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3.10: Ethers

Last updated

Mar 10, 2021
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- 3.9: Phenols
- 3.11: Organic Sulfur Compounds

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Learning Objectives

Describe the structural difference between an alcohol and an ether that affects physical characteristics and reactivity of each.
Name simple ethers.
Describe the structure and uses of some ethers.

With the general formula R-O-R′, an ether may be considered a derivative of water in which both hydrogen atoms are replaced by alkyl or aryl groups. It may also be considered a derivative of an alcohol (R-O-H) in which the hydrogen atom of the OH group is been replaced by a second alkyl or aryl group:

$\mathrm{HOH\underset{H\: atoms}{\xrightarrow{replace\: both}}R-O-R'\underset{of\: OH\: group}{\xleftarrow{replace\: H\: atom}}R-O-H}$

Simple ethers have simple common names, formed from the names of the groups attached to oxygen atom, followed by the generic name ether. For example, CH₃–O–CH₂-CH₂-CH₃ is methyl propyl ether. If both groups are the same, the group name should be preceded by the prefix di-, as in dimethyl ether (CH₃–O–CH₃) and diethyl ether CH₃-CH₂–O–CH₂-CH₃.

Ether molecules have no hydrogen atom on the oxygen atom (that is, no OH group). Therefore there is no intermolecular hydrogen bonding between ether molecules, and ethers therefore have quite low boiling points for a given molar mass. Indeed, ethers have boiling points about the same as those of alkanes of comparable molar mass and much lower than those of the corresponding alcohols (Table $\PageIndex{1}$ ).

Table $\PageIndex{1}$ : Comparison of Boiling Points of Alkanes, Alcohols, and Ethers
Condensed Structural Formula	Name	Molar Mass	Boiling Point (°C)	Intermolecular Hydrogen Bonding in Pure Liquid?
CH₃-CH₂-CH₃	propane	44	–42	no
CH₃-O-CH₃	dimethyl ether or methoxymethane	46	–25	no
CH₃-CH₂-OH	ethyl alcohol or ethanol	46	78	yes
CH₃-CH₂-CH₂-CH₂-CH₃	pentane	72	36	no
CH₃-CH₂-O-CH₂-CH₃	diethyl ether or ethoxy ethane	74	35	no
CH₃-CH₂-CH₂-CH₂-OH	butyl alcohol or 1-butanol	74	117	yes

Ether molecules do have an oxygen atom, however, and engage in hydrogen bonding with water molecules. Consequently, an ether has about the same solubility in water as the alcohol that is isomeric with it. For example, dimethyl ether and ethanol (both having the molecular formula C₂H₆O) are completely soluble in water, whereas diethyl ether and 1-butanol (both C₄H₁₀O) are barely soluble in water (8 g/100 mL of water).

The IUPAC name for CH₃-O-CH₃ is methoxymethane and for CH₃–O–CH₂-CH₂-CH₃ is 1-methoxypropane. For CH₃–O–CH₂-CH₂-CH₃, the longer carbon chain on the right side of the oxygen is considered the base name and the shorter carbon chain on the left side of the oxygen is considered the substituent. However, since the methyl substituent is connected directly to an oxygen then the substituent name become methoxy.

Example $\PageIndex{1}$

What is the IUPAC name for each ether?

CH₃-CH₂-CH₂-O-CH₂-CH₂-CH₃

Solution

The carbon groups on either side of the oxygen atom are propyl (CH₃CH₂CH₂) groups, so the compound is propoxypropane.
The three-carbon group is attached by the middle carbon atom #2. The one-carbon group is a methyl group. The compound is 2-methoxypropane.

Exercise $\PageIndex{1}$

What is the IUPAC name for each ether?

CH₃-CH₂-CH₂-CH₂-O-CH₂-CH₂-CH₂CH₃

To Your Health: Ethers as General Anesthetics

A general anesthetic acts on the brain to produce unconsciousness and a general insensitivity to feeling or pain. Diethyl ether (CH₃CH₂OCH₂CH₃) was the first general anesthetic to be used.

William Morton, a Boston dentist, introduced diethyl ether into surgical practice in 1846. This painting shows an operation in Boston in 1846 in which diethyl ether was used as an anesthetic. Inhalation of ether vapor produces unconsciousness by depressing the activity of the central nervous system. Source: Painting of William Morton by Ernest Board.

Diethyl ether is relatively safe because there is a fairly wide gap between the dose that produces an effective level of anesthesia and the lethal dose. However, because it is highly flammable and has the added disadvantage of causing nausea, it has been replaced by newer inhalant anesthetics, including the fluorine-containing compounds halothane, enflurane, and isoflurane. Unfortunately, the safety of these compounds for operating room personnel has been questioned. For example, female operating room workers exposed to halothane suffer a higher rate of miscarriages than women in the general population.

These three modern, inhalant, halogen-containing, anesthetic compounds are less flammable than diethyl ether.

Summary

To give ethers common names, simply name the groups attached to the oxygen atom, followed by the generic name ether. If both groups are the same, the group name should be preceded by the prefix di-. Ether molecules have no OH group and thus no intermolecular hydrogen bonding. Ethers therefore have quite low boiling points for a given molar mass. Ether molecules have an oxygen atom and can engage in hydrogen bonding with water molecules. An ether molecule has about the same solubility in water as the alcohol that is isomeric with it.

Concept Review Exercises

Why does ethoxyethane (CH₃-CH₂-O-CH₂-CH₃) have a much lower boiling point than 1-butanol (CH₃-CH₂-CH₂-CH₂-OH)?
Which is more soluble in water—methoxyethane (CH₃-CH₂-O-CH₃) or 1-butanol (CH₃-CH₂-CH₂-CH₂-OH)? Explain.

Answers

Diethyl ether has no intermolecular hydrogen bonding because there is no OH group; 1-butanol has an OH and engages in intermolecular hydrogen bonding.
Ethyl methyl ether (three carbon atoms, one oxygen atom) is more soluble in water than 1-butanol (four carbon atoms, one oxygen atom), even though both can engage in hydrogen bonding with water.

Exercises

How can ethanol give two different products when heated with an acid catalyst? Name these products.
Which of these ethers is isomeric with ethanol: CH₃-CH₂-O-CH₂-CH₃, CH₃-O-CH₂CH₃, or CH₃-O-CH₃?
Provide the IUPAC name each compound.
1. CH₃-O-CH₂-CH₂-CH₃
Provide the IUPAC name of each compound.
1. CH₃-CH₂-CH₂-CH₂O-CH₃
2. CH₃-CH₂-O-CH₂-CH₂CH₃
Draw the structure for each compound.
1. methoxypropane
2. 2-ethoxy-2-methyl propane
Draw the structure for each compound.
1. 2-isopropoxypropane
2. propoxycyclopropane

Answers

Intramolecular (both the H and the OH come from the same molecule) dehydration gives ethene; intermolecular (the H comes from one molecule and the OH comes from another molecule) dehydration gives ethoxyethane.

1. 1-methoxypropane
2. 2-ethoxypropane

1. CH₃-O-CH₂-CH₃

Summary

Concept Review Exercises

Answers

Exercises

Answers

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