Nitrogen Containing Organic Compounds - Nitro-Substituted Aromatic Compounds

Slide 1: Nitrogen Containing Organic Compounds - NITRO-SUBSTITUTED AROMATIC COMPOUNDS

Nitro-substituted aromatic compounds are organic compounds that contain a nitro group (-NO2) attached to an aromatic ring.
Nitro groups are composed of one nitrogen atom bonded to two oxygen atoms.
These compounds are highly important in organic chemistry due to their diverse chemical properties and applications.
Nitro-substituted aromatic compounds are often used as intermediates in the synthesis of various organic compounds.
They are also used extensively in the pharmaceutical industry for the development of drugs.

Slide 2: Structure and Nomenclature

The general molecular formula for nitro-substituted aromatic compounds is C6H5-NO2.
The nitro group is usually attached to one of the carbon atoms of the benzene ring.
The location of the nitro group is indicated by numbering the carbon atoms of the benzene ring.
The parent compound is named as a substituted benzenenitro-.
The specific position of the nitro group is indicated by the prefix nitro- followed by the number of the carbon atom to which it is attached.

Slide 3: Physical Properties

Nitro-substituted aromatic compounds are generally crystalline solids at room temperature.
They often have a pale yellow to light brown color due to the presence of conjugated double bonds in the aromatic ring.
These compounds have relatively high melting and boiling points due to the presence of strong intermolecular forces such as dipole-dipole interactions and hydrogen bonding.
The presence of the nitro group also leads to high solubility in polar solvents such as water and alcohol.

Slide 4: Preparation Methods

Nitro-substituted aromatic compounds can be prepared through various synthetic routes.
One common method is the nitration of aromatic compounds using a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4).
The nitration reaction involves the replacement of a hydrogen atom on the aromatic ring with a nitro group.
The reaction is generally exothermic and requires careful control of reaction conditions to prevent side reactions and decomposition of the product.

Slide 5: Reaction Mechanism

The nitration of aromatic compounds involves the formation of a nitronium ion (NO2+).
The nitronium ion is generated by the reaction between nitric acid and sulfuric acid.
The nitronium ion then reacts with the aromatic ring to form the nitro-aromatic compound.
The reaction proceeds through an electrophilic aromatic substitution mechanism, where the nitronium ion acts as the electrophile.
The intermediate formed during the reaction is stabilized by resonance.

Slide 6: Chemical Properties

Nitro-substituted aromatic compounds are highly reactive due to the presence of the nitro group.
They can undergo various chemical reactions such as reduction, oxidation, and substitution.
Reduction of nitro groups can lead to the formation of corresponding amino groups (-NH2) or hydroxylamine groups (-NHOH).
Oxidation of nitro groups can result in the formation of various functional groups such as carbonyl compounds or carboxylic acids.
Substitution reactions can involve the replacement of the nitro group with other functional groups.

Slide 7: Reduction of Nitro Groups

Reduction of nitro groups can be achieved using various reducing agents such as metal hydrides (e.g., lithium aluminum hydride, NaBH4) or transition metal catalysts (e.g., palladium/C or Raney nickel).
The reduction reaction involves the addition of hydrogen to the nitro group, resulting in the formation of an amino group (-NH2) or a hydroxylamine group (-NHOH).
The choice of reducing agent and reaction conditions determines the selectivity and yield of the desired product.

Slide 8: Oxidation of Nitro Groups

Oxidation of nitro groups can be achieved using oxidizing agents such as potassium permanganate (KMnO4) or chromic acid (H2CrO4).
The oxidation reaction results in the cleavage of the nitro group and the formation of various functional groups such as carbonyl compounds or carboxylic acids.
The choice of oxidizing agent and reaction conditions determines the selectivity and yield of the desired product.

Slide 9: Substitution Reactions

Nitro-substituted aromatic compounds can undergo various substitution reactions, where the nitro group is replaced by other functional groups.
Substitution reactions can be achieved using nucleophilic or electrophilic substitution mechanisms.
Nucleophilic substitutions involve the attack of a nucleophile on the electrophilic carbon atom of the nitro group, resulting in the displacement of the nitro group.
Electrophilic substitutions involve the attack of an electrophile on the aromatic ring, resulting in the displacement of the nitro group.

Slide 10: Applications

Nitro-substituted aromatic compounds find diverse applications in various industries.
They are used as intermediates in the synthesis of dyes, pigments, and pharmaceuticals.
Nitro-substituted aromatic compounds are also used as explosives due to their high reactivity and ability to release a large amount of energy upon decomposition.
They serve as starting materials for the production of agrochemicals and specialty chemicals.
The unique chemical properties of nitro-substituted aromatic compounds make them indispensable in modern organic chemistry.

Properties and Reactivity of Nitro-substituted Aromatic Compounds:

Nitro-substituted aromatic compounds are generally electron-withdrawing due to the presence of the nitro group.
The presence of the nitro group can affect the electronic properties of the aromatic ring.
The electron-withdrawing nature of the nitro group makes the aromatic ring more susceptible to nucleophilic attack.
Nitro groups can undergo addition reactions with nucleophiles such as amines or enols, leading to the formation of compounds with modified properties.
Nitro-substituted aromatic compounds can also undergo aromatic substitution reactions through electrophilic aromatic substitution mechanisms.

Reduction of Nitro Groups:

Reduction of nitro groups can be achieved using different reducing agents such as metal hydrides (e.g., lithium aluminum hydride, NaBH4), iron and hydrochloric acid (Fe/HCl), or tin and hydrochloric acid (Sn/HCl).
Reduction of nitro groups using metal hydrides typically proceeds in a stepwise manner, forming nitroso compounds (-NO) and hydroxylamines (-NHOH) as intermediates before the final reduction to primary amines (-NH2).
Reduction of nitro groups using iron and hydrochloric acid or tin and hydrochloric acid results in the direct formation of primary amines.
Reduction of nitro groups is an important synthetic transformation used in the production of various chemicals and pharmaceuticals.

Examples of Reduction Reactions:

Example 1: Reduction of nitrobenzene with iron and hydrochloric acid
- Nitrobenzene + 6HCl + 3Fe → Aniline + 3FeCl2 + 3H2O
Example 2: Reduction of nitrobenzene with lithium aluminum hydride
- Nitrobenzene + LiAlH4 → Phenylhydroxylamine + 2LiAl(OH)3
- Phenylhydroxylamine + H2/Pd → Aniline + H2O

Oxidation of Nitro Groups:

Oxidation of nitro groups can be achieved using oxidizing agents such as potassium permanganate (KMnO4) or chromic acid (H2CrO4).
Oxidation of nitro groups results in the cleavage of the nitro group, forming carbonyl compounds or carboxylic acids.
Oxidation reactions of nitro groups are important in the synthesis of various organic compounds.

Examples of Oxidation Reactions:

Example 1: Oxidation of nitromethane with potassium permanganate
- Nitromethane + KMnO4 + H2O → Formaldehyde + H2SO4 + KOH + MnO2
Example 2: Oxidation of nitrobenzene with chromic acid
- Nitrobenzene + H2CrO4 + H2O → Phenol + H2SO4 + CrO3

Electrophilic Aromatic Substitution Reactions:

Nitro-substituted aromatic compounds are highly reactive towards electrophilic aromatic substitution reactions.
The presence of the nitro group enhances the electrophilicity of the aromatic ring, making it more susceptible to attack by electrophiles.
Common electrophilic aromatic substitution reactions of nitro-substituted aromatic compounds include halogenation, sulfonation, and Friedel-Crafts acylation.

Halogenation of Nitro-substituted Aromatic Compounds:

Halogenation of nitro-substituted aromatic compounds can be achieved using halogenating agents such as chlorine (Cl2) or bromine (Br2).
The reaction typically occurs at the ortho and para positions relative to the nitro group.
The halogenation reaction proceeds through an electrophilic aromatic substitution mechanism, where the halogen acts as the electrophile.

Sulfonation of Nitro-substituted Aromatic Compounds:

Sulfonation of nitro-substituted aromatic compounds involves the addition of a sulfonic acid group (-SO3H) to the aromatic ring.
Sulfonation reactions are commonly carried out using concentrated sulfuric acid (H2SO4) as both the solvent and the sulfonating agent.
The sulfonation reaction proceeds through an electrophilic aromatic substitution mechanism, where sulfuric acid generates the sulfonium ion (SO3+) as the electrophile.

Friedel-Crafts Acylation of Nitro-substituted Aromatic Compounds:

Friedel-Crafts acylation of nitro-substituted aromatic compounds involves the addition of an acyl group (-C=O) to the aromatic ring.
The reaction is typically carried out using acyl chlorides or acid anhydrides in the presence of a Lewis acid catalyst such as aluminum chloride (AlCl3).
The Friedel-Crafts acylation reaction proceeds through an electrophilic aromatic substitution mechanism, where the acyl group acts as the electrophile.

Applications of Nitro-substituted Aromatic Compounds:

Nitro-substituted aromatic compounds find applications in the production of dyes, pigments, and explosives.
They are also used as intermediates in the synthesis of various pharmaceuticals and agrochemicals.
Nitro-substituted aromatic compounds have unique properties that make them valuable tools in organic synthesis and functional materials.

Nitro-Substituted Aromatic Compounds: Reactions with Alkyl and Aryl Grignard Reagents

Nitro-substituted aromatic compounds can react with alkyl and aryl Grignard reagents to form substituted aromatic compounds.
The reaction proceeds through a nucleophilic aromatic substitution mechanism.
The nitro group is initially reduced by the Grignard reagent to form an intermediate hydroxylamine or amine.
The intermediate then undergoes further substitution with the Grignard reagent, resulting in the formation of the final product.

Nitro-Substituted Aromatic Compounds: Reaction with Sodium Amide

Nitro-substituted aromatic compounds can react with sodium amide (NaNH2) to form azo compounds.
The reaction involves the reduction of the nitro group to an amino group, which then undergoes a coupling reaction with another aromatic compound.
The reaction is commonly used in the synthesis of azo dyes, where the azo group (-N=N-) imparts distinct color properties to the compound.

Nitro-Substituted Aromatic Compounds: Reaction with Hydrazine

Nitro-substituted aromatic compounds can react with hydrazine (N2H4) to form hydrazo compounds.
The reaction involves the reduction of the nitro group to an azo group (-N=N-), which then undergoes a coupling reaction with another aromatic compound.
The reaction is commonly used in the synthesis of hydrazo dyes, which have different color properties compared to azo dyes.

Nitro-Substituted Aromatic Compounds: Oxidation Reactions

Nitro-substituted aromatic compounds can undergo oxidation reactions to form a variety of functional groups.
Oxidation of the nitro group can result in the formation of carbonyl compounds, such as aldehydes and ketones.
The reaction is commonly carried out using oxidizing agents such as potassium dichromate (K2Cr2O7) or chromium trioxide (CrO3).
The choice of oxidizing agent and reaction conditions determines the selectivity and yield of the desired product.

Nitro-Substituted Aromatic Compounds: Reduction of Aromatic Ring

Nitro-substituted aromatic compounds can be reduced to form cyclohexylamines by catalytic hydrogenation.
The nitro group is selectively reduced to an amino group (-NH2) without affecting the aromatic ring.
The reaction is commonly carried out using a catalyst such as palladium on carbon (Pd/C) or platinum (Pt).

Nitro-Substituted Aromatic Compounds: Reduction of Nitro Group to Alkyl Group

Nitro-substituted aromatic compounds can be reduced to form alkyl groups by reductive alkylation.
The nitro group is reduced to a carbocation, which then reacts with an alkyl halide or alkylating agent to form the alkyl group.
The reaction is commonly carried out using reducing agents such as zinc dust and hydrochloric acid (Zn/HCl) or sodium borohydride (NaBH4).

Nitro-Substituted Aromatic Compounds: Nitroaldol Reaction

Nitro-substituted aromatic compounds can undergo a condensation reaction with aldehydes or ketones to form nitroaldol products.
The reaction involves the addition of the nitro group to the carbonyl group, followed by the elimination of water.
The nitroaldol reaction is commonly used in the synthesis of complex organic molecules, such as natural products and pharmaceuticals.

Nitro-Substituted Aromatic Compounds: Reduction of Nitro Group to Nitroso, Nitrosamine, and Nitroalkane Groups

Nitro-substituted aromatic compounds can be selectively reduced to form nitroso, nitrosamine, or nitroalkane groups.
The reduction reactions involve the addition of hydrogen to the nitro group, followed by further reactions to convert the intermediate to the desired product.
The choice of reducing agent and reaction conditions determines the selectivity and yield of the desired product.

Nitro-Substituted Aromatic Compounds: Biological Applications

Nitro-substituted aromatic compounds have various biological applications, especially as pharmaceuticals and antibacterial agents.
The nitro group can impart specific properties to the compound, such as increased lipophilicity or enhanced biological activity.
Examples of nitro-substituted aromatic compounds used therapeutically include nitrofurantoin and metronidazole.

Nitro-Substituted Aromatic Compounds: Safety Considerations

Nitro-substituted aromatic compounds can be hazardous due to their reactivity and potential toxicity.
They may be explosive under certain conditions, and proper safety precautions should be taken during handling and storage.
It is important to follow appropriate safety guidelines and regulations when working with nitro-substituted aromatic compounds to minimize risks to health and the environment.