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8. ALIPHATIC HYDROCARBONS eLearn.Punjab
Sodium acetylide is a very valuable reagent for
chemical synthesis and is essentially ionic in nature.
Acetylides of copper and silver are obtained by passing acetylene in the
ammoniacal solution of cuprous chloride and silver nitrate respectively.
HC ≡ CH + Cu2Cl2 + 2 NH4OH → CuC ≡ CCu+ 2 NH4Cl +2H2O
Dicopperacetylide
(Reddish brown ppt.)
Silver HC ≡ CH + 2AgNO3 + 2 NH4OH → AgC ≡ CAg+ 2 NH4NO3 +2H2O
Disilver acetylide
(white ppt.)
and copper acetylides react with acids to regenerate alkynes.
AgC ≡ CAg + H2SO4(dil.) → HC ≡ CH + Ag2SO4
AgC ≡ CAg + 2HNO3(dil.) → HC ≡ CH + 2AgNO3
These alkynides are used for the preparation, purification, separation, and
identification of alkynes.
8.5.5 Uses of Ethyne
Ethyne is used:
1. in oxyacetylene torch which is in turn used for welding and cutting metals.
2. for the preparation of alcohols, acetic acid and acetaldehyde.
3. for the manufacture of polymers like PVC, polyvinyl acetate, polyvinyl ethers,
orlon and neoprene rubber.
4. to prepare acetylene tetrachloride a solvent for varnishes, resins, and rubber.
5. for ripening of fruits.
8.5.6 Comparison of Reactivities of Alkanes, Alkenes and Alkynes
The general decreasing reactivity order of alkanes, alkenes and alkynes is as
follows:
Alkenes > Alkynes > Alkanes
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