Question

Banzoin with potassium permaganate solutions of mix are predused colour

Answer 1

ALKENES and POTASSIUM MANGANATE(VII)

This page looks at the reaction of the carbon-carbon double bond in alkenes such as ethene with potassium manganate(VII) solution (potassium permanganate solution).

Oxidation of alkenes with cold dilute potassium manganate(VII) solution

Experimental details

Alkenes react with potassium manganate(VII) solution in the cold. The colour change depends on whether the potassium manganate(VII) is used under acidic or alkaline conditions.

If the potassium manganate(VII) solution is acidified with dilute sulphuric acid, the purple solution becomes colourless.

If the potassium manganate(VII) solution is made slightly alkaline (often by adding sodium carbonate solution), the purple solution first becomes dark green and then produces a dark brown precipitate.

Chemistry of the reaction

We'll look at the reaction with ethene. Other alkenes react in just the same way.

Manganate(VII) ions are a strong oxidising agent, and in the first instance oxidise ethene to ethane-1,2-diol (old name: ethylene glycol).

Looking at the equation purely from the point of view of the organic reaction:



Note:  This type of equation is quite commonly used in organic chemistry. Oxygen written in square brackets is taken to mean "oxygen from an oxidising agent". The reason for this is that a more normal equation tends to obscure the organic change in a mass of other detail - as you will find below!

The full equations are given below, although you probably won't need them.