# Question 470b6

Dec 9, 2017

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 ${\text{OsO}}_{4}$ and a co-oxidant like ${\text{KClO}}_{3}$ in a tert-butyl alcohol-acetone-water solvent system.

Reaction with internal alkynes

Internal alkynes give α-diketones.

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

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.