8Chapter 16

8Chapter 16 - Chapter 16 Ethers, Epoxides, and Sulfides...

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Unformatted text preview: Chapter 16 Ethers, Epoxides, and Sulfides 16-1 16.1 Nomenclature of Ethers, Epoxides, and Sulfides 16-2 Substitutive IUPAC Names of Ethers Substitutive IUPAC Names of Ethers name as alkoxy derivatives of alkanes CH3OCH2 CH3 CH methoxyethane CH3CH2OCH2CH2CH2Cl 1-chloro-3-ethoxypropane CH3CH2OCH2 CH3 CH ethoxyethane 16-3 Functional Class IUPAC Names of Ethers Functional Class IUPAC Names of Ethers name the groups attached to oxygen in name alphabetical order as separate words; "ether" is last word last CH3OCH2 CH3 CH ethyl methyl ether methyl CH3CH2OCH2CH2CH2Cl 3-chloropropyl ethyl ether ethyl CH3CH2OCH2 CH3 CH diethyl ether 16-4 Substitutive IUPAC Names of Sulfides Substitutive IUPAC Names of Sulfides name as alkylthio derivatives of alkanes CH3SCH2 CH3 CH methylthioethane SCH3 (methylthio)cyclopentane CH3CH2SCH2 CH3 CH ethylthioethane 16-5 Functional Class IUPAC Names of Sulfides Functional Class IUPAC Names of Sulfides analogous to ethers, but replace “ether” as last word in the name by “sulfide.” CH3SCH2 CH3 CH ethyl methyl sulfide CH3CH2SCH2 CH3 CH SCH3 cyclopentyl methyl sulfide cyclopentyl methyl diethyl sulfide 16-6 Names of Cyclic Ethers Names of Cyclic Ethers O Oxirane (Ethylene oxide) O Oxetane O Oxolane (tetrahydrofuran) O O Oxane (tetrahydropyran) O 1,4-Dioxane 16-7 Names of Cyclic Sulfides Names of Cyclic Sulfides S S Thiirane Thietane S Thiolane S Thiane 16-8 16.2 Structure and Bonding in Ethers and Epoxides bent geometry at oxygen analogous to water and alcohols, to i.e. sp3 hybidization i.e. sp hybidization 16-9 Bond angles at oxygen are sensitive Bond angles at oxygen are sensitive to steric effects to steric effects O O H H 105° 108.5° O O CH3 CH3 112° H CH3 C(CH3)3 (CH3)3C 132° 132° 16-10 An oxygen atom affects geometry in much the An oxygen atom affects geometry in much the same way as a CH2 group same way as a CH2 group most stable conformation of diethyl ether resembles pentane 16-11 An oxygen atom affects geometry in much the An oxygen atom affects geometry in much the same way as a CH2 group same way as a CH2 group most stable conformation of tetrahydropyran resembles cyclohexane 16-12 16.3 Physical Properties of Ethers 16-13 Ethers resemble alkanes more than alcohols Ethers resemble alkanes more than alcohols with respect to boiling point with respect to boiling point boiling point 36°C 35°C O OH OH Intermolecular hydrogen bonding possible in bonding alcohols; not possible in alkanes or ethers. in 117°C 16-14 Ethers resemble alcohols more than alkanes Ethers resemble alcohols more than alkanes with respect to solubility in water with respect to solubility in water solubility in water (g/100 mL) very small 7.5 O OH OH 9 Hydrogen bonding to water possible for ethers and alcohols; not and possible for alkanes. possible 16-15 16.4 Crown Ethers 16-16 Crown Ethers Crown Ethers Crown structure cyclic polyethers derived from repeating cyclic —OCH2CH2— units —OCH properties form stable complexes with metal ions form applications applications synthetic reactions involving anions synthetic 16-17 18-Crown-6 18-Crown-6 O O O O O O negative charge concentrated in cavity inside negative the molecule the 16-18 18-Crown-6 18-Crown-6 O O O O O O negative charge concentrated in cavity inside negative the molecule the 16-19 18-Crown-6 18-Crown-6 O O O K+ O O O forms stable Lewis acid/Lewis base complex forms with K+ with 16-20 18-Crown-6 18-Crown-6 O O O K+ O O O forms stable Lewis acid/Lewis base complex forms with K+ with 16-21 Ion-Complexing and Solubility Ion-Complexing and Solubility K+F– not soluble in benzene 16-22 Ion-Complexing and Solubility Ion-Complexing and Solubility O O O O O K+F– benzene O add 18-crown-6 16-23 Ion-Complexing and Solubility Ion-Complexing and Solubility O O O O O O F– O benzene O O O K+ O O 18-crown-6 complex of K+ dissolves in benzene in 16-24 Ion-Complexing and Solubility Ion-Complexing and Solubility O O O O O O O benzene O F– carried into benzene to preserve electroneutrality to O K+ O O O + F– 16-25 Application to organic synthesis Application to organic synthesis Complexaton of K+ by 18-crown-6 "solubilizes" salt in benzene salt Anion of salt is in a relatively unsolvated state Anion in benzene (sometimes referred to as a "naked anion") "naked Unsolvated anion is very reactive Only catalytic quantities of 18-crown-6 are Only needed needed 16-26 Example Example KF CH3(CH2)6CH2Br 18-crown-6 benzene CH3(CH2)6CH2F (92%) 16-27 16.5 Preparation of Ethers 16-28 Acid-Catalyzed Condensation of Alcohols* Acid-Catalyzed Condensation of Alcohols* 2CH3CH2CH2CH2OH H2SO4, 130°C CH3CH2CH2CH2OCH2CH2CH2CH3 (60%) *Discussed earlier in Section 15.7 16-29 Addition of Alcohols to Alkenes Addition of Alcohols to Alkenes (CH3)2C=CH2 + CH3OH H+ (CH3)3COCH3 tert-Butyl methyl ether 16-30 16.6 The Williamson Ether Synthesis Think SN2! primary alkyl halide + alkoxide nucleophile 16-31 Example Example CH3CH2CH2CH2ONa + CH3CH2I Na CH CH3CH2CH2CH2OCH2CH3 + NaI NaI (71%) 16-32 Another Example Another Example CH2Cl + CH3CHCH3 ONa CH2OCHCH3 CH CH3 (84%) 16-33 Another Example Another Example Alkoxide ion can be derived Alkoxide from primary, secondary, or tertiary alcohol tertiary Alkyl halide must be primary be CH2Cl + CH3CHCH3 ONa CH2OCHCH3 CH CH3 (84%) 16-34 Origin of Reactants Origin of Reactants Origin CH3CHCH3 CH2OH OH HCl CH2Cl Na + CH3CHCH3 ONa CH2OCHCH3 (84%) CH3 16-35 What happens ififthe alkyl halide is not primary? What happens the alkyl halide is not primary? CH2ONa + CH3CHCH3 Br 16-36 What happens ififthe alkyl halide is not primary? What happens the alkyl halide is not primary? CH2ONa + CH3CHCH3 Br CH2OH + H2C CHCH3 Elimination by the E2 mechanism becomes the major reaction pathway. 16-37 16.7 Reactions of Ethers: A Review and a Preview 16-38 Summary of reactions of ethers Summary of reactions of ethers No reactions of ethers encountered to this No point. point. Ethers are relatively unreactive. Their low level of reactivity is one reason why Their ethers are often used as solvents in chemical reactions. reactions. Ethers oxidize in air to form explosive Ethers hydroperoxides and peroxides. hydroperoxides 16-39 16.8 Acid-Catalyzed Cleavage of Ethers 16-40 Example Example CH3CHCH2CH3 OCH3 HBr heat CH3CHCH2CH3 + CH3Br Br (81%) 16-41 Mechanism Mechanism Mechanism CH3CHCH2CH3 O• CH3 •• • H •• Br • •• • CH3CHCH2CH3 + O CH3 •• H 16-42 Mechanism Mechanism Mechanism CH3CHCH2CH3 O• CH3 •• • H •• Br • •• • CH3CHCH2CH3 – •• • Br • •• •• CH3CHCH2CH3 + O CH3 •• H •O •• • •• • Br • •• H CH3 16-43 Mechanism Mechanism Mechanism CH3CHCH2CH3 O• CH3 •• • CH3CHCH2CH3 Br H •• Br • •• HBr • CH3CHCH2CH3 – •• • Br • •• •• CH3CHCH2CH3 + O CH3 •• H •O •• • •• • Br • •• H CH3 16-44 Cleavage of Cyclic Ethers Cleavage of Cyclic Ethers O HI 150°C ICH2CH2CH2CH2I (65%) 16-45 Mechanism Mechanism •• ICH2CH2CH2CH2I O •• HI •• O+ H 16-46 Mechanism Mechanism •• ICH2CH2CH2CH2I O •• HI HI •• – •I• • ••• •• O+ H •• •I • •• •• •O • H 16-47 Mechanism Mechanism •• ICH2CH2CH2CH2I O •• HI HI •• – •I• • ••• HI •• O+ H •• •I • •• •• •O • H 16-48 16.9 Preparation of Epoxides: A Review and a Preview 16-49 Preparation of Epoxides Preparation of Epoxides Epoxides are prepared by two major methods. Both begin with alkenes. reaction of alkenes with peroxy acids (Section 6.19) conversion of alkenes to vicinal halohydrins, followed by treatment with base (Section 16.10) 16-50 16.10 Conversion of Vicinal Halohydrins to Epoxides 16-51 Example Example H OH H Br H NaOH H2O O H (81%) 16-52 Example Example H OH H NaOH O H2O H Br •• – •O • •• via: H H (81%) H Br • Br • •• •• 16-53 Epoxidation via Vicinal Halohydrins Epoxidation via Vicinal Halohydrins Br Br2 H2O OH anti addition 16-54 Epoxidation via Vicinal Halohydrins Epoxidation via Vicinal Halohydrins Br Br2 NaOH H2O O OH anti addition inversion corresponds to overall syn addition of oxygen to the double bond 16-55 Epoxidation via Vicinal Halohydrins Epoxidation via Vicinal Halohydrins H3C H Br H Br2 H2O CH3 H3C H NaOH H CH3 O OH anti addition inversion corresponds to overall syn addition of oxygen to the double bond 16-56 Epoxidation via Vicinal Halohydrins Epoxidation via Vicinal Halohydrins H3C H Br H Br2 H2O CH3 H3C H NaOH H CH3 H3C H O OH anti addition H CH3 inversion corresponds to overall syn addition of oxygen to the double bond 16-57 16.11 Reactions of Epoxides: A Review and a Preview 16-58 Reactions of Epoxides Reactions of Epoxides All reactions involve nucleophilic attack All at carbon and lead to opening of the ring. at An example is the reaction of ethylene oxide An with a Grignard reagent (discussed in Section 15.4 as a method for the synthesis of alcohols). as 16-59 Reaction of Grignard Reagents Reaction of Grignard Reagents with Epoxides with Epoxides R MgX CH2 H2C O R CH2 CH CH2 OMgX H3O+ RCH2CH2OH 16-60 Example Example Example CH2MgCl CH CH2 + H2C O 1. diethyl ether 2. H3O+ CH2CH2CH2OH CH (71%) 16-61 In general... In general... Reactions of epoxides involve attack by a nucleophile and proceed with ring-opening. For ethylene oxide: Nu—H Nu—H CH2 + H2C O Nu—CH2CH2O—H 16-62 In general... In general... For epoxides where the two carbons of the ring are differently substituted: Nucleophiles attack here when the reaction is catalyzed by acids: Anionic nucleophiles attack here: R CH2 C H O 16-63 16.12 Nucleophilic Ring-Opening Reactions of Epoxides 16-64 Example Example CH2 H2C O NaOCH2CH3 CH3CH2OH CH3CH2O CH2CH2OH (50%) 16-65 CH3CH2 Mechanism •• – O• •• • H2C CH2 O• •• • 16-66 CH3CH2 Mechanism •• – O• •• • CH2 H2C O• •• • CH3CH2 •• O CH2CH2 •• •• – •• O• •• • 16-67 CH3CH2 Mechanism •• – O• •• • H2C CH2 O• •• •• • CH3CH2 •• O CH2CH2 •• – •• •• O• •O • CH2CH3 H •• • 16-68 CH3CH2 Mechanism •• – O• •• • CH2 H2C O• •• •• •• • CH3CH2 •• – O CH2CH2 O •• •• •• O CH2CH2 •• •• O •• CH2CH3 H •• •• CH3CH2 •• •O • H – •• •O • •• CH2CH3 16-69 Example Example CH2 H2C O KSCH2CH2CH2CH3 ethanol-water, 0°C CH3CH2CH2CH2S CH2CH2OH (99%) 16-70 Stereochemistry Stereochemistry H H O OCH2CH3 NaOCH2CH3 CH3CH2OH H H OH (67%) Inversion of configuration at carbon being Inversion attacked by nucleophile attacked Suggests SN2-like transition state 16-71 Stereochemistry Stereochemistry H3C H R H3CH R O CH3 NH3 H2O H2N H S R H OH CH3 (70%) Inversion of configuration at carbon being Inversion attacked by nucleophile attacked Suggests SN2-like transition state 16-72 Stereochemistry Stereochemistry H3C H R CH3 R NH3 H2O O H3CH H2N H S R H OH CH3 H3N δ+ H (70%) H3C O H H3C δ- 16-73 Anionic nucleophile attacks less-crowded carbon Anionic nucleophile attacks less-crowded carbon H3C CH3 C H O NaOCH3 C CH3 CH3OH CH3O CH3 CH3CH CCH3 OH (53%) consistent with SN2-like transition state 16-74 Anionic nucleophile attacks less-crowded carbon Anionic nucleophile attacks less-crowded carbon MgBr + CHCH3 H2C O 1. diethyl ether 2. H3O+ CH2CHCH3 OH (60%) 16-75 Lithium aluminum hydride reduces epoxides Lithium aluminum hydride reduces epoxides CH(CH2)7CH3 H2C O Hydride attacks less-crowded carbon H3C 1. LiAlH4, diethyl ether 2. H2O CH(CH2)7CH3 OH (90%) 16-76 16.13 Acid-Catalyzed Ring-Opening Reactions of Epoxides 16-77 Example Example CH2 H2C O CH3CH2OH CH H2SO4, 25°C CH3CH2OCH2CH2OH (87-92%) CH3CH2OCH2CH2OCH2CH3 formed only on heating and/or longer reaction times 16-78 Example Example CH2 H2C O HBr 10°C BrCH2CH2OH (87-92%) BrCH2CH2Br formed only on heating and/or Br longer reaction times longer 16-79 Mechanism CH2 H2C •• • Br H • •• O• •• • H2C •• – • Br • •• •• H CH2 + O• • 16-80 Mechanism CH2 H2C •• • Br H • •• – • Br • •• • • HC 2 O• •• • H •• CH2 + O• • •• • Br • • • CH2CH2 •• •• OH •• 16-81 Figure 16.6 Figure 16.6 Figure Acid-Catalyzed Hydrolysis of Ethylene Oxide Acid-Catalyzed Hydrolysis of Ethylene Oxide Acid-Catalyzed Acid-Catalyzed Step 1 CH2 H2C O• H H •• •O H + • • H2C H •O • H • H CH2 + O• • • 16-82 Figure 16.6 Figure 16.6 Figure Figure Acid-Catalyzed Hydrolysis of Ethylene Oxide Acid-Catalyzed Hydrolysis of Ethylene Oxide Acid-Catalyzed Acid-Catalyzed H Step 2 H H H + O• • CH2CH2 O• •• • H2C H CH2 + O• • •• OH •• 16-83 Figure 16.6 Figure 16.6 Figure Figure Acid-Catalyzed Hydrolysis of Ethylene Oxide Acid-Catalyzed Hydrolysis of Ethylene Oxide Acid-Catalyzed Acid-Catalyzed Step 3 H H + O• • H H H O• •• • H •O• •• H + O• • CH2CH2 H CH2CH2 •• OH •• •• OH •• 16-84 Acid-Catalyzed Ring Opening of Epoxides Acid-Catalyzed Ring Opening of Epoxides Characteristics: nucleophile attacks more substituted carbon nucleophile of protonated epoxide of iinversion of configuration at site of nucleophilic nversion attack attack 16-85 Nucleophile attacks more-substituted carbon Nucleophile attacks more-substituted carbon H3C CH3 C H O C CH3 CH3OH H2SO4 OCH3 CH3CH OH CCH3 CH3 (76%) consistent with carbocation character at consistent transition state transition 16-86 Nucleophile attacks more-substituted carbon Nucleophile attacks more-substituted carbon H3C CH δ+ 3 C δ+ C H OH δ+ CH3 CH3OH H2SO4 OCH3 CH3CH OH CCH3 CH3 (76%) consistent with carbocation character at consistent transition state transition 16-86b Stereochemistry Stereochemistry H H O HBr OH H H Br (73%) Inversion of configuration at carbon being Inversion attacked by nucleophile attacked 16-87 Stereochemistry Stereochemistry H3C H R H3CH R O CH3 CH3OH H2SO4 CH3O H S R H OH CH3 (57%) Inversion of configuration at carbon being Inversion attacked by nucleophile attacked 16-88 Stereochemistry Stereochemistry H3C H R CH3 R CH3OH O CH3O H2SO4 H3CH H S R H OH CH3 H3C CH3O H δ+ H δ+ H H3C δ+ OH 16-89 H anti-Hydroxylation of Alkenes anti-Hydroxylation of Alkenes H O CH3COOH H O H2O HClO4 H H OH H (80%) OH 16-90 16.14 Epoxides in Biological Processes 16-91 Naturally Occurring Epoxides Naturally Occurring Epoxides are common are involved in numerous biological processes 16-92 Biosynthesis of Epoxides Biosynthesis of Epoxides C C + O2 + H+ + NADH enzyme C C + H2O + NAD+ O enzyme-catalyzed oxygen transfer from O2 to alkene enzymes are referred to as monooxygenases 16-93 Example: biological epoxidation of squalene Example: biological epoxidation of squalene O2, NADH monoxygenase O this reaction is an important step in the biosynthesis of cholesterol 16-94 16.15 Preparation of Sulfides 16-95 Preparation of RSR' Preparation of RSR' prepared by nucleophilic substitution (SN2) – •• S• R •• R' X • CH3CHCH CH Cl + CH2 NaSCH3 methanol R •• S •• R' CH3CHCH CH2 SCH3 16-96 16.16 Oxidation of Sulfides: Sulfoxides and Sulfones 16-97 Oxidation of RSR' Oxidation of RSR' R •• S •• R' R •• – •O • • •+ S •• R' R •• – •O • • • ++ S R' •O • – •• •• sulfide sulfoxide sulfone either the sulfoxide or the sulfone can be isolated either depending on the oxidizing agent and reaction depending conditions 16-98 Example Example •• NaIO4 NaIO •• – •O • • •+ •• water • SCH3 SCH3 (91%) Sodium metaperiodate oxidizes sulfides to sulfoxides and no further. further. 16-99 Example Example 1 equiv of H2O2 or a peroxy acid gives a sulfoxide, 2 equiv give a sulfone •• SCH •• CH2 CH H2O2 (2 equiv) •• – •O • • • ++ SCH CH2 CH •O • •• – •• (74-78%) (74-78%) 16-100 16.17 Alkylation of Sulfides: Sulfonium Salts 16-101 Sulfides can act as nucleophiles Sulfides can act as nucleophiles R •• S• + R" X R • R'' R + •• S R" X– R' product is a sulfonium salt 16-102 Example Example CH3(CH2)10CH2SCH3 CH3I + CH3(CH2)10CH2SCH3 I– CH3 16-103 Section 16.18 Spectroscopic Analysis of Ethers 16-104 Infrared Spectroscopy Infrared Spectroscopy Infrared C—O stretching: 1070 and 1150 cm-1 (strong) 16-105 Figure 16.8 Infrared Spectrum of Dipropyl Ether Figure 16.8 Infrared Spectrum of Dipropyl Ether Figure CH3CH2CH2OCH2CH2CH3 C—O—C C—O—C 3500 3000 2500 2000 1500 1000 500 Wave number, cm-1 16-106 H NMR 1 H NMR 1 H—C—O proton is deshielded by O; range is ca. δ 3.3-4.0 ppm. ca. δ 0.8 ppm 0.8 δ 1.4 ppm 1.4 δ 0.8 ppm 0.8 CH3 CH2 CH2 OCH2 CH2 CH3 CH OCH CH δ 3.2 ppm 3.2 16-107 CH3 CH2 CH2 OCH2 CH2 CH3 OC CH 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 Chemical shift (δ, ppm) 16-108 C NMR C NMR 13 13 Carbons of C—O—C appear iin the range δ 57-87 ppm. n 26.0 ppm 68.0 ppm O 16-109 UV-VIS UV-VIS Simple ethers have their absorption Simple maximum at about 185 nm and are transparent to ultraviolet radiation above about 220 nm. about 16-110 Mass Spectrometry Mass Spectrometry Molecular ion fragments to give oxygen-stabilized carbocation. •+ CH3CH2O CHCH2CH3 m/z 102 m/z 102 •• CH3 + CH3CH2O CH m/z 73 m/z 73 CH3 •• + CH3CH2O •• CHCH2CH3 m/z 87 m/z 87 16-111 End of Chapter 16 ...
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This document was uploaded on 01/03/2012.

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