I have a unknown sample of an alcohol (ceric nitrate positive) but when I did chromic acid test it was negative since it never turned into blue/green and against all odds iodoform was positive... yellow precipitate and a lot...

I have no clues of how to make sense into this. So I did lucas test as well but noticed later that it didn't help because my sample is not very soluble in water.

Judging by the great amount of precipitate I got from the iodoform test, I'm thinking that maybe my sample is indeed a primary or secondary alcohol but it has something that won't react with the chromic acid. Are there any considerations to account for when doing this test? or some limitations?

Please help!


2 Answers 2


I would recommend to repeat all the experiments one more time. The reasons for such results may be:

  1. You had dirty test tube for ceric nitrate test, and it was really false positive. You could have a methyl ketone, which gives negative chromic acid test and positive iodoform test.

  2. You added too much chromic acid, and had low amount of your "alcohol". That caused all alcohol to be oxidized, but that blue-green color was too faint, and you didn't notice it because of chromic acid excess.

Moreover, if your "alcohol" is immiscible with water, that means it is one of the higher alcohols. You could also try to identify it (if it's really an alcohol) by smell: those alcohols have pretty distinctive smells. x.x

  • 2
    $\begingroup$ Reminds me of the time when my Russian co-worker took the flask off the rotavap, sniffed it and proclaimed ‘Smells like product’. $\endgroup$
    – Jan
    Sep 26, 2017 at 8:46
  • $\begingroup$ It indeed smelled different than any other alcohols I have smelled. It had a faint mint smell. $\endgroup$
    – Alex Wong
    Sep 26, 2017 at 12:49

You could have a tertiary alcohol that also contains a methyl ketone functionality. Ceric ammonium nitrate will oxidize tertiary alcohols (because it oxidizes to an alkene rather than a carbonyl), whereas chromic acid cannot oxidize a tertiary alcohol, since that'd result in a "Texas carbon".

  • $\begingroup$ What idls a Texas carbon? $\endgroup$ Aug 30, 2023 at 20:05

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