Transcript Slide 1
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 (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 because NH2– is a very strong base (a very poor leaving group) RCH2F > RCH2OH > RCH2NH2 HF pKa = 3.2 H2O NH3 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 or organic molecules to form a host–guest complex, an example of molecular recognition Thiols are sulfur analogs of alcohols ethanethiol 3-methyl-1-butanethiol 1-propanethiol 2-mercaptoethanol They are stronger acids (pKa = 10) than alcohols, but do not exhibit hydrogen-binding 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 electron cloud is polarized Organometallic Compounds An organic compound containing a carbon–metal bond Preparation of Organolithium Compounds hexane CH3CH2CH2CH2Br + 2 Li 1-bromobutane CH3CH2CH2CH2Li + LiBr butyllithium hexane Cl chlorobenzene + 2 Li Li phenyllithium + LiCl Preparation of Organomagnesium Compounds 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) Coupling Reactions Formation of carbon–carbon bonds