JEE Main & Advanced Chemistry Carboxylic Acids Methods Of Preparation Of Monocarboxylic Acid

(1) By oxidation of alcohols, aldehydes and ketones

\[\underset{\text{alcohol}}{\mathop{RC{{H}_{2}}OH}}\,\underset{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}{\mathop{\xrightarrow{[O\}}}}\,RCHO\underset{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}{\mathop{\xrightarrow{[O]}}}\,\underset{\text{Carboxylic acid}}{\mathop{RCOOH}}\,\]

\[\underset{\text{Aldehyde}}{\mathop{RCHO}}\,\xrightarrow{[O]}\underset{\text{monocarboxylic acid}}{\mathop{RCOOH}}\,\]

• Aldehyde can be oxidized to carboxylic acid with mild oxidising agents such as ammonical silver nitrate solution \[[A{{g}_{2}}O\,\,\text{or}\ Ag(N{{H}_{3}})_{2}^{+}O{{H}^{-}}]\]

• Methanoic acid can not be prepared by oxidation method.

• Ketones can be oxidized under drastic conditions using strong oxidising agent like \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\].

• Methyl ketones can also be converted to carboxylic acid through the haloform reaction.

\[R\underset{O}{\mathop{\underset{|\,|}{\mathop{C}}\,}}\,-C{{H}_{3}}+3{{I}_{2}}+3NaOH\underset{{{H}_{2}}O}{\mathop{\xrightarrow{\Delta }}}\,\]

\[R-\underset{O}{\mathop{\underset{|\,|}{\mathop{C}}\,}}\,-OH+CH{{I}_{3}}+3NaI+3{{H}_{2}}O\]

(2) By Hydrolysis of nitriles, ester, anhydrides and acid chloride

(ii) Hydrolysis of Esters

\[\underset{\text{Ester}}{\mathop{RCOOR'}}\,+HOH\underset{O{{H}^{-}}}{\mathop{\xrightarrow{HCl}}}\,\underset{\text{Acid}}{\mathop{RCOOH}}\,+\underset{\text{Alcohol}}{\mathop{R'OH}}\,\]

(iii) Hydrolysis of Anhydrides  

\[\underset{\text{Ethanoic anhydride}}{\mathop{\begin{matrix} C{{H}_{3}}-\overset{O}{\mathop{\overset{|\,|}{\mathop{C}}\,}}\,  \\ C{{H}_{3}}-\underset{O}{\mathop{\underset{|\,|}{\mathop{C}}\,}}\,  \\ \end{matrix}\ \ \ \ \ O+HOH}}\,\xrightarrow{{{H}^{+}}/O{{H}^{-}}}\underset{\text{Ethanoic acid}}{\mathop{2C{{H}_{3}}COOH}}\,\]

(iv) Hydrolysis of acid chloride and nitro alkane

\[R-\underset{O}{\mathop{\underset{|\,|}{\mathop{C}}\,}}\,-Cl+HOH\xrightarrow{{{H}^{+}}/O{{H}^{-}}}RCOOH+HCl\]

\[R-C{{H}_{2}}-N{{O}_{2}}\xrightarrow{85%{{H}_{2}}S{{O}_{4}}}RCOOH\]

(v) Hydrolysis of Trihalogen :

(3) From Grignard Reagent

(4) From Alkene or Hydro-carboxy-addition (koch reaction)

\[C{{H}_{2}}=C{{H}_{2}}+CO+{{H}_{2}}O\underset{\begin{smallmatrix}500-1000atm \\ \And 350{}^\circ C \end{smallmatrix}}{\mathop{\xrightarrow{{{H}_{3}}P{{O}_{4}}}}}\,C{{H}_{3}}C{{H}_{2}}COOH\]   

(5) Special methods

(i) Carboxylation of sodium alkoxide     

\[\underset{\text{Sod}\text{. alkoxide}}{\mathop{RONa+CO}}\,\to \underset{\text{Sod}\text{. salt}}{\mathop{RCOONa}}\,\xrightarrow{HCl}\underset{\text{Acid}}{\mathop{RCOOH}}\,\]

(ii) Action of heat on dicarboxylic acid  

(iii) From acetoacetic ester 

(iv) Oxidation of alkene and alkyne

\[\underset{\text{Alkene}}{\mathop{RCH=CH{R}'}}\,\underset{\begin{smallmatrix} \text{Hot alkaline } \\ \,\,KMn{{O}_{4}} \end{smallmatrix}}{\mathop{\xrightarrow{[O]}}}\,RCOOH+{R}'COOH\]

\[\underset{\text{Alkyne}}{\mathop{R-C\equiv C-{R}'}}\,\underset{(ii){{H}_{2}}O}{\mathop{\xrightarrow{(i){{O}_{3}}}}}\,R-COOH+{R}'COOH\]

(v) The Arndt-Eistert synthesis  

\[R-\underset{O}{\mathop{\underset{|\,|}{\mathop{C}}\,}}\,-Cl\,\,\,\,+C{{H}_{2}}{{N}_{2}}\to R-\underset{O}{\mathop{\underset{|\,|}{\mathop{C}}\,}}\,-CH{{N}_{2}}\underset{A{{g}_{2}}O}{\mathop{\xrightarrow{{{H}_{2}}O}}}\,\]

\[R-C{{H}_{2}}-COOH\]

(vi) From acid amides   

\[\underset{\text{Amide}}{\mathop{RCON{{H}_{2}}}}\,+{{H}_{2}}O\underset{\text{or }Alkali}{\mathop{\xrightarrow{\text{Acid}}}}\,\underset{\text{Acid}}{\mathop{RCOOH}}\,+N{{H}_{3}}\]

\[\underset{\text{Amide}}{\mathop{RCON{{H}_{2}}}}\,+\underset{\text{Nitrous acid}}{\mathop{HN{{O}_{2}}}}\,\to RCOOH+{{N}_{2}}+{{H}_{2}}O\]