Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

Chemistry Class 12

NEET : Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

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1. BASIC NATURE OF AMINES

1. Aniline is less basic than ammonia. The phenyl group exerts- I (inductive effect, i.e., it withdraw electrons. This results in the lower availability of electrons on nitrogen for protonation.

2. Ethylamine and acetamide both contain an amino group but acetamide does not show basic nature. This is because lone pair of electrons on nitrogen is delocalized by resonance with the carbonyl group which makes it less available for protonation.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

3. The compound with least `s' character (sp3 hydrolized) is most basic and with more `s' character (sp-hydrilized) is least basic. Examples in decreasing order of basicity are :

(i)  Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

(ii) CH3CH2CH2NH2 > H2C = CHCH2NH2 > HC ≡ CCH2NH2

(iii) (CH3)2NH > CH3NH2>NH3 > C6H5NH2

Electron withdrawing (C6H5—) groups cause decrease in electron density on nitrogen atom and there by decreasing basicity.

(v) CH3CH2NH2 > C6H5CONH> CH3CONH2

2. METHODS OF PREPARATION

1. Hafmann's bromamide reaction : Amines (only primary) can also be prepared by Hoffmann degradation. In this method the amine will have one carbon atom less than the amide. The reaction proceeds via formation of nitrene.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

Mechanism of above reaction has been proposed as given below :

Br2 + KOH Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev K+O-Br + HBr

Mechanism

2NaOH + Br2 Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev NaOBr + NaBr + H2O

(a)  Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev  

(b)Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

R — NH2 + CO2 Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev R — N = C = O (Isocyanate)

2. Curtius, Schmidt and Lossen Rearrangment : These reaction are basically rearrangement reactions in which carbon migrates from carbon to nitrogen with the formation of an isocyanate. In these migration i.e., 1, 2 shift, migrating group is an alkyl or aryl group and leaving group may be

— Br in Hoffmann rearrangement.

— N2 in Curtius and Schmidt rearrangement.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

The isocyanate formed on hydrolysis gives amine.

(a) Curtius Reaction : Acid chloride on treatment with sodium azide give acid azides which on pyrolysis gives isocyanates on hydrolysis gives corresponding amines.

RCOCl + NaN3 Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev RCON3 + NaCl

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev
Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

(b) Schmidt Reaction : Carboxylic acid reacts with hydrozoic acid in presence of concentrated H2SO4 to give isocyanates.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev
Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

(c) Lossen Reaction : Hydroxylamine on treatement with acid chloride gives acyl derivatives of hydroxyl amine the acyl derivatives exist in two tautomeric form keto form called hydroxamic form and enol form called hydroximic acid.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

The hydroxamic form (keto form) forms o-acyl derivatives of hydroxamic form which on heating with bases forms isocyanates and finally amines upon hydrolysis.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

3. By reduction of nitroethane :

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

4. By reduction of methyl cyanide :

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

5. By reduction of acetamide : Ethylamine is obtained by reduction of acetamide with sodium and absolute alcohol or LiAlH4 in ether or hydrogen in presence of nickel catalyst.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

6. By reduction of aldoxime : Aldoxime on reduction with hydrogen and nickel catalyst or sodium and absolute alcohol or LiAlH4 in ether yields ethylamine.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

7. By the hydrolysis of ethyl isocyanate : Ethyl  isocyanate  on heating with caustic potash solution undergoes hydrolysis forming ethylamine.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

8. By the acid hydrolysis of ethyl isocyanide : Ethyl isocyanide undergoes hydrolysis with a mineral acid and forms ethylamine.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

9. By Schmidt reaction :

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

In this reaction the acyl azide (RCON)2 and alkyl isocyanate (R —NCO) are formed as an intermediate.

10. By the action of chloramine on Grignard reagent : When chloramine reacts with ethyl magnesium iodide, the formation of ethylmine occurs.

 Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

11. By Gabriel's phthalimide reaction :

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev
Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

 

12. Laboratory preparation of ethylamine : Ethylamine is prepared in the laboratory by Hoffmann's bromide reaction. Propionamides are heated with bromine and potassium hydroxide solution.

Basic Character and Preparation of Amines (All Methods) Class 12 Notes | EduRev

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