45Compounds conatining Nitrogen

📚
INTRODUCTION
▢ Nitro Compounds:
  1. Organic compounds containing –NO₂ functional group
  2. General formula: R–NO₂ / Ar–NO₂
▢ Types:
❖ Aliphatic Nitro Compounds / Nitroalkanes / Nitroparaffins: R–NO₂
❖ Aromatic Nitro Compounds / Nitroarenes: Ar–NO₂
▢ Nitrobenzene:
  1. Artificial oil of bitter almond
  2. Oil of mirabane
  3. Odour similar to bitter almond
  4. Pale yellow oily liquid
  5. Steam volatile
  6. Poisonous vapour
▢ Important Names:
❖ Benzaldehyde: Oil of bitter almond
❖ Conc. H₂SO₄: Oil of vitriol
❖ Methyl salicylate: Oil of wintergreen; chief constituent of iodex
❖ Phenyl salicylate: Salol; antiseptic
❖ 2,4,6-Trinitrophenol: Picric acid
❖ TNB: Highly explosive; moderately explosive in liquid form; extremely explosive as dry powder
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CLASSIFICATION OF NITROALKANES

Table 1: Classification based on carbon attached to –NO₂

Type
General Form
Condition
Primary nitroalkane
R–CH₂–NO₂
–NO₂ attached to 1° carbon
Secondary nitroalkane
R₂CH–NO₂
–NO₂ attached to 2° carbon
Tertiary nitroalkane
R₃C–NO₂
–NO₂ attached to 3° carbon
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NITRO GROUP AND NITRITE GROUP
▢ Functional Isomerism:
❖ Nitro Group: R–NO₂
❖ Nitrite Group: R–O–N=O
❖ Relation: Functional isomers
▢ Ambident Nature:
  1. NO₂⁻ can attach through N → nitro compound
  2. NO₂⁻ can attach through O → alkyl nitrite
  3. NO₂ and CN are ambident groups
▢ Nitroalkane vs Alkyl Nitrite:

Table 1: Nitroalkane and alkyl nitrite

Point
Nitroalkane
Alkyl Nitrite
General structure
R–NO₂
R–O–N=O
Derivative
Alkyl derivative of nitro form of nitrous acid
Alkyl derivative of nitrite form of nitrous acid
Nature
Nitro derivatives of alkanes
Alkyl esters of nitrous acid
Boiling point
Higher; nitroethane = 388 K
Lower; ethyl nitrite = 261 K
Polarity
More polar
Less polar
Stability
Thermodynamically more stable
Less stable; decomposes on heating
Distillation
Can be distilled normally
Cannot be purified by normal distillation
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ACIDIC CHARACTER OF NITRO COMPOUNDS
▢ Cause:
  1. Nitroalkanes having α-H are acidic
  2. Acidity due to formation of aci-nitro / nitronic acid form
  3. Anion stabilized by –I effect and resonance of –NO₂
▢ Condition: Acidity requires at least one α-H
▢ Acidity Order: CH₃NO₂ > RCH₂NO₂ > R₂CHNO₂
▢ More Acidic Than:
  1. Alkanes
  2. Alkenes
  3. Alkynes
  4. Cyanides
  5. Aldehydes
  6. Ketones
  7. Esters
▢ Solubility in Base:
  1. 1° nitroalkanes dissolve in base
  2. 2° nitroalkanes dissolve in base
  3. 3° nitroalkanes do not dissolve in base because α-H absent
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PREPARATION OF NITRO COMPOUNDS
▢ From Alkyl Halide and Alcoholic AgNO₂:
❖ Reaction: R–X + AgNO₂ alc. → R–NO₂ + AgX
❖ Main Product: Nitroalkane
❖ Side Product: Alkyl nitrite, R–O–N=O
❖ Yield: 70–80% nitroalkane; 10–15% alkyl nitrite
❖ Used Mainly For: 1° nitroalkanes
❖ Separation: Fractional distillation; alkyl nitrite has lower b.p.
❖ Important Notes:
  1. KNO₂ not used → gives alkyl nitrite instead of nitroalkane
  2. Aq. AgNO₃ not used → gives alcohol
  3. Alcoholic AgNO₂ used for nitroalkane preparation
▢ From α-Halogenated Acids and aq. NaNO₂:
❖ Reaction: α-halo acid + aq. NaNO₂ → α-nitro acid → nitroalkane + CO₂
❖ Example: ClCH₂COOH + NaNO₂ → NO₂CH₂COOH → CH₃NO₂ + CO₂
❖ Product: Nitroalkane
▢ Vapour Phase Nitration of Alkanes:
❖ Reagent: Fuming HNO₃ / HNO₃ + NO₂
❖ Temperature: 150–400°C
❖ Mechanism: Free radical substitution
❖ Ease of H Substitution: 3° H > 2° H > 1° H
❖ Nature: Mixture of products due to C–H bond cleavage
❖ Examples:
  1. CH₄ + HNO₃ → CH₃NO₂ + H₂O
  2. Propane + HNO₃ → 1-nitropropane + 2-nitropropane + nitroethane + nitromethane
▢ Preparation of Nitrobenzene:
❖ By Nitration of Benzene:
◉ Reaction: C₆H₆ + conc. HNO₃ + conc. H₂SO₄ → C₆H₅NO₂ + H₂O
◉ Temperature: ≈ 60°C
◉ Mixture: Nitrating mixture = conc. HNO₃ + conc. H₂SO₄
◉ Type:
  1. Electrophilic substitution reaction
  2. Irreversible reaction
  3. Monosubstitution reaction
◉ Electrophile: NO₂⁺ / nitronium ion
◉ Role of Reagents:
◈ H₂SO₄: Bronsted acid
◈ HNO₃: Bronsted base
◉ At Higher Temperature:
  1. m-dinitrobenzene forms
  2. trinitrobenzene forms
◉ With Fuming HNO₃: TNB forms
❖ From Benzene Diazonium Chloride: C₆H₅N₂⁺Cl⁻ → C₆H₅NO₂
❖ By Oxidation of Aniline:
◉ Reagent: Trifluoroperacetic acid / CF₃CO₃H
◉ Reaction: Aniline → Nitrobenzene
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PHYSICAL PROPERTIES
▢ Physical State and Smell:
  1. Nitroalkanes: colourless, pleasant-smelling liquids
  2. Nitrobenzene: pale yellow oily liquid
  3. Most nitroarenes: yellow crystalline solids
▢ Solubility:
  1. Nitroalkanes: sparingly soluble in water; soluble in organic solvents
  2. Nitroarenes: soluble in organic solvents such as alcohol, benzene, ether
▢ Boiling Point:
  1. Nitro group is polar
  2. Dipole moment: 3–4 D
  3. Boiling points higher than parent hydrocarbons
  4. Benzene b.p. = 353 K
  5. Nitrobenzene b.p. = 483 K
  6. High b.p. due to dipole–dipole interaction
▢ Stability:
  1. Nitroalkanes are stable and distillable at normal pressure
  2. Nitroarenes are less stable and may decompose explosively on heating
  3. Nitroarenes are steam distilled or distilled under reduced pressure
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CHEMICAL PROPERTIES
▢ Electronic Effect of –NO₂:
  1. Strong –I effect
  2. Resonance-stabilized group
  3. Deactivating group in aromatic ring
▢ Acidity:
❖ Condition: Presence of α-H
❖ Acidic Nitroalkanes:
  1. 1° nitroalkanes
  2. 2° nitroalkanes
❖ Non-acidic: 3° nitroalkanes; no α-H
❖ Base Solubility: 1° and 2° nitroalkanes dissolve in strong alkali
▢ Halogenation:
❖ Condition: α-H present + base
❖ Reaction: Nitroalkane → α-halogenated nitro compound
❖ Important Product: Nitrochloroform / chloropicrin
❖ Use of Chloropicrin:
  1. Insecticide
  2. War gas
▢ Reaction with Grignard Reagent:
❖ Reacting Form: Aci-form of nitroalkane
❖ Product: Alkane
▢ Acidic Hydrolysis of Nitroalkanes:

Table 1: Hydrolysis of nitroalkanes

Nitro Compound
Product
Condition
1° nitroalkane
Carboxylic acid + hydroxylamine
Boiling with HCl or 85% H₂SO₄
2° nitroalkane
Ketone + nitrous oxide
Boiling with HCl or H₂SO₄
3° nitroalkane
Not easily hydrolysed
α-H absent
Nitroarene
No hydrolysis
Aromatic nitro compounds resist hydrolysis
❖ Examples:
  1. CH₃CH₂NO₂ + H₂O → CH₃COOH + NH₂OH
  2. 2-nitropropane → acetone + nitrous oxide
❖ Use: Distinguishes 1°, 2° and 3° nitroalkanes
▢ Reaction with Nitrous Acid:
❖ Primary Nitroalkane: Forms nitrolic acid; gives red colour with alkali
❖ Secondary Nitroalkane: Forms pseudonitrol; gives blue colour
❖ Tertiary Nitroalkane: No reaction because α-H absent
❖ Use: Distinction among 1°, 2° and 3° nitroalkanes
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REDUCTION OF NITRO COMPOUNDS
▢ General Sequence: Nitro → Nitroso → Hydroxylamine → Amine
▢ Acidic Medium:
❖ Reagents:
  1. Fe/HCl
  2. Zn/HCl
  3. Sn/HCl
  4. SnCl₂/HCl
❖ Product: 1° amine
❖ Examples:
  1. R–NO₂ → R–NH₂
  2. Ar–NO₂ → Ar–NH₂
  3. Nitrobenzene → Aniline
❖ Note: Nascent hydrogen reduces nitro compound; intermediates are not isolated
▢ Neutral Medium:
❖ Reagents:
  1. Zn dust / aq. NH₄Cl
  2. Zn dust / H₂O
  3. Al-Hg couple / H₂O
❖ Product: Hydroxylamine
❖ Reaction: R/Ar–NO₂ → R/Ar–NHOH
❖ Baker-Mulliken Test:
  1. Hydroxylamine on warming with Tollens' reagent reduces it to metallic silver
  2. Used as test for nitro compounds
  3. Occurs in neutral medium
▢ Alkaline Medium:
❖ Main Feature: Condensed products
❖ Products:
◉ Zn + aq. NaOH: Hydrazobenzene
◉ Zn + alc. NaOH / Sn + NaOH: Azobenzene
◉ Na₃AsO₃ in NaOH / glucose in NaOH: Azoxybenzene
▢ Catalytic Reduction:
❖ Catalysts:
  1. Ni
  2. Pd
  3. Pt
❖ Product: 1° amine
❖ Examples:
  1. CH₃NO₂ + H₂/Ni → CH₃NH₂ + H₂O
  2. Nitrobenzene + H₂/Ni → Aniline
▢ LiAlH₄ Reduction:
❖ Aliphatic Nitro Compounds: R–NO₂ → R–NH₂
❖ Aromatic Nitro Compounds: Nitrobenzene → Azobenzene
❖ Solvent: Ether
❖ Important Note: Aromatic nitro compounds do not give 1° amine with LiAlH₄; azo compound forms
▢ Electrolytic Reduction: Final product depends on pH of medium
▢ Selective Reduction:
  1. In polynitro compounds, one –NO₂ group can be reduced without affecting others
  2. Known as selective reduction
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RING SUBSTITUTION REACTIONS OF NITROARENES
▢ General:
  1. Nitrobenzene ring participates in electrophilic and nucleophilic substitution
  2. –NO₂ strongly deactivates benzene ring
  3. Electrophilic substitution becomes difficult
▢ Electrophilic Substitution:
❖ Directive Effect: Meta-directing
❖ Reason:
  1. –NO₂ withdraws electrons by –I and –R effects
  2. Ortho and para positions are deactivated
  3. Meta position becomes comparatively more electron-rich
❖ Important Note: Nitrobenzene does not undergo Friedel-Crafts reaction because ring is highly deactivated
▢ Nucleophilic Substitution:
❖ Directive Effect: Ortho and para directing for nucleophiles
❖ Reason:
  1. Ortho and para positions are electron-deficient
  2. Strong nucleophiles attack o/p positions
❖ Nucleophiles:
  1. OH⁻ from NaOH/KOH
  2. NH₂⁻ from NaNH₂
❖ Condition: Strong heating / fusion
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EXAM-REACTION SUMMARY

Table 1: High-yield reactions

Reaction
Reagent / Condition
Product
R–X → R–NO₂
alc. AgNO₂
Nitroalkane major
R–X → R–ONO
KNO₂
Alkyl nitrite
Benzene → Nitrobenzene
conc. HNO₃ + conc. H₂SO₄, 60°C
Nitrobenzene
Nitrobenzene → Aniline
Fe/HCl, Zn/HCl, Sn/HCl or H₂/Ni
Aniline
Nitrobenzene → Hydroxylamine
Zn/NH₄Cl
Phenylhydroxylamine
Nitrobenzene → Azobenzene
Zn/alc. NaOH or Sn/NaOH
Azobenzene
Nitrobenzene → Hydrazobenzene
Zn/aq. NaOH
Hydrazobenzene
Nitrobenzene → Azoxybenzene
Na₃AsO₃/NaOH or glucose/NaOH
Azoxybenzene
1° nitroalkane hydrolysis
HCl or H₂SO₄
Carboxylic acid + NH₂OH
2° nitroalkane hydrolysis
HCl or H₂SO₄
Ketone + N₂O
3° nitroalkane hydrolysis
Not easy
No usual hydrolysis
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IMPORTANT POINTS
  1. Nitrobenzene = oil of mirabane
  2. Benzaldehyde = oil of bitter almond
  3. Methyl salicylate = oil of wintergreen
  4. Nitroalkanes are more stable than alkyl nitrites
  5. Nitroalkanes have higher b.p. than isomeric alkyl nitrites
  6. Nitroalkanes having α-H are acidic
  7. 3° nitroalkane does not show tautomerism because α-H absent
  8. Alcoholic AgNO₂ gives nitroalkane as major product
  9. KNO₂ gives alkyl nitrite
  10. Aq. AgNO₃ gives alcohol
  11. Nitration of benzene is electrophilic substitution
  12. Electrophile in nitration = NO₂⁺
  13. Nitrobenzene is meta-directing for electrophilic substitution
  14. Nitrobenzene does not undergo Friedel-Crafts reaction
  15. –NO₂ is deactivating group
  16. Chloropicrin = nitrochloroform; insecticide and war gas
  17. Baker-Mulliken test is for nitro compounds in neutral medium
  18. LiAlH₄ reduces aliphatic nitro compounds to amines but nitrobenzene to azobenzene
Q1.
The process in which amides are changed into amines is called
📅TOM 2007
Q2.
Aniline is converted into benzanilide by reacting with
📅IOM 2002
Q3.
Nitrobenzene forms aniline by
📅IOM 2002
Q4.
The reduction of nitrobenzene in acid medium gives
📅IOE
Q5.
Benzene reacts with mixture of conc. H₂SO₄ + HNO₃ to form
📅IOE
Q6.
When nitrobenzene is treated with zinc dust and aqueous ammonium chloride, we get
📅MOE Curriculum 2008
Q7.
The compound that gives positive arylamine reaction is
📅MOE Curriculum
Q8.
When nitrobenzene is reduced under alkaline conditions using zinc and NaOH, the final product obtained is
📅MOE 2065
Q9.
Carbylamine reaction is given by
📅MOE 2065•KU
Q10.
Bromination of Aniline gives
📅MOE 2008•063
Q11.
When nitrobenzene is reacted with NH₄Cl and water, the product formed is
📅MOE 2055
Q12.
Ethyl chloride on heating with silver cyanide forms a compound 'X'. The compound 'X' is
📅BPKIHS
Q13.
The process in which amides are changed into amines is called
📅IOM 2007
Q14.
Aniline is converted into benzanilide by reacting with
📅IOM 2002
Q15.
Nitrobenzene forms aniline by
📅IOM 2002
Q16.
The reduction of nitrobenzene in acidic medium gives
📅IOE
Q17.
Benzene reacts with mixture of concentrated H2SO4 and HNO3 to form
📅IOE
Q18.
When nitrobenzene is treated with zinc dust and aqueous ammonium chloride, we get
📅MOE Curriculum 2008
Q19.
The compound that gives positive carbylamine reaction is
📅MOE Curriculum
Q20.
When nitrobenzene is reduced under alkaline condition using zinc and NaOH, the final product obtained is
📅MOE 2065
Q21.
Carbylamine reaction is given by
📅MOE 2065•KU
Q22.
Bromination of aniline gives
📅MOE 2008•MOE 2063
Q23.
When nitrobenzene is reacted with NH4Cl and water in presence of reducing agent, the product formed is
📅MOE 2055
Q24.
Ethyl chloride on heating with silver cyanide forms a compound X. The compound X is
📅BPKIHS
Q25.
Hydrolysis of acetonitrile in acidic medium gives
Q26.
Nitration of toluene using fuming nitric acid and sulphuric acid gives
Q27.
The reagent that reacts with nitromethane to form methylhydroxylamine is
Q28.
Nitrobenzene on reduction by zinc and NH4Cl gives
Q29.
Decomposition of benzene diazonium chloride by Cu2Cl2/HCl to form chlorobenzene is
Q30.
Nitrobenzene on electrolytic reduction in strongly acidic medium gives
Q31.
The reagent used when nitrobenzene is converted into hydrazobenzene is
Q32.
The reaction in which nitrobenzene gives o- and p-nitrophenol with KOH is an example of
Q33.
T.N.T. is
Q34.
For blasting purposes, T.N.T. is mixed with
Q35.
How many primary amines are possible for the formula C4H11N?
Q36.
Identify the final product C in the sequence starting from CH3CN through reduction, HNO2 treatment and oxidation by Tollens' reagent
Q37.
Ethyl isocyanide on hydrolysis in acidic medium generates
Q38.
Acetamide reacts with NaOBr in alkaline medium to form
Q39.
Gabriel's phthalimide synthesis is used for the preparation of
Q40.
Hoffmann's reagent is
Q41.
Hinsberg's reagent is
Q42.
Primary, secondary and tertiary amines may be separated by using
Q43.
Boiling points of the following compounds follow the order
Q44.
Amongst the following, the most basic compound is
Q45.
Which is the strongest base?
Q46.
The correct order of increasing basicity of methylamine, ammonia and aniline is
Q47.
Gas evolved during the reaction of sodium metal on ethylamine is
Q48.
The action of nitrous acid on ethylamine gives
Q49.
Carbylamine reaction is given by
Q50.
C2H5NH2 + CHCl3 + 3KOH gives X + Y + 3H2O. Compounds X and Y are
Q51.
Phenyl isocyanides are prepared from which reaction?
Q52.
Reaction of primary amines with aldehyde yields
Q53.
The compound which on reaction with aqueous nitrous acid at low temperature produces an oily nitrosoamine is
Q54.
Which of the following compounds gives dye test?
Q55.
Primary, secondary and tertiary amines can be distinguished by
Q56.
Schiff's base is formed when aniline is heated with
Q57.
Aniline on treatment with bromine in presence of CS2 at low temperature gives
Q58.
Bromine water reacts with aniline to give
Q59.
Aniline on treatment with concentrated HNO3 and concentrated H2SO4 mixture yields
Q60.
Towards electrophilic substitution, the most reactive is
Q61.
Primary amines on heating with CS2 followed by treatment with excess of mercury(II) chloride yield isothiocyanate. The reaction is called
Q62.
Aniline when treated with HNO2 and HCl at 0°C gives
Q63.
Benzene diazonium chloride when reacts with hypophosphorous acid produces
Q64.
The product obtained when phenol reacts with benzene diazonium chloride is
Q65.
The indicator obtained by coupling the diazonium salt of sulphanilic acid with N,N-dimethylaniline is
Q66.
The end product in the sequence ethylamine → HNO2 → PCl5 → NH3 is
Q67.
An isonitrile on reduction gives
Q68.
Ethyl chloride on heating with AgCN forms a compound X; the functional isomer of X is
Q69.
Which of the following would undergo Hoffmann's reaction to give a primary amine?
Q70.
Mixture of aniline and chlorobenzene can be separated by using
Q71.
Isocyanide is prepared by
Q72.
Which one of the following on reduction with lithium aluminium hydride yields a secondary amine?
Q73.
Which on reduction does not give primary amine?
Q74.
Which of the following is the strongest base in aqueous solution?
Q75.
Which of the following is more basic than aniline?
Q76.
Hinsberg reagent is used to distinguish between
Q77.
The amine which will not liberate nitrogen on reaction with HONO is