Laboratory Preparation of Ethyne/Acetylene – Alkynes

Table of Contents

Laboratory Preparation of ethyne/acetylene, its principle, procedure, and uses in organic chemistry have been discussed here:

Preparation of ethyne or higher alkynes

Some of the important methods of preparation of alkynes in the laboratory are discussed below:

Preparation of ethyne from calcium carbide

When calcium carbide is treated with water, acetylene gas is produced.

Preparation of ethyne from calcium carbide

Preparation from carbon and hydrogen

Acetylene is synthesized by passing a stream of hydrogen through an electric arc between carbon electrodes. This preparation process is performed at 3000oC.

preparation of acetylene

Preparation of ethyne from ethene

preparation of ethyne from ethene

Synthesis from acetylene

On treating sodium salt with alkyl halides, higher alkyne can be synthesized from acetylene.

preparation of ethyne from acetylene

From dehydrohalogenation of dihalides

When vicinal dihalides are treated with an alcoholic solution of KOH, then acetylene/higher alkynes are prepared by a dehydrohalogenation reaction.

dehydrohalogenation reaction

From dehalogenation of dihalides

Alkynes are formed by dehalogenation reaction when tetrahalogen derivatives of alkanes are heated with zinc dust in ethanol.

dehalogenation reaction, preparation of alkyne

Laboratory preparation of Acetylene

Following method is one of the major laboratory methods for manufacturing ethyne or acetylene in the laboratory.

Principle involved in laboratory preparation of acetylene

Acetylene can be prepared in the laboratory by treating calcium carbide with water.

preparation of ethyne

Procedure for the preparation of acetylene

Lumps of calcium carbide are placed on the layer of sand in a conical flask fitted with a dropping funnel and delivery tube. The free end of the delivery tube is inserted into a wash bottle containing acidified copper sulphate solution, and the wash bottle’s exit end is fitted into the beehive shelf, which is placed in a trough containing water.

When water is dropped into the flask, a violent reaction occurs, resulting in the formation of ethyne gas. The ethylene gas so produced contains impurities like H2S and PH3 and is eliminated by passing it through an acidified CuSO4 solution. Pure ethyne/acetylene gas is collected by the downward displacement of water.

laboratory preparation of acetylene
Figure: Laboratory preparation of acetylene

Lab Preparation of Acetylene video

Uses of ethyne

  • For the artificial ripening of fruits.
  • Used to generate light.
  • Used to prepare various organic compounds like ethanol, acetic acid, acetaldehyde, etc.
  • For the manufacture of plastics, rubber, synthetic fibers, and so on.

References

  • Morrison, R. T., & Boyd, R. N., Organic chemistry, Allyn and Bacon, Inc. 1987.
  • March, J., Advanced Organic Chemistry, Wiley Eastern Limited, 1986.
  • Bahl, B.S., A., Advanced Organic Chemistry, S. Chand and Company Ltd, New Delhi, 1992.
  • Finar, I. L., Organic Chemistry, Vol. I and Vol. II, Prentice-Hall, London, 1995.

laboratory preparation of ethyne

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