Question

Question #470b6

Answer 1

It depends on the nature of the alkyne.

Explanation:

The usual procedure doesn't work with alkynes, but you can modify the conditions.

The modified conditions

You use catalytic amounts of `"OsO"_4` and a co-oxidant like `"KClO"_3` in a tert-butyl alcohol-acetone-water solvent system.

Reaction with internal alkynes

Internal alkynes give α-diketones.

`underbrace("C"_6"H"_5"-C≡C-C"_6"H"_5)_color(red)("diphenylacetylene") stackrelcolor(blue)("OsO"_4, "KClO"_3 color(white)(mm))(→) underbrace("C"_6"H"_5"-C(=O)C(=O)-C"_6"H"_5)_color(red)("benzil")`

Reaction with terminal alkynes

Terminal alkynes give a carboxylic acid with one less carbon atom.

`underbrace("C"_6"H"_5"-C≡C-H")_color(red)("phenylacetylene") stackrelcolor(blue)("OsO"_4, "KClO"_3 color(white)(mm))(→) underbrace("C"_6"H"_5"-COOH")_color(red)("benzoic acid") + "CO"_2`

In each case, the reaction is behaving as if it forms a 1,1,2,2-tetraol (the diketone dihydrate), which then loses water in the usual way.