Discuss the methods of preparation of primary amines through reduction reactions and Gabriel Phthalimide synthesis. Also, explain the basic character of amines in aqueous phase.

Q: Discuss the methods of preparation of primary amines through reduction reactions and Gabriel Phthalimide synthesis. Also, explain the basic character of amines in aqueous phase.

Reduction of Nitro Compounds\nNitro compounds are reduced to amines by passing hydrogen in the presence of finely divided nickel, palladium or platinum, or by reduction with metals in acidic medium. For example, nitrobenzene on reduction with iron scrap and hydrochloric acid gives aniline. $$C6H5NO2 + 3H2 \xrightarrow{Ni/Pt} C6H5NH2 + 2H2O$$ Reduction of Nitriles and Amides\nNitriles on catalytic hydrogenation or reduction with sodium amalgam and alcohol or lithium aluminium hydride ($LiAlH4$) yield primary amines. This method is used for ascending the amine series, i.e., for formation of amines containing one carbon atom more than the starting alkyl halide. $$R-CN + 4H \xrightarrow{LiAlH4} R-CH2-NH2$$ Gabriel Phthalimide Synthesis\nGabriel synthesis is used for the preparation of primary aliphatic amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium phthalimide, which on heating with an alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine. Basic Character of Amines in Aqueous Phase\nAmines are basic due to the presence of an unshared pair of electrons on the nitrogen atom. In the gaseous phase, the basic strength depends upon the inductive effect ($+I$ effect) of the alkyl groups. However, in the aqueous phase, the basic strength is determined by a combination of three factors: Inductive effect: Electron-donating alkyl groups increase the electron density on nitrogen, stabilizing the ammonium cation and increasing basicity. Solvation effect: Greater stabilization of the substituted ammonium cation through hydrogen bonding with water molecules increases basicity. Steric hindrance: Bulky alkyl groups sterically hinder the approach and hydration of the ammonium ion, decreasing basicity. \nCombining these effects, the order of basic strength of methyl and ethyl substituted amines in aqueous solution is:\nFor methylamines: $(CH3)2NH > CH3NH2 > (CH3)3N$\nFor ethylamines: $(C2H5)2NH > (C2H5)3N > C2H5NH2$

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Reduction of Nitro Compounds
Nitro compounds are reduced to amines by passing hydrogen in the presence of finely divided nickel, palladium or platinum, or by reduction with metals in acidic medium. For example, nitrobenzene on reduction with iron scrap and hydrochloric acid gives aniline. $$C6H5NO2 + 3H2 \xrightarrow{Ni/Pt} C6H5NH2 + 2H2O$$ Reduction of Nitriles and Amides
Nitriles on catalytic hydrogenation or reduction with sodium amalgam and alcohol or lithium aluminium hydride ($LiAlH4$) yield primary amines. This method is used for ascending the amine series, i.e., for formation of amines containing one carbon atom more than the starting alkyl halide. $$R-CN + 4H \xrightarrow{LiAlH4} R-CH2-NH2$$ Gabriel Phthalimide Synthesis
Gabriel synthesis is used for the preparation of primary aliphatic amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium phthalimide, which on heating with an alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine. Basic Character of Amines in Aqueous Phase
Amines are basic due to the presence of an unshared pair of electrons on the nitrogen atom. In the gaseous phase, the basic strength depends upon the inductive effect ($+I$ effect) of the alkyl groups. However, in the aqueous phase, the basic strength is determined by a combination of three factors: Inductive effect: Electron-donating alkyl groups increase the electron density on nitrogen, stabilizing the ammonium cation and increasing basicity. Solvation effect: Greater stabilization of the substituted ammonium cation through hydrogen bonding with water molecules increases basicity. Steric hindrance: Bulky alkyl groups sterically hinder the approach and hydration of the ammonium ion, decreasing basicity. 
Combining these effects, the order of basic strength of methyl and ethyl substituted amines in aqueous solution is:
For methylamines: $(CH3)2NH > CH3NH2 > (CH3)3N$
For ethylamines: $(C2H5)2NH > (C2H5)3N > C2H5NH2$

CBSE · Class 12 · Chemistry · AminesDiscuss the methods of preparation of primary amines through reduction reactions and Gabriel Phthalimide synthesis. Also, explain the basic character of amines in aqueous phase.

1. Reduction of Nitro Compounds\nNitro compounds are reduced to amines by passing hydrogen in the presence of finely divided nickel, palladium or platinum, or by reduction with metals in acidic medium. For example, nitrobenzene on reduction with iron scrap and hydrochloric acid gives aniline.