Describe two methods of preparaton of ethane. Given any three reaction of ethylene with the Cold and dil.alk `KMnO_(4)` ?

Explanation

Preparation of enthalene :
1. Dehydrohalogenation of alkyl hallde: When ethyl beomides is heated with alcoholic KOH. Ethylene is formed.
`underset("Ethyl bromide") ( CH_(3) CH _(2) Br + KOH) overset( "Alcoholic KOH") to H _(2) C = underset( " Ethylene") ( CH_(2) + KBr + H _(2) O )`
2. Dehydration of ethanol: When ethanol is heated with conc. `H _(2) SO_(4)` at `170^(@)C,` ethylene is obtained.
`H - underset( " Ethanol") underset(H) underset(|) overset(H) overset(|) (C) - underset( H) underset(|) overset(OH) overset(|) (C) - H overset(conc. H _(2) SO _(4)) underset(170^(@)C) to underset("Ethylene") ( H _(2) C = CO _(2) + H_(2)O)`
Cold and dil. alk. `KMnO _(4):` Pink coloured cold adn dil. alkaline `KMnO _(4)` solution is Bayers reagent. Ethylene decolour ises Bayers reagent to give ethylene glycol. This is test for unsaturation.
`H _(2) C = CH _(2) + H _(2)O + O {:(OH " "OH) , ( | " "|), (CH _(2) -CH _(2)), ("Ethylene glycol"):}`