General Methods of Preparation of Alkynes

General Methods Of Preparation Of Alkynes

1. Preparation of alkynes from alkenes:

This process involves two steps:

(i) Halogenation of alkenes to form vicinal dihalides

(ii) Dehalogenation of vicinal dihalides to form alkynes.

2. Preparation of alkene from gem dihalides:

A compound containing two halogen atoms on the same carbon atom is called gem dihalide (Latin word 'Gemini' means twins). On heating with alcoholic KOH, gem dihalides give alkynes.

3. Preparation Of Alkenes From Elec-trolysis Of Salts Of Unsaturated Di-carboxylic Acids. (Kolbe’s Electrolytic Method)

Electrolysis of sodium or potassium salt of maleic or fumaric acid yields alkynes.

4. Industrial prefaration of ethyne:

Ethyne can be manufactured in large scale by action of calcium carbide with water.

Calcium carbide required for this re-action is prepared by heating quick lime and coke in an electric furance at 3273 K