Discuss the reactions and synthesis of carboxyl... - SS3 Chemistry Organic Chemistry: Aldehydes, Ketones, and Carboxylic Acids Question

Reactions and Synthesis of Carboxylic Acids:

1.    Oxidation of Primary Alcohols:

Primary alcohols can be oxidised to carboxylic acids using oxidising agents such as potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4). The oxidation reaction involves the conversion of the alcohol's -OH group into a carboxyl group (COOH).

Example: Ethanol → Ethanoic Acid

CH3CH2OH + [O] → CH3COOH

Significance: This method is widely used in the laboratory and industrial synthesis of carboxylic acids from readily available primary alcohols.

2.    Oxidation of Aldehydes:

Aldehydes can be further oxidised to carboxylic acids using the same oxidising agents. The aldehyde group (-CHO) is converted into a carboxyl group (-COOH) during the oxidation process.

Example: Ethanal → Ethanoic Acid

CH3CHO + [O] → CH3COOH

Significance: This oxidation reaction allows the transformation of aldehydes, which are common intermediates in organic synthesis, into carboxylic acids, expanding the range of available compounds.

3.    Hydrolysis of Nitriles:

Nitriles can be hydrolyzed to carboxylic acids using either acidic or basic conditions. The nitrile group (-CN) is converted into a carboxyl group (-COOH) by adding water.

Example: Ethyl Cyanide → Ethanoic Acid

CH3CH2CN + 2H2O → CH3COOH + NH3

Significance: This method is important for the synthesis of carboxylic acids from nitriles, which can be obtained from a variety of starting materials, providing versatility in organic synthesis.

4.    Carboxylation of Grignard Reagents:

Carboxylic acids can be synthesised by reacting Grignard reagents (RMgX) with carbon dioxide (CO2) to form carboxylate ions. Acidification of the reaction mixture yields the corresponding carboxylic acids.

Example: Ethylmagnesium Bromide + Carbon Dioxide → Ethanoic Acid

CH3CH2MgBr + CO2 → CH3COOH

Significance: This method enables the direct incorporation of carbon dioxide into organic molecules, allowing the efficient synthesis of carboxylic acids with different alkyl substituents.

Real-World Applications:

1.    Pharmaceutical Synthesis: The synthesis of carboxylic acids is crucial in pharmaceutical manufacturing as many drugs contain carboxyl groups in their structures.

2.    Food Industry: Carboxylic acids play a vital role in the food industry as they are responsible for the sour taste of fruits (e.g., citric acid in citrus fruits) and are used as food preservatives (e.g., benzoic acid).

3.    Biological Significance: Carboxylic acids are involved in various biological processes, such as in the citric acid cycle, where they act as intermediates in cellular respiration.

In conclusion, carboxylic acids can be synthesised through various methods, including oxidation of primary alcohols and aldehydes, hydrolysis of nitriles, and carboxylation of Grignard reagents. These reactions have significant applications in organic synthesis, pharmaceuticals, and the food industry. The versatility and importance of carboxylic acids in various fields make their synthesis a key aspect of organic chemistry.