ETHER King Saud University Chemistry Department 145 Chem1

Structure and nomenclature of ethers Ethers are compounds of formula R -O-R', where R and R' may be alkyl groups or aryl groups. Common names (Alkyl Alkyl Ether Names) Common names of ethers are formed by naming the two alkyl groups on oxygen and adding the word ether. Under the current system, the alkyl groups should be named in alphabetical order Chem King Saud University Chemistry Department

145 Chem3 King Saud University Chemistry Department H 3 C-O-CH 3 H 3 C-CH 2 -O-CH 2 -CH 3 H 2 C=CH-O-CH=CH 2 CommonDimethyl etherDiethyl etherDivinyl ether IUPAC Methoxy methaneEthoxy ethane H 3 C-O-C 6 H 13 H 3 C-O-CH 2 -CH 3 H 3 C-O-CH=CH 2 CommonHexyl methyl etherEthyl methyl etherMethyl vinyl ether IUPAC Methoxy hexanemehoxy ethaneMethoxy ethene Examples

145 Chem4 King Saud University Chemistry Department Common: Diphenyl ether IUPAC : Phenoxy benzene Common: Methyl Phenyl ether (anisole) IUPAC : Methoxy benzene 3-Methoxyhexane 5-Ethoxy-2-heptene 1-Phenoxy-1-propene Examples

Physical Properties of Ether Boiling Points The boiling points of ethers are lower than those of alcohols having the same molecular weights. Solubility in water  Ethers are much less soluble in water than alcohols.  More water-soluble than hydrocarbons of similar molecular weight. compoundFormulaMWBp (°C) ethanolCH 3 -CH 2 -OH4678 Dimethyl etherCH 3 -O-CH propaneCH 3 -CH 2 -CH Chem5 King Saud University Chemistry Department

Preparation of ehers Ethers by 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: Examples Chem King Saud University Chemistry Department

145 Chem7 King Saud University Chemistry Department The Williamson synthesis of ethers

The alkoxide is commonly made by adding Na or K to the alcohol Examples Chem King Saud University Chemistry Department 3,3-dimethyl-2-pentanol2-Methoxy-3,3-dimethypentane

Cleavage of ethers by hot concentrated acids When ethers are heated in concentrated acid solutions, the ether linkage is broken General equation: Specific example The acids most often used in this reaction are HI, HBr, and HCl. 9 Reaction of Ether 145 Chem King Saud University Chemistry Department

 If an excess of acid is present, the alcohol initially produced is converted into an alkyl halide by the reaction. For example 145 Chem10 King Saud University Chemistry Department

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. 11 Cyclic Ethers Epoxide 145 Chem King Saud University Chemistry Department

Chem King Saud University Chemistry Department 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 Chem King Saud University Chemistry Department

 Their reactivity 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. 145 Chem14 King Saud University Chemistry Department

2- Epoxides open in acidic alcohol solutions to form 2-alkoxy alcohols. 3- When an epoxide reacts with a hydrohalic acid ( HCl,HBr, or HI), a halide ion attacks the protonated epoxide. 4- Reactions of Epoxides with Grignard and Organolithium Reagents Chem King Saud University Chemistry Department

Exercise 1 Give a correct name for each of the following compounds. 16 Exercise 2 Propose a Williamson synthesis of 3-butoxy-1,1- dimethylcyclohexane from 3,3-dimethylcyclohexanol and butanol. 145 Chem King Saud University Chemistry Department

Exercise 3 Predict the products of the following reactions Chem King Saud University Chemistry Department