Chemical Reactions of Carboxylic Acids

Fatty acids are a term we’ve all heard before. So, what exactly are they? Carboxylic acids are the group in which they belong. Fatty acids are aliphatic carboxylic acids that are found in natural fats in the form of glycerol esters and range in length from C12 to C18. The word carboxylic acids come from a carbon molecule that has both a carbonyl and a carboxyl group. Carboxylic acids can be found all over the world. It’s also a precursor for a variety of important organic compounds such as acid chlorides, esters, anhydrides, and amides, among others. Let’s look at the carboxylic acid concept in considerable detail!

What is a Carboxylic Acid?

An organic substance with a carboxyl functional group is called carboxylic acid. 

They’re found all over the place in nature, and humans can also make them synthetically. Carboxylic acids deprotonate to produce a carboxylate anion with the general formula R-COO^–, which can be used to make a variety of salts, including soaps. C=O prominent functional group is carboxylic acids. 

Some carboxylic acids, such as citric acid, lactic acid, or fumaric acid, are created through fermentation, and the majority of these carboxylic acids are used in the food sector.

Chemical Reactions of Carboxylic Acid

A carboxylic acid (carbon molecule with carboxyl group) will go through several chemical processes.

Reaction as an Acid

• Metals Reaction – Carboxylic acids react with metals like potassium, sodium, magnesium, and calcium to create salts. A proton will be liberated from the carboxyl group of the carboxylic acid throughout the reaction step, which is where the metal substitution will take place. H₂ gas is produced in this process.

• Carbonates and Bicarbonates Reaction – Carboxylic acids decompose into salts, water, and carbon dioxide gas when they come into contact with carbonates and bicarbonates.

This reaction can also be used to see if a carboxyl group is present. Effervescence is produced when carboxylic acids combine with a saturated sodium bicarbonate solution, releasing CO₂. In an aqueous NaHCO₃ solution, however, most phenols do not produce effervescence. As a result, the reaction of bicarbonate with carboxylic acids aids in the differentiation of phenols from carboxylic acids.

• Alkalis Reaction – Carboxylic acids react with alkalis, forming salts and water in the process.

Reduction

• Reduction to Alcohol – Reducing Agents: LiA1H₄ in ether solution or with H₀ in the presence of a copper chromite (CuCr₂O₄) catalyst, BH₃/THF (or diborane, B₂H₆), H₂, Ru, and so on.

Nucleophilic Acyl Substitution

• Formation of Acid Chlorides – Acid chlorides are formed when carboxylic acids combine with thionyl chloride (SOCl₂), phosphorus pentachloride (PCl₅), or phosphorus pentachloride. To understand the reaction, look at the examples below.

• Esterification – When carboxylic acids and alcohols are heated in the presence of strong sulphuric acid or dry hydrochloric acid, fruity esters result.

Sulphuric acid is used as a dehydrating agent in this reaction. An equilibrium reaction is a reaction for example. As a result, to keep the reaction moving forward, the ester is distilled.

• Anhydrides Formation – The generation of acid anhydrides occurs when two molecules of carboxylic acid are heated with a dehydrating agent such as phosphorus pentoxide.

• Amide Compound Formation – Ammonium salts are produced by treating carboxylic acids with ammonia. Ammonium salts lose a water molecule when heated, resulting in amide production.

Reaction of Carboxyl Group

• Decarboxylation – When sodium salts of carboxylic acids are distilled with soda lime (NaOH + CaO), a decarboxylation process occurs, resulting in alkanes.

• Dry Distillation of Calcium Salts –

Formaldehyde is produced by heating calcium formate.

An aldehyde is generated when a calcium salt of an acid (other than formic acid) and calcium formate are heated together.

• Kolbe’s Synthesis – Alkanes are produced by the electrolysis of fatty acid salts (concentrated aqueous solution).

Radial intermediates are present during the reaction.

• Hunsdiecker Reaction – When monocarboxylic acid’s silver salt is treated with halogen, an alkyl halide is produced.

• Hell-Volhard Zelinsky Reaction – In the presence of a catalyst, a carboxylic acid with an a-hydrogen is treated with CI₂ or Br₂. Chlorine or bromine atoms substitute for the α-hydrogen.

• Simonini Reaction – Simonini Relations refer to the reaction of silver carboxylic acid salts with iodine.≡

• Conversion to Nitriles – Alkane nitrile is formed by passing a combination of acid and NH₃ overheated alumina.

Uses of Carboxylic Acid 

1. Carboxylic acid has antimicrobial properties.
2. In textile treatments, the most basic carboxylic acid, “formic acid,” serves as a reducing agent.
3. Acetic acid, a carboxylic acid, is used to make esters and cellulose plastics.
4. Soaps, medications, candles, cosmetics, protective coatings, and other products contain palmitic acid and stearic acid.
5. Acetic acid is utilized in the manufacturing of aspirin as a precursor for the synthesis of an ester of salicylic acid.
6. Acrylic acid is an ester that is used to make polymers and acrylates. Lucite is formed by polymerizing methacrylic acid.
7. Rubber production processes benefit from stearic acid.

Sample Questions 

Question 1: What are carboxylic acids made from carbon compounds?

Answer:

Carboxylic acids are carbon compounds containing the carboxyl group (– COOH). The carboxyl group is made up of a carbonyl group (> C=O) and a hydroxyl group (−OH).

Question 2: What is an aromatic carboxylic acid example?

Answer :

Methanoic acid (Formic acid) has the formula -HCOOH, whereas ethanoic acid (Acetic acid) has the formula -CH₃COOH. Aromatic carboxylic acids are carboxylic acids that have the -COOH group linked to an aryl group.

Question 3: Write four uses of Carboxylic Acid.

Answer:

Uses of Carboxylic Acid –

1. Carboxylic acid has antimicrobial properties.
2. In textile treatments, the most basic carboxylic acid, “formic acid,” serves as a reducing agent.
3. Acetic acid, a carboxylic acid, is used to make esters and cellulose plastics.
4. Soaps, medications, candles, cosmetics, protective coatings, and other products contain palmitic acid and stearic acid.

Question 4: What causes carboxylic acids to be acidic?

Answer:

The hydrogen in the -COOH group makes the carboxylic acids acidic, according to the definition of an acid as a “stuff that donates protons (hydrogen ions) to other substances.” In a water solution, a hydrogen ion is transferred from the -COOH group to a water molecule.

Question 5: Explain the Reaction of Kolbe’s Synthesis.

Answer:

Kolbe’s Synthesis – Alkanes are produced by electrolysis of fatty acid salts (concentrated aqueous solution).

Radial intermediates are present during the reaction.