FSc Notes Part 2 Chemistry Important Chemicals Aldehyde & Ketone CHO and CO and Carboxylic Acid COOH

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Aldehyde & Ketone CHO and CO

Definition of Aldehyde

Organic compounds that contain monovalent functional group – CHO are known as aldehydes.

General Formula of Aldehyde

They are denoted by RCHO, where R may be any alkyl group. The general formula for aldehyde is

CnH2n – CHO

Where n may be any natural number.

Structure of Aldehyde

The structural formula of aldehyde shows that it contains a carbonyl group.

Examples of Aldehyde

CH3CHO | Acetaldehyde

HCHO | Formaldehyde

Definition of Ketone

Organic compounds that contain divalent functional group – CO – are called Ketones.

General Formula of Ketone

They are denoted by R may be any alkyl group. The general formula for Ketone is

CnH2n+1 – CO – CnH2n+1

Where n may be any natural number.

Structure of Ketone

The structural formula of ketone shows that it contains a carbonyl group.

Example of Ketone

CH3COCH3 (Acetone)

Preparation of Aldehyde & Ketone

Aldehyde and Ketone can be prepared by the following methods.

1. From Dehydrogenation of Alcohol

Removal of hydrogen from a compound is called dehydrogenation. In presence of catalyst, Cu – Ni couple when alcohol is heated at 180ºC then dehydrohalogenation takes place. As a result, aldehyde and ketone are formed.

H-CH2OH —-> H-CH=O + H2

CH3-CH2OH —-> H-CH=O + H2

(CH3)2-CH-OH —-> (CH3)2-C=O + H2

2. From Oxidation of Alcohol

In presence of oxidizing agents, K2Cr2O7 or concentrated H2SO4, alcohols are oxidized to form aldehyde or ketone.

H-CH2OH + [O] —-> H-CH=O + H2O

CH3-CH2OH + [O] —-> H-CH=O + H2O

(CH3)2-CH-OH + [O] —-> (CH3)2-C=O + H2O

3. From Dry Distillation

By the dry distillation of calcium formate (Calcium salt of formic acid), form aldehyde is obtained.

Ca(COOH)2 —-> HCHO + CaCO3

By the dry distillation of calcium salt of formic acid and calcium salt of carboxylic acid, aldehydes are obtained.

Ca(CH3OOH)2 + Ca(COOH)2 —-> CH3CHO + CaCO3

By the dry distillation of calcium salt of carboxylic acid, Ketone is formed.

Ca(CH3OOH)2 —-> CH3CHO + CaCO3

4. From Ethyne

This method is used for the preparation of acetaldehyde. In presence of catalyst H2SO4 and HgSO4 when ethyne reacts with water than unstable, intermediate vinyle alcohol is formed which on rearrangement of atoms convert into acetaldehyde.

H-C≡C-H + H2O —-> H2C-HCOH —-> H3C-COH

Preparation of Acetone By Pyrolysis of Acetic Acid

In presence of catalyst MnO2, when the acetic acid is heated at about 500ºC then acetone is formed.

CH3COOH —-> CH3-CHO + CO2 + H2O

Uses of Aldehyde

1. Aldehyde is used a preservative for biological specimen, as antiseptic and as disinfectant.
2. It is used in the synthesis of resins and plastics.
3. It is used to prepare drying oils and dyes.
4. It is used in the silvering of mirror.
5. It is used in processing of anti-polio vaccine.
6. It is used to prepare highly explosive cyclonite.

Uses of Ketones

1. It is used as a solvent for organic compounds.
2. It is used for storage of acetylene in solution form.
3. It is used in the preparation of iodoform, chloroform, etc.
4. It is used in the preparation of scent.
5. It is used as nail-polish remover.
6. It is used in the preparation of smokeless gun power and synthetic rubber.

Carboxylic Acid COOH

Definition

Organic compounds that contain monovalent functional group – COOH are called Ketones.

General Formula

They are denoted by R may be any alkyl group. The general formula for ketone is

CnH2n+1 – COOH

Where n may be any natural number.

Structure

The Structural formula of Carboxylic Acid shows that it contains a carbonyl group.

ROH-C=O

Examples

Acetic Acid (CH3COOH)

Preparation

Carboxylic Acid can be prepared by the following methods.

1. From Grignard’s Reagent

In presence of dry ether and halogen acid when Grignard’s reagent with carbondioxide then Carboxylic Acid is formed.

R-Mg-X + O=C=O —-> COOR-Mg-X —-> RCOOH + MgX2

CH3-Mg-X + 0=C=0 —-> COOCH3-Mg-X —-> CH3COOH + MgX2

2. From Oxidation of Alcohol

In presence of oxidizing agent such as a mixture of K2Cr2O7 and concentrated K2SO4, when primary alcohol is oxidized then aldehyde is form, which on further oxidation convert into Carboxylic Acid.

RCH2-OH —-> RCHO —-> RCOH-O

CH3CH2-OH —-> CH3CHO —-> CH3COH=O

3. From Dehydrogenation of Alcohol

In presence of catalyst Co – Mo couple, when primary alcohol is heated at elevated temperature then aldehyde is formed, which in presence of a mixture of oxidizing agent such as K2Cr2O7 and concentrated H2SO4 convert into Carboxylic Acid.

RCH2-OH —-> RCHO —-> RCOH-O

CH3CH2-OH —-> CH3CHO —-> CH3COH=O

4. From Ethyne

This method is used for the preparation of acetaldehyde. In presence of catalyst H2SO4 and HgSO4 when ethyne reacts with water than unstable, intermediate vinyle alcohol is formed which on rearrangement of atoms convert into acetaldehyde.

H-C≡C-H + H-OH —-> C2H3OH —-> CH3-CHO —-> CH3-COOH

Uses of Carboxylic Acid

1. Carboxylic Acids are used as laboratory reagents.
2. Acetic acid is used as solvent for phosphorus, sulphur, gums and resins.
3. It is widely used in artificial leather production.
4. Acetic acid is used to prepare acetates, esters and cellulose acetate silk.
5. After colouring, it is used as vinegar