1 0 , 2 0 Alcohols, Aldehydes
(Use all five knowns): 1-butanol (1
); 2-butanol (2
); tert-butyl alcohol (3
Set up a table in the notebook to record the results of the Jones Test (This is separate table from the “master” table.) Set up 6 small (12 X 75mm) test tubes in a test tube rack in the hood. Label the test tubes #1-6. Add ~5 mg of a solid unknown/known or 0.25ml of a liquid unknown/known to each test tube. Use test tube #1 for the unknown and tubes # 2-6 for each of the known alcohols to be tested. Add 2 drops of the Jones reagent to tubes
#1-6. Observe each tube for an immediate (2-5 sec) color change. Add 2 ml of distilled water to each tube to better visualize the results.
The orange-yellow Jones reagent will immediately turn green in the presence of 1
alcohols and aldehydes. The color change is typically observed only for these functional groups and this color change constitutes a “positive” result. Tertiary alcohols do not react with Jones reagent. Sometimes amines, ethers, ketones, alkenes and alkynes will give a positive test after 2-5 seconds due to contamination with alcohols.
Phenols are not alcohols but will react with the Jones reagent to give a very dark solution.
The Jones reagent is chromium trioxide (CrO
) in sulfuric acid (H
). It is a potent oxidizing agent which rapidly oxidizes primary alcohols and aldehydes to carboxylic acids, and secondary alcohols to ketones.
Alcohols react with the yellow-orange Jones reagent containing a Cr (VI) atom. Over the course of the organic oxidation, the Cr is reduced to Cr (III). The first two steps of the reaction mechanism help to explain why tertiary alcohols do not undergo oxidation with the Jones reagent. In step 2, water reacts with a proton of the chromate ester that is bonded to the carbon atom of the former alcohol functional group. Tertiary alcohols do not have a hydrogen atom bonded to this carbon, therefore the reaction could not proceed beyond this point
H O Cr O
O Cr O