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Carboxylic Acids - Structure, Preparation, Physical and Chemical Properties, Uses, Practice Problems and FAQ

You've probably heard of the term "Omega-3 fatty acids," which has been used proudly in numerous commercials and advertisements. It is an active ingredient in many dietary supplements and wellness products used to boost the immune system and keep the blood vessels, lungs, and heart in good working order. Many branded supplements have become best-sellers as a result of this magical substance.

To comprehend its significance and operation, it is necessary to first learn about the basic structural components and their corresponding properties. The omega-3 fatty acid is a carboxylic acid with a long chain. In fact, this class of organic compounds known as 'carboxylic acids' is extremely versatile. They have widespread applications in a variety of components.

Carboxylic acids have a wide variety of structures, properties, and applications. From the tomatoes or black grapes you intake to the perfumes you spray, everywhere there is the prevalence of carboxylic acids.

TABLE OF CONTENTS

  • What are Carboxylic Acids?
  • Structure of Carboxylic Acids
  • Nomenclature of Carboxylic Acids
  • Preparation of Carboxylic Acids
  • Physical Properties of Carboxylic Acids
  • Chemical Properties of Carboxylic Acids
  • Uses of Carboxylic Acid
  • Practice Problems
  • Frequently Asked Questions - FAQ

What are Carboxylic Acids?

Carboxylic acid is a family of chemical compounds distinguished by the existence of a carboxyl (-COOH) group. Carboxylates are carboxylic acid salts and esters. Most of the carboxylic acids of biological origin are found as esters of glycerol, that is, as triacylglycerols. Fatty acids occurring in natural fats as esters of glycerol are some higher members of aliphatic carboxylic acids (C12-C18).

Deprotonation of a carboxyl group results in the formation of a carboxylate ion as its conjugate base. Their stability is enhanced by the resonance stabilisation of the carboxylate ions. This contributes to acidity in comparison to alcohol. Different techniques for preparing carboxylic acids are also available.

Carboxylic acids are also made in human body.. The study of organic compounds contains carboxylic acids, which are one of the most significant functional groups.

Structure of Carboxylic Acids

The general formula of carboxylic acids is R-COOH, where -COOH signifies the carboxyl group and R denotes the rest of the molecule to which this group is attached. This carboxyl group has a carbon with a single bond to a hydroxyl group and a double bond to an oxygen atom. The general formula is CnH2nO2.

  • A hydroxyl group is connected to a carbonyl carbon in a carboxylic acid. Due to the electronegativity of the oxygen atom, this functional group can undergo ionisation and discharge a proton.
  • The presence of two oxygen atoms stabilises the carboxylate ion, which is formed when a proton is removed from the carboxyl group (through which the negative charge can move). Example- Acetic acid and Oxalic Acid
  • The carbon of C=O bond in carboxylic acid and its derivatives is sp2 hybridised. It uses three sp2 orbitals to form 𝛔 bonds. The three atoms attached to the carbonyl carbon are in the same plane and their bond angles are each approximately 120°.

  • Carboxylic carbonyl carbon is less electrophilic than carbonyl carbon of aldehydes and ketones (because of +R effect of -OH group).

Nomenclature of Carboxylic Acids

These chemical compounds are commonly referred to by their common names, which include the suffix "-ic acid." Acetic acid is an example of a carboxylic acid with a common name (CH3COOH). The suffix "-oic acid" is allocated to these substances in the IUPAC nomenclature. Numbering is done in such a way that the substituent (ethyl here) gets the minimum possible number.

The following rules are to be followed for the IUPAC nomenclature of carboxylic acids.

  • "Oic acid" replaces the suffix "e" in the name of the matching alkane.
  • The carboxylic carbon is always numbered one when there is only one carboxyl group in an aliphatic chain.

Example: CH3COOH - Ethanoic acid

  • Carbon atoms in the longest chain having more than one carboxyl group are counted, and the number of carboxyl groups is denoted by prefixes such as "di-," "tri-," and so on.

Example: Oxalic acid (COOH)2Propane-1,2,3 tricarboxylic acid.

  • The suffixes or prefixes are next added to the parent alkyl chain, thereby giving the name to the carboxylic acid. The locations of the carboxyl group are shown by Arabic numerals.
  • A carboxyl substituent on a carbon chain is sometimes known as a "carboxylic acid" or "carboxy."

Example: The name 2-carboxy furan for the chemical 2-Furoic acid is an example of such nomenclature.

  • Another example: CH3CH=CH-COOH has the IUPAC name – But-2-enoic Acid.

Preparation of Carboxylic Acid

  • Carboxylic acids are also made from aldehydes and primary alcohols. CrO3 in aqueous sulphuric acid is known as Jones reagent.

  • From aldehydes: Aldehydes on oxidation produce carboxylic acid.

Tollen’s reagent is a solution of AgNO3 (silver nitrate) in aqueous ammonia (NH3) and some amount of sodium hydroxide, used to maintain a basic pH of the reagent solution.

Fehling’s solution is a mixture of hydrated copper sulphate and sodium hydroxide containing small amounts of potassium sodium tartrate (KNaC4H4O6.4H2O) also known as Rochelle’s salt.

  • Alkyl benzenes also undergo oxidation in presence of alkaline or acidic KMnO4 or chromic acid to give aromatic carboxylic acids. 1° and 2° alkyl benzene are oxidised but the tertiary group is not affected. Tertiary alkyl benzenes do not undergo oxidation.

  • Unsaturated alkyl chain is also oxidised to carboxylic acids, the cleavage of –C=C– takes place to –COOH.

  • Carboxylic acids can be prepared from nitriles and amides too with mild conditions at the step of amide formation.
  • From Grignard reagent: Grignard reagents react with carbon dioxide to form salts of carboxylic acids, which in turn give corresponding carboxylic acids after acidification with mineral acid.

Grignard reagents react with carbon dioxide to form salts of carboxylic acids, which, when acidified with mineral acid, yield the corresponding carboxylic acids.

  • From Acyl halides and anhydrides: Acyl halides when hydrolysed give carboxylic acids. Acyl halides are more readily hydrolysed with an aqueous base to give carboxylate ions. Carboxylate ions on acidification produce corresponding carboxylic acids.

  • Anhydrides are hydrolysed to give corresponding acid(s) with water.

  • From Esters: Acidic and basic hydrolysis of esters can produce carboxylic acid. Acidic hydrolysis of ester directly gives carboxylic acids. Basic hydrolysis gives carboxylate ions, Which on acidification give corresponding carboxylic acids.

Physical Properties of Carboxylic Acid

  • Carboxylic acid molecules are polar due to the presence of two electronegative oxygen atoms.
  • They also participate in hydrogen bonding because of the presence of the carbonyl group (C=O) and the hydroxyl group.

  • When these compounds are placed in non-polar liquids, the hydroxyl groups of one carboxylic acid and the carbonyl group of the other form dimers due to hydrogen bonding.
  • The size of carboxyl functional group-containing substances determines their solubility in water. The smaller the chemical, the higher the solubility (the shorter the R group).
  • Carboxylic acids have a higher boiling point than aldehydes, alcohols, and ketones with the same molecular mass. The higher boiling point is at times attributed to the hydrogen bonding present in the carboxylic acids.
  • Carboxylic acids can also be dissolved in less polar organic solvents such as ether, alcohol, benzene, chloroform, and others.
  • The boiling point of a carboxylic acid is usually higher than that of water.
  • Because these substances have the ability to give protons, they are known as Bronsted-Lowry acids.
  • They have a strong sour odour in general. Esters of carboxylic acid have a pleasant odour and are used in perfumery.

Chemical Properties of Carboxylic Acid

  • The Hell-Volhard-Zelinsky reaction is a characteristic reaction of carboxylic acids where the -carbon of a carboxylic acid gets halogenated.

  • The Schmidt reaction can be used to convert carboxylic acids into amines.

  • A carboxylic acid produces alcohol on hydrogenation reaction with hydrogen.
  • Carboxylic acid produces esters when they react with alcohol in an acidic medium.

  • -COOH is a meta directing and deactivating group towards electrophilic substitution reaction in aromatic carboxylic acids.

Example: Nitration of benzoic acid.

Uses of Carboxylic Acid

  • Higher fatty acids are frequently used in soap manufacturing.
  • Acetic acid is used as a coagulant in the rubber manufacturing process.
  • Carboxylic acids are utilised for a variety of reasons in the rubber, leather, and textile industries.
  • Hexanedioic acid is a chemical that is utilised in the manufacture of nylon-6,6.
  • Chelating compounds like ethylenediaminetetraacetic acid (EDTA) are widely used in a variety of applications.
  • Chemicals with the carboxyl functional group are used to make several polymers.
  • For humans, carboxylic acids are the building blocks of essential fatty acids. Omega-6 and omega-3 fatty acids are two examples of this.
  • The majority of carboxylic acids are employed in the production of soft drinks and other foods.
  • These compounds are utilised in the manufacture of a variety of pharmaceuticals. As a result, carboxylic acids are extremely important in the pharmaceutical industry.
  • Organic acids are commonly used to make colours, perfumes, and rayon.
  • Carboxylic acid acts as a disinfectant.
  • The most basic carboxylic acid, "formic acid," is used as a reducing agent in textile treatments.
  • Acetic acid is a carboxylic acid that is used to produce esters and cellulose polymers.
  • As a precursor to the synthesis of an ester with salicylic acid, acetic acid is used in the creation of aspirin.
  • Palmitic acid and stearic acid are found in soaps, pharmaceuticals, cosmetics, candles, protective coatings, and other items.
  • Acrylic acid is a type of ester that helps to make polymers and acrylates. As a result, methacrylic acid polymerizes into Lucite.
  • Oleic acid, a carboxylic acid, is also used in the manufacture of soaps and detergents. It's also utilised in the manufacture of textiles.

Practice Problems

Q. 1. The IUPAC name of is

Answer: The IUPAC name of the given compound is 2-phenylethanoic acid.

Q. 2. The IUPAC name of is

Answer: The IUPAC name of the given compound is 2-methylcyclopentanecarboxylic acid.

Q. 3. The structure of Hex-2-en-4-ynoic acid is

Answer: The structure of hex-2-en-4-ynoic acid is

Q. 4. Acetate ion contains

  1. One C – O and two C=O bonds
  2. Two C = O bonds
  3. One C = O bond and also one C - O bond
  4. Two C – O bonds

Answer: Acetate ion is CH3COO-. Acetate ion contains One C–O bond and one C=O bond.

So, option C) is the correct answer.

Frequently Asked Questions - FAQ

1. What is the reason that benzoic acid does not give Friedel Craft reaction?
Answer:
Because the carboxyl group deactivates and the catalyst aluminium chloride (Lewis acid) bonds to the carboxyl group, benzoic acid does not undergo the Friedel-Crafts reaction.

2. Which foods naturally contain carboxylic acid?
Answer:
Certain carboxylic acids occur naturally in plants and animals. Lemons and oranges have citric acid.. Citric acid is a large carboxylic acid having three hydrogen atoms that can be ionised. It's found in citrus fruits and gives them a sour or tart flavour. Black grapes have tartaric acid. Apple has maleic acid.

3. Carboxylic Acids are weak acids or strong acids?
Answer:
Carboxylic acids are classified as weak acids because they do not fully dissociate to form H+ cations in a neutral aqueous solution. Between the individual molecules of the acid and the water molecules, hydrogen bonds are produced. As a result, they partially ionise to produce H+ and RCOO- ions. As a result, they are weak acids.

4. Why are carboxylic Acids acidic in nature?
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.

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