Hoffmann Bromamide Reaction : In this reaction a amide is treated in an aqueous or ethanoic solution of NaOH or KOH , with bromine then primary amine is formed.
Arrange the following : In decreasing order of basic strength in gas phase $C_2 H_5 NH_2,\left(C_2 H_5\right)_2 NH,\left(C_2 H_5\right)_3 N \text { and } NH_3$
Answer
$\left(C_2 H_5\right)_3 N>\left(C_2 H_5\right)_2 NH>C_2 H_5 NH_2>NH_3$ (Decreasing order of basic strength in gas phase)
Arrange the following : In incresing order of basic strength : (a) Aniline, p-nitroaniline and p-toluidine (b) $C _6 H _5 NH _2, C _6 H _5 NHCH _3, C _6 H _5 CH _2 NH _2$
Answer
(b) $C _6 H _5 NH _2< C _6 H _5 NHCH _3< C _6 H _5 CH _2 NH _2$
Arrange the following : In increasing order of basic strength : $C _6 H _5 NH _2, C _6 H _5 N\left( CH _3\right)_2,\left( C _2 H _5\right)_2 NH$ and $CH _3 NH _2$
Answer
$C _6 H _5 NH _2< C _6 H _5 N\left( CH _3\right)_2< CH _3- NH _2<$ $\left( C _2 H _5\right)_2 H$ (Increasing order of basic strength)
Arrange the following : In decreasing order of the $pK _{ b }$ values : $C _2 H _5 NH _2, C _6 H _5 NHCH _3,\left( C _2 H _5\right)_2 NH$ and $C _6 H _5 NH _2$
Answer
$C _6 H _5 NH _2> C _6 H _5 NHCH _3> C _2 H _5 NH _2>$ $\left( C _2 H _5\right)_2 NH$ (Decreasing order of $pK _{ b }$ value means increasing order of basic strength)
Account for the following : Gabriel phthalimide synthesis is preferred for synthesising primary amines.
Answer
In Garbriel phthalimide synthesis $RNH _2$ is formed from R-X in which pure primary amine is formed and no other side products are formed. Because phthallic acid obtained is used again while in other reactions mixture of products is formed. So Gabriel phthallimide synthesis is preferred for synthesising primary amines.
Account for the following : Diazonium salts of aromatic amines are more stable than those of aliphatic amines.
Answer
Diazonium salts of aromatic amines are more stable than diazonium salts of aliphatic amines because due to resonance they attains stability. Resonating structures of $C _6 H _5 N_2^{+}$are as under : Arene diazonium salts are stable for some time in solution at low temperature (273-278 K).
Account for the following : Aniline does not undergo Friedel-Crafts reaction.
Answer
Aniline does not show Friedel-Craft reaction because in this reaction $AlCl _3$ is used as catalyst which is Lewis acid which form salt with aniline (Lewis base). Due to salt formation nitrogen of aniline attains + ve charge which is strong deactivating group so reactivity of this decreases.
Account for the following : Ethyl amine is soluble in water whereas aniline is not.
Answer
Ethyl amine $\left( C _2 H _5- NH _2\right)$ forms hydrogen bond with water while aniline does not have tendency to form hydrogen bond with water due to large size non-polar $C _6 H _5-$ group so ethyl amine is soluble in water whereas aniline is not.
Give one chemical test to distinguish between the pair of compound : Aniline and N-methyl aniline
Answer
Aniline $\left(1^{\circ}\right)$. Gives carbyl amine test with $CHCl _3$ and alkali while N -methyl aniline $\left(2^{\circ}\right)$ do not give carbyl amine test.
Give one chemical test to distinguish between the pair of compound : Aniline and benzyl amine
Answer
Aniline form azo dye by the reaction with benzene diazonium chloride $\left( C _6 H _5 \stackrel{+}{ N }_2 \overline{ C } l \right)$ while in benzyl amine this does not occurs.
Give one chemical test to distinguish between the pair of compound : Ethyl amine and aniline
Answer
Ethyl amine does not form azo dye by the reaction with benzene diazonium chloride while aniline forms azo dye (yellow) by the reaction with benzene diazonium chloride.
Give one chemical test to distinguish between the pair of compound : Secondary and tertiary amines
Answer
Secondary amine $\left( R _2 NH \right)$ reacts with Hinsberg reagent in a product formed insoluble in alkali while tertiary amine $\left( R _3 N\right)$ does not react with Hinsberg reagent.
Give one chemical test to distinguish between the pair of compound : Methylamine and dimethyl amine
Answer
Methylamine $CH _3- NH _2\left(1^{\circ}\right)$ reacts $\left( C _6 H _5 SO _2 Cl \right)$ and product formed is soluble in alkali while product formed by the reaction of dimethyl amine $CH _3- NH -$ $CH _3\left(2^{\circ}\right)$ with Hinsberg reagent (benzene sulphonyl chloride) is insoluble in alkali.
Give plausible explanation of : Why are amines less acidic than alcohols of comparable molecular masses?
Answer
Amines are less acidic than alcohols of comparable molecular masses because in amines polarity of $N - H$ bond is less than $- O - H$ bond of alcohols due to more electronegativity of oxygen than nitrogen. So amines have less tendency to denote $H ^{+}$in comparison alcohols.
Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis ?
Answer
Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis because in aryl halide double bond character is attained in carbon halogen bond due to resonance ( + M effect) so bond becomes strong due to which aryl halide do not undergo nucleophilic substitution with the anion formed by phthalimide.