CLASS-XII CHEMISTRY

• Amines
• Unit 13
• Part 1
• prepared by
• K.Venkateswara Rao
• PGT CHEMISTRY
• JNV BALLARI
• HYDERABAD REGION

7/3/2020

PART- 1 OUT LINE

• INTROUDECTION
• CLASSIFICATION
• NOMENCLATURE
• PREPARATION
• PHYSICAL PROPERTIES

7/3/2020

Intraduction of amines

• Amines are derived from ammonia .
• Alkyl derivaties of ammonia is called as amines
• Whenever one, two or three hydrogens replaced from ammonia corresponding no.of alkyl group produces amines

7/3/2020

Classification of amines: amines are classified into 4 types

• Primary amine R-NH₂
• Secondary amine R₂ -NH
• Tertiary amine R₃-N
• Quaternary amine R₄-N⁺
• Primary amines : The compounds which are having general formulae R-NH₂ are called primary amines.
• Example: CH₃-NH₂ , CH₃-CH₂-NH₂ , C₆H₅NH₂
• Secondary amines : The compounds which are having general formulae

R₂-NH are called secondary amines

Example : (CH₃)₂-NH, CH₃-N(H)-C₂H₅

Tertiary amines : The compounds which are having general formulae R₃N are called tertiary amines

Examples : ( CH₃)₂-N-CH₃, ( CH₃)₂-N-C₂H₅

Quaternary amines: The compounds which are having general formulae R₄N⁺

​

7/3/2020

Nomenclature :There are two types of nomenclature systems

• Common system: in this system amines are named by alkyl amines.
• Example: CH₃-NH₂ Methyl amine, CH₃CH₂NH₂ Ethyl amine
• CH₃-CH(CH₃)-NH₂ Iso propyl amine, C₆H₅NH₂ Aniline.
• IUPAC System: In case of primary amines replacement of “e” from alkanes by amines
• CH₃NH₂ Methanamine , C₂H₅NH₂ Ethanamine, CH₃CH(NH₂)CH₂CH₃ Butan-2-amine
• In case of 2◦ amines these are named by N-alkanamine
• In case of 3◦ amines N,N-alkanamine
• Example :CH₃-NH(CH₂-CH₃) N-Methyl ethanamine
• CH₃N(CH₃)₂ N,N-di methyl methanamine
• C₆ H₅N(CH₃)₂ N,N-di methyl Benzenamine.

7/3/2020

Preparation of amines :amines are prepared by the following methods

• Reduction of nitro compounds ,nitriles ,amides,
• Nitro compounds are reduced to by passing H₂ in presence of Pt, Pd, Ni in acidic medium
• C₆H₅-NO₂ +H₂ +Pd → C₆H₅NH₂
• Reduction of nitro compounds with iron scrap and hydrochloric acid is prepared.
• C₆ H₅NO₂ +Fe+HCl → C₆H₅NH₂
• Nitriles are reduced into amines by LiAlH₄ (LAH). This reaction is used for preparation of one carbon atom more than the starting amines
• R-CN + LAH → R-CH₂-NH₂
• Amides are reduced into amines by using LAH
• R-CONH₂ +LAH +H₂O → R-CH₂-NH₂

​

​

7/3/2020

Ammonolysis of alkyl halides : �

• When alkyl halides are reacted with ammonia produce substituted ammonium salts
• NH₃+ R-X → R-⁺NH₃X⁻
• When alkyl halides are taken in excess then quaternary ammonium salts are formed
• NH₃ +R-X( excess) → R₄N⁺X⁻
• The order of reactivity of alkyl halide with amines is RI>RBr>RCl

7/3/2020

Hoffmann bromide degradation reaction :By using this method we can prepare one carbon less than amine.

• R-CONH₂ +Br₂+ 4 NaOH → R-NH₂ + Na₂CO₃ +2NaBr +2 H₂O
• Gabriel phthalimide synthesis : it is used for the preparation of primary amines.

​

​

​

​

7/3/2020

Physical properties :

• Lower amines are exists in gaseous state .
• Higher amines are exists in solid state .
• Lower amines are soluble in water .as the alkyl groups in amines increases solubility decreases . Due to increase of the lyophobic nature.
• As the molecular weights increases boiling point increases.
• If amines have same molecular weights b.p order primary amines > secondary amines > tertiary amines

7/3/2020

Basicity of amines :

• Basicity of aliphatic amines is more when compared with ammonia because in aliphatic amines alkyl group attached to N-atom exert electron releasing effect (+I) .due to which e- density on nitrogen atom increases .ease of protonation also increases .and also ammonium ion formed after protonation is also more stabilized.
• R-NH₂ + H⁺ → R-NH₃⁺
• Basicity ἀ stability of protonated amine
• In gas phase or non-aq. Solvents basicity of amines depends on inductive effect only .
• In gas phase or non-aq .solvents order basicity of aliphatic amines is primary amines < secondary amines < tertiary amines .
• As no .of electron releasing alkyl group increases from primary amines to tertiary amines.
• In aq solutions basicity of aliphatic amines depends on inductive, hydration effect, stearic effects. i.e basicity of aliphatic amines depends on these three factors.

7/3/2020

Inductive effect :in going from primary amines to tertiary as no.of electron releasing groups increases. e⁻ density on N-atom increases.hence ease of protonation increases. So order of basicity 1◦ <2◦ < 3◦ amines

• Hydration effect : in aq. Solution the protonated amines are stabilized by hydrogen bonding. Or hydration .
• As extent of hydration increases, stability of protonated amine and basicity of amines also increases.
• Extent of hydration of amines decreases on going from 1◦ amines to 3◦ amines .
• order of basicity 1◦ > 2◦> 3◦ amines

7/3/2020

7/3/2020

Stearic factor :

• As the no. of bulky alkyl groups around N-atom increases on going primary amines to tertiary amines the ease of attacking of proton at N-atom decreases .hence basicity also decrease .
• order of basicity is 1◦ amine > 2◦ amine > 3◦ amine
• By combining effect of inductive, hydration ,and stearic effects among aliphatic amines “secondary amines are most basic”.
• In case of methyl amines extent of hydrogen bonding dominates inductive . Hence order of basicity of methyl amines is
• 2◦ amine > 1◦ amine > 3◦ amine
• in case of alkyl amines other than methyl amines inductive effect dominates extent of hydrogen bonding .
• order of basicity of alkyl amines is 2◦amine> 3◦amine > 1◦ amine

7/3/2020

CHEMISTRY CLASS XII

• Unit 13
• Amines
• part –II
• Sub topic - Chemical properties of amines
• prepared by
• K.Venkateswara Rao
• PGT CHEMISTRY
• JNV BALLARI
• HYDERABAD REGION

7/3/2020

OUTLINE

• Review of previous session
• Chemical properties of Amines
• Acylation
• Carbylamine reaction
• Reaction with nitrous acid
• Reaction with arylsulphonyl chloride
• Electrophilic substitution
• Alkylation

7/3/2020

Review of previous session:

• Classification of Amines
• Nomenclature of Amines
• Preparation of Amines
• Physical properties
• Basicity of Amines

7/3/2020

chemical properties :

• Acylation : whenever aliphatic and aromatic primary ,secondary amines react with acid chlorides ,anhydrides and esters N-substituted alkanamides and N-substituted aryl amides are formed.
• C₂H₅-NH₂ + CH₃COCl → C₂H₅-NH-COCH₃ +HCl
• N-Ethylethanamide
• C₂H₅-NH-C₂H₅ + CH₃COCl → C₂H₅-N-COCH₃ +HCl
• C₂H₅
• N,N- Diethylethanamide
• This reaction is nucleophilic substitution reaction.
• This reaction is known as acylation . In this reaction strong base like pyridine is used which removes HCl so formed and shifts reaction towards products side.
• CH₃NH₂ + C₆H₅COCl → CH₃NHCOC₆H₅ +HCl
• This reaction is known as benzoylation .

7/3/2020

Carbylamine reaction:

• When aliphatic and aromatic primary amines on heating with chloroform and ethanolic KOH form carbylamines.
• R-NH₂ +CHCl₃ +3KOH → R-NC +3KCl + 3 H₂O
• 3◦ Amines and secondary amines do not show this reaction .
• This reaction is used for test for primary amines.
• Reaction with nitrous acid :
• (a) primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts next these are converted into alcohols. due to unstability of aliphatic diazonium salts.
• R-NH₂ + HNO₂ → ( R-N₂⁺Cl⁻ ) H₂O → R-OH +N₂ +HCl
• (b) Aromatic amines react with nitrous acid at low temperatures to form diazonium salts.at 273-278k
• C₆H₅-NH₂ + NaNO₂ +2 HCl → C₆H₅N₂⁺Cl⁻ +NaCl +2 H₂O
• Benzenediazonium chloride
• Secondary ,tertiary amines react with nitrous acid different manner.

​

7/3/2020

Reaction with hinsberg’s reagent : benzene sulphonyl chloride (C₆H₅SO₂Cl ) is also known as hinsberg’s reagent

• (a) the reaction of benzenesulphonyl chloride with primary amine yields N-ethylbenzenesulphonyl amide
• C₆H₅SO₂Cl +C₂H₅NH₂ → C₆H₅SO₂-NH-C₂H₅ +HCl
• The “ H” attached to nitrogen in sulphonamide is strongly acidic. It is soluble in alkali. l
• (b) in the reaction with secondary amine N,N- Diethylbenzenesulphonamide is formed. It is insoluble in alkali.
• C₆H₅SO₂Cl + C₂H₅-NH-C₂H₅ → C₆H₅SO₂-N-(C₂H₅)₂ + HCl
• Tertiary amines do not react with benzene sulphonyl chloride.
• This property is used to distinguish primary, secondary, tertiary amines

7/3/2020

Electrophilic substitution : Due to loan pair present on N-atom in aniline ,aniline has following resonance structures

• .

7/3/2020

In the five resonating structures of aniline the electron density more at ortho, para positions.NH₂ acts as ring activating group.

• (a) Bromination: when aniline reacts with bromine water it gives 2,4,6-tribromoaniline.

7/3/2020

Due to high activating nature of NH₂ group tri substituted product formed.by reacting acetic anhydride we can controle this activating nature of NH₂ on benzene ring.

7/3/2020

(b) Nitration :Due to more acidic nature of nitration mixture it gives tarry oxidation products.

7/3/2020

By protecting the NH₂ group with acetylation the nitration reacrion can be controlled and p-nitro derivative obtained.

7/3/2020

Sulphonation: aniline reacts with concentrated sulphuric acid it produces anilinium hydrogensulphate.which on further heating it gives sulphanilic acid

7/3/2020

Alkylation of amines :

• When amines reacted with alkyl halides excess produces quaternary salts.
• R-NH₂ +R-X excess → R₄N⁺X⁻
• In this reaction mixture of amines are formed.
• Separation of amines are difficult.

7/3/2020

CLASS XII CHEMISTRY

• Amines
• Unit 13
• Part III
• Subtopic : DIAZONIUM SALTS
• Prepared by
• K. Venkateswara Rao
• PGT CHEMISTRY
• JNV BALLARI
• HYDERABAD REGION

7/3/2020

PART III OUT LINE

• Introduction of diazonium salts
• Preparation of diazonium salts
• chemical reactions
• Applications

7/3/2020

Review of previous sessions :

• Chemical properties of amines .
• What are the differnating tests for amines
• How primary amines are identified
• Why aliphatic diazonium salts are unstable
• Why aniline does not undergo friedel-crafts reaction

7/3/2020

Introduction of Diazonium salts :

• The general formulae of diazonium salts is RN₂⁺x⁻.
• Here R = Aryl group , X= Cl⁻ , Br⁻, BF₄⁻ etc.
• The name of C₆H₅N₂⁺Cl⁻ Benzenediazoniumchloride.
• N₂ group is called diazonium group. Due to resonance aromatic diazoniumsalts are stable.

7/3/2020

Preparation of diazonium salts :

• Benzene diazoniumchloride is prepared by the reaction of aniline with nitrous acid.at 273-278k.nitrous acid is produced by the reaction with sodium nitrite and hydrochloric acid.
• Diazotization : the conversation of primary aromatic amines into diazonium salts.
• C₆H₅NH₂ +NaNO₂ + 2 HCl → C₆H₅N₂⁺Cl⁻ + NaCl + 2 H₂O
• Physical properties : benzene diazonium chloride is a coiourless crystalline solid. Readily soluble in water. Stable in cold.
• Benzene diazonium fluoroborate is water insoluble and stable at room temperature.

7/3/2020

Chemical properties of diazonium salts :

• The reactions of diazonium salts can be divided into two categories.
• A . Reactions involving displacement of nitrogen
• Sandmeyer reaction : when benzenediazonium chloride is reacted with Cu(i)ion produces halo benzene.
• ArN⁺₂Cl⁻ + Cu₂Cl₂/HCl → ArCl +N₂
• ArN⁺₂Cl⁻ + Cu₂Br₂/HBr → ArBr + N₂
• ArN⁺₂Cl⁻ + CuCN/KCN → ArCN +N₂
• Gattermann reaction: when benzenediazonium salts is reacted with Cu powder it gives halo benzene.
• ArN⁺₂Cl⁻ +Cu/HCl → ArCl +N₂+ CuCl
• ArN₂⁺Cl⁻ +Cu/HBr → ArBr +N₂ +CuCl
• The yield in sandmeyer reaction is found to be better than gattermann reaction .

7/3/2020

Preparation of iodo, fluro , nitro benzene and phenol from benzenediazoniumchloride

• Diazonium group being a good leaving group it is substituted by other groups.
• Replacement by iodide ion: generally preparation of iodo benzene is very difficulty. But diazoniumchloride is treated with KI iodo benzene is formed.
• ArN⁺₂Cl⁻ +KI → ArI +KCl +N₂
• Replacement by fluoride ion: when benzene diazoniumchloride is treated with floroboric acid it gives flurobenzene.
• C₆H₅N₂⁺Cl⁻ +HBF₄ → ArN₂⁺BF₄⁻ +∆ → Ar-F +BF₃ +N₂
• Replacement by H : when bezene diazonium salts are treated with mild reducing agents reduces to arenes .
• ArN₂⁺Cl⁻ + H₃PO₂ +H₂O → ArH + N₂ +H₃PO₂ +HCl
• Replacement by hydroxyl group :
• ArN⁺₂Cl⁻ +H₂O → ArOH +N₂ +HCl
• Replacement by NO₂ Group :
• C₆H₅N⁺₂Cl⁻+ HBF₄ → ArN⁺₂BF⁻₄ +NaNO₂ +Cu → ArNO₂ +N₂+NaBF₄

7/3/2020

B. Reactions involving retention of diazo group :

• When benzenediazochloride reacts with phenol it forms orange dye substance, and with aniline yellow dye substance.

7/3/2020