有機化學-英文-chapter(10)PPT課件

1、Organic ChemistryWilliam H. BrownChristopher S. FooteBrent L. Iverson標題添加點擊此處輸入相關(guān)文本內(nèi)容點擊此處輸入相關(guān)文本內(nèi)容總體概述點擊此處輸入相關(guān)文本內(nèi)容標題添加點擊此處輸入相關(guān)文本內(nèi)容Ethers & EpoxidesChapter 11StructureThe functional group of an ether is an oxygen atom bonded to two carbon atomsin dialkyl ethers, oxygen is sp3 hybridized with bond angl

2、es of approximately 109.5. in dimethyl ether, the C-O-C bond angle is 110.3Structurein other ethers, the ether oxygen is bonded to an sp2 hybridized carbonin ethyl vinyl ether, for example, the ether oxygen is bonded to one sp3 hybridized carbon and one sp2 hybridized carbonNomenclature: ethersIUPAC

3、: the longest carbon chain is the parent name the OR group as an alkoxy substituentCommon names: name the groups bonded to oxygen in alphabetical order followed by the word ether2-Methoxy-2-methylpropane(tert-Butyl methyl ether)Ethoxyethane(Diethyl ether)CH3CH3CH3CH2OCH2CH3CH3OCCH3trans-2-Ethoxy-cyc

4、lohexanolOCH2CH3OHNomenclature: ethersAlthough cyclic ethers have IUPAC names, their common names are more widely usedIUPAC: prefix ox- shows oxygen in the ringthe suffixes -irane, -etane, -olane, and -ane show three, four, five, and six atoms in a saturated ringPhysical PropertiesAlthough ethers ar

5、e polar compounds, only weak dipole-dipole attractive forces exist between their molecules in the pure liquid statePhysical PropertiesBoiling points of ethers are lower than alcohols of comparable MWclose to those of hydrocarbons of comparable MW Ethers are hydrogen bond acceptorsthey are more solub

6、le in H2O than are hydrocarbonsPreparation of EthersWilliamson ether synthesis: SN2 displacement of halide, tosylate, or mesylate by alkoxide ionPreparation of Ethersyields are highest with methyl and 1 halides, lower with 2 halides (competing -elimination)reaction fails with 3 halides (-elimination

7、 only)Preparation of EthersAcid-catalyzed dehydration of alcoholsdiethyl ether and several other ethers are made on an industrial scale this waya specific example of an SN2 reaction in which a poor leaving group (OH-) is converted to a better one (H2O)Preparation of EthersStep 1: proton transfer giv

8、es an oxonium ionStep 2: nucleophilic displacement of H2O by the OH group of the alcohol gives a new oxonium ionPreparation of EthersStep 3: proton transfer to solvent completes the reactionPreparation of EthersAcid-catalyzed addition of alcohols to alkenesyields are highest using an alkene that can

9、 form a stable carbocationand using methanol or a 1 alcohol that is not prone to undergo acid-catalyzed dehydrationPreparation of EthersStep 1: protonation of the alkene gives a carbocationStep 2: reaction of the carbocation (an electrophile) with the alcohol (a nucleophile) gives an oxonium ionPrep

10、aration of EthersStep 3: proton transfer to solvent completes the reactionCleavage of EthersEthers are cleaved by HX to an alcohol and a haloalkanecleavage requires both a strong acid and a good nucleophile; therefore, the use of concentrated HI (57%) and HBr (48%)cleavage by concentrated HCl (38%)

11、is less effective, primarily because Cl- is a weaker nucleophile in water than either I- or Br-Cleavage of EthersA dialkyl ether is cleaved to two moles of haloalkaneCleavage of EthersStep 1: proton transfer to the oxygen atom of the ether gives an oxonium ionStep 2: nucleophilic displacement on the

12、 1 carbon gives a haloalkane and an alcoholthe alcohol is then converted to an haloalkane by another SN2 reactionCleavage of Ethers3, allylic, and benzylic ethers are particularly sensitive to cleavage by HXtert-butyl ethers are cleaved by HCl at room tempin this case, protonation of the ether oxyge

13、n is followed by C-O cleavage to give the tert-butyl cationOxidation of EthersEthers react with O2 at a C-H bond adjacent to the ether oxygen to give hydroperoxidesreaction occurs by a radical chain mechanismHydroperoxide: a compound containing the OOH groupSilyl Ethers as Protecting GroupsWhen deal

14、ing with compounds containing two or more functional groups, it is often necessary to protect one of them (to prevent its reaction) while reacting at the othersuppose you wish to carry out this transformationSilyl Ethers as Protecting Groupsthe new C-C bond can be formed by alkylation of an alkyne a

15、nionthe OH group, however, is more acidic (pKa 16-18) than the terminal alkyne (pKa 25)treating the compound with one mole of NaNH2 will give the alkoxide anion rather than the alkyne anionSilyl Ethers as Protecting GroupsA protecting group mustadd easily to the sensitive groupbe resistant to the re

16、agents used to transform the unprotected functional group(s)be removed easily to regenerate the original functional groupIn this chapter, we discuss trimethylsilyl (TMS) and other trialkylsilyl ethers as OH protecting groupsSilyl Ethers as Protecting GroupsSilicon is in Group 4A of the Periodic Tabl

17、e, immediately below carbonlike carbon, it also forms tetravalent compounds such as the followingSilyl Ethers as Protecting GroupsAn -OH group can be converted to a silyl ether by treating it with a trialkylsilyl chloride in the presence of a 3 amineSilyl Ethers as Protecting Groupsreplacement of on

18、e of the methyl groups of the TMS group by tert-butyl gives a tert-butyldimethylsilyl (TBDMS) group, which is considerably more stable than the TMS groupother common silyl protecting groups include the TES and TIPS groupsSilyl Ethers as Protecting Groupssilyl ethers are unaffected by most oxidizing

19、and reducing agents, and are stable to most nonaqueous acids and basesthe TBDMS group is stable in aqueous solution within the pH range 2 to 12, which makes it one of the most widely used -OH protecting groupssilyl blocking groups are most commonly removed by treatment with fluoride ion, generally i

20、n the form of tetrabutylammonium fluorideSilyl Ethers as Protecting Groupswe can use the TMS group as a protecting group in the conversion of 4-pentyn-1-ol to 4-heptyn-1-olEpoxidesEpoxide: a cyclic ether in which oxygen is one atom of a three-membered ringsimple epoxides are named as derivatives of

21、oxiranewhere the epoxide is part of another ring system, it is shown by the prefix epoxy-common names are derived from the name of the alkene from which the epoxide is formally derivedOxirane(Ethylene oxide)CH2H2CO123cis-2,3-Dimethyloxirane(cis-2-Butene oxide)1,2-Epoxycyclohexane(Cyclohexene oxide)C

22、OCHCH3HH3CHHO12Synthesis of EpoxidesEthylene oxide, one of the few epoxides manufactured on an industrial scale, is prepared by air oxidation of ethyleneOxirane(Ethylene oxide)CH2H2CO2CH2=CH2Ag2+O2Synthesis of EpoxidesThe most common laboratory method is oxidation of an alkene using a peroxycarboxyl

23、ic acid (a peracid)CO-COOHMg2+CH3COOHCOOHClMagnesium monoperoxyphthalate(MMPP)2Peroxyacetic acid (Peracetic acid)meta-chloroperoxy-benzoic acid(MCPBA)OOOOSynthesis of EpoxidesEpoxidation of cyclohexeneSynthesis of EpoxidesEpoxidation is stereospecific: epoxidation of cis-2-butene gives only cis-2,3-

24、dimethyloxiraneepoxidation of trans-2-butene gives only trans-2,3-dimethyloxiraneSynthesis of EpoxidesA mechanism for alkene epoxidation must take into account that the reactiontakes place in nonpolar solvents, which means that no ions are involvedis stereospecific with retention of the alkene confi

25、guration, which means that even though the pi bond is broken, at no time is there free rotation about the remaining sigma bond Synthesis of Epoxides A mechanism for alkene epoxidationSynthesis of EpoxidesEpoxides are can also be synthesized via halohydrinsthe second step is an internal SN2 reactionS

26、ynthesis of Epoxideshalohydrin formation is both regioselective and stereoselective; for alkenes that show cis,trans isomerism, it is also stereospecific (Section 6.3F)conversion of a halohydrin to an epoxide is stereoselectiveProblem: account for the fact that conversion of cis-2-butene to an epoxi

27、de by the halohydrin method gives only cis-2,3-dimethyloxirane cis-2,3-Dimethyloxiranecis-2-ButeneCCHCH3HH3CCCH3CHOCH3H1. Cl2, H2O2. NaOH, H2OSynthesis of EpoxidesSharpless epoxidationstereospecific and enantioselectiveReactions of EpoxidesEthers are not normally susceptible to attack by nucleophile

28、sBecause of the strain associated with the three-membered ring, epoxides readily undergo a variety of ring-opening reactionsReactions of EpoxidesAcid-catalyzed ring openingin the presence of an acid catalyst, such as sulfuric acid, epoxides are hydrolyzed to glycols+Oxirane(Ethylene oxide) 1,2-Ethan

29、ediol(Ethylene glycol)H2OH+HOOHOReactions of EpoxidesStep 1: proton transfer to oxygen gives a bridged oxonium ion intermediateStep 2: backside attack by water (a nucleophile) on the oxonium ion (an electrophile) opens the ringStep 3:proton transfer to solvent completes the reactionReactions of Epox

30、idesAttack of the nucleophile on the protonated epoxide shows anti stereoselectivity hydrolysis of an epoxycycloalkane gives a trans-1,2-diolReactions of EpoxidesCompare the stereochemistry of the glycols formed by these two methodsEpoxidesthe value of epoxides is the variety of nucleophiles that wi

31、ll open the ring and the combinations of functional groups that can be prepared from themReactions of EpoxidesTreatment of an epoxide with lithium aluminum hydride, LiAlH4, reduces the epoxide to an alcoholthe nucleophile attacking the epoxide ring is hydride ion, H:-Phenyloxirane(Styrene oxide)1-Ph

32、enylethanolCH2OCHOH1. LiAlH42. H2OCH-CH3Ethylene Oxide ethylene oxide is a valuable building block for organic synthesis because each of its carbons has a functional groupEthylene Oxidepart of the local anesthetic procaine is derived from ethylene oxidethe hydrochloride salt of procaine is marketed

33、under the trade name NovocaineEpichlorohydrinThe epoxide epichlorohydrin is also a valuable building block because each of its three carbons contains a reactive functional groupepichlorohydrin is synthesized from propeneEpichlorohydrinthe characteristic structural feature of a product derived from e

34、pichlorohydrin is a three-carbon unit with -OH on the middle carbon, and a carbon, nitrogen, oxygen, or sulfur nucleophile on the two end carbonsEpichlorohydrinan example of a compound containing the three-carbon skeleton of epichlorohydrin is nadolol, a b-adrenergic blocker with vasodilating activityCrown EthersCrown ether: a cyclic polyether derived from ethylene glycol or a substituted ethylene glycolthe parent name is crown, preceded by a number describing t