December 23, 2024, 08:58:15 PM
Forum Rules: Read This Before Posting


Topic: Iodoform  (Read 21663 times)

0 Members and 1 Guest are viewing this topic.

Offline 408

  • Chemist
  • Full Member
  • *
  • Posts: 796
  • Mole Snacks: +103/-30
Re: Iodoform
« Reply #15 on: April 06, 2010, 03:09:35 PM »
Maybe what happens is NOT that iodoform forms at all, but that the highly electron-rich phenoxide anion reacts with iodine in all three ortho and para positions, decolouring the reagent, as in a POSITIVE iodoform reaction. A FALSE positive.
However, there is no way to form iodoform in such reaction...

That is what I have been getting at.  I still believe this to be the case.

Or that someone did april fools a few days early.

Offline stewie griffin

  • Full Member
  • ****
  • Posts: 384
  • Mole Snacks: +61/-7
Re: Iodoform
« Reply #16 on: April 06, 2010, 06:11:06 PM »
Yes ok I agree then that it's a false positive. Sorry 408.. I didn't fully understand what you were originally trying to say about giving a "positive" test a few posts ago, but now I understand you.
But then I guess there's still a semantic argument to be made and the book needs to do a much better job at explaining itself. The iodoform is a qualitative test where a positive is appearance of a yellowish solid. But it's also only truly positive (IMHO) if this solid produced is actually iodoform. In this phenol example, we're not making iodoform, but instead the triiodophenol. That's fine and dandy if triiodophenol just happens to be a yellowish solid, BUT it should NOT be considered a positive iodoform test. At the very best it should be considered a false positive, and a full explanation should follow to explain why the false positive is occurring.
What book is this?  I think it's done you a disservice.

Offline Schrödinger

  • Chemist
  • Sr. Member
  • *
  • Posts: 1162
  • Mole Snacks: +138/-98
  • Gender: Male
Re: Iodoform
« Reply #17 on: April 06, 2010, 11:43:47 PM »
The iodoform is a qualitative test where a positive is appearance of a yellowish solid. But it's also only truly positive (IMHO) if this solid produced is actually iodoform. In this phenol example, we're not making iodoform, but instead the triiodophenol. That's fine and dandy if triiodophenol just happens to be a yellowish solid, BUT it should NOT be considered a positive iodoform test. At the very best it should be considered a false positive, and a full explanation should follow to explain why the false positive is occurring.
What book is this?  I think it's done you a disservice.
I completely agree.
http://www.iodine.com/triiodophenol.htm clearly states that triiodophenol is a white powder. So, we are not even getting close to iodoform.



"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
- William Jennings Bryan

Offline nj_bartel

  • Sr. Member
  • *****
  • Posts: 1487
  • Mole Snacks: +76/-42
Re: Iodoform
« Reply #18 on: April 07, 2010, 12:56:13 AM »
p-iodophenol though is a 'tan solid', so that's at least getting closer.  One of the list of possible (mono/di/tri)iodophenols may be yellow

Offline orgoclear

  • Full Member
  • ****
  • Posts: 176
  • Mole Snacks: +9/-13
Re: Iodoform
« Reply #19 on: April 07, 2010, 01:51:09 AM »
yup that just might be what it wants to say. but not at all very clearly.

The book's just into its first edition and there are bound to be mistakes (i guess)

Offline Schrödinger

  • Chemist
  • Sr. Member
  • *
  • Posts: 1162
  • Mole Snacks: +138/-98
  • Gender: Male
Re: Iodoform
« Reply #20 on: April 07, 2010, 01:52:40 AM »
p-iodophenol though is a 'tan solid', so that's at least getting closer.  One of the list of possible (mono/di/tri)iodophenols may be yellow
But we have an activated ring here. So, the reaction, IMHO, will not stop with mono/di iodination. Iodine is a weakly deactivating group, isn't it?
"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
- William Jennings Bryan

Offline nj_bartel

  • Sr. Member
  • *****
  • Posts: 1487
  • Mole Snacks: +76/-42
Re: Iodoform
« Reply #21 on: April 07, 2010, 01:59:11 AM »
yes, weakly deactivating.  Fairly sterically large as well, but I'm not sure if that will come into play here.

Sponsored Links