406 ETHERS, EPOXIDES, AND SULFIDES of the tosylate with a nucleophile proceeds by inversion of configuration in an Sy2 process. The product has the S configuration H,C H H-C CH3(CH)CH CH3(CH2)CH (R)-2-0ctanol (R)-l-Methy heptyl tosylate chloride HC yo}cm;+cAsx一 CHS (R)-1-Methy heptyl tosylate (S)1-Methylheptyl phenyl sulfide benzenethiolate 16.17 Phenyl vinyl sulfoxide lacks a plane of symmetry and is chiral. Phenyl vinyl sulfone is achiral a plane of symmetry passes through the phenyl and vinyl groups and the central sulfur atom. CSHE CH H,C=CH O H,C=CH Phenyl vinyl sulfoxide (chiral) 16.18 As shown in the text, dodecyldimethylsulfonium iodide may be prepared by reaction of dodecyl methyl sulfide with methyl iodide. An alternative method is the reaction of dodecyl iodide with dimethyl sulfide (CH3)2S+ CH, (CH))loCH,I CH3(CH)1oCHrS(CH3)2I Dimethyl The reaction of a sulfide with an alkyl halide is an Sn2 process. The faster reaction will be the one that uses the less sterically hindered alkyl halide. The method presented in the text will procee faster 16.19 The molecular ion from sec-butyl ethyl ether can also fragment by cleavage of a carbor bond in its ethyl group to give an oxygen-stabilized cation of m/z87 -CHCH,CHa CH3 CH2= CH3 m/87 16.20 All the constitutionally isomeric ethers of molecular formula CsHno belong to one of two general groups: CH,OCAHo and CH,CH,OC3H, Thus, we have CH_OCH, CH CH, CH3 CHyOCHCH, CH CH, OCH,CH(O CH,OC(CH,) Isobutyl methyl ether tert-Butyl methyl ether CHaCH2OCH, CH,, and CH, CH,OCH(CH3) Ethyl propyl ether Ethyl isopropyl ether Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
of the tosylate with a nucleophile proceeds by inversion of configuration in an SN2 process. The product has the S configuration. 16.17 Phenyl vinyl sulfoxide lacks a plane of symmetry and is chiral. Phenyl vinyl sulfone is achiral; a plane of symmetry passes through the phenyl and vinyl groups and the central sulfur atom. 16.18 As shown in the text, dodecyldimethylsulfonium iodide may be prepared by reaction of dodecyl methyl sulfide with methyl iodide. An alternative method is the reaction of dodecyl iodide with dimethyl sulfide. The reaction of a sulfide with an alkyl halide is an SN2 process. The faster reaction will be the one that uses the less sterically hindered alkyl halide. The method presented in the text will proceed faster. 16.19 The molecular ion from sec-butyl ethyl ether can also fragment by cleavage of a carbon–carbon bond in its ethyl group to give an oxygen-stabilized cation of mz 87. 16.20 All the constitutionally isomeric ethers of molecular formula C5H12O belong to one of two general groups: CH3OC4H9 and CH3CH2OC3H7. Thus, we have CH3CH2OCH2CH2CH3 and CH3CH2OCH(CH3)2 Ethyl propyl ether Ethyl isopropyl ether CH3OCH2CH(CH3)2 Isobutyl methyl ether CH3OC(CH3)3 tert-Butyl methyl ether CH3OCH2CH2CH2CH3 Butyl methyl ether CH3OCHCH2CH3 CH3 sec-Butyl methyl ether CH3 CH2 CHCH2CH3 CH3 O CH3 CH2 CHCH2CH3 CH3 O m/z 87 Dimethyl sulfide Dodecyl iodide Dodecyldimethylsulfonium iodide (CH3)2S CH3(CH2)10CH2 I CH3(CH2)10CH2S(CH3)2 I Phenyl vinyl sulfoxide (chiral) S C6H5 O H2C CH Phenyl vinyl sulfone (achiral) S C6H5 O O H2C CH 2 C6H5S Na Sodium benzenethiolate C6H5S C (R)-1-Methylheptyl tosylate (S)-1-Methylheptyl phenyl sulfide O S CH3 O O H CH3 C H H3C CH3(CH2)4CH2 CH2(CH2)4CH3 C OH H H3C CH3(CH2)4CH2 (R)-2-Octanol Cl CH3 O S O p-Toluenesulfonyl chloride C O H H3C CH3(CH2)4CH2 CH3 O S O (R)-1-Methylheptyl tosylate 406 ETHERS, EPOXIDES, AND SULFIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ETHERS, EPOXIDES, AND SULFIDES 407 These ethers could also have been named as"alkoxyalkane. Thus sec-butyl methyl ether would become 2-methoxybutane 16.21 Isoflurane and enflurane are both halogenated derivatives of ethyl methyl ether F-C-CH-O—CHF2 1-Chloro-2, 2, 2-trifluoroethyl Enflurane ClC-C-0—CHF 2-Chloro-1, 1, 2-trifluoroethyl difluoromethyl ether 16.22 (a) The parent compound is cyclopropane. It has a three-membered epoxide function, and thus a reasonable name is epoxycyclopropane. Numbers locating positions of attachment(as in 1, 2-epoxycyclopropane")are not necessary, because no other structures (1, 3 or 2, 3)are pos sible here (b) The longest continuous carbon chain has seven carbons, and so the compound is named as a derivative of heptane. The epoxy function bridges C-2 and C-4. Therefore H H H,CH3 (c) The oxygen atom bridges the C-1 and C-4 atoms of a cyclohexane ring 1, 4-Epoxycyclohexane (d) Eight carbon atoms are continuously linked and bridged by an oxygen. We name the com Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
These ethers could also have been named as “alkoxyalkanes.” Thus, sec-butyl methyl ether would become 2-methoxybutane. 16.21 Isoflurane and enflurane are both halogenated derivatives of ethyl methyl ether. Isoflurane: Enflurane: 16.22 (a) The parent compound is cyclopropane. It has a three-membered epoxide function, and thus a reasonable name is epoxycyclopropane. Numbers locating positions of attachment (as in “1,2-epoxycyclopropane”) are not necessary, because no other structures (1,3 or 2,3) are possible here. (b) The longest continuous carbon chain has seven carbons, and so the compound is named as a derivative of heptane. The epoxy function bridges C-2 and C-4. Therefore is 2-methyl-2,4-epoxyheptane. (c) The oxygen atom bridges the C-1 and C-4 atoms of a cyclohexane ring. (d) Eight carbon atoms are continuously linked and bridged by an oxygen. We name the compound as an epoxy derivative of cyclooctane. 1 5 2 3 4 6 7 8 O 1,5-Epoxycyclooctane O 1 2 3 5 4 6 1,4-Epoxycyclohexane CH2CH2CH3 H3C H3C 1 2 3 4 567 O O Epoxycyclopropane Cl C F H F F C O CHF2 2-Chloro-1,1,2-trifluoroethyl difluoromethyl ether F C F Cl F CH O CHF2 1-Chloro-2,2,2-trifluoroethyl difluoromethyl ether ETHERS, EPOXIDES, AND SULFIDES 407 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
408 ETHERS, EPOXIDES, AND SULFIDES 6.23 (a) There are three methyl-substituted thanes two of which are chiral (b) The locants in the name indicate the positions of the sulfur atoms in 1, 4-dithiane and 1,3,5- 1. 4-Dithiane 13.5-Trithiane (c) Disulfides possess two adjacent sulfur atoms. 1, 2-Dithiane is a disulfide. 1. 2-Dithiane (d) Two chair conformations of the sulfoxide derived from thane are possible; the oxygen atom may be either equatorial or axial 16.24 Intramolecular hydrogen bonding between the hydroxyl group and the ring oxygens is possible when the hydroxyl group is axial but not when it is equatorial HO Less stable conformation: More stable conformation: no intramolecular hydrogen bonding hydrogen bonding 16.25 The ethers that are to be prepared are CHaOCH, CH,CH3 CH,OCH(CH3)2 CH CH,OCH, Methyl propyl ether Isopropyl methyl ether Diethyl ether First examine the preparation of each ether by the williamson method. Methyl propyl ether can be prepared in two ways: CH, ONa CH, CHCH,Br CH,OCH,CH,CH 1-Bromopropane Methyl propyl ether CH3 Br CH3 CH, CH,ONa CH,OCH, CH, CH Sodium propoxide Methyl propyl ether Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
16.23 (a) There are three methyl-substituted thianes, two of which are chiral. (b) The locants in the name indicate the positions of the sulfur atoms in 1,4-dithiane and 1,3,5- trithiane. (c) Disulfides possess two adjacent sulfur atoms. 1,2-Dithiane is a disulfide. (d) Two chair conformations of the sulfoxide derived from thiane are possible; the oxygen atom may be either equatorial or axial. 16.24 Intramolecular hydrogen bonding between the hydroxyl group and the ring oxygens is possible when the hydroxyl group is axial but not when it is equatorial. 16.25 The ethers that are to be prepared are First examine the preparation of each ether by the Williamson method. Methyl propyl ether can be prepared in two ways: CH3Br Methyl bromide CH3CH2CH2ONa Sodium propoxide CH3OCH2CH2CH3 Methyl propyl ether CH3ONa Sodium methoxide CH3CH2CH2Br 1-Bromopropane CH3OCH2CH2CH3 Methyl propyl ether CH3OCH2CH2CH3 and Methyl propyl ether CH3OCH(CH3)2 Isopropyl methyl ether CH3CH2OCH2CH3 Diethyl ether O HO O Less stable conformation; no intramolecular hydrogen bonding O O O H More stable conformation; stabilized by hydrogen bonding S O S O S S 1,2-Dithiane S S 1,4-Dithiane S S S 1,3,5-Trithiane S CH3 2-Methylthiane (chiral) S CH3 3-Methylthiane (chiral) S CH3 4-Methylthiane (achiral) 408 ETHERS, EPOXIDES, AND SULFIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ETHERS, EPOXIDES, AND SULFIDES 409 Either combination is satisfactory. The necessary reagents are prepa shown CHOH CH ONa Methanol Sodium CHCH..OH (or HBr) CH,CH - Bromopropane CHB Meth Meth CHCH, CH,OH CHaCH,CHLONa Isopropyl methyl ether is best prepared by the reaction CHa Br +(CH3)2CHONa CH3OCH(CH3) Methyl bromide Sodium isopropoxide The reaction of sodium methoxide with isopropyl bromide will proceed mainly by elimination Methyl bromide is prepared as shown previously; sodium isopropoxide can be prepared by adding sodium to isopropyl alcohol. Diethyl ether may be prepared as outlined CHaCHLOH CHCHONa Sodium ethoxide CHa CH2OHfor HBr) CH3CH2Br Ethyl bromide CHaCHLONa CH3 CH, Br CHa CH,OCH- CH3 NaBr Sodium ethoxide Ethyl bromide Diethyl ether bromide 16.26 (a) Secondary alkyl halides react with alkoxide bases by E2 elimination as the major pathway The Williamson ether synthesis is not a useful reaction with secondary alkyl hali CH3CH CHCH3 CH; CH,CHCH,+ NaBr Sodium 2-butanolate Bromocyclohexane yclohexene Sodium (b) Sodium alkoxide acts as a nucleophile toward iodoethane to yield an alkyl ethyl ether. CH,CH, CH3 CHCH CH3 O Na CHaCH, -OCH,CH (R)-2-Ethoxybutane Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
Either combination is satisfactory. The necessary reagents are prepared as shown. Isopropyl methyl ether is best prepared by the reaction The reaction of sodium methoxide with isopropyl bromide will proceed mainly by elimination. Methyl bromide is prepared as shown previously; sodium isopropoxide can be prepared by adding sodium to isopropyl alcohol. Diethyl ether may be prepared as outlined: 16.26 (a) Secondary alkyl halides react with alkoxide bases by E2 elimination as the major pathway. The Williamson ether synthesis is not a useful reaction with secondary alkyl halides. (b) Sodium alkoxide acts as a nucleophile toward iodoethane to yield an alkyl ethyl ether. (R)-2-Ethoxybutane O Na CH3CH2 C I C OCH2CH3 CH CH3 3CH2 H CH CH3 3CH2 H CH3CH2CHCH3 ONa Sodium 2-butanolate Br Bromocyclohexane CH3CH2CHCH3 OH 2-Butanol Cyclohexene NaBr Sodium bromide CH3CH2ONa CH3CH2Br Sodium ethoxide Ethyl bromide CH3CH2OCH2CH3 Diethyl ether NaBr Sodium bromide CH3CH2OH Ethanol CH3CH2Br Ethyl bromide PBr3 (or HBr) CH3CH2OH Ethanol CH3CH2ONa Sodium ethoxide Na CH3Br Methyl bromide (CH3)2CHONa Sodium isopropoxide CH3OCH(CH3)2 Isopropyl methyl ether CH3CH2CH2OH 1-Propanol CH3CH2CH2ONa Sodium propoxide Na CH3OH Methanol CH3Br Methyl bromide PBr3 (or HBr) CH3CH2CH2OH 1-Propanol CH3CH2CH2Br 1-Bromopropane PBr3 (or HBr) CH3OH Methanol CH3ONa Sodium methoxide Na ETHERS, EPOXIDES, AND SULFIDES 409 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website