Carboxylic Acid

What are Carboxylic Acids?

A carboxylic acid refers to an organic chemical compound which contains a carboxyl functional group (C(=O)OH) joined with an R – group. The general carboxylic acid formula is R – COOH and these are considered to be the essential functional group having C = O.

These acids are found in nature, while also being manufactured synthetically by human beings. If carboxylic acids undergo deprotonation, it produces a carboxylate anion whose general formula is R – COO-. Notably, this is a vital chapter in your curriculum, as well as competitive exams in the future.


Structure of Carboxylic Acids

With regards to the chemical formula of carboxyl acids COOH is the carboxyl group, and R is the remaining molecule which is attached. In this group, a carbon shares a single bond and double bond with a hydroxyl group and oxygen atom, respectively.

You can take a look at the following illustration of general carboxylic acid structure.

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According to the above image, it is seen that one carboxylic acid consists of one hydroxyl group joined to one carbonyl atom. Owing to this oxygen atom’s electronegativity, the functional group may experience ionisation and release a proton.

As a proton gets removed from the carboxyl group, it yields a carboxylate ion. This ion is further stabilised in the presence of two atoms of oxygen.

Next, let us move on to its examples and terminology.


Nomenclature and Examples of Carboxylic Acid

Generally, these organic compounds are known by their trivial names, but IUPAC suggested names are also there. According to IUPAC nomenclature, carboxylic acids hold a suffix – oic acid. For example, butyric acid is called butanoic acid as per IUPAC rules.

When talking about the carboxylate anion, it is named using the suffix – ate. Also, the general pattern of –ic acid for a conjugate acid and –ate for its conjugate base is maintained. For instance, acetate is the conjugate base of acetic acid.

Following is a tabular representation of saturated and straight-chain carboxylic acids along with their common and IUPAC names, formula, carbon atoms and their existence or use.


Atoms of Carbon

Common Name

IUPAC Name

Chemical Formula

Location or Use

1

Carbonic acid

Carbonic acid

OHCOOH

Tissues and in blood

2

Formic acid

Methanoic acid

HCOOH

Insect bites

3

Acetic acid

Ethanoic acid

CH₃COOH

Vinegar

4

Propionic acid

Propanoic acid

CH₃CH₂COOH

Preservative for milk, cheese, grains, etc.

5

Butyric acid

Butanoic acid

CH₃(CH₂)2COOH

Butter

6

Valeric acid

Pentanoic acid

CH₃(CH₂)3COOH

Valerian

7

Caproic acid

Hexanoic acid

CH₃(CH₂)4COOH

Goat fat

8

Enanthic acid

Heptanoic acid

CH₃(CH₂)5COOH

Vine blossom

9

Caprylic acid

Octanoic acid

CH₃(CH₂)6COOH

Coconuts

10

Pelargonic acid

Nonanoic acid

CH₃(CH₂)7COOH

Pelargonium

11

Capric acid

Decanoic acid

CH₃(CH₂)8COOH

Palm kernel oil and coconut


Besides the mentioned ones, here are some other unsaturated carboxylic acids with their uses or existence:

  • Fatty Acids: Nutritional supplements.

  • Amino Acids: Protein building blocks.

  • Keto Acids: Have biochemical significance.

  • Aromatic Carboxylic Acids: Food preservatives and skincare products.

  • Dicarboxylic Acids: Used for nylon production.

  • Tricarboxylic Acids: Present in citrus fruits.

  • Divinyl Ether Fatty Acids: Found in a few plants.

  • Alpha Hydroxy Acids: Present in sour milk and wine.


Carboxylic Acid Properties

As carboxyl group is present in this compound, it results in the maximum properties of the same. Have a look at the below-mentioned carboxylic acid physical properties followed by chemical properties.

  1. Physical properties

  • Solubility

Being both hydrogen bond donors and hydrogen bond acceptors, carboxylic acid molecules are polar. Also, they take part in hydrogen bonding. The carbonyl and hydroxyl group together forms a carboxyl group. Higher carboxylic acids (more than 5 carbons) have restricted solubility because of alkyl chain’s rising hydrophobic nature. On the other hand, the smaller ones (1 – 5 carbons) are water-soluble. The acids which have long chains are soluble in solvents like alcohols and ethers.

  • Boiling Points

These acids have boiling points higher than water as they have vast surface areas and tend to make stabilised dimers via hydrogen bonds. For the boiling process to take place, the dimer bonds have to be broken, or the complete arrangement of dimer requires to be vaporised, which will increase the needs of latent heat of vaporisation significantly.

  • Acidity

Carboxylic acids are the most general kind of organic acids and are called Bronsted Lowry acids as they are donors of proton (H+). They are also notably the weak acids as they partially separate into RCOO- and H3O+ anions in neutral water solution. For instance, in a solution of 1 mole of acetic acid, only 0.4 per cent of the acid gets disassociated.

Here is a Table that Depicts Carboxylic Acids with Their Acid Dissociation Constant (pKa).

Carboxylic Acids

pKa

Acetic acid

4.76

Benzoic acid

4.2

Formic acid

3.75

Chloroacetic acid

2.86

Dichloroacetic acid

1.29

Oxalic acid (first disassociation)

1.27

Oxalic acid (second disassociation)

4.14

Trichloroacetic acid

0.65

Trifluoroacetic acid

0.23


  • Odour

These acids are observed to have a strong sour smell. However, its esters have a pleasing fragrance, and hence they are used in making perfumes.

  • Characterisation

Infrared spectroscopy is used to identify carboxylic acids fast. Due to C – O bond vibration, these compounds show a sharp band, ranging from 1680 to 1725 cm-1. A typical VO-H bond occurs like a broad peak within the region of 2500 and 3000 cm-1. By using nuclear magnetic resonance spectrometry, hydroxyl H2 occurs between 10 – 13 ppm. However, it is either not observed or broadened as exchange with water take place.

  1. Chemical Properties

  • The alpha carbon which belongs to a carboxylic acid can be halogenated feasibly with the help of Hell Volhard Zelinsky reaction.

  • With the help of Schmidt reaction, carboxylic acids can be transformed into amines.

  • Reduction of this compound to alcohol is possible by treating the same with hydrogen to form a hydrogenation reaction.

  • When carboxylic acids react with alcohols, they produce esters.

By now, you must have understood both physical and chemical carboxylic acid properties, so let us proceed with its occurrence.


Occurrence

Fatty acid esters are the primary elements of lipids, and amino carboxylic acid polyamides are the main ingredient of proteins. These acids are utilised in producing polymers, solvents, pharmaceuticals and food additives. Following are the names of carboxylic acids which are essential for industries along with useful products:

  • Acetic Acid: Ingredient of vinegar and precursor to coatings and solvents.

  • Methacrylic and Acrylic Acids: Adhesives and precursor to polymers.

  • Adipic Acid: Polymers.

  • Citric Acid: Food and beverage flavour and preservative.

  • Fatty Acids: Coatings.

  • Ethylenediaminetetraacetic Acid: Chelating agent.

  • Maleic Acid: Polymers.

  • Propionic Acid: Preservative of food.

  • Terephthalic Acid: Polymers.

  • Apart from these, soaps are also essential carboxylate salts.


Synthesis of Carboxylic Acids

  1. Through Industrial Routes

Generally, industrial paths to carboxylic acids contradict from the ones used for small scale purposes as they demand special equipment. Here are some industrial methods to synthesize carboxylic acid:

  • With the help of Cativa process, alcohol carbonylation takes place to produce acetic acid. Contrarily, formic acid is yielded by another distinct pathway of carbonylation which also starts from methanol.

  • The oxidation reaction of aldehydes with air, while utilising manganese and cobalt catalysts. The needed aldehydes are quickly received from alkanes via hydroformylation.

  • Ethanol fermentation in manufacturing of vinegar.

  • Kolbe Schmitt reaction for salicylic acid, which is a precursor of aspirin.

  1. Laboratory Processes

Small scale reaction to produce carboxylic acid for production of chemicals and research work usually requires costly consumable reagents. These processes are:

  • Aldehyde or primary alcohol oxidation with potassium dichromate, potassium permanganate, Jones reagent or sodium chloride. This process is more feasible for laboratories than in industries as it produces inorganic products like manganese and chromium oxides.

  • Oxidative breakage of olefins through ozonolysis or by potassium dichromate or potassium permanganate.

  • Nitrile, amide or ester hydrolysis with base or acid catalysis.

  • Carbonation of organolithium and Gridnard reagent.

            RLi + CO2 → RCO2Li

            RCO2Li + HCl → RCO2H + LiCl

  1. Less Used Reactions

Many reactions yield carboxylic acids but are applied only in certain scenarios or primarily for academic regard.

  • Aldehyde disproportionation in Cannizzaro reaction

  • Diketone rearrangement in benzilic acid rearrangement which involves benzoic acid generation through Kolbe Schmitt reaction (from phenols) and von Richter reaction (from nitrobenzenes).


Reduction

Reduction of carboxylic acids to alcohols can be done by the process of hydrogenation or utilising alkyl or hydride transferring agents.

N, N Dimethyl ammonium chloride is an extremely chemoselective agent for the reduction of carboxylic acid.


Do it Yourself

i) When carboxylic acids undergo deprotonation, they yield which amongst the following?

a) ion b) anion c) electron d) acetic acid

ii) Long-chain acids are insoluble in less polar solvents. Choose the correct option for the sentence.

a) true b) false

In the above content, carboxylic acid properties, its definition, structure, nomenclature, uses, occurrence, synthesis and reduction are concisely discussed. To know more about other chemical compounds, download the Vedantu app today. It offers convenient access to detailed study material and online sessions.

FAQ (Frequently Asked Questions)

1. Which are the Four Initial Carboxylic Acids?

Ans. The first four carboxylic acid derivatives from alkanes are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.

2. Which one is the Most Potent Carboxylic Acid?

Ans. As an acid, chloroacetic acid is a hundred times stronger than acetic acid.

3. What is the Dissimilarity Between Alcohol and Carboxylic Acid?

Ans. The significant difference between them is that in alcohol, the functional group is a hydroxyl group, while carboxylic acid functional group is a carboxyl group.

4. What are Esters Mainly Used for?

Ans. Esters are widely used in cosmetics, perfumes and flavours. Moreover, specific volatile esters are used in making solvents for paints, lacquers and varnishes.