Nitrogen Containing Organic Compounds

FEATURE OF NITROGEN-CONTAINING AROMATIC COMPOUNDS

  • Nitrogen-containing aromatic compounds contain a benzene ring with one or more nitrogen atoms.
  • The nitrogen atom(s) can replace carbon atom(s) in the aromatic ring.
  • These compounds play a crucial role in pharmaceuticals, dyes, and other industrial applications.

Types of Nitrogen-Containing Aromatic Compounds

  1. Amines:
    • Primary amines: NH2 replaces hydrogen atom(s) in the aromatic ring.
    • Secondary amines: Two NH2 groups replace hydrogen atom(s) in the aromatic ring.
    • Tertiary amines: Three NH2 groups replace hydrogen atom(s) in the aromatic ring.
  1. Pyridines:
    • Pyridine is a nitrogen-containing aromatic compound with the formula C5H5N.
    • It consists of a benzene ring fused to a pyridine ring.
  1. Quinolines:
    • Quinoline is a nitrogen-containing aromatic compound with the formula C9H7N.
    • It consists of a benzene ring fused to a pyridine ring, similar to pyridine.

Preparation of Nitrogen-Containing Aromatic Compounds

  1. Amines:
    • Gabriel synthesis: Reaction between phthalimide and alkyl halide, followed by hydrolysis.
    • Reduction of nitro compounds: Nitro compounds are reduced by hydrogenation to form amines.
  1. Pyridines:
    • Chichibabin synthesis: Reaction between acetylene and ammonia, followed by cyclization.
  1. Quinolines:
    • Conrad–Limpach synthesis: Reaction between aniline and β,β-dichloroethyl ether, followed by oxidation.

Example:

  • Preparation of aniline from bromobenzene:
    1. Bromination of benzene to form bromobenzene
    2. Conversion of bromobenzene to aniline using reducing agents like tin and hydrochloric acid.

Physical and Chemical Properties

  1. Amines:
    • Solubility: Low molecular weight amines are soluble in water, while higher molecular weight amines are not.
    • Basicity: Amines act as bases due to the presence of a lone pair of electrons on the nitrogen atom.
  1. Pyridines:
    • Solubility: Pyridines are soluble in nonpolar solvents but have limited solubility in water.
  1. Quinolines:
    • Solubility: Quinolines are poorly soluble in water but soluble in organic solvents.

Reactivity of Nitrogen-Containing Aromatic Compounds

  1. Amines:
    • Acylation: Amines react with acyl chlorides to form amides.
    • Alkylation: Amines react with alkyl halides to form N-alkylamines.
  1. Pyridines:
    • Electrophilic substitution reactions: Pyridines are susceptible to nitration, halogenation, and sulfonation.
  1. Quinolines:
    • Oxidation: Quinolines can be oxidized to quinolinic acid using strong oxidizing agents.

Equations:

  • Formation of an amide:
    • R-NH2 + R’-COCl ⟶ R-NH-CO-R’ + HCl
  • Alkylation of amines:
    • R-NH2 + R’-X ⟶ R-NH-R’ + HX
  • Electrophilic substitution on pyridines:
    • C5H5N + HNO3 ⟶ C5H4N-NO2 + H2O
  • Oxidation of quinolines:
    • C9H7N + 3[O] ⟶ C9H6NCOOH

Remember to study and understand the properties, reactions, and synthesis of nitrogen-containing aromatic compounds. These compounds have various applications and can be extensively explored in organic chemistry. ``markdown

  1. Physical Properties of Nitrogen-Containing Aromatic Compounds
  • Amines:
    • Boiling points: Boiling points of amines are higher than similar-sized alkanes due to the presence of hydrogen bonding.
    • Odor: Amines often have distinctive odors, which can range from fishy to ammonia-like.
  • Pyridines:
    • Boiling points: Pyridines have higher boiling points than similar-sized hydrocarbons due to the presence of an electronegative nitrogen atom.
    • Basicity: Pyridines are weak bases compared to amines due to the electron-withdrawing effect of the aromatic ring.
  • Quinolines:
    • Melting points: Quinolines have higher melting points compared to similar-sized hydrocarbons due to the presence of an aromatic ring.
    • Solubility: Quinolines are sparingly soluble in water but dissolve in organic solvents.
  1. Chemical Properties of Nitrogen-Containing Aromatic Compounds
  • Amines:
    • Carbylamine reaction: Amines react with chloroform and alcoholic KOH to form isocyanides.
    • Hofmann degradation: Amines react with nitrous acid (HNO2) to form alkyl isocyanates.
  • Pyridines:
    • Electrophilic aromatic substitution: Pyridines undergo electrophilic substitution reactions at various positions on the ring.
    • Oxidation: Pyridines can be oxidized to pyridine N-oxides through the action of various oxidizing agents.
  • Quinolines:
    • Electrophilic substitution: Quinolines undergo electrophilic aromatic substitution reactions at different positions on the ring.
    • Reduction: Quinolines can be reduced to dihydroquinolines using reducing agents.
  1. Uses of Nitrogen-Containing Aromatic Compounds
  • Amines:
    • Pharmaceuticals: Amines are used as components in many drugs, such as antihistamines and antidepressants.
    • Dyes: Amines are used in the dye industry for producing vibrant colors.
  • Pyridines:
    • Medicinal Chemistry: Pyridines are fundamental components in the synthesis of many drugs, including antimalarial and anti-inflammatory drugs.
    • Pesticides: Pyridines are used as active ingredients in various insecticides and herbicides.
  1. Uses of Nitrogen-Containing Aromatic Compounds (contd.)
  • Quinolines:
    • Polymer synthesis: Quinolines are employed in the manufacturing of polymers, such as polyquinoline.
    • Photodynamic therapy: Quinolines are used in photodynamic therapy as sensitizers for the treatment of certain cancers.
  1. Reactions of Amines with Acids
  • Reactions with mineral acids: Amines react with mineral acids (e.g., HCl) to form ammonium salts.
    • Example: R-NH2 + HCl ⟶ R-NH3+Cl-
  • Quaternization: Amines can be converted into quaternary ammonium salts by reaction with alkyl halides.
    • Example: R-NH2 + R’-X ⟶ R-NH-R’+X-
  1. Reactions of Amines with Acids (contd.)
  • Reactions with carboxylic acids: Amines react with carboxylic acids to give amides.
    • Example: R-NH2 + R’-COOH ⟶ R-NH-CO-R’ + H2O
  • Salt formation: Amines can form salts with other acids, such as sulfuric acid.
    • Example: R-NH2 + H2SO4 ⟶ R-NH3+HSO4-
  1. Electrophilic Aromatic Substitution of Pyridines
  • Nitration: Pyridines can be nitrated using a mixture of concentrated sulfuric acid and nitric acid.
    • Example: C5H5N + HNO3 ⟶ C5H4N-NO2 + H2O
  • Halogenation: Halogens (e.g., bromine) can react with pyridines in the presence of Lewis acids to form halopyridines.
    • Example: C5H5N + Br2 ⟶ C5H4N-Br + HBr
  1. Electrophilic Aromatic Substitution of Pyridines (contd.)
  • Sulfonation: Pyridines can be sulfonated by treating them with sulfuric acid or chlorosulfonic acid.
    • Example: C5H5N + H2SO4 ⟶ C5H4N-SO3H + H2O
  • Friedel-Crafts alkylation: Pyridines can react with alkyl halides in the presence of a Lewis acid to yield N-alkylpyridinium salts.
    • Example: C5H5N + CH3Cl ⟶ C5H5N-CH3+Cl-
  1. Electrophilic Aromatic Substitution of Quinolines
  • Nitration: Quinolines are prone to nitration using a mixture of concentrated sulfuric acid and nitric acid.
    • Example: C9H7N + HNO3 ⟶ C9H6N-NO2 + H2O
  • Halogenation: Quinolines can be halogenated using halogens (e.g., bromine) in the presence of Lewis acids.
    • Example: C9H7N + Br2 ⟶ C9H6N-Br + HBr
  1. Electrophilic Aromatic Substitution of Quinolines (contd.)
  • Sulfonation: Quinolines can be sulfonated by reacting with sulfuric acid or chlorosulfonic acid.
    • Example: C9H7N + H2SO4 ⟶ C9H6N-SO3H + H2O
  • Friedel-Crafts alkylation: Quinolines can undergo Friedel-Crafts alkylation with alkyl halides in the presence of a Lewis acid.
    • Example: C9H7N + CH3Cl ⟶ C9H7N-CH3+Cl- Remember to study and understand the physical and chemical properties of nitrogen-containing aromatic compounds, as well as their various reactions and applications.markdown
  1. Reactions of Quinolines with Acids
  • Formation of quinolinium salts: Quinolines can be converted into quinolinium salts by reacting with strong acids.
    • Example: C9H7N + HCl ⟶ C9H7NH+Cl-
  • Reaction with carboxylic acids: Quinolines can react with carboxylic acids to form acid quinolyl esters.
    • Example: C9H7N + R-COOH ⟶ C9H7N-COOR + H2O
  1. Oxidation of Amines
  • Oxidation to nitro compounds: Amines can be oxidized to nitro compounds using suitable oxidizing agents.
    • Example: R-NH2 + [O] ⟶ R-NO2 + H2O
  • Oxidation to N-oxides: Amines can also be oxidized to N-oxides using mild oxidizing agents like hydrogen peroxide (H2O2).
    • Example: R-NH2 + H2O2 ⟶ R-NO + H2O
  1. Oxidation of Pyridines
  • Oxidation to pyridine N-oxides: Pyridines can be oxidized to pyridine N-oxides using various oxidizing agents like hydrogen peroxide (H2O2).
    • Example: C5H5N + H2O2 ⟶ C5H5NO + H2O
  • Oxidation to pyridine N-oxides using peracids: Pyridines can also be oxidized to pyridine N-oxides using peracids like peracetic acid (CH3CO3H).
    • Example: C5H5N + CH3CO3H ⟶ C5H5NO + CH3COOH
  1. Functional Group Interconversion: Amines
  • Conversion of amines to amides: Amines can be converted to amides by reacting with carboxylic acid derivatives like acid chlorides or esters.
    • Example: R-NH2 + R’-COCl ⟶ R-NH-CO-R’ + HCl
  • Conversion of amides to amines: Amides can be converted back to amines by hydrolysis using strong acids or bases.
    • Example: R-CO-NH2 + H2O ⟶ R-COOH + NH3
  1. Functional Group Interconversion: Pyridines
  • Conversion of pyridines to carboxylic acids: Pyridines can undergo oxidation reactions to form carboxylic acids.
    • Example: C5H5N + 2[O] ⟶ C5H4O2 + H2O
  • Conversion of pyridines to nitriles: Pyridines can also be converted to nitriles by reaction with alkyl halides and sodium cyanide.
    • Example: C5H5N + R’-X + NaCN ⟶ C5H4N-C≡N + NaX
  1. Functional Group Interconversion: Quinolines
  • Conversion of quinolines to carboxylic acids: Quinolines can be oxidized to carboxylic acids using strong oxidizing agents.
    • Example: C9H7N + 3[O] ⟶ C9H6O2 + H2O
  • Conversion of quinolines to nitriles: Quinolines can also be converted to nitriles by reaction with alkyl halides and sodium cyanide.
    • Example: C9H7N + R’-X + NaCN ⟶ C9H6N-C≡N + NaX
  1. Importance of Nitrogen-Containing Aromatic Compounds in Pharmaceuticals
  • Nitrogen-containing aromatic compounds serve as important building blocks for pharmaceutical drug synthesis.
  • Many drugs, including antibiotics, antivirals, and anti-inflammatory agents, contain nitrogen-containing aromatic compounds as essential components.
  1. Importance of Nitrogen-Containing Aromatic Compounds in Dyes
  • Nitrogen-containing aromatic compounds are widely used in the dye industry to produce vibrant and long-lasting colors.
  • These compounds provide excellent dyeing properties, stability, and lightfastness.
  1. Importance of Nitrogen-Containing Aromatic Compounds in Agrochemicals
  • Nitrogen-containing aromatic compounds find extensive use in the field of agrochemicals as active ingredients in pesticides and herbicides.
  • These compounds play a crucial role in protecting crops from pests and diseases, enhancing agricultural productivity.
  1. Environmental Impact of Nitrogen-Containing Aromatic Compounds
  • Some nitrogen-containing aromatic compounds, such as certain pesticides, can have detrimental effects on the environment.
  • Proper disposal and regulation are necessary to minimize the negative impact of these compounds on ecosystems and human health. ``

Remember to study and understand the various functional group interconversions, importance of nitrogen-containing aromatic compounds in pharmaceuticals, dyes, and agrochemicals, and the environmental impact associated with these compounds. These topics will be crucial for your 12th Boards exam.