Sciencemadness Discussion Board

Ozonelabs- Synthesis of 2-Iodobenzoic Acid

Ozonelabs - 19-8-2009 at 12:23


Just a new PDF we did in some downtime today- any comments are welcome as always.

Sincere regards,

The Ozonelabs Team

Attachment: 2-Iodobenzoic acid.pdf (213kB)
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DJF90 - 19-8-2009 at 12:56

Nice work as always. What do you intend to do with the product? Oxidation with KBrO3 IIRC gives the oxidant IBX, which can then be acetylated to DMP.

The reaction is NOT a Sandmeyer though - the only similarity is that it is a reaction of a diazonium salt. A Sandmeyer reaction involves a single electron transfer mechanism, using the Cu (I)/Cu (II) couple. So formation of the chloride, bromide, or nitrile using CuCl, CuBr or CuCN respectively would be a Sandmeyer reaction.

Ozonelabs - 19-8-2009 at 13:16

Thanks a lot ,

Our intended use is yet undetermined, however 2-Iodoxybenzoic acid seems likely.

As a point of interest, does a sandmeyer reaction not follow a simple SRN1 pathway? And although the majority use copper based reagents as these provide good nucleophiles, it is well documented that not all of them do.

From here we can see that Sandmeyer-type reaction can involve various other non-copper based reagents, including thiols, water, hypophosphorous acid.

It is not our desire to argue semantics of a particular reaction name, but to merely show others that a copper-based reagent is not always necessary.

Best regards,

The Ozonelabs Team

[Edited on 19-8-2009 by Ozonelabs]

entropy51 - 19-8-2009 at 14:46

For what it's worth, in industry we referred to all of these as "Sandmeyer", even when no Cu was involved. I think that is consistent with a lot of the literature. Except we called the HBF4 route the Schiemann.

This 2-Iodobenzoic prep, almost identical to ozonelabs, also refers to them as Sandmeyer.

As a cautionary note, there are reports in the literature of runaways when KI is added to the diazonium (although you can usually get away with it). Better to add the diazonium to the KI.

Sandmeyer - 18-4-2010 at 08:04

I prefer the oxone method over KBrO3 for preparation of IBX, I have never had problems with explosions that scientists sometimes warn us about... IBX and its sisters are very useful reagents and have came to rescue more than once.

This method works exactly as stated in the paper "A User-Friendly Entry to 2-Iodoxybenzoic Acid (IBX)"


IBX, 1-Hydroxy-1,2-benziodoxol-3(1H)-one 1-Oxide (1) (≥95% Purity). 2-Iodobenzoic acid (50.0 g, 0.20 mol) was added all at once to a solution of Oxone (181.0 g, 0.29 mol, 1.3 equiv) in deionized water (650 mL, 0.45 M) in a 2 L flask. The reaction mixture was warmed to 70−73 °C over 20 min and mechanically stirred at this temperature for 3 h. The aspect of the mixture varies consistently during the reaction. The initial thick slurry coating the walls of the flask eventually becomes a finely dispersed, easy to stir suspension of a small amount of solid that sedimented easily upon stopping the stirring. The suspension was then cooled to 5 °C and left at this temperature for 1.5 h with slow stirring. The mixture was filtered through a medium porosity sintered-glass funnel, and the solid was repeatedly rinsed with water (6 × 100 mL) and acetone (2 × 100 mL). The white, crystalline solid was left to dry at rt for 16 h and weighed 44.8−45.7 g (79−81%).
Mother and washing liquors were oxidizing and acidic. They were treated with solid Na2SO3 (70 g, 0.55 mol) and neutralized with NaOH (1 M) before disposal. The internal temperature rose to 30 °C.

The purity of IBX obtained by this method was ≥95% (1H NMR, elemental analysis). The remainder was 2-iodosobenzoic (4%) and 2-iodobenzoic (0.5%) acids, as judged by integration of the triplets at 7.70 and 7.47 ppm, respectively, in the 1H NMR spectrum (ca. 5 mg in 0.5 mL of DMSO-d6).

[Edited on 18-4-2010 by Sandmeyer]

Arrhenius - 18-4-2010 at 22:10

IBX is a bit of a pain compared to the Dess-Martin reagent, but I'm positive you could prepare IBX using swimming pool oxone. I found it necessary to use 3eq of oxone as per the 'analytical' material prep in the paper you quoted in order to oxidize all the way up to the iodoxy compound. The KBrO3 prep is nasty - lots of bromine fumes and poor purity product (in my experience at least! :P).

[Edited on 19-4-2010 by Arrhenius]

Sandmeyer - 27-4-2010 at 06:12

I got exactly the same results as in the paper and I did the reaction several times. It is a valuable method since IBX is very expensive and very useful at the same time, IMO of course.

Organic chemistry portal gives it an entry:

I tried the Nicolaou-Baran* protocol to oxidize a complex toluene to corresponding benzaldehyde with IBX - but it did not work, I saw no aldehyde-proton in NMR spectum - only the same old toluene -CH3. However, I diMd not use hexafluorobenzene as co-solvent as Baran did since I saw no reason to do so.


Iodine(V) Reagents in Organic Synthesis. Part 4. o-Iodoxybenzoic Acid as a Chemospecific Tool for Single Electron Transfer-Based Oxidation Processes

K. C. Nicolaou,* T. Montagnon, P. S. Baran, and Y.-L. Zhong


[Edited on 27-4-2010 by Sandmeyer]

chemical - 6-4-2012 at 02:20

I tried preparing 2-iodobenzoic acid using the method in the pdf posted by ozone labs. I get 2-iodobenzoic acid with an m.p. of 161 deg. cel. but however the color of my final product is brown.
How can i change the color to slightly yellow?
Also, how to test the purity of 2-iodobenzoic acid?

DJF90 - 6-4-2012 at 02:59

Recrystallise it. There ought to be a solvent given in Armarego's purification book. Commercial stuff from S-A is off white, as I witnessed when the DPhils in the hood next to me made IBX on 30g scale using the oxone method (followed by acetylation to DMP on 20g scale) - quite a sight to see!

chemical - 6-4-2012 at 04:04

I recrystallised 2-iodobenzoic acid using methanol. On the contrary the color became darker. Is it something to do with the fact that 2-iodobenzoic acid is light sensitive?

Any idea about method of testing the purity of my 2-iodobenzoic acid?

DJF90 - 6-4-2012 at 04:13

The aforementioned book (5th ed.) says the following:

o-Iodobenzoic acid [88-47-5] M 248.4, m 162*C, pKa 2.93. Crystd repeatedly from water and EtOH. Sublimed under vacuum at 100*C.

Have you tried washing it with cold ethanol or methanol? What colour is the filtrate?

chemical - 6-4-2012 at 04:24

yes, i have washed it with cold methanol and the color of filtrate is yellow to orange...

DJF90 - 6-4-2012 at 04:55

That suggests iodine contamination to me. Try washing with petrol and look for a pink colour. If its there, take your product up into an organic solvent (something like ethyl acetate or ether will do) and wash with thiosulfate solution (sodium sulfite or metabisulfite do the same thing) to get rid of the iodine. Separate the phases and remove the solvent, then proceed to recrystallise as normal. Drying can be omitted here (wash with brine, dry over mag sulfate) as you're to recrystallise from aqueous ethanol. I'm not sure how well methanol works as a substitute.

chemical - 6-4-2012 at 05:07

I am not quite sure whether iodine would be present since i gave a sodium bisulfite wash to my crude 2-iodobenzoic acid and then went for the recrystallization.

I thank you for the suggestions and will get back with the results.

DJF90 - 6-4-2012 at 07:03

Sounds strange. I didnt think it'd be that light sensitive though. Was all the iodine removed in your wash? (colourless/very slightly coloured organic phase?)

chemical - 9-4-2012 at 03:44


I am back with my results and can conclude that the color is not due to iodine since the bisulfite wash does not lighten the color

there seems to be some impurities giving the color

Any method for checking the purity ???

AndersHoveland - 9-4-2012 at 04:49

Perhaps you will also make 2-Iodoxybenzoic acid?
This is a very useful regent for oxidizing alcohols to aldehydes, without undesirable further oxidation to carboxylic acids.


2-Iodoxybenzoic acid can be prepared by the slow addition, over a half hour, of potassium bromate (76.0 g, 0.45 mol) to a vigorously stirred sulfuric acid mixture (0.73 M, 730 mL) containing 2-iodobenzoic acid (85.2 g, 0.34 mol).

[Edited on 9-4-2012 by AndersHoveland]

Arrhenius - 9-4-2012 at 06:56


Perhaps you will also make 2-Iodoxybenzoic acid?

Perhaps someone didn't read the thread. Unless you added bromate or another strong oxidation, it's impossible to form this, not to mention that IBX is colorless.

The color is still probably iodine contamination. Most aryl and alkyl iodides are pretty unstable, and release iodine on storage or exposure to light. I don't know why you're so concerned though. Why don't you check the melting point, and continue? Remember, color is easy for your eye to see, but might constitute a trace impurity. Melting point will tell you whether or not to be concerned. I don't necessarily recommend it here, but activated charcoal can sometimes decolorize products quite effectively.

[Edited on 9-4-2012 by Arrhenius]

chemical - 11-4-2012 at 02:00

hi, the m.p. is 161 deg. cel. I found in literature it should be 164 deg. cel. hence i concluded that the dip in m.p. is due some impurity which is giving color to my 2-iodobenzoic acid

Nicodem - 11-4-2012 at 07:37

It is not solely the melting point that gives a conclusive information in regard to the purity. It is more the melting interval that is heavily dependent on purity (not always though, some compounds just have a wide interval even pure). The melting point depends on the calibration and reliability of your apparatus (excluding the polymorphs with different mp), so compounds generally have a very wide range of literature reported mp (that is, not only due to purity or misidentified products).

DJF90 - 11-4-2012 at 08:21

There are some compounds that melt very sharply and their melting points are tabulated. I believe sigma aldrich sells a set of them, allowing you to correct your melting points. You'd need to make a plot of "corrected mp", which is the literature value for these compounds, against "measured mp", which is what you measure on your apparatus. You should then have a straight line plot (perfectly diagonal and passing through the origin if your apparatus is bang on) which you can then refer to to obtain corrected melting point values.

The other alternative explanation for your low mp is that you ramped the temperature up too fast (within 10*C of the expected melting point the heating rate should be lowered from 20*C/min to 1*C/min or lower). Consequently, the material melts before thermal equilibrium is attained between the thermometer and the heating block, giving a lower reading than it should be.

DJF90 - 12-4-2012 at 03:29

The OrgSyn prep of DMP via IBX has a note saying that the 2-iodobenzoic acid is recrystallised from toluene before use (5ml/g). These guys know what they're talking about, so I'd advocate following their advice.

Arrhenius - 12-4-2012 at 06:35

The 2-iodobenzoic acid I used to make IBX was faintly yellow. Notice that Ozonelabs' material is not colorless either. If you found a mp of 161, it's the right stuff. Though I agree with Nicodem; you should always report melting point as a range. Anyway, here is the Sigma Aldrich specs sheet for this compound.

"Appearance (color) White to Pale Yellow".

[Edited on 12-4-2012 by Arrhenius]

Texium - 21-3-2018 at 16:49

I completed my own synthesis of 2-iodobenzoic acid, following the same procedure as Ozonelabs, but on a smaller scale since I don't have much anthranilic acid currently (I found it independently and didn't see this thread until later. Funny how that works out).

I'd also like to make IBX to experiment with. My product is a light brown as well, but you can see that the proton NMR that I took of my product is pretty clean!