1 Dr Nahed Elsayed

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 H 2 O, ROH, HX, Grignard and organolithium eagents

Structure Of Ethers is a class of organic compounds that contain an ether linkage — an oxygen atom connected to two alkyl or aryl groups via σ bonds. thus Ethers feature C-O-C linkage — of general formula R–O–R or Ar–O–Ar or Ether: is a class of organic compounds that contain an ether linkage — an oxygen atom connected to two alkyl or aryl groups via σ bonds. thus Ethers feature C-O-C linkage — of general formula R–O–R or Ar–O–Ar ororganic compoundsoxygenatomalkylarylorganic compoundsoxygenatomalkylarylAr–O–R 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,----)

Alkyl group NameAlkoxy Group Name CH 3 – Methyl CH 3 O– Methoxy CH 3 CH 2 – Ethyl CH 3 CH 2 O– Ethoxy (CH 3 ) 2 CH– Isopropyl (CH 3 ) 2 CHO– Isopropoxy (CH 3 ) 3 C– tert-Butyl (CH 3 ) 3 CO– tert-Butoxy C6H5–C6H5–C6H5–C6H5–Phenyl C 6 H 5 O– Phenoxy The common alkoxy substituents are given names derived from their alkyl component

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

Physical Properties of Ether Physical properties of ethers Boiling Points The boiling points of ethers are lower than those of alcohols having the same molecular weights. Solubility in water compoundFormulaMWBp (°C) EthanolCH 3 -CH 2 -OH4678 Dimethyl etherCH 3 -O-CH PropaneCH 3 -CH 2 -CH  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)..

1) Dehydration of alcohols: 1) Dehydration of alcohols: The dehydration of alcohols takes place in the presence of acid catalysts (H 2 SO 4, H 3 PO 4 ) under controlled temperature. The general reaction for ether formation is Preparation of Ethers Examples

Preparation of Ethers 2)The Williamson synthes This method is usually used for preparation of unsymmetrical ethers ethers

9 Examples The alkoxide is commonly made by adding Na or K to the alcohol

Reactions Of Ethers Cleavage of ethers by hot concentrated acids General equation: The acids most often used in this reaction are HI, HBr, and HCl Specific example  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

 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. For example

 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 Cyclic Ethers  In cyclic ethers (heterocyclic), one or more carbons are replaced with oxygen.

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. Example 13

 Epoxides are much more reactive than common dialkyl ether this is due to 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 of ethylene oxide that form commercially important products are: 1- Epoxides open in acidic solutions to form glycols.

2- Epoxides open in acidic alcohol solutions to form alkoxy alcohols 3- When an epoxide reacts with a hydrohalic acid ( HCl, HBr, or HI), a halide ion attacks the protonated epoxide to give halo alcohol Reactions of Epoxides with Grignard and Organolithium Reagents to give longer alcohols

5- Ring opening of epoxides with amines

Exercise 1 Give a correct name for each of the following compounds. 17 Exercice 2 Propose a Williamson synthesis of 3-butoxy-1,1- dimethylcyclohexane from 3,3-dimethylcyclohexanol and butanol

Questions?