Miscellaneous Reactions shown by alkynes:

1.Isomerization :

         

2.Action of N₂ :

         CH≡CH + N₂  2HCN

3. Formation of heterolytic compounds :

         

4.Nucleophilic addition : Acetylene undergoes nucleophilic addition with CH₃OH in presence of CH₃ONa.

         

5. Substitution reaction : Acetylene on passing through sodium hypochlorite solution at 0^oC in absence of light shows substitution of H by chlorine atom.

(a)Formation of sodium acetylide or alkynides :

          

(b) Formation of Acetylenic  Grignard reagent :

           CH≡CH + R MgX → CH≡CMgX

(c)Formation of copper alkynides : on passing alkynes through ammoniacal cuprous chlorides solution, a red precipitate of cuprous alkynide is obtained.

 

          

d) Formation of silver alkynides : On passing alkynes through ammoniacal silver nitrate solution (Tollens reagent) a white precipitate of silver alkynides is obtained

CH≡CH + 2AgNO₃ + 2NH₄OH → AgC≡CAg + 2NH₄NO₃ + 2H₂O

                               silver acetylide

                                   while ppt.)

RC≡CH + AgNO₃ + NH₃OH → RC≡CAg + NH₄NO₃ + H₂O

Note : 

(i) These alkynides are ionic in nature

(ii) Alkynides are generally explosive and unstable when dry.

(iii) Copper and silver alkynides are very sensitive to shock when dry & may explode

(iv) These alkynides are easily converted to original alkynes when treated with dilute acids.

                       NaC≡CNa + 2HNO₃ → HC≡CH + 2NaNO₃

(v) Acidic nature of alkyne can be utilized to separate, purify and identify alkyne-1 from other hydrocarbons. 

Uses : Among alkynes, acetylene has got wide applications in industries.

(i) As oxy-acetylene flame for welding.

(ii) As illuminating agent in hawker's lamps and light houses.

(iii) In artificial ripening of fruits.

(iv) In preparation of monomeric unit (vinyl chloride, vinyl cyanide, vinyl cyanide, vinyl acetate, vinyl acetylene, etc.) to get polymers (PVC, PVA, chloroprene, Buna-S etc.) widely used in textile, plastic, shoe and rubber industries.

(v) In preparation of poisonous gas, Lewiste.

(vi) In preparation of solvents such as westron, westrosol and other useful chemicals e.g., C₆H₆, acetaldehyde, acetone etc.

(vii) It is used as general anaesthetic under the name Naracylene