Question

Carbon suboxide $\left( {{\text{C}}_{3}}{{\text{O}}_{2}} \right)$ is formed when:
(A) carbon reacts with concentrated ${{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}$
(B) malonic acid reacts with ${{\text{P}}_{4}}{{\text{O}}_{10}}$
(C) carbon reacts with strong alkali solution
(D) oxalic acid is heated strongly

Answer 1

Hint: Carbon suboxide is an anhydride of a dicarboxylic acid and is produced when the carboxylic acid of the molecular formula ${{\text{C}}_{3}}{{\text{H}}_{4}}{{\text{O}}_{4}}$ is treated with a strong dehydrating agent.

Complete step by step solution: Carbon suboxide, as the name suggests, belongs to the system of oxide of carbon and its chemical formula is ${{\text{C}}_{3}}{{\text{O}}_{2}}$. It is a linear molecule and since its structural formula contains four cumulative bonds (consecutive carbons attached by double bonds); it comes under the category of cumulene.

It is formed when a dry mixture of phosphorus pentoxide and malonic acid is heated. In this process phosphorus pentoxide acts as a strong dehydrating agent and it is an anhydride of phosphoric acid.
The reaction involved in the synthesis of carbon suboxide is given below:

Additional information: It is a lacrimatory gas which stimulates tears in our eyes. It can be carefully stored as a gas in a bulb but at certain conditions (300 k, 1 atm), the suboxide forms a yellow, red, or brown colored polymer.

Hence, the correct answer to the given question is (B) malonic acid reacts with ${{\text{P}}_{4}}{{\text{O}}_{10}}$.

Note: Phosphorus pentoxide exists as a dimer in its usual forms and that is why it is written as ${{\text{P}}_{4}}{{\text{O}}_{10}}$ more often and not as ${{\text{P}}_{2}}{{\text{O}}_{5}}$. However, both perform the same reactions and the only difference is that the latter is the empirical formula of the former.