Question

What is Z in the following reaction?
\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{-- C}}{{\text{H}}_{\text{2}}}{\text{ -- C}}{{\text{O}}_{\text{2}}}^{\text{ - }}{\text{N}}{{\text{a}}^{\text{ + }}}{\text{ }}\xrightarrow[{{\text{NaOH/CaO}}}]{{{\Delta }}}\,\,{\text{ Z }}\]
A. Propane
B. N-butane
C. Ethane
D. Ethyne

Answer 1

Hint: We know that decarboxylation reaction is the chemical reaction that eliminates a carboxyl group leading to the liberation of carbon dioxide \[\left( {{\text{C}}{{\text{O}}_{\text{2}}}} \right)\]. Here, the reaction is a decarboxylation reaction. The product formed will have a carbon atom less than the reagent.

Complete step by step answer:
Let’s understand the decarboxylation reaction in detail. Decarboxylation is a step-down reaction in which the product has a carbon atom less that the reactant. Carboxylation is a reversible process. Here a carboxyl group is replaced by a hydrogen atom. The sodium salt carboxylic acid is heated with soda lime (mixture of sodium hydroxide and calcium oxide) gives alkanes containing one carbon less than the carboxylic acid, elimination a molecule of carbon dioxide
Sodium salt of carboxylic acid is heated with soda lime, an alkane is obtained.
\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{-- C}}{{\text{H}}_{\text{2}}}{\text{ -- C}}{{\text{O}}_{\text{2}}}^{\text{ - }}{\text{N}}{{\text{a}}^{\text{ + }}}{\text{ }}\xrightarrow[{{\text{NaOH/CaO}}}]{{{\Delta }}}\,\,{\text{C}}{{\text{H}}_{\text{3}}}{\text{--}}\,\,{\text{C}}{{\text{H}}_{\text{3}}}\,\, + \,\,N{a_2}C{O_{\text{3}}}\]
The product alkane contains one C atom less than the reactants. Hence, the compound Z is ethane. This can be used to reduce the number length of the carbon chain. Decarboxylation reactions are the basis of a lot of named reactions. Some of them are Barton decarboxylation, Kolbe’s electrolysis, Kochi reaction etc. These all are radical reactions. In a ketonic decarboxylation a carboxylic acid is converted to a ketone.

So, the correct answer is Option C.

Note: Carboxylic acid is a group of organic compounds that contain a carboxyl group \[\left( {{\text{ - COOH}}} \right)\] in them. The general formula for carboxylic acid is \[{\text{R - COOH}}\]. Acidity of carboxylic acid is higher than that of alcohols and phenols. This is because the carboxylate anion is stabilised by resonance.
Electron donating groups donate electrons to the carbon atom in which they are attached and Electron withdrawing groups withdraw electrons from the carbon atom to which they are attached.