Question

When malonic acid is dehydrated using \[{P_4}{O_{10}}\] at \[{150^o}C\], species formed has total number of atoms ________

Answer 1

Hint: An acid anhydride of malonic acid is formed on dehydration of malonic acid with \[{{\text{P}}_{\text{4}}}{{\text{O}}_{{\text{10}}}}\], which is used as a source of carbon. It is also a stable member of linear oxocarbons \[O{\text{ }} = {\text{ }}{C_n} = {\text{ }}O\].

Complete step by step answer:
When malonic acid reacts with phosphorus pentoxide, it produces pyrophosphoric acid and tricarbon dioxide.
Here is the chemical equation representing the reaction occurred-
\[2C{H_2}{(COOH)_2}{\text{ }} + {\text{ }}{P_4}{O_{10}}{\text{ }} \to {\text{ }}2{H_4}{P_2}{O_7}{\text{ }} + {\text{ }}2{C_3}{O_2}\]
The tricarbon dioxide formed is also known as carbon suboxide. It is a linear and symmetrical molecule, a stable member of linear oxocarbons, represented as
\[O{\text{ }} = {\text{ }}C{\text{ }} = {\text{ }}C{\text{ }} = {\text{ }}C = {\text{ }}O\]
It is an acid anhydride of malonic acid i.e. produces acid when reacted slowly with water. It decomposes by the process of photolysis to form ketene, \[{C_2}O\], which is a very reactive molecule.
Hence, the total number of atoms present in carbon suboxide are 5.

Note:
Other than malonic acid, carbon suboxide is also formed during heme oxidation by heme oxygenase-1 enzyme. It can undergo polymerization into macrocyclic polycaron structures with \[{({C_3}{O_2})_n}\] the common formula.