Sunday, January 27, 2008

IIT JEE Revision - Alkynes - Chemical Properties and Reactions

Reactions specifically mentioned in the syllabus are posted in more detail as separate topics.


a) Combustion

b) Oxidation with alkaline potassium permanganate

c) Ozonolysis

Alkynes react with ozone to form ozonides.

These ozonides on decomposition with water in the presence of zinc give diketones(two carbonyl groups).

Ethyne gives glyoxal on reacting with ozone. Glyoxal also has two carbonyl groups.

III. Polymerization

a) Acytylene dimerizes (two molecules come together as one molecule) in the presence of cuprous chloride and ammonium chloride to give vinyl acetylene which on reacting with HCl gives chloroprene.

The later polymerizes to give neoprene - a synthetic rubber.

b) Cyclic polymerization

This takes place when alkyne is passed through red hot iron tube at 400 degress celsius.

Occurs in two stages. Acetylene becomes mesitylene.

IV. Isomerization

1-alkyne gets converted to 2-alkyne and vice versa.

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