Ethers: Nomenclature - Synthesis - Properties

Ethers

Ethers are shown as R'-O-R. Although they have a general formula as (CnH2n+2O) that is similar to that of alcohols, ethers have two alkyl groups and an oxygen atom. If alkyl groups are the same (R=R'), they are called as simple ethers, if alkyl groups are different (R≠R'), they are called as complex ethers. The functional group of ether is C-O-C.

Nomenclature of Ethers

Ethers (alkoxy alkanes) are named according to IUPAC system as shown in the following steps:

1.      From alkyl groups which are bonded to oxygen atom, one with the longer chain is chosen and accepted as the main chain.

2.     Main chain is numbered starting from the closest carbon to oxygen with the lowest number.

3.     The –oxy suffix is added to name of the main chain.

4.     Other alkyl groups are written with their numbers mentioned.

 You can see the names of some –oxy (RO-) groups below:

Example 1

Write down systematic names for the following compounds:

Solution:

Synthesis of Ethers

Ethers can be synthesized through many methods in industry and laboratories. We will explain one of the laboratory methods here.

1. Williamson Method

Ethers are prepared by the method which took the name of the scientist Williamson. In this method, sodium alcoholate forms from mixing of sodium metal with a suitable alcohol.

Then alkyl halide and sodium alcoholate reacts and target ether is obtained.

In order to synthesize methoxyethane and ethoxyethane, sodium reacts with methanol and ethanol. Formed sodium methylate and sodium ethylate react with bromoethane and following ethers are produced:

In these reactions, always primary alcohols are used. Secondary and tertiary alcohols cause formation of unwanted compounds.

Physical Properties of Ethers

Methoxymethane and ethoxymethane are in gas form at room temperature. Ignition and boiling points are too low. Therefore, they vaporize readily. They are colorless and they have pleasant odors. As they don’t have hydrogen bonds between their molecules, they have lower boiling points than alcohols. Ethers do not dissolve in water as they cannot form hydrogen bonds with water. But those with small alkyl groups dissolve partially in water.

Note:

Through reaction of ethers with oxygen in air, epoxides are formed. While purifying ethers, peroxides accumulate somewhere and at the end of the process, this causes explosions with elevated tem- peratures. Therefore, prolonged exposure of ethers with air must be definitely prevented.

Chemical Properties

Ethers are stable compounds, thus they don’t react with bases and active metals, they don’t undergo oxidation reactions. Ethers can only undergo following reactions:

A- They form alcohols when they are heated with dilute sulfuric acid.

But when they react with concentrated sulfuric acid or HCl, ethers donate a air of electrons to hydrogen ion and form oxonium salts which can dissolve in acidic solutions. Ethers can be obtained again when oxonium salts are mixed with water. This reaction is used to differentiate alkanes and ethers as alkanes don’t react with concentrated acids. For example:

B- Reaction with PCl5

Ethers react with phosphorus pentachloride and form alkyl chloride.

Do you know that

The organic compound used to re- move nail polish is the simplest form of ketones that is acetone (propa- none)?

See also

1.      Alcohols: nomenclature – synthesis - Properties

2.     Alkyl halides: nomenclature - synthesis - Properties

References

1.      K. J. Denniston c J. J.Topping c and R. L.Caretc “General Organic and Biochemistry”c Mc-Graw- Hillc New York   (2004).

2.     K.W. Whittenc R.E. Davis  and L. M. Peckc “General Chemistry” 7th ed. Holt Rinehart and Winstonc New York (2010).

3.     Clayden, J.; Greeves, N. and Warren, S. (2012) Organic Chemistry. Oxford University Press. pp. 1–15. ISBN 0-19-927029-5.

4.     Streitwieser, Andrew; Heathcock, Clayton H.; Kosower, Edward M. (2017). Introduction to Organic Chemistry. New Delhipages=3–4: Medtech (Scientific International, reprint of revised 4th edition, Macmillan, 1998). ISBN 978-93-85998-89-8.