Nitrogen Containing Organic Compounds

Slide 2

  • Organic compounds that contain nitrogen in their structure
  • Nitrogen can be present in various functional groups
  • Nitrogen has a valency of 3 and can form three covalent bonds

Primary Amines

  • Primary amines have one alkyl or aryl group (R) attached to the nitrogen atom
  • General formula: RNH₂
  • Examples:
    • Methylamine (CH₃NH₂)
    • Ethylamine (C₂H₅NH₂)
    • Aniline (C₆H₅NH₂)

Secondary Amines

  • Secondary amines have two alkyl or aryl groups (R) attached to the nitrogen atom
  • General formula: R₂NH
  • Examples:
    • Dimethylamine (CH₃)₂NH
    • Diethylamine (C₂H₅)₂NH
    • N-methylethanamine (CH₃CH₂NHCH₃)

Tertiary Amines

  • Tertiary amines have three alkyl or aryl groups (R) attached to the nitrogen atom
  • General formula: R₃N
  • Examples:
    • Trimethylamine (CH₃)₃N
    • Triethylamine (C₂H₅)₃N
    • N,N-dimethylbenzenamine (CH₃)₂NH(C₆H₅)

Amides

  • Amides are derived from carboxylic acids
  • They have a carbonyl group (C=O) and a nitrogen atom attached to it
  • General formula: RCONR₂
  • Examples:
    • Acetamide (CH₃CONH₂)
    • N,N-dimethylpropanamide (CH₃COC(CH₃)₂NH₂)

Nitriles

  • Nitriles have a carbon triple bond to a nitrogen atom
  • General formula: RC≡N
  • Examples:
    • Ethanimenitrile (CH₃C≡N)
    • Propionitrile (CH₃CH₂C≡N)
    • Benzonitrile (C₆H₅C≡N)

Nitro Compounds

  • Nitro compounds have a nitro group (-NO₂) attached to a carbon atom
  • Examples:
    • Nitromethane (CH₃NO₂)
    • Nitrobenzene (C₆H₅NO₂)
    • 2-nitropropane (CH₃CH(NO₂)CH₃)

Amines as Bases

  • Amines can behave as bases due to the lone pair of electrons on the nitrogen atom
  • Amines can accept a hydrogen ion (H⁺) to form an ammonium ion
  • Example: Ammonia (NH₃) + Hydrogen Chloride (HCl) → Ammonium Chloride (NH₄Cl)

Summary

  • Nitrogen-containing organic compounds include primary, secondary, and tertiary amines, amides, nitriles, and nitro compounds
  • Amines can act as bases by accepting a hydrogen ion
  • Understanding the different functional groups is crucial in organic chemistry

Nitrogen Containing Organic Compounds

  • Nitrogen can exhibit a variety of oxidation states (-3, -2, 0, +1, +2, +3, +4, +5)
  • The oxidation state of nitrogen affects the reactivity and properties of organic compounds
  • Nitrogen-containing compounds have diverse applications in medicine, industry, and agriculture
  • Examples include pharmaceutical drugs, dyes, explosives, and fertilizers
  • Understanding the chemistry of nitrogen-containing compounds is essential in organic chemistry studies

Nomenclature of Amines

  • Amines are named by prefixing the appropriate alkyl or aryl group to the word “amine”
  • For primary amines, the -e ending of the alkane name is replaced by -amine
  • For secondary amines, the -e ending of the alkane name is replaced by -imine
  • For tertiary amines, the -e ending of the alkane name is replaced by -amine as a suffix
  • Examples:
    • CH₃NH₂: Methanamine (primary)
    • (CH₃)₂NH: N-methylethanamine (secondary)
    • (CH₃)₃N: Trimethylamine (tertiary)

Physical Properties of Amines

  • Amines have a fishy odor at low concentrations
  • They are soluble in water due to hydrogen bonding with the water molecules
  • As the size of the alkyl groups increases, the solubility in water decreases
  • Amines have higher boiling points compared to alkanes due to intermolecular hydrogen bonding
  • The boiling points increase as the number of alkyl groups attached to the nitrogen atom increases

Basicity of Amines

  • Amines can act as bases by donating a lone pair of electrons to a proton (H⁺)
  • The basicity of amines depends on the availability of the lone pair of electrons
  • Primary amines are more basic than secondary amines, and secondary amines are more basic than tertiary amines
  • The pKa values of amines determine their relative basicity
  • Ammonia (NH₃) has a pKa of 38 and is a relatively weak base

Reaction with Acids

  • Amines react with acids to form salts
  • The lone pair of electrons on the nitrogen atom accepts a proton from the acid
  • The resulting ammonium salts are ionic compounds
  • Examples:
    • CH₃NH₂ (Methylamine) + HCl (Hydrochloric Acid) → CH₃NH₃⁺Cl⁻ (Methylammonium Chloride)
    • (CH₃)₂NH (Dimethylamine) + HNO₃ (Nitric Acid) → (CH₃)₂NH₂⁺NO₃⁻ (Dimethylammonium Nitrate)

Reaction with Alkyl Halides

  • Amines can undergo nucleophilic substitution reactions with alkyl halides
  • The lone pair of electrons on the nitrogen atom attacks the carbon of the alkyl halide, displacing the halide ion
  • This leads to the formation of a new carbon-nitrogen bond
  • The reaction can be catalyzed by a base such as NaOH
  • Examples:
    • CH₃NH₂ (Methylamine) + CH₃Br (Methyl Bromide) → CH₃NHCH₃ (Dimethylamine)
    • (CH₃)₂NH (Dimethylamine) + C₆H₅CH₂Cl (Benzyl Chloride) → (CH₃)₂NCH₂C₆H₅ (N,N-Dimethylbenzylamine)

Preparation of Amines

  • Amines can be prepared by various methods, including:
    1. Reduction of nitro compounds
    2. Gabriel synthesis
    3. Hofmann degradation
    4. Reactions of cyanides
    5. Reductive amination
    6. By reacting primary amines with alkyl halides or acid chlorides

Example of Reduction of Nitro Compounds

  • Nitro compounds can be reduced to primary amines by using reducing agents
  • Common reducing agents include:
    • Hydrogen gas (H₂) and a metal catalyst (e.g., Raney nickel)
    • Lithium aluminum hydride (LiAlH₄)
    • Iron and hydrochloric acid (Fe/HCl)
  • Example:
    • CH₃NO₂ (Nitromethane) + 6[H] → CH₃NH₂ (Methylamine)

Example of Gabriel Synthesis

  • Gabriel synthesis is used to prepare primary amines from potassium phthalimide
  • Phthalimide is treated with an alkyl halide, followed by hydrolysis to form the amine
  • The reaction is performed under basic conditions
  • Example:
    • Potassium Phthalimide (C₆H₄(CO)₂NK) + CH₃CH₂Br (Ethyl Bromide) → CH₃CH₂NH₂ (Ethylamine) + Potassium Bromide (KBr) + Phthalic Acid (C₆H₄(COOH)₂)

Example of Reductive Amination

  • Reductive amination is a versatile method for synthesizing amines
  • It involves the combination of an aldehyde or ketone with ammonia or a primary amine in the presence of a reducing agent
  • The reducing agent can be sodium cyanoborohydride (NaBH₃CN) or sodium borohydride (NaBH₄)
  • Examples:
    • CH₃CHO (Acetaldehyde) + NH₃ (Ammonia) + NaBH₃CN → CH₃CH₂NH₂ (Ethylamine)
    • CH₃COC₂H₅ (Ethyl methyl ketone) + CH₃NH₂ (Methylamine) + NaBH₄ → CH₃C(NHCH₃)OC₂H₅ (N,N-Dimethylaminoethyl ethyl ketone)

Reactions of Amines

  • Amines can undergo various reactions, including:
    1. Substitution reactions
    2. Oxidation reactions
    3. Redox reactions
    4. Condensation reactions
    5. Polymerization reactions

Substitution Reactions

  • Amines can undergo nucleophilic substitution reactions similar to alcohols
  • Primary and secondary amines can react with alkyl halides to form new amines with different substituents
  • The reaction mechanism involves the attack of the lone pair on the nitrogen atom to the electrophilic carbon of the alkyl halide, followed by displacement of the halide ion
  • Example:
    • CH₃NH₂ (Methylamine) + CH₃Cl (Methyl Chloride) → CH₃NHCH₃ (Dimethylamine) + HCl

Oxidation Reactions

  • Amines can be oxidized to various products depending on the reaction conditions
  • Primary amines can be oxidized to corresponding nitroso compounds (RNO)
  • Secondary amines can be oxidized to corresponding nitrones (RR’N═O)
  • Tertiary amines do not undergo oxidation under normal conditions
  • Example:
    • CH₃NH₂ (Methylamine) + HNO₂ (Nitrous Acid) → CH₃NO (Methyl Nitroso) + H₂O

Redox Reactions

  • Amines can participate in redox reactions, especially when they are part of a larger molecule
  • For example, amines can be used as reducing agents in the reduction of aldehydes or ketones to alcohols
  • The lone pair of electrons on the nitrogen atom donates electrons to the carbonyl carbon, leading to the formation of a new carbon-oxygen single bond
  • Example:
    • CH₃CH₂NH₂ (Ethylamine) + CH₃CHO (Acetaldehyde) → CH₃CH₂CH₂OH (1-Propanol)

Condensation Reactions

  • Amines can undergo condensation reactions to form various types of compounds
  • A common condensation reaction is the formation of amides from amines and carboxylic acids or acid derivatives
  • The carbonyl group of the acid derivative reacts with the lone pair on the nitrogen atom, resulting in the formation of an amide bond
  • Example:
    • CH₃COOH (Acetic Acid) + CH₃NH₂ (Methylamine) → CH₃CONHCH₃ (N-Methylacetamide)

Polymerization Reactions

  • Amines can participate in polymerization reactions, forming chains of repeating units
  • These reactions can occur through different mechanisms, such as condensation polymerization or addition polymerization
  • Polyamides, for example, are formed through the condensation polymerization of dicarboxylic acids and diamines
  • Examples:
    • Nylon-6:6 - H₂N(CH₂)₆NH₂ + HOOC(CH₂)₆COOH
    • Polyurethane - CO(NH₂)C₆H₄NH₂ + OC(CH₂)₈OC₆H₄NCO

Applications and Uses of Nitrogen Containing Organic Compounds

  • Nitrogen-containing organic compounds have diverse applications in various fields, including:
    1. Pharmaceuticals: Many drugs contain nitrogen-containing compounds as active ingredients
    2. Dyes and Pigments: Nitrogen-containing compounds are used in the production of dyes and pigments for textiles, plastics, and paints
    3. Fertilizers: Ammonium nitrate and urea are widely used as nitrogen fertilizers in agriculture
    4. Explosives: Nitroglycerin and TNT are examples of nitrogen-containing explosives
    5. Synthetic materials: Polymers such as polyamides and polyurethanes have various industrial uses

Environmental Impact of Nitrogen Containing Compounds

  • Nitrogen-containing compounds can have environmental effects, especially when they are released into the air or water:
    1. Nitrogen Oxides (NOx): Emissions from vehicles and industrial processes contribute to air pollution and the formation of smog and acid rain
    2. Nitrate Contamination: Excessive use of nitrogen-based fertilizers can lead to nitrate contamination in groundwater, affecting drinking water quality
    3. Eutrophication: Excessive nitrogen from agricultural runoff can cause eutrophication in lakes and rivers, leading to algae blooms and oxygen depletion

Summary

  • Nitrogen-containing organic compounds include amines, amides, nitriles, and nitro compounds
  • Amines act as bases and can undergo various reactions, including substitution, oxidation, and condensation
  • Amines find applications in pharmaceuticals, dyes, fertilizers, explosives, and synthetic materials
  • Nitrogen-containing compounds can have environmental impacts, such as air pollution, water contamination, and eutrophication
  • Understanding the properties and reactions of nitrogen-containing compounds is important in the study of organic chemistry

References

  • Organic Chemistry by Morrison and Boyd
  • NCERT Chemistry Textbooks for Class 12
  • Khan Academy - Organic Chemistry
  • Chemistry LibreTexts - Nitrogen Compounds
  • Organic Chemistry Portal