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Preparation of Butyric Acid by Oxidation of n-butanol with Permanganate

Below is a crisp and clear, step by step Utoob on the alkaline oxidation of n-butanol with potassium permanganate (KMnO4), to the fairly foul smelling butyric acid (butanoic acid, think rancid butter or vomit).

In those conditions, the butanol is oxidised to sodium butyrate (which smells much less strongly because it is much less volatile) and the KMnO4 is reduced to brown, insoluble MnO2. Going by the video that reaction appears to proceed rather slowly.

After the oxidation has been completed, the MnO2 is filtered off and the clear filtrate acidified to release the butyric acid. That is then extracted by means of diethyl ether and after evaporation of the solvent, purish butyric acid obtained.

I rather fancy doing something similar but in acid conditions, which should proceed much faster, very exothermally and requiring stoichiometrically 40 % less KMnO4. In acid conditions the reduction of permanganate is all the way down to Mn (II), thus absorbing 5 electrons instead of 3 in alkaline conditions.

The drawback is that the alcohol would be oxidised to the smelly acid (and not buryrate), thus requiring a fairly closed system with reflux condenser to keep things bearable, olfactorily speaking. After cooling the butyric acid could then be extracted with diethyl ether (or dichloromethane?)

It’s one of these little ironies in chemistry that butyric acid is foul smelling but that its short chain esters smell and taste wonderfully fruity. Pineapple, one of them, allegedly…

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