question_answer

Which one of the following acids will undergo easy thermal decarboxylation?

A)  \[C{{H}_{3}}.\,C{{H}_{2}}COOH\]            

B)  \[HOOCC{{H}_{2}}COOH\]

C)  \[C{{H}_{2}}COOH\]

D)  \[{{C}_{6}}{{H}_{5}}COOH\]

Correct Answer: B

Solution :

                 Key Idea Decarboxylation-The removal of carbon dioxide from carboxylic group is called decarboxylation.) When two carboxylic groups are attached to same carbon atom, decarboxylation takes place easily. In malonic acid  carboxylic groups are attached to the same carbon atom, hence, it undergoes easy thermal decomposition. malonic acid   : While in \[C{{H}_{3}}C{{H}_{2}}COOH,C{{H}_{3}}COOH\] and \[{{C}_{6}}{{H}_{5}}COOH\] decarboxylation takes place on heating with soda lime \[(NaOH+CaO)\]. \[C{{H}_{3}}COONa+NaOH\xrightarrow{CaO,heat}\]\[C{{H}_{4}},+N{{a}_{2}}C{{O}_{3}}\] \[{{C}_{6}}{{H}_{5}}COONa+NaOH\xrightarrow{CaO,\text{ }heat}{{C}_{6}}{{H}_{6}}\]                                                                 \[+N{{a}_{2}}C{{O}_{3}}\]