Doc: Polyhalogen Compounds Class 12 Notes | EduRev

Chemistry Class 12

Created by: Mohit Rajpoot

Class 12 : Doc: Polyhalogen Compounds Class 12 Notes | EduRev

The document Doc: Polyhalogen Compounds Class 12 Notes | EduRev is a part of the Class 12 Course Chemistry Class 12.
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Polyhalogen derivatives

Trichloromethane (Chloroform), CHCl3

 Preparation

CH4 + Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CH3Cl + HCl

                               Chloromethane

CH3Cl + Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CH2Cl2 + HCl

                                  Dichloromethane

CH2Cl2 + Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CHCl3 + HCl

                             Trichloromethane

CHCl3 + Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CCl4 + HCl

                             Tetrachloromethane

The mixture of CH3Cl, CH2Cl2, CHCl3 and CCl4 can be separated by fractional distillation.

2. From chloral hydrate, Pure chloroform can prepare.

NaOH + CCl3CHO → HCOONa + CHCl3

chloral

NaOH + CCl3CH(OH)2 → HCOONa + CHCl3 + H2O

                Chloral hydrate    sodium formate Chloroform

 

3. Laboratory Method : From ethanol or acetone by reaction with a paste of bleaching powder and water.

In case of ethanol, the reaction occurs as follows

CaOCl2 + H2O ° Ca(OH)2 + Cl2

CH3CH2OH + Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CH3CHO + 2HCl

CH3CHO + 3Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CCl3CHO + 3HCl

                                                              Chloral

Ca(OH)2 + 2CCl3 CHO Doc: Polyhalogen Compounds Class 12 Notes | EduRev 2CHCl3 + (HCOO)2Ca

                                                               Chloroform Calcium formate

4. From carbontetrachloride

CCl4 + 2[H] Doc: Polyhalogen Compounds Class 12 Notes | EduRev CHCl3 + HCl (partial reduction)

 

5. Haloform reaction

Doc: Polyhalogen Compounds Class 12 Notes | EduRev

Doc: Polyhalogen Compounds Class 12 Notes | EduRev (Haloform)

Step 1 : Attack of the Step 2 : Elimination Step 3 : Proton transfer

nucleophile of the leaving group

 

Prob. Compare rate of elimination (Dehydro halogenation in presence of alcoholic KOH ) i.e., E2 :

1. (a) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (b) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (c) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (d) Doc: Polyhalogen Compounds Class 12 Notes | EduRev

c > b > a > d

 

2. (a) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (b) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (c) Doc: Polyhalogen Compounds Class 12 Notes | EduRev

c > b > a

 

3. (a) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (b) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (c) Doc: Polyhalogen Compounds Class 12 Notes | EduRev

c > b > a

 

4. (a) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (b) Doc: Polyhalogen Compounds Class 12 Notes | EduRev (c) Doc: Polyhalogen Compounds Class 12 Notes | EduRev

b > a > c

 

Dehyodro Dehalogenation : - (-X2) E2

Doc: Polyhalogen Compounds Class 12 Notes | EduRev

Dehalogenation : - (-X2) E2

Doc: Polyhalogen Compounds Class 12 Notes | EduRev

Ec or Ei (Intramolecular or cyclic elimination mechanism):

(1) Lg and Base present in same molecule

(2) It proceed by cyclic transition state.

(3) Overall it is syn ellimination.

(4) Hoffmann is major product as it is obtain by least hinberd site/cyclic transition state.

(5) No rearrangement.

Example of Ec/Ei

Pyrolysis of Ester :

Doc: Polyhalogen Compounds Class 12 Notes | EduRev
Doc: Polyhalogen Compounds Class 12 Notes | EduRev

 

1. Doc: Polyhalogen Compounds Class 12 Notes | EduRev

2. Doc: Polyhalogen Compounds Class 12 Notes | EduRev

 

1.8.2 Physical properties of chloroform

Chloroform is a colourless, heavy liquid which has sweetish, sickly odour and taste. It boils at 334º K and is slightly soluble in water. It is heavier than water. As inhaling of the vapours of chloroform induces unconsciousness therefore it can be used as an anaesthetic agent for surgery.

1.8.3 Chemical properties of chloroform

1. Action of sun light and air

2 CHCl3 + O2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev 2COCl2 + 2HCl
                                                                    Phosgene

As chloroform is used for anaesthetic purposes, therefore in order to maintain a high purity of chloroform, this reaction can be avoided by storing it in dark bottles, completely filled upto brim. The use of dark bottles (brown or blue) cuts off active light radiations and filling upto brim keeps out air. Apart from this a small amount of enthanol (1%) is usually added to bottles of chloroform. Addition of a little ethanol fixes the toxic COCl2 as non-poisonous diethyl carbonate.

COCl2 + 2C2H5OH Doc: Polyhalogen Compounds Class 12 Notes | EduRev O = C(OC2H5) + 2HCl
                                                 diethyl carbonate

2. Hydrolysis :

H - CCl3 + (aq.) 3KOHDoc: Polyhalogen Compounds Class 12 Notes | EduRev Doc: Polyhalogen Compounds Class 12 Notes | EduRev HCOOK

3. Reduction :

Zn + 2HCl Doc: Polyhalogen Compounds Class 12 Notes | EduRev ZnCl2 + 2[H]

CHCl3 + 2[H] Doc: Polyhalogen Compounds Class 12 Notes | EduRev CH2Cl2 + HCl

                             Dichloromethane

                            (Methylene chloride)

CHCl3 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CH4 + 3HCl

4. Reaction with acetone :

(CH3)2C = O + CHCl3 Doc: Polyhalogen Compounds Class 12 Notes | EduRev Doc: Polyhalogen Compounds Class 12 Notes | EduRev

                                                                     Chlroetone

Use : Chloretone is used as hypnotic (a sleep inducing) drug.

5. Reaction with nitric acid

2CHCl+ HONO2 Doc: Polyhalogen Compounds Class 12 Notes | EduRev CCl3. NO2 + H2O

                                                (chloropicrin)

Use : Chloropicrin is used as an insecticide and war gas.

6. Reaction with silver powder :

Doc: Polyhalogen Compounds Class 12 Notes | EduRev

7. Chlorination :

CHCl3 + Cl2 Doc: Polyhalogen Compounds Class 12 Notes | EduRevCCl4 + HCl

8. Reimer-Tiemann reaction:

Doc: Polyhalogen Compounds Class 12 Notes | EduRev + CHCl3 + 3NaOH Doc: Polyhalogen Compounds Class 12 Notes | EduRev Doc: Polyhalogen Compounds Class 12 Notes | EduRev + 2NaCl + 2H2O


1.8.4 Uses of chloroform

1. As solvent in oils and varnishes

2. As preservative for anatomical specimens

3. As laboratory reagent

4. As an anaesthetic

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