Ethers and Epoxides in Organic Chemistry

Ethers and Epoxides 1435 1435- -1436 2014 2014- -2015 1436 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 bonds. thus Ethers are compounds of general formula R O R or Ar O Ar or Ar O R R O R R O H H O H water ether alcohol 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 CH3O Methyl Methoxy CH3CH2 CH3CH2O Ethyl Ethoxy (CH3)2CH (CH3)2CHO Isopropyl Isopropoxy (CH3)3C (CH3)3CO tert-Butyl tert-Butoxy C6H5 C6H5O Phenyl Phenoxy 4

Ethers and Epoxides O H3C O CH3 O O Common Dimethyl ether Diethyl ether Divinyl ether Diphenyl ether IUPAC Methoxy methane Ethoxy ethane Phenoxy benzene O CH3 H3C O C6H13 O O Common Hexyl methyl ether Ethyl methyl ether Ethyl vinyl ether Methyl Phenyl ether IUPAC Methoxy hexane Methoxy ethane Ethoxy ethene Methoxy benzene CH3 CH3 (anisole) O O O CH3 H3C CH3 H3C CH3 IUPAC 3-Methoxyhexane 5-Ethoxy-2-heptene Propenyloxy benzene 5

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 ethanol Dimethyl ether propane Formula CH3-CH2-OH CH3-O-CH3 CH3-CH2-CH3 MW 46 46 44 Bp ( 78 -25 -42 C) 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 + H2O Examples heat symmetric ether H+ 2 H3 C O H H3 C O CH3 + H2O heat methyl ether (100 %) methyl alcohol H+ 2 CH3CH2 O H CH3CH2 O CH2CH3 H2O + heat ethyl alcohol ethyl ether (88 %) 7

Ethers and Epoxides Preparation of Ethers 2)The Williamson synthesis of ether This method is usually used for preparation of unsymmetrical ethers .. O .... Na+ R O R R + NaX R X + ether alkyl halide sodium alkoxide .. O .... Na+ O R + NaX R X + alkyl halide ether sodium phenoxide OHNaOH 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 Na+ O OH OCH2CH3 Na CH3CH2 Br + NaBr sodium ethoxycyclohexane cyclohexanol 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 heat General equation: + R O R H X R OH R X + (concentrated) Specific example heat CH3CH2O CH2CH3 + H I + CH3CH2I CH3CH2OH (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. 2 R X + H2O R O R 2 + H X For example heat CH3CH2 O CH2CH3 2 CH3CH2Br + H2O + 2HBr (conc, excess) 11

Ethers and Epoxides Cyclic Ethers-Epoxides: In cyclic ethers (heterocyclic), one or more carbons are replaced with oxygen. O O O O O Tetrahydrofuran 1,4-Dioxane Furan Oxirane Ethylene Oxide (epoxide) Epoxides are cyclic ethers in which the ether oxygen is part of a three- membered 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 O + R-C-O-O-H + R-C-O-H Example MCPBA O CH2Cl2 cyclohexene epoxycyclohexane Cl O 13 MCPBA : C-O-O-H

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. O OH + H3O CH CH R R R CH CH R OH 14

Ethers and Epoxides 2- Acid Catalyzed ring opening of epoxides in alcohol to form alkoxy alcohols CH3 O O + .. H3O + CH CH R OH H3 C R CH CH R 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 + CH CH R H X R CH CH R R OH 15

Ethers and Epoxides 4- Ring opening of epoxides with Grignard and Organolithium Reagents to give longer alcohols OH O 1) ether + CH CH R R R' MgX R CH CH R 2) H3O+ R' or R' Li 5- Ring opening of epoxides with amines NHCH3 O H3O+ CH3NH2 + R CH CH R R CH CH R OH 16

Ethers and Epoxides Exercise 1 Give a correct name for each of the following compounds. H3 C O CH2CH2CH3 CH2 O CH2CH3 CH3CHCH2CH3 CH2=CHCH2O CH2CH=CH2 O CH3 O O CH3 CH3CH2CHCH=CH2 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. CH3MgBr conc, HBr (e) (a) Di-n-butyl ether O H2O heat CH3O CH3OH (f) (b) CH3OH O O MCPA HBr (c) (g) O CH2Cl2 H3O+ LiAlH4 (d) (e) O O H2O 18

Ethers and Epoxides Thank You for your kind attention ! Questions? Comments 19