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Chapter 12 Reactions of Alcohols, Ethers, Epoxides, and Sulfur-Containing Compounds Organometallic Compounds. Irene Lee Case Western Reserve University Cleveland, OH. Reactions of Alcohols. reaction with hydrogen halides acid-catalyzed dehydration (E 1 Rxn) - PowerPoint PPT Presentation
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Chapter 12
Reactions of Alcohols,Ethers, Epoxides, and
Sulfur-Containing Compounds
Organometallic Compounds
Irene LeeCase Western Reserve University
Cleveland, OH
Reactions of Alcohols
•reaction with hydrogen halides
•acid-catalyzed dehydration (E1 Rxn)
•reaction with thionyl chloride
•reaction with phosphorous tribromide & PCl3
•conversion to sulfonate esters
Secondary and tertiary alcohols undergo SN1 reactions with hydrogen halides
Primary alcohols undergo SN2 reactions with hydrogen halides
ZnCl2 can be used to catalyze certain SN2 reactions
Rearrangement of secondary or tertiary alcohols can occur in the SN1 reaction
Amines do not undergo substitution reactions becauseNH2
– is a very strong base (a very poor leaving group)
RCH2F > RCH2OH > RCH2NH2
HF H2O NH3
pKa = 3.2 pKa = 15.7 pKa = 36
Other Methods for Converting Alcohols into Alkyl Halides
Activation by SOCl2
Converting Alcohols into Sulfonates(Excellent Leaving Groups)
Several sulfonyl chlorides are available to react with -OH group
SN2 Reactions of Activated Sulfonates
Dehydration of Alcohols
To prevent the rehydration of the alkene product, one needs to remove the product as it is formed
Carbocation Rearrangement
Ring Expansion
Primary Alcohols Undergo Dehydration by an E2 Pathway
Stereochemistry of the E1 Dehydration
Milder Dehydration
Substitution Reactions of Ethers
Activation of ether by protonation
Reactions of Epoxides
Epoxides
Nucleophilic attack of hydroxide ion on ethylene oxide and on diethyl ether
Ring Opening
When a nucleophile attacks an unprotonated epoxide,the reaction is a pure SN2 reaction
Epoxides Are Synthetically Useful Reagents
Crown Ethers
A crown ether specifically binds certain metal ions ororganic molecules to form a host–guest complex, an
example of molecular recognition
Thiols are sulfur analogs of alcohols
They are stronger acids (pKa = 10) than alcohols, but do not exhibit hydrogen-binding
ethanethiol 1-propanethiol
3-methyl-1-butanethiol 2-mercaptoethanol
In protic solvent, thiolate ions are better nucleophiles than alkoxide ions
CH3OH
The sulfur analogs of ethers are called sulfides or thioethers
Sulfur is an excellent nucleophile because its electroncloud is polarized
Organometallic CompoundsAn organic compound containing a carbon–metal bond
Preparation of Organolithium Compounds
CH3CH2CH2CH2Br + 2 Li CH3CH2CH 2CH 2Li + L iBr
Cl + 2 Li Li + L iCl
hexane
hexane
1-bromobutane butyllithium
chlorobenzene phenyllithium
Preparation of Organomagnesium Compounds
Alkyl halides, vinyl halides, and aryl halides can all be used to form organolithium and organomagnesiumcompounds
However, these organometallic compounds cannot be prepared from compounds containing acidic groups (OH, NH2, NHR, SH, C=CH, CO2H)
Coupling Reactions
Formation of carbon–carbon bonds