Science Class 12 - Ketones And-Carboxylic-Acids Notes

Ketones and Carboxylic Acids

Welcome to the chapter on Ketones and Carboxylic Acids for Class 12. In this chapter, you will learn about the structure, nomenclature, properties, preparation, and uses of ketones and carboxylic acids. By the end of this chapter, you will be able to identify, name, and explain the reactions of these important organic compounds.

Introduction

Ketones and carboxylic acids are important classes of organic compounds containing the carbonyl group (>C=O). They play a vital role in chemistry, biology, and industry.

Ketones

• Functional group: Carbonyl group (>C=O) bonded to two alkyl or aryl groups.
• General formula: R-CO-R'
• Example: Acetone (CH₃COCH₃)

Nomenclature

• IUPAC: Replace the -e of the parent alkane with -one (e.g., Propanone).
• Common: Name the alkyl groups attached to the carbonyl carbon followed by "ketone" (e.g., Dimethyl ketone).

Preparation of Ketones

• Oxidation of secondary alcohols.
• Dry distillation of calcium salts of carboxylic acids.
• By hydration of alkynes (e.g., acetylene to acetone).

Physical Properties

• Generally liquids at room temperature (except formaldehyde).
• Soluble in water (lower members); pleasant smell.

Chemical Properties

• Nucleophilic addition reactions (e.g., addition of HCN, NaHSO₃).
• Reduction to secondary alcohols.
• Oxidation to carboxylic acids.
• Reaction with hydrazine, phenylhydrazine, semicarbazide to form derivatives.

Uses of Ketones

• Solvents (e.g., acetone in nail polish remover).
• Intermediate in organic synthesis.
• Pharmaceuticals and perfumes.

Carboxylic Acids

• Functional group: Carboxyl group (-COOH).
• General formula: R-COOH
• Example: Acetic acid (CH₃COOH)

Nomenclature

• IUPAC: Replace the -e of the parent alkane with -oic acid (e.g., Ethanoic acid).
• Common: Use common names (e.g., Formic acid, Acetic acid).

Preparation of Carboxylic Acids

• Oxidation of primary alcohols and aldehydes.
• Hydrolysis of nitriles and esters.
• Reaction of Grignard reagents with CO₂ followed by hydrolysis.

Physical Properties

• Usually liquids or solids at room temperature.
• Soluble in water (lower members); have a sour taste and sharp smell.

Chemical Properties

• Acidic in nature; turn blue litmus red.
• React with bases to form salts and water.
• React with alcohols to form esters (esterification).
• Decarboxylation (removal of CO₂).
• Reduction to primary alcohols.

Uses of Carboxylic Acids

• Vinegar (acetic acid) used in food.
• Preservatives and medicines.
• Manufacture of polymers, dyes, and perfumes.

Practice Questions

1. Write the IUPAC names of the following: (a) CH₃COCH₃ (b) HCOOH
2. How is acetone prepared from isopropyl alcohol?
3. What happens when acetic acid reacts with sodium carbonate?
4. Explain the difference between ketones and aldehydes.
5. Give two uses of carboxylic acids.

Challenge Yourself

• Draw the structure of propanone and ethanoic acid.
• Explain the mechanism of nucleophilic addition to the carbonyl group.
• Describe a test to distinguish between a ketone and an aldehyde.

Did You Know?

• Acetone is the simplest and most important ketone, widely used as a solvent.
• Formic acid is found in ant stings!

Glossary

• Ketone: An organic compound with a carbonyl group bonded to two carbon atoms.
• Carboxylic Acid: An organic compound containing the carboxyl group (-COOH).
• Carbonyl Group: A functional group composed of a carbon atom double-bonded to an oxygen atom (>C=O).
• Esterification: The reaction of a carboxylic acid with an alcohol to form an ester and water.

Answers to Practice Questions

1. (a) Propanone, (b) Methanoic acid (formic acid)
2. By oxidation of isopropyl alcohol (secondary alcohol) using an oxidizing agent like K₂Cr₂O₇/H₂SO₄.
3. Acetic acid reacts with sodium carbonate to produce sodium acetate, carbon dioxide, and water.
4. Ketones have the carbonyl group (>C=O) bonded to two carbon atoms, while aldehydes have it bonded to at least one hydrogen atom.
5. Used in food (vinegar), medicines, and making polymers.

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Understanding ketones and carboxylic acids is key to mastering organic chemistry!