Ethers and Epoxides 1435-1436 2014-2015 1 1 Ethers and Epoxides Learning Objectives Chapter seven discusses the following topics and by the end of this chapter the students will: Know the structure of ethers Know the different methods of naming ethers Know the physical properties of ethers Know the different methods used in preparation of ethers Know the reactions of opened ethers with HX Know the different methods used in synthesis of epoxides Know the reactions of epoxides with different nucleophiles such as H2O, ROH, HX, Grignard and organolithium eagents 2 Ethers and Epoxides Structure Of Ethers Ether: is a class of organic compounds in which an oxygen atom connected to two organic groups (alkyl or aryl"benzene ring") by σ bonds. thus Ethers are compounds of general formula R–O–R or Ar–O–Ar or Ar–O–R H O water H R O H alcohol R O R ether Nomenclature Of Ethers Common names The common names of ethers are derived by naming the alkyl groups bonded to the oxygen then listing them in alphabetical order followed by the word "ether". IUPAC names The ether functional group does not have a characteristic IUPAC nomenclature suffix, so it is necessary to designate the smaller alkyl group as an alkoxy substituent of a parent compound (alkane , or alkene, or alkyne,or alcohol,----) 3 Ethers and Epoxides The common alkoxy substituents are given names derived from their alkyl component Alkyl group Name Alkoxy Group Name CH3– Methyl CH3O– Methoxy CH3CH2– Ethyl CH3CH2O– Ethoxy (CH3)2CH– Isopropyl (CH3)2CHO– Isopropoxy (CH3)3C– tert-Butyl (CH3)3CO– tert-Butoxy C6H5– Phenyl C6H5O– Phenoxy 4 Ethers and Epoxides O H3C O CH3 O O Common Dimethyl ether Diethyl ether IUPAC Methoxy methane Ethoxy ethane Divinyl ether Diphenyl ether Phenoxy benzene O H3C O C6H13 Common Hexyl methyl ether IUPAC Methoxy hexane O O Ethyl methyl ether Ethyl vinyl ether Methyl Phenyl ether (anisole) Methoxy ethane Ethoxy ethene Methoxy benzene CH3 CH3 CH3 IUPAC 3-Methoxyhexane O O O H3C CH3 H3C 5-Ethoxy-2-heptene CH3 Propenyloxy benzene5 CH3 Ethers and Epoxides Physical Properties of Ether 1) Boiling Points The boiling points of ethers are lower than those of alcohols having the same molecular weights. compound Formula MW Bp (°C) CH3-CH2-OH 46 78 Dimethyl ether CH3-O-CH3 46 -25 propane CH3-CH2-CH3 44 -42 ethanol 2) Solubility in water Ethers are much less soluble in water than alcohols (Because they don’t have –OH group, So they are not hydrogen bond donors). More water-soluble than hydrocarbons of similar molecular weight (Because they are polar). 6 Ethers and Epoxides Preparation of Ethers 1) Dehydration of alcohols: (only Symmetric ether) The dehydration of alcohols takes place in the presence of acid catalysts (H2SO4, H3PO4) under controlled temperature (140 oC). The general reaction for ether formation is H R O H + H O R + R O R heat Examples 2 H3C O H H + H2O symmetric ether + H3C heat methyl alcohol O CH3 + H2O methyl ether (100 %) 2 CH3CH2 O H H + CH3CH2 O CH2CH3 + H2O heat ethyl alcohol ethyl ether (88 %) 7 Ethers and Epoxides Preparation of Ethers 2)The Williamson synthes This method is usually used for preparation of unsymmetrical ethers R .. . . O .. Na + R + Na + + sodium phenoxide OH NaOH R R + NaX ether alkyl halide sodium alkoxide .. . O ... R O X O X alkyl halide R + NaX ether ONa 8 Ethers and Epoxides 3)Alkoxide from alcohol The alkoxide is commonly made by adding Na or K to the alcohol The phenoxide is commonly made by adding NaOH to the phenol Examples + O Na OH Na OCH2CH3 CH3CH2 Br + sodium cyclohexanol NaBr ethoxycyclohexane cyclohexyloxide OH OCH3 1) Na 2) CH3I 3,3-dimethyl-2-pentanol 2-Methoxy-3,3-dimethylpentane 9 Ethers and Epoxides Reactions Of Ethers Cleavage of ethers by hot concentrated acids Ethers are quite stable compounds. Ethers react only under strongly acidic condition.When ethers are heated in concentrated acid solutions, the ether linkage is broken General equation: R O R + heat H X R OH + R X (concentrated) Specific example CH3CH2 O CH2CH3 + heat H I CH3CH2OH + CH3CH2I (concentrated) The acids most often used in this reaction are HI, HBr, and HCl 10 Ethers and Epoxides If an excess of acid is present, the alcohol initially produced is converted to alkyl halide thus the net products will be 2 moles of alkyl halide. R O R 2 R X + 2H X + H2O For example heat CH3CH2 O CH2CH3 + 2HBr 2 CH3CH2Br + H2O (conc, excess) 11 Ethers and Epoxides Cyclic Ethers-Epoxides: In cyclic ethers (heterocyclic), one or more carbons are replaced with oxygen. O O O Tetrahydrofuran O O Furan 1,4-Dioxane Oxirane Ethylene Oxide (epoxide) Epoxides are cyclic ethers in which the ether oxygen is part of a threemembered ring. The simplest and most important epoxide is ethylene oxide. 12 Ethers and Epoxides Peroxyacid Epoxidation Peroxyacids (sometimes called peracids) are used to convert alkenes to epoxides. If the reaction takes place in aqueous acid, the epoxide opens to a glycol. Because of its desirable solubility properties, meta-chloroperoxybenzoic acid (MCPBA) is often used for these epoxidations. O + O R-C-O-O-H Example O + R-C-O-H MCPBA O CH2Cl2 cyclohexene Cl MCPBA : epoxycyclohexane O C-O-O-H 13 Ethers and Epoxides Epoxides are much more reactive than common dialkyl ether, because of the strain in the three-membered ring, which is relieved when the epoxide ring is opened after a reaction has taken place. Examples of ring-opening reactions(cleavage carbon-oxygen bond) of ethylene oxide that form commercially important products are: 1- Acid –Catalyzed ring opening of epoxides in water to form glycols. OH O R CH H3O CH R + R CH CH R OH 14 Ethers and Epoxides 2- Acid –Catalyzed ring opening of epoxides in alcohol to form alkoxy alcohols .. H3C OH O + R CH CH R OCH3 + H3O R CH CH R OH 3- Acid –Catalyzed ring opening of epoxides with a hydrohalic acid (HCl, HBr, or HI), a halide ion attacks the protonated epoxide to give halo alcohol . X O H X + R CH CH R R CH CH R OH 15 Ethers and Epoxides 4- Ring opening of epoxides with Grignard and Organolithium Reagents to give longer alcohols OH O R' MgX + R CH 1) ether CH R R CH CH R 2) H3O+ or R' R' Li 5- Ring opening of epoxides with amines NHCH3 O CH3NH2 + R CH CH R H3O+ R CH CH R OH 16 Ethers and Epoxides Exercise 1 Give a correct name for each of the following compounds. H3C O CH2CH2CH3 CH3CHCH2CH3 CH2 O CH2CH3 CH2=CHCH2 O CH2CH=CH2 O CH3 O CH3CH2CHCH=CH2 CH3 O CH3 O CH2CH3 Exercice 2 Propose a Williamson synthesis of 3-butoxy-1,1-dimethylcyclohexane from 3,3-dimethylcyclohexanol and butanol 17 Ethers and Epoxides Exercise 3 Predict the products of the following reactions. (a) Di-n-butyl ether conc, HBr CH3MgBr (e) O heat CH3OH (b) CH3O (f) O O HBr (c) CH2Cl2 H3O+ LiAlH4 (e) O CH3OH MCPA (g) O (d) H2O O H2O 18 Ethers and Epoxides Thank You for your kind attention ! Questions? Comments 19