Preparation of alkene by hydrogenation explain with example.

1.	Preparation of alkene by hydrogenation explain with example.
Answer» Solution :(a) Hydrogenation of alkyne forming "Cis ALKENE". General reaction : Process : (i) As per requirement of alkene, number of hydrogens are TAKEN accordingly. (ii) Lindlar.s catalyst is used as catalyst. (iii) palladised charcoal partially DEACTIVATED with poisons like sulphur compounds or quinoline. Partially deactivated palladised charcoal is known as lindlar.s catalyst. (b) Partial hydrogenation of alkyne forming trans alkene (Birch Reduction). `underset("Alkyne")(RC-=CR.+H_(2)) underset("Partial reduction")overset("Na/liquid "NH_(3))rarr` Preparation : (i) For the preparation of alkene, counted number of dihydrogens are used. (ii) This reaction is done with liquid ammonia and sodium metal. (iii) Reaction between`(Na+NH_(3))` with `H_(2)`, there is PARTICLE reduction. "Trans - alkane" is formed as product. (c) Low carbon oxyne reduced to alkene by lindlar.s catalyst. EG.-(i) : `underset("Ethyne")(CH-=CH+H_(2))overset(Pd//C)rarr underset("Ethen")(CH_(2)=CH_(2))` Eg.-(ii) : `underset("Propyne")(CH_(3)C-=CH+H_(2))overset(Pd//C)rarr underset("Propene")(CH_(3)CH=CH_(2))`

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