Question

What is the major organic product of the following reaction excess Cl2 ? H2C-C=CH НЫС

Answer 1

Answer:

cl cl H₂C -C C-H H₂C cl al

Explanation:

The given compound is an alkyne with carbon-carbon triple bond . It has two pi bonds so it is electron rich compound , reacts with excess equivalent of chlorine (Cl2) to form the tetrachloro alkane compound. So overall transformation is addition of four chlorine atom at alkyne so hybridised carbon atoms ( each carbon atom gets 2 chlorine atoms).

Reaction mechanism:

The reaction is said to be electrophilic addition reaction in which pi electrons of alkyne acts like nucleophile .

Initial one equivalent of Cl2 reacts with alkyne to give 1,2-dichloro alkene intermediate. Another equivalent of Cl2 on reaction with 1,2-dichloro alakene gives 1,1,2,2-tetrachloro alkane product.

Step:1

The pi electrons of alkyne acts like nucleophile attacks the Cl2 molecule , displacing Cl- ion and forming a cyclic chloronium ion intermediate.

Step-1: -C=CH HC-CH₂-CECH 0.. + C) H₂C-CH₂ I v :cl: :ان - اح: + chloride ion Gi Cyclic chloronium ion intermediate

Step:2

Chloride ion is a nucleophile , attacks the cyclic chloronium ion intermediate from the side away from the chloronium ion center in an SN2 like fashion opens the cuclic chloronium ion to give overall anti addition product . The product is called 1,2-dichlorobutene.

the intermediate compound formed in step-2 of the mechanism undergoes reaction with Cl2 (we provided with excess Cl2) and follows the same mechanism explained above and gives 1,1,2,2-tetrachlorobutane as the final product as shown in below picture

Step-2; + HC-CH₂-C=CH :C1: cl H₂C-CH₂C=CH :c!: 1,2-dichlorobutene Son

:cl: ch ic: iċi: HC-CH₂-C-CH HE-CH2-C=( :ch only :C: ich: 1,1,2,2-tetrachlorobutane Overall reaction : HE-CH2-C30H Excess czy He -CH2-C02 - CH2 1,1,2,2-terachlorobutane

Conclusion:

Alkyne on reaction with excess Cl2 gives tetrachloro alkanes as the major product.