Halogen Derivatives PDF

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Summary

Complete reactions of Halogen reactions...

Description

CONTENTS

Page

1.

Classification

1

2.

Monohalides

1

3.

Dihalides

4

4.

Trihalides

7

5.

Grignard reagent

7.

Exercise-I (Conceptual Questions)

8.

Exercise-II (Previous Years Questions)

9.

Exercise-III (Analytical Questions)

10.

Exercise-IV (Assertion & Reason)

12 14

17

19 20

Se

A

ss

io

n

20

19

Haloarenes

-2 0

EN

11

6.

LL

HAL HALOGEN OGEN D DERIV ERIV ERIVA ATIVES

S. No.

E

NEET SYLLABUS Haloalkanes : Nomenclature, nature of C-X bond, physical and chemical properties, Haloarenes : Nature of

C-X bond, substitution reactions (directive influence of halogen for monosubstituted compounds only), Uses and environmental effect of dichloromethane, trichloromethane, Iodoform, freons, DDT

EN

OBJECTIVES After studying this unit, we will be able to :

from their given structures; •

-2 0

Name haloalkanes and haloarenes according to the IUPAC system of nomenclature

Describe the reactions involved in the preparation of haloalkanes and haloarenes and

19

•

understand various reactions that they undergo;

•

Use stereochemistry as a tool for understanding the reaction mechanism;

•

Appreciate the applications of organo-metallic compounds;

•

Highlight the environmental effects of polyhalogen compounds

ss

io

n

20

Correlate the structures of haloalkanes and haloarenes with various types of reactions;

A LL

•

Se

"Failure will never overtake me if my determination to succeed is strong enough"

A.P.J. Abdul Kalam

Pre-Medical : Ch Che emistry

ALLEN

HALOGEN DERIVATIVES 1.0 HALOGEN DERIVATIVES Compounds derived from hydrocarbons by replacement of one or more H-atoms by corresponding no. of halogen atoms are known as halogen derivatives.

2.0 CLASSIFICATION On the basis of nature of hydrocarbon from which they are obtained, halogen derivatives can be classified as :

Halogen Derivatives

Primary halides

Di-halides

3.0 MONOHALIDES :

Tetra halides

Tertiary halides

Genreal Methods of Preparation of Monohalides (1) By direct halogenation of alkanes :

A LL

20

U.V.light R—H + Cl2 ¾¾¾¾ ® R—Cl + HCl

(excess)

CH2 + HX

eg: CH3–CH

¾¾® CH 3 —CH2X

CH2 + HX ¾¾® CH3

CH

Se

X

CH 3

io

CHR + HX ¾¾® RCH2—CHXR

ss

eg: CH2

n

(2) By the addition of H—X on alkenes : R—CH

Aryl haides

19

3.1

Tri-halides

Secondary halides

Alkynyl halides

-2 0

Mono halides

Alkenyl halides

EN

Alkyl halides

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Isopropyl halide

E

(3) By Alcohols :

(a) By the action of hydrogen halides : H -X R—CH 2—OH ¾¾¾ ® RCH 2—X

(b) By the action of phosphorous halides : R—OH + PCl5

¾¾® R—Cl + POCl3 + HCl

3R—OH + PCl3 ¾¾® 3RCl + H3PO3 PBr3 and PI3 are less stable, thus for bromides ( P + Br 2) and for iodides ( P + I2) mixture is used. (c)

By reaction with thionyl chloride (Darzen's procedure) : R—OH One mole

+ SOCl2

¾Pyridine ¾¾ ¾ ®R—Cl + SO2 + HCl (1 mole)

One mole

Because of less stability of SOBr2 and SOI2, R—Br and RI can not be obtained by this method.

1

Pre-Medic Pre-Medical al : Chemistry

ALLE ALLEN N

(4) Borodine – Hunsdicker's reaction : R—COOAg

+

Silver salt of

CCl4 R—X + CO2 + AgX ¾¾¾® D

X2

(Cl2 or Br2)

a fatty acid (5) By halide exchange : Acetone R–I + KCl or KBr (Conant finkelstein reaction) R–Cl or R—Br + KI ¾¾¾¾®

¾¾® 2CH 3–F + Hg2Cl2 (Swart reaction) 2CH3Cl + Hg2F2 ¾ Water Note : Finkelstein reaction can only be used to prepare R–I and swart's reaction can only be used to prepare R– F 3.2

Physical Properties

Higher B.P. than parent alkanes. Decreasing order of B.P. is :

R–I >

R—Br

among isomeric R—X, decreasing order of B.P. is : (c)

>

R—Cl

> R—F

Primary > Secondary >

R—F and R—Cl ¾¾® lighter than water

R—X are polar co-valent compounds but insolu ble in w ater becau se they can not f orm H–bonds. They dissolve in organic solvents.

20

(d)

R—I > R—Br > R—Cl > R—F

19

R—Br and R—I ¾¾® heavier than water Decreasing order of density is :

tertiary

-2 0

(b)

EN

(a) The lower members CH3F, CH 3Cl, CH3Br , C2H5Cl and C2H5F are gases at room temp.

(ii)

Chemical Properties

HOH(Boil)

(a)

X by — OH KOH aq.

(b) (c)

(d)

Se

3.3.1 Nucleophilic substitution reaction ( SN ) :

X by — OH

R—X¾ ®

moist Ag2 O

X by — OH KSH alc. X by –SH

(Mercapto Gp.) (e) (f)

2

NaSR' X by SR R' COOAg,D X by(R'COO)

Cl >

Cl

R—OH (alcohol) + HX R—OH (alcohol) + KX R—OH (alcohol) + AgX

R—SH + KX Alkane thiol (Mercaptane) RSR' + NaX Thioether R' COOR + AgX (Alkyl alkanoate) ester

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3.3

CH3Cl > CH 3F > CH3Br > CH3I

ss

(i)

io

Dipole moment order–

A LL

(f)

n

(e) R—X (except R—F) burns with a green flame when interacted with Cu wire.(Beliestein test)

E

Pre-Medical : Ch Che emistry

ALLEN (g)

Reaction with KCN and AgCN : d+

d–

¾ ® R—C N + R—NC + KX R— X + KCN ¾ Alc. D ¾ Ionic ` cyanide Isocyanide (major) (minor) CN ion is an ambident nucleophile. d+

d-

R —X

Alc.

¾ ¾¾®

R— N C + R—CN + AgX isocyanide Cyanide (Major) (Minor)

D

Reaction with KNO2 and AgNO2 : d-

R—X

d+

Alc.

KO—NO ¾ ¾D¾ ® Ionic

+

d-

R —X

+

R —O—N

O + R—NO2 + KX

Alkyl nitrite (Major)

Nitro alkane (Minor)

.. Alc. Ag—O—N=O ¾ ¾D¾ ® covalent

O

R— N

O Nitroalkane (major)

+ R—O—N=O + AgX Alkyl nitrite (minor)

Reaction with NaOR' (Sodium alkoxide) : R—X + NaOR' ¾¾®

R—OR' + NaX

Reaction with NH3:

20

(williamson synthesis reaction) (j)

io

n

R

CNa :

D R—C CNa ¾¾®

R—X + CH

R

R

R X

R

ss

Se

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E

Reaction with CH

N

¾®

A LL

D R —X R—X R— X + NH3 ¾¾® R — NH2 ¾¾¾¾ ® R—NH—R ¾¾¾®

(k)

-2 0

d+

(i)

.. Ag—CN covalent

19

(h)

+

EN

l

R

Å

N R X1 R

(Quaternary salt)

CH + NaX

CH3

If

C

CH3

X + CH

CH3 (3º halide)

–+ D CNa ¾ ¾ ®

CH3

C

CH2+ NaX + CH

CH

CH3 (Elimination is more)

3.3.2 Dehydrohalogenation : Alkyl halides undergo b - elimination on treatment with KOH (alc.) or NaNH2. b

a

D R — C H2 — CH 2 — X + KOH (alc.) ¾¾ ® R—CH

CH2 + HX

D CH3—CH2—CH CH3—CH2—CH2—CH2—Br + KOH(alc.) ¾¾®

CH2 + HBr

3

Pre-Medic Pre-Medical al : Chemistry

ALLE ALLEN N ¾ Alc.KOH ¾D ¾ ¾CH3—CH

CH—CH3 + CH3—CH2—CH

But-2 -ene (80%)

CH2 + HBr

But-1-ene (20%)

Dry ether 3.3.3 Wurtz Reaction : 2RX + 2Na ¾¾¾¾¾ ®R - R + 2NaX

When a mixture of different alkyl halides, (R1 - X) and (R2 - X) is used a mixture of alkane is formed Dry ether D R1—X + 2Na + X—R2 ¾¾¾¾¾ ® R1 —R2 + R1—R1 + R2—R2 + NaX

3.3.4 Formation of Organometallic compounds :

(ii)

2C2H5Br +

(iii)

4C2H5Cl

dry ether ¾¾¾¾ ¾ ®RMgX

+ Mg

+

2Zn

(Grignard reagent)

dry ether ¾¾¾¾ ¾ ®(C2H5)2 Zn (Frankland reagent) +

4Na / Pb

¾¾® (C2H5)4 Pb

Sodium lead Alloy 3.3.5 Friedel - Crafts reaction :

ZnBr 2

+

4NaCl

+

3Pb

Tetra ethyl lead (used as antiknocking agent)

CH3

AlCl 3(anhyd)

¾¾¾¾¾®

4.0

HCl

Toluene

DIHALIDES

20

Benzene

+

19

+ CH3 Cl

-2 0

R—X

EN

(i)

A LL

General formula CnH2nX2 .Two H - atom of alkanes, replaced by two halogen atoms to form dihalides.

n

Dihalides are classified as :

io

(a) Gem dihalide : The term Gem is derived from geminal means - same position. Two similar halogen atoms are attached to same C - atom

(1, 1 - Dihalo ethane)

Isopropylidene dihalide

(2, 2 - Dihalo propane)

(b) Vic dihalides : Vic term from - Vicinal means adjacent C - atoms Two halogen atoms are attached on adjacent carbon atom.

H

Ex. CH 2 X

CH2

H C

X

H

CH CH2 X

Vic and Gem dihalides are position isomers.

X

Ethylene dihalide

Propylene dihalide

(1,2-Dihaloethane)

(1,2-Dihalopropane)

(c) a, w dihalides : Halogen atoms are attached with terminal C - atom. They are separated by 3 or more C - atoms. They are also known as polymethylene halides. Ex. CH2 X

4

CH2

CH 2

CH2

(1,4-Dihalobutane)

X

Tetramethylene dihalide

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ss

Ethylidene dihalide

Se

Ex. CH3CHX2

E

Pre-Medical : Ch Che emistry

ALLEN 4.1

General Methods of Preparation (a) Gem dihalides : (i)

By the reaction of PCl5 on carbonyl compound. O CH 3

Cl

C

H

+ P Cl5 ¾¾® C H 3

C

H + P O C l3

Cl Acetaldehyde

Ethylidene chloride Cl

O CH3

CH3 + PCl 5 ¾¾® CH3

C

C

CH3+ POCl 3

Cl

Acetone

By addition of halogen acids on alkynes : CH + HBr ¾¾® CH2

HBr CHBr ¾¾¾ ® CH3 CHBr2

Vinyl bromide

1, 1 - Dibromoethane

Br

CH + HBr ¾ ¾ ® CH3

Propyne

A LL

By the addition of halogens to alkenes :

CH3

CH

CH2 Br 1, 2 - Dibromoethane

CH2 + Br2 ¾ ¾ ® CH3

CH

CH 2

n

CH2 Br

io

CH2

+ Br 2 ¾ ¾ ®

CH3

ss

CH2

C

Br 2, 2 - Dibromopropane

Br

(b) Vic-dihalides : (i)

¾ ® CH3 CH2 ¾ ¾HBr

C

19

C

20

CH3

-2 0

CH

EN

(ii)

2, 2 - Dichloropropane

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(ii)

E

By the action of PCl5 on glycols :

C H 2O H C H 2O H

4.2

4.3

+ 2 P C l5

¾¾®

Se

Br Br 1, 2 - Dibromo propane

C H 2C l

C H 2C l

+ 2PO Cl 3 + 2HCl

Physical Properties

(i)

Lower members are colourless, oily liquids with sweet smell. Higher members are solid.

(ii)

These are heavier than water.

Chemical Properties (i)

Action of KOH(alc.) : (Dehydrohalogenation) CH2 X CH2 X

or

CH3 CHX2

KO H (a lc.)

¾¾¾® – 2H X

CH CH

5

Pre-Medic Pre-Medical al : Chemistry

ALLE ALLEN N

(ii) Action of KOH(aq.) : (Hydrolysis) It is a distinction test for gem - and vic - dihalides. (a)

CH 2

Cl

CH2

Cl

+ 2KOH(aq.) ¾¾¾®

CH2

OH

CH2

OH

+ 2KCl

Glycol Vic-dihalide. (b)

1, 2 - Ethanediol KOH(aq.) ¾¾¾¾¾ ®

CH 3CHXCH 2X Vic-dihalide

CH3

CH

CH2

OH OH Propane - 1, 2 - diol

KO H

CHX2

CH3

(aq .) ¾¾¾¾®

CH 3

KO H (aq .) and CH 3CX 2CH 3 ¾¾¾¾® CH 3COCH 3

CHO

(Ketone)

Gem-dihalides

Vic-dihalide

CN

CH2

CN

H O/H +

¾ ¾2 ¾ ¾ ®

CH2

COOH

CH2

COOH

D

¾¾¾¾® —H2 O

Succinic acid

Cl CH3 CH

Cl Gem-dihalide

¾ ¾2KCN ¾ ¾ ® CH3 — 2KCl

CN

CH

CN

COOH

+

2O/H ¾H¾ ¾ ® CH3

CH

COOH

CH2

CO

CH2

CO

O

-2 0

— 2KCl

CH2

Succinic anhydride

¾ ¾D¾ ® CH3 —CO

19

CH2 Cl

+ 2KCN ¾ ¾ ¾ ¾ ®

2

CH2 COOH

Propanoic acid

20

CH2 Cl

EN

(iii) Reaction with KCN :

– CN group on acid hydrolysis gives - COOH

(ii)

Two – COOH group on one C – atom always loose CO2 to form monocarboxylic acid on heating.

A LL

(i)

n

(iii) Two – COOH group on vic. C – atom loose H2O to form cyclic anhydride on heating.

CH2 Br

a-w w..

CH2

CH 3OH

¾¾¾® Heat

CH2Br

CH2Br

+ Zn

a, w - dihalide.

CH 2

+ ZnBr2 CH 2 Same Carbon Product CH OH

3 ¾¾¾¾®

D

H2 C

CH2 CH2

+ ZnBr 2

Cyclopropane

BEGINNER'S BOX-1

1.

Which of the following is not organometallic compound

(1) RMgX 2.

6

(2) R2Zn

(3) RONa

Which is Finkelstein reaction ? acetone (1) R–X + NaI ¾¾¾ ¾ ®

(2) R–X + AgF ¾¾®

(3) R–X + NaF ¾¾®

(4) R–F + AgCl ¾¾®

(4) R2Hg

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+ Zn

ss

CH2 Br

Se

Vic.

io

(iv) Dehalogenation :

E

Pre-Medical : Ch Che emistry

ALLEN 5.0 TRI HALIDES (Haloform CHX3) 5.1

General Method of Preparation (i)

hn CH4 +3Cl2 ¾¾ ¾ ®CHCl3 +3HCl

From CH4 :

(ii) By Haloform reaction (lab method) : CH3 CH2 OH or CH3 COCH3

Bleaching powder [CaOCl2 ] ¾¾¾¾¾¾ ¾¾¾¾¾¾¾¾ ¾® H 2O / D

+

CHCl3

(HCOO)2Ca or (CH 3COO) 2Ca

Mechanism : CaOCl2 + H2O¾¾® 2Cl + Ca (OH)2 CH3CH 2–OH + 2Cl ¾¾® CH3CHO + 2HCl

EN

(Oxidation)

¾¾® CCl3CHO + 3HCl

(Halogenation)

CCl3CHO + Ca (OH)2 ¾¾® CHCl3 + (HCOO)2Ca

(Hydrolysis)

If CH 3COCH3 is used then CHCl3 is formed into 2 steps (Chlorination and Hydrolysis)

-2 0

CH3CHO + 6Cl

CH — CH

3

CH

3

,

OH

3

CH — C H 2— C H 3

,

OH

Aldehydes : Only acetaldehyde C H

3

C

H

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Ketones :

E

CH

3

C

Z

O

Ex . C H

3

C

C H 3, CH 3

C

CH

3

C

C H 2 —C H 3 , C H

O

O

CO O H , C H

O

3

3

C H —C H 2....... CH 3 etc. OH

Se

O

CH

ss

CH

20

A LL

OH

n

CH 3—CH—Z

io

Ex. Alcohols :

19

(+) ve haloform reaction : Reaction which gives haloform with alkali and X 2 is called as (+) ve haloform reaction.

3

C

C H 2 ........ C H 3 etc. (All methyl ketones)

O

C

C H O Also show haloform reaction.

O

(–) ve haloform reaction : Reaction in which haloforms are not formed with X 2 and alkali. Ex.

,

,

,

. do not show haloform reaction.

7

Pre-Medic Pre-Medical al : Chemistry

ALLE ALLEN N

(iii) Preparation of pure CHCl 3 : CCl3CHO. 2H2O ¾ NaOH ¾¾¾ ®CHCl3 + HCOONa + 2H2O D Chloral hydrate

(Pure Chloroform)

Chloral can also be used in preparation of D.D.T. Cl

H SO

2 4 CCl3CH Cl ¾ ¾® (conc.)

CCl3 CH O + 2H

Cl

CH3 CH2 —OH or CH3COCH3 5.2

aq. NaCl/electrolysis

Physical Properties

CHCl3

HCOONa or CH3 COONa

-2 0

(iv) Industrial preparation :

...