Question

An organic compound A having the molecular formula C₃H₈O is a liquid at room temperature. The organic liquid A reacts with sodium metal to evolve a gas which burns causing a little explosion. When the organic liquid A heated with concentrated sulphuric acid at 170°C, it forms a compound B which decolourizes bromine water. The compound B adds on one molecule of hydrogen in the presence of Ni as catalyst to forms compound C which gives substitution reactions with chlorine.
(a) What is compound A?
(b) What is compound B?
(c) What type of reaction occurs when A is converted into B?
(d) What is compound C?
(e) What type of reaction takes place when B is converted into C?

Answer 1

(a) The organic compound, A, is propanol (CH₃-CH₂-CH₂OH) which is a liquid (alcohol) at room temperature. Propanol reacts with sodium to evolve hydrogen with a pop sound.
(b)  When propanol is heated with concentrated sulphuric acid at 170^oC, a compound 'B' called propene is formed. Propene is an unsaturated hydrocarbon; therefore, it decolourizes bromine water.
(c) Propanol is converted to propene through dehydration. Dehydration is a chemical reaction which involves the loss of water molecule from the reacting molecules. When an alcohol (propanol) is converted to alkene (propene), loss of water molecule or dehydration reaction takes place.
The chemical equation for conversion of propanol to propene is as follows:
CH₃-CH₂-CH₂-OH → CH₃-CH=CH₂ + H₂O
(d) The compound, C, is propane (CH₃-CH₂ -CH₃). When alkenes (unsaturated hydrocarbons) add one molecule of hydrogen, in the presence of nickel as a catalyst, alkanes are formed (saturated hydrocarbons). Therefore, propene (alkene) adds one hydrogen to form propane.
(e) As the conversion of propane to propene involves addition of hydrogen, the reaction is known as hydrogenation or addition reaction.
The conversion of propene to propane by the addition of hydrogen is as follows:
CH₃-CH=CH₂ + H₂ → CH₃-CH₂-CH₃