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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 & Preparation of Amines | Chemistry Class 12 - NEET

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 & Preparation of Amines | Chemistry Class 12 - NEET

(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 & Preparation of Amines | Chemistry Class 12 - NEET

Mechanism of above reaction has been proposed as given below :

Br2 + KOH Basic Character & Preparation of Amines | Chemistry Class 12 - NEET K+O-Br + HBr

Mechanism

2NaOH + Br2 Basic Character & Preparation of Amines | Chemistry Class 12 - NEET NaOBr + NaBr + H2O

(a)  Basic Character & Preparation of Amines | Chemistry Class 12 - NEET  

(b)Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

R — NH2 + CO2 Basic Character & Preparation of Amines | Chemistry Class 12 - NEET 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 & Preparation of Amines | Chemistry Class 12 - NEET

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 & Preparation of Amines | Chemistry Class 12 - NEET RCON3 + NaCl

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET
Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

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

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET
Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

(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 & Preparation of Amines | Chemistry Class 12 - NEET

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

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 & Preparation of Amines | Chemistry Class 12 - NEET

3. By reduction of nitroethane :

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

4. By reduction of methyl cyanide :

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

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 & Preparation of Amines | Chemistry Class 12 - NEET

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 & Preparation of Amines | Chemistry Class 12 - NEET

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

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

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

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

9. By Schmidt reaction :

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

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 & Preparation of Amines | Chemistry Class 12 - NEET

11. By Gabriel's phthalimide reaction :

Basic Character & Preparation of Amines | Chemistry Class 12 - NEET
Basic Character & Preparation of Amines | Chemistry Class 12 - NEET

 

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 & Preparation of Amines | Chemistry Class 12 - NEET

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FAQs on Basic Character & Preparation of Amines - Chemistry Class 12 - NEET

1. What are amines and why are they important in chemistry?
Amines are organic compounds that contain a nitrogen atom bonded to one or more carbon atoms. They are important in chemistry because they have a wide range of applications, including being used as solvents, intermediates in the synthesis of pharmaceuticals, and as building blocks for the production of polymers and dyes.
2. How can amines be prepared?
Amines can be prepared through various methods. Some common methods include the reduction of nitro compounds using reducing agents such as hydrogen gas or metal catalysts, the reaction of ammonia or primary amines with alkyl halides, and the Gabriel synthesis which involves the reaction of phthalimide with alkyl halides followed by hydrolysis.
3. Can amines be prepared from alcohols?
Yes, amines can be prepared from alcohols through a process called reductive amination. In this process, the alcohol is first converted to an aldehyde or ketone, which is then reacted with ammonia or a primary amine in the presence of a reducing agent such as sodium borohydride or lithium aluminum hydride. This results in the formation of the corresponding amine.
4. Are there any natural sources of amines?
Yes, there are several natural sources of amines. Amines can be found in various foods such as fish, meat, and dairy products, where they are formed through the breakdown of proteins. They can also be found in plants, where they play important roles in biological processes. Additionally, amines are present in the human body as neurotransmitters, which are chemical messengers involved in the transmission of nerve impulses.
5. What are the properties of amines?
Amines have some common properties, including being soluble in water and having a characteristic odor. They can act as weak bases and can form salts with acids. The basicity of an amine depends on the presence of electron-donating groups on the nitrogen atom. Amines also have higher boiling points compared to hydrocarbons of similar molecular weight due to the presence of hydrogen bonding between the amine molecules.
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