Question

Arndt-Eistert synthesis is used to convert an acetyl chloride (ROCl) into

A. a methyl ester
B. a diazoketone
C. a ketone $\left( {{\rm{R}} - {\rm{CH}} = {\rm{C}} = {\rm{O}}} \right)$

D. a higher acid$\left( {{\rm{RC}}{{\rm{H}}_{\rm{2}}}{\rm{COOH}}} \right)$

Answer 1

We know that, homologous series is a series of organic compounds possessing similar properties (chemical) and difference between them is ${\rm{C}}{{\rm{H}}_{\rm{2}}}$
group. Let’s take the example of methane and ethane. Chemical formula of methane is ${\rm{C}}{{\rm{H}}_{\rm{4}}}$ and chemical formula of ethane is ${{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{6}}}$. Difference between the compounds is ${\rm{C}}{{\rm{H}}_{\rm{2}}}$ group. So, they are part of a homologous series.

Complete step by step answer:

Let’s understand the Arndt-Eistert synthesis in detail. Arndt-Eistert synthesis is the series of chemical reactions that results in conversion of carboxylic acid to a higher homologue of carboxylic acid that means, addition of one carbon atom takes place. This reaction is named after two scientists namely, Fritz Arndt and Bernd Eistert. This reaction is popular in production of $\beta$ amino acids from $\alpha$ amino acids.
Now, we discuss the reaction of acid chloride. The reaction of acid chloride with diazomethane produces diazoketone. The formed diazoketone again reacts with a metal catalyst $\left( {{\rm{A}}{{\rm{g}}_{\rm{2}}}{\rm{O}}} \right)$ and a nucleophile (water) to form desired acid homologues.

Now, come to the question, we have to identify the product formed in Arndt-Eistert synthesis. Already from the discussion we get to know that this reaction produces acid homologues. Now, we write the reaction.

So, the product formed is ${\rm{RC}}{{\rm{H}}_{\rm{2}}}{\rm{COOH}}$ and it has one more carbon atom than RCOCl.
Hence, the correct answer is D, that is, a higher acid.

Note:
Arndt-Eistert synthesis is a homologation reaction. A homologation reaction is a chemical reaction that produces a next member of a homologous series of the reactant. Kiliani Fischer synthesis is another example of homologation reaction.