Amines Class 12 Notes

In this revision lecture notes, we will learn about Amines Class 12 Chemistry Notes. We will cover all basic scientific knowledge about Amines in this article. So, enjoy learning chemistry with Chemistry Notes Info @ https://chemistrynotesinfo.com

Amines Class 12 Chemistry Notes

AMINES INTRODUCTION

            Amines are the organic derivatives of ammonia (NH3) in which one, two, or all three hydrogen atoms attached to nitrogen are replaced by equivalent number of same or different alkyl and/ or aryl groups.

Like ammonia, amines have pyramidal geometry and the nitrogen atom in amines, the nitrogen is attached to sp3 hybridized carbon of alkyl group and in aromatic amines to sp2 hybridized carbon of aryl group. H – N – H , C – N – H or C – N – C bond angle is less than 109ᵒ28’.

CLASSIFICATION OF AMINES

            Depending upon the number of hydrogen atoms replaced by alkyl or aryl groups attached to nitrogen atom in ammonia molecule, amines are classified as –

1) Primary (1ᵒ) Amines

The functional group present is – NH2 (Amino group)

e.g.     CH3 – NH2 Methylamine

2) Secondary (2ᵒ) Amines

The functional group present is – NH-  (Amino group)

e.g.     CH3 – NH– CH3 Dimethylamine

3) Tertiary (3ᵒ) Amines                

The functional group present is -N= (Tertiary nitrogen atom)

Secondary and tertiary amines are further classified as

Secondary and Tertiary amines of Amines Class 12 Notes are further classified into two groups i.e.

a) Simple / Symmetrical amines

In simple amines same alkyl or aryl groups are attached to the nitrogen.

b) Mixed / Unsymmetrical amines

In mixed amines different alkyl or aryl groups are attached to the nitrogen.

METHOD OF PREPARATION OF AMINES

1) By ammonolysis of alkyl halides

            When ethyl bromide is heated with alcoholic ammonia at 373K in sealed copper tube, it gives mixture of ethylamine, diethyl amine and triethyl amine along with tetraethyl ammonium bromide.

C2H5 – Br + NH3     Δ → C2H5 – NH2 + HBr

C2H5 – NH2 + C2H5 – Br    Δ  → (C2H5)2NH + HBr

(C2H5)2NH + C2H5 – Br    Δ  → (C2H5)3N + HBr

(C2H5)3 + C2H5 -Br    Δ  → (C2H5)4N+Br–

Thus,

NH3     RX→ R – NH2    RX→ R2NH  RX→ R3N    RX→ R4N+X–

2) By reduction of Nitro Compounds

            Both aliphatic and aromatic primary amines can be prepared by the reduction of nitro compounds by either catalytically with H2 in the presence of Raney Ni, Pt or Pd or chemically with active metals.

e.g.       CH3NO2    +     3H2   Raney Ni/Pt→     CH3NH2     +     2H2O         Nitromethane                   Ethanol          Methylamine

3) By Gabriel phthalimide synthesis

            Phthalmide reacts with ethanolic potassium hydroxide to give potassium salt of phthalmide. In this step N – H proton is removed to give imide ion. It is then heated to give N – alkyl phthalimide, which on alkaline hydrolysis give a primary amine. Share these Amines Class 12 Notes of chemistry with your friends.

4) By Reduction of Alkyl nitrites / cyanides

            Nitriles on reduction with lithium aluminium hydride (LiAlH4) or catalytic hydrogenation produce primary amines.

   R – CN (Alkyl cyanide)     — H2 / Ni & Na(Hg) / C2H5OH  →   R – CH2 – NH2  (1ᵒ Amine)                  

5) By reduction of amides

            Acid amides on reduction with lithium aluminium hydride give corresponding amines.

6) By Hoffmann bromamide degradation

            The conversion of amides into amines in the presence of bromine and alkali is known as Hoffmann degradation of amides.

R – CO – NH2 (Amides) +   Br2  +   4NaOH       →   R – NH2  (Amine) +  Na2CO3  +  2NaBr  +  2H2O

PHYSICAL PROPERTIES OF AMINES

1) Aliphatic amines with low molecular weight are colourless, gaseous compounds with fishy odour. High molecular weight aliphatic amines are solid.

2) Pure aromatic amines such as aniline are colourless liquid. Arylamines are toxic in nature.

3) Aliphatic amines are soluble in water. As the molar mass increase solubility decreases.

4) Amines are less polar than the corresponding alcohol but more polar than corresponding alkanes.

5) Amines are higher boiling points than corresponding alkanes but lower than corresponding alcohols or carboxylic acids. The order or boiling points of isomeric amines is 1ᵒ > 2ᵒ > 3ᵒ.

REACTIONS OF AMINES

            The lone pair of electron on nitrogen makes amines both basic and nucleophilic. They react with acids to form salts and react with nucleophiles in many reactions.

1) Basic nature of Amines

            Nitrogen atom of amines contains a lone pair of electron which can be donated. Thus, amines act as Lewis bases and are Lowery – Bronsted bases as they accept a proton.

The parent amine is regenerated when alkyl ammonium halide is treated with NaOH.

R – NH3+X– (Alkyl Ammonium Halide) + NaOH → R – NH2 (Amine)  + NaX  + H2O

Amines are weak bases. They dissolve in water and produce OH– ions. Aqueous Solutions of amines turn the color of litmus paper from red to blue.

  R – NH2     +     H – O – H     ↔     R – NH3+    +     OH–

Weak Base                                                           Strong base

            The equilibrium lies far to the left as OH– is a stronger base than amines. The expressions for the equilibrium constant K, basicity constant Kb and pKb values are as follows.

PKb = -logKb

Strong bases have high values of Kb and low values of PKb.

2) Action of nitrous acid

• On primary (1ᵒ) amines

Except methylamine, primary amines react with nitrous acid, in cold condition to give alcohol and nitrogen gas.

  R – NH2  (1ᵒ amines) +   NaNO2  +  2HCl   273 – 278K→   R – OH  +  HCl  +  N2  ↑

• On secondary (2ᵒ) amines

Secondary amines react with nitrous acid to give the N – nitrosoamines which are generally pale yellow oils.

 R2 – NH (2ᵒ amine) +  HNO2  —NaNO2 + dil. HCl (at 273 – 278K)

→ R2N – N = O  +  H2O

• On tertiary (3ᵒ) amines

Tertiary amines react with nitrous acid to form water soluble nitrite salt. As visible change observed, it is said that there is no reaction.

     R3N (3ᵒ amine) + HNO2  NaNO2 / dil. HCl ( at 273 – 278K )

→    [ R3NH ]+NO–2   (No change)

3) Acylation of amines

            Acylation is the replacement of a hydrogen atom of amino group by acyl group (R – CO). It is nucleophilic substitution reaction. Acetylation of primary / secondary amines with acetyl chloride or acetic anhydride gives corresponding amine.

4) Carbylamine reaction  

            Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines. This reaction is known as carbylamines reaction or isocyanides test.

R – NH2  +  CHCl3  +  3KOH  Heat→   R – NC   +   3KCl  +   3H2O

5) Reaction with arylsulphonyl Chloride (Hinsberg’s test)

• Primary amines when reacts with benzene Sulphonyl chloride ( Hinsberg’s reagent),

it yields N – ethylbenzene sulphonamide.

• Secondary amines reacts with benzene sulphonyl chloride, it yields N, N – dimethylbenzene sulphonamides.

• Tertiary amines do not react with benzene sulphonyl chloride.

6) Electrophilic aromatic substitution

• Bromination

Reaction of aniline with bromine water at room temperature results in the formation of white precipitate of 2, 4, 6 – tribromoaniline.

• Nitration

In direct nitration of aniline with concentrated nitric acid at 288K in the presence of sulphuric acid, a mixture of ortho, meta and para isomers of nitroaniline are obtained as product. Also, dark coloured tars are obtained due to oxidation.

• Sulphonation

Reaction of aniline with cold concentrated Sulphuric acid gives anilinium hydrogen sulphate. Heating anilinium hydrogen sulphate with Sulphuric acid at 453K to 473K gives p – aminobenzene sulfonic acid (sulphonic acid) as major product.

DIAZONIUM SALTS

            The diazonium salts have the general formula RN2+X– where R stands for aryl group and X– ion may be Cl–, Br–, HSO4, BF4–, etc.

The N2+ group is called diazonium group.

e.g.  C6H5N2+Cl– IS named as benzenediazonium chloride.

The conversion of primary aliphatic or aromatic amines into diazonium salts is known as diazotization.

PREPARATION OF DIAZONIUM SALTS

            Diazonium salts are prepared by the reaction of nitrous acid in cold condition with alkyl/aryl primary amines (other than methylamine).

e.g.  

REACTION OF DIAZONIUM SALTS

Reaction involving displacement of nitrogen (Diazonium group)

• Replacement by -Cl , -Br and –CN

The reaction in which copper (1) salts are used to replace nitrogen in diazonium salt is called sandmeyer reaction

Yield in sandmeyer reaction is better than yield in Gattermann reaction.

•  Replacement by – I

Ar – N+2X–   +   KI       Δ  →    Ar – I   +   KX   +   N2    ↑

• Replacement by – F

Ar – N+2X–       HBr  →  Ar – N+2BF–4     Δ  →    Ar – F   +   BF3   +   N2    ↑

• Replacement by – H

Ar – N+2X  + H3PO2  +  H2O      CuCl  →  ArH   +   H3PO3   +   HX   +   N2    ↑

• Replacement by – OH

Ar – N+2X  + H2O   Dil. H2SO4  →  Ar – OH    +   HX   +   N2    ↑

• Replacement by – NO2

Ar – N+2X      HBF4  →  Ar – N+2BF–4     NaNO2 / Cu &  Δ  →    Ar – NO2   +  NaBF4   +   N2    ↑

IMPORTANCE OF DIAZONIUM SALTS

1) Arene diazonium salts can be prepared from nearly all primary amines and are helpful in the synthesis of variety of organic compounds.

2) Arenes diazonium salts are used as useful intermediates to introduce various groups into aromatic ring. Such as – F, – Cl, -Br, – I, -CN, -NO2, -OH, -H, etc.

3) The halide or Cyano group can be easily introduced in aromatic ring through diazonium salts.

4) The compounds which cannot be prepared by direct electrophilic aromatic substitution can be prepared by replacement of diazo group.

5) Azo compounds obtained from diazonium salts are strongly coloured and are used as dyes. 

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Aldehydes, Ketones and Carboxylic Acids Class 12 Notes

In this revision web notes, we will learn about Aldehydes, Ketones and Carboxylic Acids Class 12 Chemistry Notes. We will cover all basic knowledge about Aldehydes, Ketones and Carboxylic Acids in this article. So, enjoy learning chem with Chemistry Notes Info @ http://chemistrynotesinfo.com

Aldehydes, Ketones and Carboxylic Acids Class 12 Chemistry Notes

A functional group in which a carbon atom is attached to an oxygen atom by a double bond and the remaining two valences of carbon atom are free is called carbonyl group (> C = O). Organic compounds containing a carbonyl group (> C = O) are called carbonyl compounds. Aldehyde and ketones are carbonyl compounds.

In aldehydes, carbonyl carbon is bonded to a hydrogen atom and an alkyl group (R), while in ketones it is attached to two same or different alkyl groups.

In carboxylic acids, the carbonyl carbon atom is attached to an alkyl group (R) and – OH group.

Structure of carbonyl functional group

In aldehydes and ketones, the carbon of carbonyl group is SP2 hybridised and bonded to three other atoms. Carbon atom forms three sigma (σ) bonds with the bond angle of 120ᵒ which lie in one plane.

ALDEHYDE AND KETONES

PREPARATION OF ALDEHYDE AND KETONES

1. From alcohols (by oxidation)

Aldehydes and ketones are generally prepared by oxidation of primary and secondary alcohols, respectively in the presence of oxidizing agents like KMnO4, acidified K2Cr2O7 and CrO3.

2. From Hydrocarbons

• By ozonolysis of alkenes

Ozonolysis of alkenes followed by reduction with zinc dust and water gives aldehyde, ketones or a mixture of both.

• By hydration of alkynes

Addition of water to acetylene in presence of H2SO4 and HgSO4 gives acetaldehyde while all other alkynes give ketones.

PREPARATION OF ALDEHYDE

1. From acylchloride (Rosenmund reduction)

Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate.

2. From nitriles and esters (Stephen reaction)

Nitriles are reduced to corresponding imine with tin chloride in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde.

RCN   +   SnCl2   +   HCl    →    RCH = NH    ___H3O+→   R – CHO

3. From aromatic hydrocarbons

• By oxidation of methylbenzene

Chromyl chloride (CrO2Cl2) oxidizes methyl group to chromium complex which on hydrolysis give corresponding benzaldehyde. This reaction is known as Etard reaction.

• By Gatterman – Koch reaction

When benzene or its derivative is treated with CO and HCl in presence of anhydrous AlCl3 or CuCl, it gives benzaldehyde.

• By side chain chlorination followed by hydrolysis

Side chain chlorination of toluene gives benzal chloride, which on hydrolysis gives benzaldehyde.

PREPARATION OF KETONES

1) From acyl chloride

On treating acyl chlorides with dialkyl-cadmium chloride with Grignard reagent, gives ketones.

2) From nitriles

Treating a nitrile with Grignard reagent followed by hydrolysis yields a ketone.

3) Friedel Crafts Acylation reaction (substituted benzenes)

PHYSICAL PROPERTIES OF ALDEHYDE AND KETONES

1) Physical nature : Formaldehyde is a gas while Acetaldehyde and acetone are colourless and exist in liquid state.

2) Odour :  Aldehydes and ketones have generally pleasant smell.

3) Solubility : Aldehydes and ketones upto four carbons atoms are miscible with water and are soluble in organic solvents such as ether, alcohol etc.

4) Boiling Point: Boiling points of aldehydes and ketones are higher than those of hydrocarbons of comparable molecular masses but lower than those of corresponding alcohols and carboxylic acid.

CHEMICAL REACTIONS OF ALDEHYDE AND KETONES

1. Nucleophilic addition reactions

• Addition of hydrogen cyanide (HCN)

When hydrogen cyanide is added to an aldehyde or a ketone, cyanohydrins compounds are formed. In this reaction, nucleophile CN– attacks carbonyl group. Addition of hydrogen cyanide to carbonyl group is a reversible reaction.

• Addition of Sodium bisulphate (NaHSO3)

Aldehydes and ketones when treated with saturated aqueous solution of sodium bisulphate give addition products. This reaction is used for separation and purification of aldehyde and ketones from other organic compounds.

• Addition of Grignard Reagents (R – MgX)

The addition of Grignard reagent, (R – MgX) on carbonyl compounds lead to the formation of alcohols.

Formaldehyde → primary alcohols (10)

Higher aldehyde → secondary alcohols (20)

Ketones → tertiary alcohols (30)

• Addition of alcohols

Aldehydes react with alcohols in presence of an acid to form acetal.

While ketones react with alcohols in presence of  an acid to form ketal.

• Addition of ammonia and its derivatives

Nucleophiles, such as ammonia and its derivatives H2N – Z add to the carbonyl group of aldehydes and ketones.

Z = Alkyl, aryl, OH, NH2 etc.

2. Reduction

• Reduction of alcohols

Aldehydes and Ketones can be easily reduced to primary and secondary alcohols respectively by using NaBH4, LiAH4, Sodium – amalgam and water or by hydrogenation.

• Reduction of hydrocarbons

Aldehyde and ketones can be reduced to hydrocarbons by using two different reducing agents.

Clemmensen Reduction

Wolff – kishner reduction

3. Oxidation

Oxidation of aldehyde gives carboxylic acid containing the same number of carbon atoms as the original aldehyde.

Oxidation of ketone gives carboxylic acid containing less number of carbon atoms than the original ketone.

e.g. Acetone on oxidation using CrO3 gives acetic acid.

Ketones and aldehyde can be distinguished by using following mild oxidizing reagents.

• Tollen’s test

R – CHO (Aldehyde)    +    2[Ag(NH3)2]+ (Tollen’s reagent)  +   3O–H    →    R – COO–   +   2Ag   +   2H2O   +   NH3  

• Fehling’s test

R – CHO (Aldehyde)  +   2Cu2+  +   5OH-   (Fehling’s solution) →    R – COO–   +   Cu2O   +   3H2O

4. Haloform reaction

A Ketone having at least one methyl group attached to carbonyl carbon and acetaldehyde is oxidized by sodium hypo-halite to give sodium salt of carboxylic acid and haloform.

5. Adol Condensation

Two molecules of an aldehyde or ketone (containing α – H – atom) in the presence of dilute basic solution of NaOH, KOH, Ba(OH)2, K2CO3, or Na2CO3 or dil. HCl undergo addition reaction to give corresponding β – hydroxy aldehyde (adol) or β – hydroxy Ketones (Ketol). This reaction is called adol condensation or self oxidation.

e.g.

1) Acetaldehyde and 2) Acetone

6. Cannizzaro reaction

Self Oxidation and reduction of aldehydes (which do not posses on α – hydrogen atom) in the presence of concentrated alkali (aqueous or alcoholic) is known as Cannizzaro reaction. The reaction products are alcohol and salt of carboxylic acid. e.g.     

7. Electrophilic Substitution reaction

Carbonyl group in the aromatic aldehydes and ketones is deactivating and metadirecting. Thus, aromatic aldehydes and ketone undergo electrophilic substitution to give m – nitrobenzaldehyde.

e.g. Benzaldehyde undergoes electrophilic substitution to give m – nitrobenzaldehyde.

USES OF ALDEHYDES

1) Formalin is used as preservative for biological specimens. Formaldehyde is used for silvering mirror and for production of several plastic and resins, Bakelite etc.

2) Acetaldehyde is used in the manufacture of acetic acid, ethyl acetate, vinyl acetate, polymers and drugs.

3) Benzaldehyde is used in perfumery and in dye industries.

USES OF KETONES

1) Acetone and ethyl methyl ketone are common industrial solvents.

2) Many ketones are well known for their odors and flavors e.g. acetophenone.

3) Acetone is also use as one of the constituents of liquid nail polish. It is used in manufacture of explosive, lacquers, paint removers, plastics, drugs, adhesives and disinfectants.

We are learning chemistry notes of XII class NCERT CBSE Books chapter “Aldehydes, Ketones and Carboxylic Acids Class 12 Notes”. Firstly we learn about Aldehydes and Ketones, Finally we learn about Carboxylic Acids.

CARBOXYLIC ACIDS

Carboxylic acids are the organic compounds containing one or more carboxyl group in their molecule. The functional group of the carboxylic acids is carboxyl group or – COOH. The carboxylic acids may be aliphatic (R – COOH) or aromatic (Ar – COOH) depending upon whether – COOH group is attached to aliphatic alkyl chain or aryl group respectively.

The general formula is-

STRUCTURE OF CARBOXYLIC GROUP

The carbon atom in carboxylic group is sp2 hybridized. The C – C = O and O = C – O bond angles are approximately 120ᵒ.

METHODS OF PREPARATION OF CARBOXYLIC ACID

1) From primary alcohols and aldehydes (by oxidation)

Primary alcohols and aldehydes are easily oxidized to carboxylic acid by oxidizing agents like acidic or alkaline KMnO4, acidified K2Cr2O7 or CrO3 in glacial acetic acid.

R – CH2OH (1ᵒ Alcohol)   —K2Cr2O7 or dil. H2SO4 —> R – CHO (Aldehyde)      —K2Cr2O7 or dil. H2SO4 —-> R – COOH (Carboxylic Acid)  

2) From alkyl benzenes (by oxidation)

Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzene with chromic acids or acidic or alkaline potassium permanganate or acidified K2Cr2O7.

3) From nitriles and amines (by hydrolysis)

When a nitrile (alkyl cyanide) is boiled with dilute mineral acid, it gives corresponding carboxylic acids. Amide is the intermediate product.

4) From Grignard reagent

When solution of Grignard reagent in dry ether is added to solid carbon dioxide (dry ice), it gives complex (magnesium salt of carboxylic acid), which on acid hydrolysis gives the corresponding carboxylic acid.

5) From acyl halide and anhydride

Acid chloride when hydrolyzed with water gives carboxylic acid.

R – COCl (Acid Chloride)     H2O  →    R – COOH (Carboxylic acid)   +    HCl

6) From esters

When an ester is heated with dilute H2SO4 undergo hydrolysis to give carboxylic acid and alcohol.

PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS

1) Physical nature

Aliphatic carboxylic acids upto nine carbon atoms are colourless liquids. The higher acids are waxy solids.

2) Odour

 Aliphatic carboxylic acids upto nine carbon atoms have pungent smell, while higher acids are odourless.

3) Solubility

All are soluble in organic solvents like alcohol and ether. Benzoic acid is nearly soluble in cold water but is soluble in hot water, alcohol, ether.

4) Boiling points

Carboxylic acids have higher boiling points than aldehydes, ketones, ether and even alcohol of comparable molecular masses.

REACTIONS OF CARBOXYLIC ACIDS

1) Reaction involving cleavage of O – H bond

Acidic Nature

Among the organic compounds, the carboxylic acids have maximum acidity. However, their acidity is lower than that of mineral acids.

Carboxylic acid dissociates in water to give resonance stabilized carboxylate anions and hydronium ion.

The equilibrium constant is Keq is given by

  Keq   =    [RCOO–] [H3O+] / [RCOOH] [H2O]

Since concentration of water remains constant.

 Ka  =   Keq X[H2O]   =   [RCOO–][H3O+] / [RCOOH]

The strength of carboxylic acid is also expressed in terms of their pKa values. The stronger carboxylic acids have lower pKa values,

  pKa   =   – log Ka

Following reactions explain the acidic properties of carboxylic acids

i) Action of active metals

2R – COOH  +  2Na  →  2R – COO–Na+  +  H2  ↑

ii) Action of NaOH

R – COOH (Acid)  +  NaOH (Alkali)   –Neutralization  →   R – COO–Na+ (Salt)  +    H2O 

iii) Action of NaHCO3 or Na2CO3

R – COOH  +  2NaHCO3  →  R – COO–Na+  +  H2O   +   CO2  ↑

2R – COOH  +  Na2CO3  →  2R – COO–Na+  +  H2O   +   CO2  ↑

2) Reaction involving cleavage of C – OH bond

i) Formation of anhydride

Carboxylic acids on heating with minerals acids such as H2SO4 or with P2O5 give corresponding anhydride.

ii) Esterification (Action of alcohols)

Carboxylic acids are esterified with alcohols or phenols in the presence of mineral acid such as concentrated H2SO4 or HCl gas as a catalyst.

iii) Reaction with ammonia

Carboxylic acids or acid chlorides react with ammonia to give ammonium salts which on heating decomposes to form amides.

iv) Reaction with PCl3, PCl5 and SOCl2

3R – COOH   +   PCl3    →   3R – COCl    +    H3PO3

R – COOH   +   PCl5    →    R – COCl   +   POCl3   +   HCl

R – COOH   +   SOCl3    →    R – COCl   +   SO2   +   HCl

3) Reactions involving – COOH group

i) Formation of primary alcohols (Reduction)

Strong reducing agents like lithium aluminium hydride or diborane reduces carboxylic acids to primary alcohols.

R – COOH (Carboxylic Acid) —  i) LiAlH4/ ether ii) H3O+   →    R – CH2OH (Primary Alcohol)

ii) Formation of hydrocarbons (decarboxylation)

Carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with sodalime.

R – COONa (Sodium Carboxylate) + NaOH    Δ CaO  → R – H (Alkane) + Na2CO3

4) Substitution reaction in the hydrocarbon part

i) Halogenation (Hell – volhard – zelinsky reaction)

ii) Ring Substitution (Friedel Crafts reaction)

USES OF CARBOXYLIC ACIDS

1. Methanoic (formic) acid is used in rubber, textile, dyeing, leather and electroplating industries.

2. Ethanoic (Acetic) acid is a solvent and used as vinegar in food industry.

3. Esters of benzoic acid are used in perfume industries.

4. Sodium benzoate is used as a food preparation of soaps and detergents.

5. Higher fatty acids are used in preparation of soaps and detergents.