Terms and Their Meanings
1. Amines Alkyl or aryi derivatives of ammonia.
2. Nomenclature Common name is derived by writing name of alkyl group followed by suffix "amine". IUPAC generic name is 'alkanamine.
3. Isomerism They exhibit chain, position, metamerism.
4. Hoffmanns degradation When amid{es} are heated with sodium hydroxide solution and bromine, corresponding primary amines are formed.
5. Alkylation Substitution of hydrogen of ammonia by alkyl groups to form amines is Hoffmann's alkylation.
6. Carbylamine reaction When primary amine and chloroform are heated with alcoholic KOH solution, carbylamine (isonitrile or isocyanide) is formed which has a foul smell.
7. Acylation Substitution of hydrogen of amines by acyl group.
Descriptive Chemistry
1. Classification Depending upon number of hydrogen atoms substituted by alkyl or aryl groups from a molecule of ammonia, amines are classified as primary (1°), secondary (2°) and tertiary (3°) amines.
2. General methods of preparation
(i) From nitrohydrocarbons
4. Basic character Due to lone pair of electrons on nitrogen, amines are basic. When electron releasing group (—CH3) is attached to nitrogen, due to + I effect basic strength increases. Resonance effect delocalises lone pair of electrons of—NH2 group hence basic strength of aromatic amines decreases.
5. Uses of aniline Manufacture of aniline black, sulphadrugs, schiff's bases. In preparation of benzene diazonium chloride, acetanilide etc.
6. Tests to distinguish between 1°, 2° and 3° amines
Tests | 1° amine | 2° amine | 3° amine |
Alkylation test | Three molecules of CH3I | Two molecules of CH3I are . | One molecule of CH3I |
Compound + CH3I, | used up forming | used up forming quaternary | added forming quaternary |
heat in sealed tube | quaternary salt. | salt. | salt. |
Hinsberg test |
|
|
|
Compound + benzene | White solid soluble in | White solid insoluble in | No reaction |
sulphonyl chloride. | excess of NaOH solution. | NaOH solution. |
|
Illustrations
1. One mol of compound A(C3H9N) reacts with three moles of methyl iodide to form quaternary salt. Compound A' is
(1) N,N-dimethylethanamine (2) N-methylethanamine
(3) propanamine (4) N, N-dimethylmethanamine
Answer (3) A' is primary amine as it reacts with three moles of methyl iodide to form quaternary
salt.
2. The compunds X and Z in the following reaction sequence are
(1) nitrobenzene and acetyl chloride (2) aniline and acetic anhydride
(3) aniline and methylchloride (4) bromobenzene and acetamid{e}
Answer (1)
3. Increasing order of basic strength of NH3 (I), CH3CH2NH2(II) 'and C6H5NH2(III) is (1)1 <11< III (2) III < I < II (3) II < I < III (4) II < III < I Answer (2) Due to +1 effect of ethyl group, CH3CH2NH2 is most basic while —R effect reduces the basicity of aniline, hence option (2) is correct.
4. Carbylamine reaction is answered by
(1) N-methylethanamine. (2) NJSJ-dimethylethanamine
(3) N-methylbenzenamine ' (4) benzenamine
Answer (4) Primary amines respond to carbylamine reaction.
5. A compound X (C7H7ON) when heated with bromine in alkali solution, compound 'Y' is formed.
Compound X is formed when benzoic acid is heated with ammonia. Compound Y is (1) benzamid{e} (2) benzyl amine
. (3) benzenamine (4) N-methyl benzamid{e}
Answer (3) Benzamid{e} (C?H7ON) on Hofmann degradation reaction gives aniline (benzenamine)