Organic Chemistry

Section 12.6 Substitution Reactions of Ethers 453

Table 12.2 Some Ethers That Are Used as Solvents

CH 3 CH 2 OCH 2 CH 3 CH 3 OCH 2 CH 2 OCH 3 CH 3 OC(CH 3 ) 3

OO

O

diethyl ether

"ether"

tetrahydrofuran

THF

1,4-dioxane 1,2-dimethoxyethane

DME

tert-butyl methyl ether

MTBE

tetrahydropyran

O

Amputation of a leg

without anesthetic in 1528.

is a better nucleophile than Only a substitution product is obtained because the

bases present in the reaction mixture (halide ions and ) are too weak to abstract a

proton in an E2 reaction, and any alkene formed in an E1 reaction would undergo

electrophilic addition with HBr or HI to form the same alkyl halide as would be

obtained from the substitution reaction. Concentrated HCl cannot cleave ethers

because is too poor a nucleophile.

Because the only reagents with which ethers react are hydrogen halides, ethers are

frequently used as solvents. Some common ether solvents are shown in Table 12.2.

Cl-

H 2 O

Br-.

3-D Molecules:

Diethyl ether;

Tetrahydrofuran

PROBLEM 13

Explain why methyl propyl ether forms both methyl iodide and propyl iodide when it is

heated with excess HI.

PROBLEM 14

Can HF be used to cleave ethers? Explain.

ANESTHETICS

Because diethyl ether (commonly known simply as ether) is a short-lived muscle

relaxant, it has been widely used as an inhalation anesthetic. However, because it

takes effect slowly and has a slow and unpleasant recovery period, other compounds, such as

enflurane, isoflurane, and halothane, have replaced ether as an anesthetic. Diethyl ether is still

used where there is a lack of trained anesthesiologists, since it is the safest anesthetic to administer

by untrained hands. Anesthetics interact with the nonpolar molecules of cell membranes, causing

the membranes to swell, which interferes with their permeability.

Sodium pentothal (also called thiopental sodium) is commonly used as an intravenous anesthetic.

The onset of anesthesia and the loss of consciousness occur within seconds of its administration.

Care must be taken when administering sodium pentothal because the dose for effective anesthesia

is 75% of the lethal dose. Because of its toxicity, it cannot be used as the sole anesthetic. It is

generally used to induce anesthesia before an inhalation anesthetic is administered. Propofol is an

anesthetic that has all the properties of the “perfect anesthetic”: It can be used as the sole anesthetic

by intravenous drip, it has a rapid and pleasant induction period and a wide margin of safety, and

recovery from the drug is rapid and pleasant.

sodium pentothal propofol

CH 3 CH 2 CH 2 CH

CH 3 CH 2

CH 3

CH 3

N

N

H

O

O

S− Na+

CHCH 3

CH 3

CH 3 CH

OH

"ether"

CH 3 CH 2 OCH 2 CH 3

isoflurane

CF 3 CHClOCHF 2

enflurane

CHClFCF 2 OCHF 2

halothane

CF 3 CHClBr

Alcohols and ethers undergo SN2/E2

reactions unless they would have to

form a primary carbocation, in which

case they undergo SN1/E1 reactions.

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