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Sulfur-Containing Compounds
Organic Chemistry 4th Edition Paula Yurkanis Bruice Chapter 12 Reactions of Alcohols, Ethers, Epoxides, and Sulfur-Containing Compounds Organometallic Compounds Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall
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Alcohols and ethers have to be activated before they can undergo a substitution or an elimination reaction Convert the strongly basic leaving group (OH–) into a good leaving group Only weakly basic nucleophiles can be used
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Secondary and tertiary alcohols undergo SN1 reactions
with hydrogen halides
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Primary alcohols undergo SN2 reactions with hydrogen
halides
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ZnCl can be used to catalyze certain SN2 reactions
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Look out for rearrangement product in the SN1 reaction
of the secondary or tertiary alcohol
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Amines do not undergo substitution reactions because
NH2– is a very strong base (a very poor leaving group) RCH2F > RCH2OH > RCH2NH2 HF H2O NH3 pKa = 3.2 pKa = 15.7 pKa = 36 Protonation of the amine moiety does not solve the problem
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Other Methods for Converting Alcohols
into Alkyl Halides
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Activation by SOCl2
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Converting Alcohols into Sulfonates
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Several sulfonyl chlorides are available to activate OH
groups
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SN2 of the Activated Sulfonates
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Dehydration of Alcohols
To prevent the rehydration of the alkene product, one needs to remove the product as it is formed
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Look out for carbocation rearrangement
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Ring Expansion
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Primary Alcohols Undergo Dehydration by an E2 Pathway
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The Stereochemical Outcome of the E1 Dehydration
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A Milder Way to Dehydrate an Alcohol
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Substitution Reactions of Ethers
Activation of ether by protonation
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Reactions of Epoxides Epoxides
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Nucleophilic attack of hydroxide ion on ethylene oxide
and on diethyl ether
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Ring Opening
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When a nucleophile attacks an unprotonated epoxide,
the reaction is a pure SN2 reaction
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Epoxides Are Synthetically Useful Reagents
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Crown Ethers
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A crown ether specifically binds certain metal ions or
organic molecules to form a host–guest complex, an example of molecular recognition
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Thiols are sulfur analogs of alcohols
ethanethiol 1-propanethiol 3-methyl-1-butanethiol 2-mercaptoethanol are stronger acids (pKa = 10) than alcohols are not good at hydrogen-binding
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In protic solvent, thiolate ions are better nucleophiles
than alkoxide ions CH3OH
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The sulfur analogs of ethers are called sulfides or
thioethers Sulfur is an excellent nucleophile because its electron cloud is polarized
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Organometallic Compounds
An organic compound containing a carbon–metal bond
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Preparation of Organolithium Compounds
hexane 1-bromobutane butyllithium hexane chlorobenzene phenyllithium
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Preparation of Organomagnesium Compounds
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Alkyl halides, vinyl halides, and aryl halides can all be
used to form organolithium and organomagnesium compounds However, these organometallic compounds cannot be prepared from compounds containing acidic groups (OH, NH2, NHR, SH, C=CH, CO2H)
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A Grignard reagent will undergo transmetallation if it is added to a metal halide whose metal is more electropositive than magnesium
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Coupling Reactions Formation of carbon–carbon bonds
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The Heck Reaction Pd(PPh3)4 (CH3CH2)3N Pd(PPh3)4 (CH3CH2)3N
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The Stille Reaction Pd(Ph3)4 THF Pd(Ph3)4 THF
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The Suzuki Coupling Pd(PPh3)4 NaOH Pd(PPh3)4 NaOH
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