A primary or secondary aliphatic alcohol dissolved in pure glacial acetic acid decolourizes a water solution of KMnO*, while a tertiary alcohol fails to do so. A secondary alcohol will continue to react with KMn04 solution if a little concentrated sulphuric acid is added, while a primary alcohol does not. By means of diosc reactions one may distinguish between primary, secondary, and tertiary alcohols of the paraffin scries. Further, no more than one drop of the alcohol is ncccssary to make the test, which fact should make it especially interesting in investigations where only small quantities of alcohol arc available.
A convenient procedure is as follows: A 4-inch test-tube is fitted with a onc-holc rubber stopper carrying a glass rod which rcachcs to the
bottom of the test-tube. Glacial acetic acid (3 ml.) is introduced into die test-tube, and then one drop of the pure unknown is added. A saturated, filtered solution of KMn04 in water is added, a drop at a time, to the contents of the tube, with stoppering and vigorous shaking between each addition.
If no dccolourization of the KMn04 takes placc, the alcohol is tertiary. If dccolourization takes placc (best ascertained from time to time by spotting the mixture by means of the glass rod into filter paper), the addition of KMn04 is continued a drop at a time until the pink colour of KMn04 persists. When dccolourization has ceased to take placc, a drop of conccntratcd H2S04 is added and the addition of KMn04 with shaking is continued. If the pink colour is not discharged under these conditions, the alcohol is primary. If dccolourization proceeds again after the addition of H2S04, followed by a final permanent pink colour, the alcohol is secondary.
It is advisable to run a blank test of the glacial acctic acid used, because some glacial acid samples contain extraneous materials which rcact with KMn04 solution.
This method has been found reliable for all aliphatic alcohols through the amyl group. Whether it can be extended to other classes of alcohols has not been determined.
To the student in the laboratory it would seem that this different approach to the differentiation of the alcohols would be much more simple and dircct than the Lucas test currently in manuals.