CHE 242 Unit V

Structure and Reactions of Alcohols, Ethers and Epoxides; Basic Principles of NMR Spectroscopy

CHAPTER FOURTEEN Terrence P. Sherlock Burlington County College 2004

Boiling Points Similar to alkanes of comparable molecular weight.

Chapter 14 2

Hydrogen Bond Acceptor • Ethers cannot H-bond to each other.

• In the presence of -OH or -NH (donor), the lone pair of electrons from ether forms a hydrogen bond with the -OH or -NH. Chapter 14 3 =>

Solvent Properties • Nonpolar solutes dissolve better in ether than in alcohol.

• Ether has large dipole moment, so polar solutes also dissolve.

• Ethers solvate cations. • Ethers do not react with strong bases.

Chapter 14 4 =>

Ether Complexes • Grignard reagents • Electrophiles O + H _ B H H BH 3 THF • Crown ethers Chapter 14 5 =>

Common Names of Ethers • Alkyl alkyl ether • Current rule: alphabetical order • Old rule: order of increasing complexity • Symmetrical: use dialkyl, or just alkyl.

• Examples: CH 3 CH 3 O C CH 3 CH 3 CH 2 O CH 2 CH 3 diethyl ether or ethyl ether Chapter 14 CH 3

t

-butyl methyl ether or methyl

t

-butyl ether => 6

IUPAC Names • Alkoxy alkane • Examples: CH 3 O CH 3 C CH 3 CH 3 2-methyl-2-methoxypropane Chapter 14 O CH 3 Methoxycyclohexane 7 =>

Naming Epoxides • Alkene oxide, from usual synthesis method H peroxybenzoic acid O cyclohexene oxide H • Epoxy attachment to parent compound, 1,2-epoxy-cyclohexane • Oxirane as parent, oxygen number 1

O H CH 3 CH 2 CH 3 H

trans

-2-ethyl-3-methyloxirane Chapter 14 8 =>

Spectroscopy of Ethers • IR: Compound contains oxygen, but O-H and C=O stretches are

absent

.

• MS:  -cleavage to form oxonium ion, or loss of either alkyl group.

• NMR: 13 C-O signal between  65  90, 1 H-C-O signal between  3.5  4. => 9 Chapter 14

Williamson Synthesis • Alkoxide ion + 1  alkyl bromide (or tosylate) • Example: CH 3 CH 3 O H + K CH 3 CH 3 _ O K + CH 3 CH 3 CH 3 CH 3 _ O CH 3 + CH 3 CH 2 H C H Br CH 3 CH 3 O CH 3 CH 2 CH 2 CH 3 + Br _ Chapter 14 => 10

Phenyl Ethers • Phenoxide ions are easily produced for use in the Williamson synthesis.

• Phenyl halides or tosylates cannot be used in this synthesis method.

O H + NaOH O _ Na + + HOH => Chapter 14 11

Bimolecular Dehydration of Alcohols • Industrial method, not good lab synthesis.

• If temperature is too high, alkene forms.

CH 3 CH 2 O H + H O CH 2 CH 3 H 2 SO 4 CH 3 CH 2 O CH 2 CH 3 140°C => 12 Chapter 14

Cleavage of Ethers • Ethers are unreactive toward base, but protonated ethers can undergo substitution reactions with strong acids.

• Alcohol leaving group is replaced by a halide.

• Reactivity: HI > HBr >> HCl => 13 Chapter 14

Mechanism for Cleavage • Ether is protonated.

CH 3 O CH 3 H Br CH 3 H O + CH 3 + Br _ _ • Alcohol leaves as halide attacks.

Br _ CH 3 H O + CH 3 Br CH 3 + H O CH 3 • Alcohol is protonated, halide attacks, and another molecule of alkyl bromide is formed. => Chapter 14 14

Phenyl Ether Cleavage • Phenol cannot react further to become halide.

• Example: O CH 2 CH 3 HBr OH + CH 3 CH 2 Br => 15 Chapter 14

Autoxidation of Ethers • In the presence of atmospheric oxygen, ethers slowly oxidize to hydroperoxides and dialkyl peroxides.

• Both are highly explosive.

• Precautions:  Do not distill to dryness.

 Store in full bottles with tight caps. => Chapter 14 16

POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5 TH EDITION” L.G. WADE ALL MATERIALS USED WITH PERMISSION OF AUTHOR PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE ORGANIC CHEMISTRY COURSE BY: ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN Chapter 14 17