question_answer

In which of the following reactions carbon-carbon bond formation takes place?

A)  Cannizaro reaction

B)  Reimer-Tiemann reaction

C)  HVZ reaction

D)  Schmidt reaction

Correct Answer: B

Solution :

(i) Cannizaro reaction: This reaction is shown by aldehydes which do not have a-hydrogen atoms. Half of the molecules are oxidised and other half are reduced when reacted with aq. alkali. \[\underset{formaldehyde}{\mathop{2HCHO}}\,+NaOH\to \underset{methanol}{\mathop{C{{H}_{3}}OH}}\,+\underset{sodium\text{ }formate}{\mathop{HCOONa}}\,\] No C?C bond is formed. (ii) HVZ reaction: Carboxylic acids having a-hydrogen atom when react with chlorine or bromine in presence of red P, \[\alpha \]-H atoms are replaced by chlorine or bromine. \[C{{H}_{3}}COOH\xrightarrow[-HCl]{C{{l}_{2}}/P}ClC{{H}_{2}}COOH\] It is substitution reaction and no new C?C bond is formed. (iii) Schmidt reaction: During this reaction carbonyl compounds react with hydrazoic acid to form cyanides and formyl derivative of 1° amine. \[\underset{aldehyde}{\mathop{RCHO}}\,+\underset{\begin{smallmatrix}  hydrazoic \\  acid \end{smallmatrix}}{\mathop{{{N}_{3}}H}}\,\xrightarrow{{{H}_{2}}S{{O}_{4}},\Delta }RCN\] \[+RNHCHO+{{N}_{2}}\] \[\underset{ketone}{\mathop{RCOR}}\,+\underset{\begin{smallmatrix}  hydrazoic \\  acid \end{smallmatrix}}{\mathop{{{N}_{3}}H}}\,\xrightarrow{{}}RCONHR+{{N}_{2}}\] No new C?C bond is formed during the reaction. (iv) Reimer-Tiemann reaction: In this reaction phenol reacts with chloroform and alkali and salicylaldehyde is formed. one new C?C bond is formed during the reaction.