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14.8 Ethers

Learning Objectives

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

With the general formula ROR′, an etherAn organic compound that has an oxygen atom between two hydrocarbon groups. 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 It may also be considered a derivative of an alcohol (ROH) in which the hydrogen atom of the OH group is been replaced by a second alkyl or aryl group:

HOH→H atomsreplace bothROR′←of OH groupreplace H atomROH

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–CH2CH2CH3 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 CH3CH2–O–CH2CH3.

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 14.4 "Comparison of Boiling Points of Alkanes, Alcohols, and Ethers").

Table 14.4 Comparison of Boiling Points of Alkanes, Alcohols, and Ethers

Condensed Structural Formula Name Molar Mass Boiling Point (°C) Intermolecular Hydrogen Bonding in Pure Liquid?
CH3CH2CH3 propane 44 –42 no
CH3OCH3 dimethyl ether 46 –25 no
CH3CH2OH ethyl alcohol 46 78 yes
CH3CH2CH2CH2CH3 pentane 72 36 no
CH3CH2OCH2CH3 diethyl ether 74 35 no
CH3CH2CH2CH2OH butyl alcohol 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).

Example 5

What is the common name for each ether?

  1. CH3CH2CH2OCH2CH2CH3

Solution

  1. The carbon groups on either side of the oxygen atom are propyl (CH3CH2CH2) groups, so the compound is dipropyl ether.
  2. The three-carbon group is attached by the middle carbon atom, so it is an isopropyl group. The one-carbon group is a methyl group. The compound is isopropyl methyl ether.

Skill-Building Exercise

    What is the common name for each ether?

  1. CH3CH2CH2CH2OCH2CH2CH2CH3

  2.  

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, from http://commons.wikimedia.org/wiki/File:Morton_Ether_1846.jpg.

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.

Concept Review Exercises

  1. Why does diethyl ether (CH3CH2OCH2CH3) have a much lower boiling point than 1-butanol (CH3CH2CH2CH2OH)?

  2. Which is more soluble in water—ethyl methyl ether (CH3CH2OCH3) or 1-butanol (CH3CH2CH2CH2OH)? Explain.

Answers

  1. Diethyl ether has no intermolecular hydrogen bonding because there is no OH group; 1-butanol has an OH and engages in intermolecular hydrogen bonding.

  2. 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.

Key Takeaways

  • 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.

Exercises

  1. How can ethanol give two different products when heated with sulfuric acid? Name these products.

  2. Which of these ethers is isomeric with ethanol—CH3CH2OCH2CH3, CH3OCH2CH3, or CH3OCH3?

  3. Name each compound.

    1. CH3OCH2CH2CH3

  4. Name each compound.

    1. CH3CH2CH2CH2OCH3
    2. CH3CH2OCH2CH2CH3

  5. Draw the structure for each compound.

    1. methyl ethyl ether
    2. tert-butyl ethyl ether

  6. Draw the structure for each compound.

    1. diisopropyl ether
    2. cyclopropyl propyl ether

Answers

  1. Intramolecular (both the H and the OH come from the same molecule) dehydration gives ethylene; intermolecular (the H comes from one molecule and the OH comes from another molecule) dehydration gives diethyl ether.

    1. methyl propyl ether
    2. ethyl isopropyl ether

    1. CH3OCH2CH3