Preparation and Reactions of Epoxides, Chemistry tutorial

Introduction:

Whenever an oxygen atom is attached to carbon atoms of a carbon chain making a three membered ring, the compound are known as Epoxides.

Methods of Formation:

Epoxides can be made up from the given methods:

1) The oxidation of alkenes with peroxy acids. Illustration of peroxy acids are:

  • perbenzoic acid (C6H5COOOH)
  • monoperphthalic acid (C6H5(COOH)2)
  • p-nitrobenzoic acid (C6H4(NO2)COOH)

For illustration:

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Fig: Oxidation of alkenes with peroxy acids

2) Ethylene oxide can be prepared via treating ethylene chlorohydrins by potassium hydroxide.

1687_Ethylene oxide preparation.jpg

Fig: Ethylene oxide preparation

3) Ethylene oxide can as well be prepared via passing a mixture of ethene and air over silver catalyst under pressure at a temperature of around 200 to 400oC

195_Preparation of Ethylene oxide.jpg

Fig: Preparation of Ethylene oxide

Chemical Properties of Epoxides:

Epoxy ethane is a gas at ordinary temperature. They are very reactive and the ring opens at different reactions.

Acid catalyzed cleavage:

i) Conversion to 1, 2-diol: Whenever treated with dilute acid solution, Epoxides are transformed to 1, 2-diol.

ii) Epoxides react by alcohols in the presence of small amount of acid catalyst to form the monoethers.

iii) Epoxides react by concentrated halogen acid solution to form halogenohydrins

iv) Epoxides react by hydrogen cyanide, HCN, to form the ethylene cyanohydrins.

All the example of Acid catalyzed cleavage is illustrated below:

1576_Acid catalysed cleavage.jpg

Fig: Acid catalyzed cleavage

Base catalyzed cleavage:

i) Reaction by sodium ethoxide: The Epoxides react by sodium ethoxide to give 2-ethoxy ethanol (that is, ethyl cellosive).

ii) Epoxides react by methanol under pressure to form 2-methoxy ethanol (methyl cellosolve).

iii) Epoxides react by cellosolves to form carbitols.

iv) Reaction by ammonia: Ammonia reacts by Epoxides to give 2-amino ethanol. This reaction generally forms a mixture of three amino acids.

All the example of base catalyzed cleavage is illustrated below:

1346_Base catalyzed cleavage.jpg

Fig: Base catalyzed cleavage

Reaction with Grignard reagent:

Epoxides react with Grignard reagents by the cleavage of carbon-oxygen bond to give primary alcohols having a greater number of carbon atoms. The chain is increased via the number of carbon-atoms present in the alkyl radical of the Grignard reagent. For illustration:

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Fig: Reaction with Grignard reagent

Reaction with organolithium compounds:

Epoxides whenever treated with lithium diethylamide are transformed to allylic alcohols. For illustration:

1006_Reaction with organolithium compounds.jpg

Fig: Reaction with organolithium compounds

Reduction of Epoxides:

Epoxides can be reduced by using lithium aluminium hydride to yield alcohol. Unsymmetrical Epoxides provide highly substituted alcohols as major product. For illustration:

1183_Reduction of epoxides.jpg

Fig: Reduction of Epoxides

Oxidation of Epoxides:

Epoxides are oxidized to α-hydroxyl ketones through dimethyl sulphoxide.

CH3-CH-CH=CH2 + Me2SO → (H+) → CH3CHOHCOCH3 + Me2S

Reaction with ethanoic acid:

Epoxides react by ethanoic acid to make glycol monoethanoate.

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Fig: Reaction with ethanoic acid

Action of heat:

Epoxides go through rearrangement on heating to form the ethanal.

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Fig: Action of heat

Reaction with glycol:

Whenever heated with ethane-1, 2-diol (that is, ethelene glycol) epoxide forms the diethelene glycol.

379_Reaction with glycol.jpg

Fig: Reaction with glycol

Uses of Epoxides:

1) Epoxides are utilized as fumigant and insecticides for grain, tobacco and dried fruits.

2) They are basically employed in the preparation of glycol ethers which are used as industrial solvents.

3) Methyl cellosolve, ethyl cellosolve and butyl cellosolve are used as solvents for the cellulose.

4) Epoxides are employed in the manufacture of non-ionic surface active agents.

5) Plyethylene glycols made up from Epoxides are employed as industrial solvents.

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