as mild reducing agents.
Notes	Sulfides are used as a second step in the ozonolisis reactions to reduce the ozonide to the dicarbonyl compound. In the process the disulfide will be oxidized to dimethyl sulfoxide (DMSO).
Keywords	reducing agents, oxidation, ozonolisis, DMSO

14-05-29UN

Title	Peroxyacid Oxidation
Caption	Peroxyacids are used to convert alkenes to epoxides. If the reaction takes place in aqueous acid, the epoxide opens to a glycol. Therefore, to make an epoxide, we use a weakly acidic peroxyacid that is solubel in aprotic solvents.
Notes	meta-Chloroperoxybenzoic acid (MCPBA) is the peroxyacid most commonly used to carry out epoxidations.
Keywords	peroxyacids, epoxides, glycol

14-05-31UN

Title	Epoxidation Mechanism
Caption	The epoxidation takes place in a one-step concerted reaction that maintains the stereochemistry of any substituents on the double bond.
Notes	One of the oxygens of the peroxyacid is transferred to the double bond.
Keywords	epoxide, concerted mechanism, stereochemistry

14-05-32UN

Title	Epoxidation Examples
Caption	The peroxyacid epoxidation is quite general, with electron rich double bonds reacting faster. This selectivity makes difficult transformations possible.
Notes	MCPBA and MMPP are the most common peroxyacids used. MMPP is often used in large scale epoxidations.
Keywords	epoxidation, MCPBA, MMPP

14-05-33UN

Title	Base-Promoted Cyclization of Halohydrins
Caption	A second synthesis of epoxides and other cyclic ethers involves a variation of the Williamson synthesis. If an alkoxide and a halogen are located in the same molecule, the alkoxide may displace a halide ion and form a ring. Treatment of a halohydrin with a base leads to an epoxide through this internal SN2 attack.
Notes	Halohydrins are synthesized by treating alkenes with aqueous solutions of halogens (X2/H2O). In terms of cyclic ether formation, a 3-membered ring is formed faster than 5- or 6-membered ones.
Keywords	halohydrin, cyclic ether, Williamson synthesis

14-05-34UN

Title	Synthesis of Chlorohydrins
Caption	Bromine water and chlorine water add across double bonds with Markovnikov orientation.
Notes	In the mechanism a chlorine atom is added to the double bond forming the chloronium ion intermediate. Opening of the 3-membered intermediate by water (anti attack) produces an enantiomeric mixture of chlorohydrins. Addition of base to the halohydring deprotonates the hydroxyl group which will displace the chloride forming the epoxide.
Keywords	chloronium ion, halohydring, epoxide

14-05-39UN

Title	Mechanism of Acid-Catalyzed Opening of an Epoxide
Caption	Acid-catalyzed hydrolysis of epoxides gives glycols with anti stereochemistry. Anti stereochemistry results from the back-side attack of water on the protonated epoxide.
Notes	The acid protonates the oxygen of the epoxide and the water attacks and opens the ring in an SN2 reaction followed by deprotonation. The reaction produces an enantiomeric mixture of trans-1,2-diols.
Keywords	acid-catalyzed hydrolysis, anti stereochemistry, diol, glycol

14-05-41UN

Title	Acid-Catalyzed opening of an Epoxide in an Alcohol Solution
Caption	When the acid-catalyzed opening of an epoxide takes place with an alcohol as the solvent, a molecule of alcohol acts as the nucleophile. This reaction produces an alkoxy alcohol with anti stereochemistry. This is an excellent method for making compounds with alcohol and ether functional groups on adjacent carbons.
Notes	The epoxide is protonated by the acid. The alcohol present attacks and opens the ring. Deprotonation of the product affors an enantiomeric mixture of alkoxy alcohol.
Keywords	alkoxy alcohol

14-05-42UN

Title	Opening of Epoxides with Hydrohalic Acids
Caption	When an epoxide reacts with a hydrohalic acid (HBr, HCl, HI), a halide ion attacks the protonated epoxide. This reaction is analgous to the cleavage of ethers by HBr or HI.
Notes	The epoxide is protonated by the acid, and the halide ion displaced will acts as a nucleophile attacking and opening the epoxide to form a halohydrin.
Keywords	hydrohalic acid, epoxide, halohydrin

14-08

Title	Potential Energy Diagram for the Base-Catalyzed Opening of Epoxides
Caption	An epoxide is higher in energy than an acyclic ether by about 25 kcal/mol ring strain. The ring strain is released in the product, giving it an energy similar to the products from acyclic ethers. Release of the ring strain makes the displacement of an epoxide thermodynamically favored.
Notes	The base-catalyzed opening of an epoxide is more favored than the cleavage of an acyclic ether because the ring strain energy is released. Base-catalyzed opening requires harsher conditions than the acid-catalyzed opening.
Keywords	thermodynamic product

14-08-01UN

Title	Mechanism of Base-Catalyzed Opening of an Epoxide
Caption	Base attacks and opens the ring.
Notes	The hydroxide ion (HO-) attacks the epoxide opening the ring. The alkoxide is protonated by water. The final product of the reaction is an enantiomeric mixture of trans-1,2-diols
Keywords	alkoxide

14-08-04UN

Title	Orientation of Epoxide Ring Opening
Caption	Unsymmetrically substituted epoxides give different products under acid-catalyzed and base-catalyzed conditions.
Notes	Under acidic conditions the nucleophile will attack the more substituted carbon of the epoxide. Under basic conditions, the less subtituted carbon will be attacked by the nucleophile.
Keywords	unsymmetrical epoxide

14-08-10UN

Title	Reaction of Epoxides with Grignards
Caption	Like other strong nucleophiles, Grignard and organolithium reagents attack epoxides to give (after hydrolysis) ring-opened alcohols.
Notes	Anionic nucleophiles such as Grignards and organolithiums will attack unsymmetrical epoxides on the less substituted carbon. Organolithiums are more selective at attacking the less hindered carbon.
Keywords	Grignard reagents, organolithium reagents

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