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{{redirect|IBX}} {{redirect|IBX}}
{{chembox {{chembox
|Verifiedfields = correct
| verifiedrevid = 443314523
|Watchedfields = correct
| ImageFile = IBXAcid.png
|verifiedrevid = 477213687
| ImageSize =
|ImageFile = IBXAcid.png
| ImageFileL1 = 2-iodoxybenzoic-acid-3D-balls.png
| ImageFileR1 = 2-iodoxybenzoic-acid-3D-vdW.png |ImageFileL1 = 2-iodoxybenzoic-acid-from-xtal-1997-3D-balls.png
|ImageFileR1 = 2-iodoxybenzoic-acid-from-xtal-1997-3D-sf.png
| IUPACName =
| OtherNames = 1-hydroxy-1λ<small><sup>5</sup></small>,2-benziodoxol-1,3-dione<br /> |PIN = 1-Hydroxy-1λ<sup>5</sup>,2-benziodoxole-1,3-dione
1-hydroxy-1λ<small><sup>3</sup></small>,2-benziodoxol-3(1''H'')-one 1-oxide |OtherNames = 1-Hydroxy-1λ<sup>3</sup>,2-benziodoxol-3(1''H'')-one 1-oxide
| Section1 = {{Chembox Identifiers |Section1 = {{Chembox Identifiers
|CASNo_Ref = {{cascite|correct|??}}
| InChI = 1/C7H5IO4/c9-7-5-3-1-2-4-6(5)8(10,11)12-7/h1-4H,(H,10,11)
|CASNo = 61717-82-6
| InChIKey = CQMJEZQEVXQEJB-UHFFFAOYAL
|Beilstein = 976364
| SMILES1 = c1ccc2c(c1)C(=O)OI2(=O)O
| ChEMBL_Ref = {{ebicite|correct|EBI}} |ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 118857 |ChEMBL = 118857
| StdInChI_Ref = {{stdinchicite|correct|chemspider}} |ChEBI_Ref = {{ebicite|correct|EBI}}
|ChEBI = 52701
| StdInChI = 1S/C7H5IO4/c9-7-5-3-1-2-4-6(5)8(10,11)12-7/h1-4H,(H,10,11)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 300947
| StdInChIKey = CQMJEZQEVXQEJB-UHFFFAOYSA-N
|PubChem = 339496
| CASNo_Ref = {{cascite|correct|??}}
|UNII = 3K0C43POH0
| CASNo = 61717-82-6
|InChI = 1/C7H5IO4/c9-7-5-3-1-2-4-6(5)8(10,11)12-7/h1-4H,(H,10,11)
| PubChem = 339496
|InChIKey = CQMJEZQEVXQEJB-UHFFFAOYAL
| ChEBI_Ref = {{ebicite|correct|EBI}}
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| ChEBI = 52701
|StdInChI = 1S/C7H5IO4/c9-7-5-3-1-2-4-6(5)8(10,11)12-7/h1-4H,(H,10,11)
| SMILES = O=C1OI(=O)(O)c2ccccc12
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = CQMJEZQEVXQEJB-UHFFFAOYSA-N
| ChemSpiderID = 300947
|SMILES = O=C1OI(=O)(O)c2ccccc12
}}
|SMILES1 = c1ccc2c(c1)C(=O)OI2(=O)O
| Section2 = {{Chembox Properties
| Formula = C<sub>7</sub>H<sub>5</sub>IO<sub>4</sub>
| MolarMass = 280.02 g/mol
| Appearance =
| Density =
| MeltingPt =
| BoilingPt =
| Solubility =
}}
| Section7 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| Autoignition =
| RPhrases = {{R22}} {{R34}} {{R44}}
}}
}} }}
|Section2 = {{Chembox Properties
|Formula = C<sub>7</sub>H<sub>5</sub>IO<sub>4</sub>
|MolarMass = 280.02 g/mol
|MeltingPt = 233 °C (decomposes)
}}
|Section7 = {{Chembox Hazards
|GHSPictograms = {{GHS05}}{{GHS07}}
|GHSSignalWord = Danger
|HPhrases = {{H-phrases|314|315|319|335}}
|PPhrases = {{P-phrases|260|261|264|271|280|301+330+331|302+352|303+361+353|304+340|305+351+338|310|312|321|332+313|337+313|362|363|403+233|405|501}}
}}
}}

'''2-Iodoxybenzoic acid''' ('''IBX''') is an ] used in ] as an ]. This ] is especially suited to ] ]s to ]s. IBX is most often prepared from ] and a strong oxidant such as ] and ],<ref>{{OrgSynth | title = Dess–Martin periodinane: 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1''H'')-one | author = Boeckman, R. K. Jr. | author2 = Shao, P. | author3 = Mullins, J. J. | year = 2000 | volume = 77 | pages = 141 | collvol = 10 | collvolpages = 696 | prep = v77p0141 }}</ref> or more commonly, ]. One of the main drawbacks of IBX is its limited solubility; IBX is insoluble in many common organic solvents. IBX is an impact- and heat-sensitive explosive (>200°C).<ref name="Santagostino">{{ cite journal | title = A User-Friendly Entry to 2-Iodoxybenzoic Acid (IBX) |author1=Frigerio, M. |author2=Santagostino, M. |author3=Sputore, S. | journal = ] | year = 1999 | volume = 64 | issue = 12 | pages = 4537–4538 | doi = 10.1021/jo9824596 }}</ref> Commercial IBX is stabilized by ]s such as ] and ].

==Preparation==
IBX can be prepared in a single step by adding an excess of ] to an aqueous solution of ]. After warming the solution to 70°C for three hours, the precipitated IBX is collected as a white crystalline solid (80% yield, ≥95% purity). Decomposition of IBX to 2-iodosobenzoic acid and ] occurs at elevated temperatures, and therefore purification by ] from water is not possible. Purity can be increased (≥99%) by shorting the reaction time to one hour at 70°C, at the cost of slightly reducing yield to 77%.<ref name="Santagostino">{{ cite journal | title = A User-Friendly Entry to 2-Iodoxybenzoic Acid (IBX) |author1=Frigerio, M. |author2=Santagostino, M. |author3=Sputore, S. | journal = ] | year = 1999 | volume = 64 | issue = 12 | pages = 4537–4538 | doi = 10.1021/jo9824596 }}</ref>


]{{clear-left}}
'''IBX acid''' or '''2-iodoxybenzoic acid''' is an ] used in ] as an ]. This ] is especially suited to ] ]s to ]s. The IBX acid is prepared from 2-iodobenzoic acid, ] and ].<ref>{{cite journal | title = Dess-Martin periodinane: 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1''H'')-one &#x5B;1,2-Benziodoxol-3(1''H'')-one, 1,1,1-tris(acetyloxy)-1,1-dihydro-&#x5D; | author = Robert K. Boeckman, Jr., Pengcheng Shao, and Joseph J. Mullins | journal = ] | volume = 77 | pages = 141 | year = 2000 | url = http://www.orgsyn.org/orgsyn/prep.asp?prep=v77p0141 }} ''(also in the (PDF)).''</ref> Frigerio and co-workers have also demonstrated, in ] that potassium bromate may be replaced by commercially available ].<ref name="Santagostino">{{cite journal | title = A User-Friendly Entry to 2-Iodoxybenzoic Acid (IBX) | author = Marco Frigerio, Marco Santagostino, and Simona Sputore | journal = ] | year = 1999 | volume = 64 | issue = 12 | pages = 4537–4538 | doi = 10.1021/jo9824596 | url = http://pubs.acs.org/doi/abs/10.1021/jo9824596 | format = abstract }}</ref> One of the main drawbacks of IBX is its limited solubility; IBX is insoluble in many common organic solvents. In the past, it was believed that IBX was ], but it was later proposed that samples of IBX were shock sensitive due to the residual potassium bromate left from its preparation.<ref name="Santagostino" /><ref name="DMP">{{citation | author=Dess, D. B.; Martin, J. C.|journal=]|title=A useful 12-I-5 triacetoxyperiodinane (the Dess-Martin periodinane) for the selective oxidation of primary or secondary alcohols and a variety of related 12-I-5 species|year=1991|volume=113|pages=7277|doi=10.1021/ja00019a027}}</ref> Commercial IBX is stabilized by ]s such as ] and ].


==Reaction mechanism== ==Reaction mechanism==
The ] for an oxidation of an ] to an ] according to the ]<ref>{{ cite journal | title = Enhancing 2-Iodoxybenzoic Acid Reactivity by Exploiting a Hypervalent Twist |author1=Su, J. T. |author2=Goddard, W. A. III | journal = ] | year = 2005 | volume = 127 | issue = 41 | pages = 14146–14147 | doi = 10.1021/ja054446x | pmid = 16218584 |url=https://authors.library.caltech.edu/76780/2/ja054446xsi20050824_011746.pdf }}</ref> involves a ] replacing the hydroxyl group by the alcohol followed by a twist and an ]. The twist is a requirement because the iodine to oxygen ] is oriented out of plane with the ] group and the ] elimination would not be able to take place. This twist reaction is a rearrangement in which the oxygen atom is moved into a proper plane for a 5 membered cyclic ] in the elimination reaction and is calculated by ] to be the ] in the oxidation. The twist mechanism also explains why oxidation is faster for larger alcohols than for small alcohols. The twist is driven forward by the ] that exists between the ] hydrogen atom and the protons from the ] group and larger alkoxy groups create larger steric repulsion. The same computation predicts a much faster reacting IBX derivative with a 100 fold ] when this ortho hydrogen atom is replaced by a ] group thus facilitating the twist until the elimination reaction takes prevalence as the rate determining step.
] during conversion of ] to ]: a) ligand exchange reaction (] 9.1 ]/] (38 ]/mol), b) hypervalent twist 12.1 kcal/mol (51 kJ/mol), c) elimination 4.7 kcal/mol (20 kJ/mol)). There is steric repulsion between protons in red.]]
The ] for an oxidation of an ] to an ] according the so-called ]<ref>{{cite journal | title = Enhancing 2-Iodoxybenzoic Acid Reactivity by Exploiting a Hypervalent Twist | author = Julius T. Su and William A. Goddard III | journal = ] | year = 2005 | volume = 127 | issue = 41 | pages = 14146–14147 | doi = 10.1021/ja054446x | url = http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2005/127/i41/abs/ja054446x.html | format = abstract | pmid = 16218584 }}</ref> involves a ] replacing the hydroxyl group by the alcohol followed by a twist and a ]. The twist is a requirement because the iodine to oxygen ] is oriented out of plane with the ] group and the ] elimination would not be able to take place. This twist reaction is a rearrangement in which the oxygen atom is moved into a proper plane for a 5 membered cyclic ] in the elimination reaction and is calculated by ] to be the ] in the oxidation. The twist mechanism also explains why oxidation is faster for larger alcohols than for small alcohols. The twist is driven forward by the ] that exists between the ] hydrogen atom and the protons from the ] group and larger alkoxy groups create larger steric repulsion. The same computation predicts a much faster reacting IBX derivative with a 100 fold ] when this ortho hydrogen atom is replaced by a ] group thus facilitating the twist until the elimination reaction takes prevalence as the rate determining step.


] during conversion of ] to ]: a) ligand exchange reaction (] 9.1 ]/] (38 ]/mol), b) hypervalent twist 12.1 kcal/mol (51 kJ/mol), c) elimination 4.7 kcal/mol (20 kJ/mol)).]]{{clear-left}}
IBX exists as two ]s one of which is the ]. The ] of IBX which has been determined in water (] 2.4) and ] (pKa 6.65)<ref name="gallen">{{cite journal | title = o-Iodoxybenzoic Acid (IBX): pK<sub>a</sub> and Proton-Affinity Analysis | author = Michael J. Gallen, Régis Goumont, Timothy Clark, François Terrier, Craig M. Williams | journal = ] | volume = 45 | issue = 18 | pages = 2929–2934 | year = 2006 | doi = 10.1002/anie.200504156 | pmid = 16566050}}</ref> is known to affect organic reactions, for instance acid-catalyzed ] accompanying oxidations.

IBX exists as two ]s, one of which is the ]. The ] of IBX which has been determined in water (] 2.4) and ] (pKa 6.65)<ref name="gallen">{{ cite journal | title = o-Iodoxybenzoic Acid (IBX): pK<sub>a</sub> and Proton-Affinity Analysis |author1=Gallen, M. J. |author2=Goumont, R. |author3=Clark, T. |author4=Terrier, F. |author5=Williams, C. M. | journal = ] | year = 2006 | volume = 45 | issue = 18 | pages = 2929–2934 | doi = 10.1002/anie.200504156 | pmid = 16566050| doi-access = free }}</ref> is known to affect organic reactions, for instance acid-catalyzed ] accompanying oxidations.


==Scope== ==Scope==
IBX is also available as ] or ] bound IBX. In many application IBX acid is replaced by ] which is more soluble in common organic solvents. A sample reaction is a IBX oxidation used in the ] of ]:<ref>{{cite journal | title = Asymmetric total synthesis of eicosanoid | author = Debendra K. Mohapatra and Gorakhanath S. Yellol | journal = ] | url = http://www.arkat-usa.org/home.aspx?VIEW=MANUSCRIPT&MSID=1210 | volume = 2005 | issue = iii }}</ref> IBX is also available as ] or ] bound IBX. In many applications, IBX is replaced by ] which is more soluble in common organic solvents. A sample reaction is an IBX oxidation used in the ] of ]:<ref>{{ cite journal | author1 = Mohapatra, D. K. | author2 = Yellol, G. S. | title = Asymmetric Total Synthesis of Eicosanoid | journal = ] | year = 2005 | volume = 2005 | issue = 3 | pages = 144–155 | doi = 10.3998/ark.5550190.0006.316 | doi-access = free| hdl = 2027/spo.5550190.0006.316 | hdl-access = free }}</ref> More and Finney<ref>{{cite journal |last1=More |first1=J.D. |last2=Finney |first2=N.S. |title=A Simple and Advantageous Protocol for the Oxidation of Alcohols with o-Iodoxybenzoic Acid (IBX) |journal=Organic Letters |date=2002 |volume=4 |issue=17 |pages=3001–3003 |doi=10.1021/ol026427n|pmid=12182609}}</ref> and Van Arman<ref>{{cite journal |last1=Van Arman |first1=S |title=2-Methyl-2-propanol as solvent for o-iodoxybenzoic acid (IBX) oxidation of 1˚ alcohols to aldehydes |journal=Tetrahedron Letters |date=2009 |volume=50 |issue=33 |pages=4693–4695 |doi=10.1016/j.tetlet.2009.06.045 }}</ref> have demonstrated that common organic solvents are suitable for many IBX oxidations, despite its low solubility, and in fact may simplify product purification.


] to ] key data: a) IBX, ], ], 4h, 94% ] (Mohapatra, 2005)]]. :] to ], 94% ] (Mohapatra, 2005)]]{{clear-left}}


In 2001, ] and co-workers published a series of papers in the ] demonstrating, among other transformations, the use of IBX to oxidize benzylic carbons to conjugated aromatic carbonyl compounds. In 2001, ] and co-workers published a series of papers in the '']'' demonstrating, among other transformations, the use of IBX to oxidize primary and secondary benzylic carbons to aromatic aldehydes and ketones, respectively.<ref>{{Cite journal|last1=Nicolaou|first1=K. C.|last2=Montagnon|first2=T.|last3=Baran|first3=P. S.|last4=Zhong|first4=Y.-L.|date=2002-03-01|title=Iodine(V) Reagents in Organic Synthesis. Part 4. o-Iodoxybenzoic Acid as a Chemospecific Tool for Single Electron Transfer-Based Oxidation Processes|journal=Journal of the American Chemical Society|volume=124|issue=10|pages=2245–2258|doi=10.1021/ja012127+|pmid=11878978|issn=0002-7863}}</ref> The presence of additional water in the solution is now considered to be an essential part of those oxidations.<ref>{{Cite blog|website=Blog Syn|title=Secret Ingredient|author=See Arr Oh|date=2013-03-03|url=https://blog-syn.blogspot.com/2013/03/blog-syn-003a-secret-ingredient.html}}<!--Self-pub anonymous source, but see linked citations in post--></ref>


===Oxidative cleavage=== ===Oxidative cleavage===
IBX is notable for oxidizing vicinal diols (or glycols) to diketones without cleavage of the carbon-carbon bond,<ref name="diol oxidation">{{citation | author=Frigerio, M.; Santagostino, M.|journal=]|title=A mild oxidizing reagent for alcohols and 1,2-diols: o-iodoxybenzoic acid (IBX) in DMSO|year=1994|volume=35|pages=8019|doi=10.1016/0040-4039(94)80038-3}}</ref> but oxidative cleavage of glycols to dialdehydes or diketones can occur when modified conditions are used (elevated temperatures or trifluoroacetic acid solvent).<ref>{{cite journal |title=Oxidative cleavage of vicinal diols: IBX can do what Dess–Martin periodinane (DMP) can |journal=Org. Biomol. Chem. |year=2007 |volume=5 |pages=767–771 |doi=10.1039/b618135j |author=Jarugu Narasimha Moorthy, Nidhi Singhal and Kalyan Senapati |pmid=17315062 |issue=5}}</ref> IBX is notable for oxidizing vicinal diols (or glycols) to diketones without cleavage of the carbon-carbon bond,<ref name="diol oxidation">{{ cite journal |author1=Frigerio, M. |author2=Santagostino, M. | title = A Mild Oxidizing Reagent for Alcohols and 1,2-Diols: o-Iodoxybenzoic Acid (IBX) in DMSO | journal = ] | year = 1994 | volume = 35 | issue = 43 | pages = 8019–8022 | doi = 10.1016/0040-4039(94)80038-3 }}</ref> but oxidative cleavage of glycols to two aldehydes or ketones can occur when modified conditions are used (elevated temperatures or trifluoroacetic acid solvent).<ref>{{ cite journal |author1=Moorthy, J. N. |author2=Singhal, N. |author3=Senapati, K. | title = Oxidative Cleavage of Vicinal Diols: IBX can do what Dess–Martin Periodinane (DMP) can | journal = Organic & Biomolecular Chemistry | year = 2007 | volume = 5 | issue = 5 | pages = 767–771 | doi = 10.1039/b618135j | pmid = 17315062 }}</ref>


:] :]


The reaction mechanism for this ] is based on initial formation of an adduct between ] IBX and DMSO to an 12-I-5 intermediate '''3''' in which DMSO acts as a ] for incoming ] '''4''' to intermediate '''5'''. One equivalent of water is split off forming 12-I-5 spirobicyclic periodinane '''6''' setting the stage for fragmentation to '''7'''. With hydroxyl alpha protons presents oxidation to the ] competes. ] is found to facilitate the overall reaction. The reaction mechanism for this ] is based on initial formation of an adduct between ] IBX and DMSO to a 12-I-5 intermediate '''3''' in which DMSO acts as a ] for incoming ] '''4''' to intermediate '''5'''. One equivalent of water is split off forming 12-I-5 spirobicyclic periodinane '''6''' setting the stage for fragmentation to '''7'''. With hydroxyl alpha protons present, oxidation to the ] competes. ] is found to facilitate the overall reaction.


:] :]


===&alpha;-Hydroxylations=== ===α-Hydroxylations===
Kirsch and co-workers were able to hydroxylate keto compounds with IBX in α-position under mild conditions.<ref>{{cite journal | journal= J. Org. Chem. | year=2005 | volume=70 | issue= 24 | pmid= 16292876 | pages=10210–10212 | doi=10.1021/jo051898j | author = Kirsch, S.F. | title=IBX-Mediated α-Hydroxylation of α-Alkynyl Carbonyl Systems. A Convenient Method for the Synthesis of Tertiary Alcohols}}</ref> This method could be extended to β-keto esters.<ref>{{cite journal | journal=Chem. Europ. J. | volume=15 | issue=41 | pages=10713–10717 | doi=10.1002/chem.200901867 | author=Kirsch, S.F.; Duschek, A. | title=Novel Oxygenations with IBX | year=2009}}</ref> Kirsch and co-workers were able to hydroxylate keto compounds with IBX in α-position under mild conditions.<ref>{{ cite journal | author = Kirsch, S. F. | title = IBX-Mediated α-Hydroxylation of α-Alkynyl Carbonyl Systems. A Convenient Method for the Synthesis of Tertiary Alcohols | journal = Journal of Organic Chemistry | year = 2005 | volume = 70 | issue = 24 | pages = 10210–10212 | doi = 10.1021/jo051898j | pmid = 16292876}}</ref> This method could be extended to β-keto esters.<ref>{{ cite journal |author1=Kirsch, S. F. |author2=Duschek, A. | title = Novel Oxygenations with IBX | journal = Chemistry: A European Journal | year = 2009 | volume = 15 | issue = 41 | pages = 10713–10717 | doi=10.1002/chem.200901867 |pmid=19760735}}</ref>

===Oxidation of β-hydroxyketones to β-diketones===
Bartlett and Beaudry discovered that IBX is a valuable reagent for the transformation of β-hydroxyketones to β-diketones. IBX provides yields superior to both the Swern and Dess–Martin oxidation protocols.<ref>{{ cite journal |author1=Bartlett, S.L. |author2=Beaudry, C.M. | title = High Yielding Oxidation of ''β''-Hydroxyketones to ''β''-Diketones Using ''o''-Iodoxybenzoic Acid | journal = Journal of Organic Chemistry | year = 2011 | volume = 76 | issue = 23 | pages = 9852–9855 | doi=10.1021/jo201810c |pmid=22023037 }}</ref>


==References== ==References==
{{reflist}}
<references/>


{{DEFAULTSORT:Iodoxybenzoic acid, 2-}} {{DEFAULTSORT:Iodoxybenzoic acid, 2-}}
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Latest revision as of 23:44, 16 January 2025

"IBX" redirects here. For other uses, see IBX (disambiguation).
2-Iodoxybenzoic acid
Names
Preferred IUPAC name 1-Hydroxy-1λ,2-benziodoxole-1,3-dione
Other names 1-Hydroxy-1λ,2-benziodoxol-3(1H)-one 1-oxide
Identifiers
CAS Number
3D model (JSmol)
Beilstein Reference 976364
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.157.592 Edit this at Wikidata
PubChem CID
UNII
CompTox Dashboard (EPA)
InChI
  • InChI=1S/C7H5IO4/c9-7-5-3-1-2-4-6(5)8(10,11)12-7/h1-4H,(H,10,11)Key: CQMJEZQEVXQEJB-UHFFFAOYSA-N
  • InChI=1/C7H5IO4/c9-7-5-3-1-2-4-6(5)8(10,11)12-7/h1-4H,(H,10,11)Key: CQMJEZQEVXQEJB-UHFFFAOYAL
SMILES
  • O=C1OI(=O)(O)c2ccccc12
  • c1ccc2c(c1)C(=O)OI2(=O)O
Properties
Chemical formula C7H5IO4
Molar mass 280.02 g/mol
Melting point 233 °C (decomposes)
Hazards
GHS labelling:
Pictograms GHS05: CorrosiveGHS07: Exclamation mark
Signal word Danger
Hazard statements H314, H315, H319, H335
Precautionary statements P260, P261, P264, P271, P280, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P332+P313, P337+P313, P362, P363, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). checkverify (what is  ?) Infobox references
Chemical compound

2-Iodoxybenzoic acid (IBX) is an organic compound used in organic synthesis as an oxidizing agent. This periodinane is especially suited to oxidize alcohols to aldehydes. IBX is most often prepared from 2-iodobenzoic acid and a strong oxidant such as potassium bromate and sulfuric acid, or more commonly, oxone. One of the main drawbacks of IBX is its limited solubility; IBX is insoluble in many common organic solvents. IBX is an impact- and heat-sensitive explosive (>200°C). Commercial IBX is stabilized by carboxylic acids such as benzoic acid and isophthalic acid.

Preparation

IBX can be prepared in a single step by adding an excess of oxone to an aqueous solution of 2-iodobenzoic acid. After warming the solution to 70°C for three hours, the precipitated IBX is collected as a white crystalline solid (80% yield, ≥95% purity). Decomposition of IBX to 2-iodosobenzoic acid and 2-iodobenzoic acid occurs at elevated temperatures, and therefore purification by recrystallization from water is not possible. Purity can be increased (≥99%) by shorting the reaction time to one hour at 70°C, at the cost of slightly reducing yield to 77%.

IBX Preparation from 2-iodobenzoic acid and Oxone.

Reaction mechanism

The reaction mechanism for an oxidation of an alcohol to an aldehyde according to the hypervalent twisting mechanism involves a ligand exchange reaction replacing the hydroxyl group by the alcohol followed by a twist and an elimination reaction. The twist is a requirement because the iodine to oxygen double bond is oriented out of plane with the alkoxy group and the concerted elimination would not be able to take place. This twist reaction is a rearrangement in which the oxygen atom is moved into a proper plane for a 5 membered cyclic transition state in the elimination reaction and is calculated by Computational chemistry to be the rate-determining step in the oxidation. The twist mechanism also explains why oxidation is faster for larger alcohols than for small alcohols. The twist is driven forward by the steric hindrance that exists between the ortho hydrogen atom and the protons from the alkoxy group and larger alkoxy groups create larger steric repulsion. The same computation predicts a much faster reacting IBX derivative with a 100 fold reaction rate when this ortho hydrogen atom is replaced by a methyl group thus facilitating the twist until the elimination reaction takes prevalence as the rate determining step.

Hypervalent twisting mechanism
The hypervalent twisting mechanism during conversion of methanol to formaldehyde: a) ligand exchange reaction (activation energy 9.1 kcal/mol (38 kJ/mol), b) hypervalent twist 12.1 kcal/mol (51 kJ/mol), c) elimination 4.7 kcal/mol (20 kJ/mol)).

IBX exists as two tautomers, one of which is the carboxylic acid. The acidity of IBX which has been determined in water (pKa 2.4) and DMSO (pKa 6.65) is known to affect organic reactions, for instance acid-catalyzed isomerization accompanying oxidations.

Scope

IBX is also available as silica gel or polystyrene bound IBX. In many applications, IBX is replaced by Dess–Martin periodinane which is more soluble in common organic solvents. A sample reaction is an IBX oxidation used in the total synthesis of eicosanoid: More and Finney and Van Arman have demonstrated that common organic solvents are suitable for many IBX oxidations, despite its low solubility, and in fact may simplify product purification.

IBX oxidation of alcohol to aldehyde, 94% chemical yield (Mohapatra, 2005)

In 2001, K. C. Nicolaou and co-workers published a series of papers in the Journal of the American Chemical Society demonstrating, among other transformations, the use of IBX to oxidize primary and secondary benzylic carbons to aromatic aldehydes and ketones, respectively. The presence of additional water in the solution is now considered to be an essential part of those oxidations.

Oxidative cleavage

IBX is notable for oxidizing vicinal diols (or glycols) to diketones without cleavage of the carbon-carbon bond, but oxidative cleavage of glycols to two aldehydes or ketones can occur when modified conditions are used (elevated temperatures or trifluoroacetic acid solvent).

Oxidative cleavage of vicinal diols

The reaction mechanism for this glycol cleavage is based on initial formation of an adduct between 10-I-4 IBX and DMSO to a 12-I-5 intermediate 3 in which DMSO acts as a leaving group for incoming alcohol 4 to intermediate 5. One equivalent of water is split off forming 12-I-5 spirobicyclic periodinane 6 setting the stage for fragmentation to 7. With hydroxyl alpha protons present, oxidation to the acyloin competes. Trifluoroacetic acid is found to facilitate the overall reaction.

Oxidative cleavage of vicinal diols: mechanism

α-Hydroxylations

Kirsch and co-workers were able to hydroxylate keto compounds with IBX in α-position under mild conditions. This method could be extended to β-keto esters.

Oxidation of β-hydroxyketones to β-diketones

Bartlett and Beaudry discovered that IBX is a valuable reagent for the transformation of β-hydroxyketones to β-diketones. IBX provides yields superior to both the Swern and Dess–Martin oxidation protocols.

References

  1. Boeckman, R. K. Jr.; Shao, P.; Mullins, J. J. (2000). "Dess–Martin periodinane: 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one". Organic Syntheses. 77: 141; Collected Volumes, vol. 10, p. 696.
  2. ^ Frigerio, M.; Santagostino, M.; Sputore, S. (1999). "A User-Friendly Entry to 2-Iodoxybenzoic Acid (IBX)". Journal of Organic Chemistry. 64 (12): 4537–4538. doi:10.1021/jo9824596.
  3. Su, J. T.; Goddard, W. A. III (2005). "Enhancing 2-Iodoxybenzoic Acid Reactivity by Exploiting a Hypervalent Twist" (PDF). Journal of the American Chemical Society. 127 (41): 14146–14147. doi:10.1021/ja054446x. PMID 16218584.
  4. Gallen, M. J.; Goumont, R.; Clark, T.; Terrier, F.; Williams, C. M. (2006). "o-Iodoxybenzoic Acid (IBX): pKa and Proton-Affinity Analysis". Angewandte Chemie International Edition. 45 (18): 2929–2934. doi:10.1002/anie.200504156. PMID 16566050.
  5. Mohapatra, D. K.; Yellol, G. S. (2005). "Asymmetric Total Synthesis of Eicosanoid". Arkivoc. 2005 (3): 144–155. doi:10.3998/ark.5550190.0006.316. hdl:2027/spo.5550190.0006.316.
  6. More, J.D.; Finney, N.S. (2002). "A Simple and Advantageous Protocol for the Oxidation of Alcohols with o-Iodoxybenzoic Acid (IBX)". Organic Letters. 4 (17): 3001–3003. doi:10.1021/ol026427n. PMID 12182609.
  7. Van Arman, S (2009). "2-Methyl-2-propanol as solvent for o-iodoxybenzoic acid (IBX) oxidation of 1˚ alcohols to aldehydes". Tetrahedron Letters. 50 (33): 4693–4695. doi:10.1016/j.tetlet.2009.06.045.
  8. Nicolaou, K. C.; Montagnon, T.; Baran, P. S.; Zhong, Y.-L. (2002-03-01). "Iodine(V) Reagents in Organic Synthesis. Part 4. o-Iodoxybenzoic Acid as a Chemospecific Tool for Single Electron Transfer-Based Oxidation Processes". Journal of the American Chemical Society. 124 (10): 2245–2258. doi:10.1021/ja012127+. ISSN 0002-7863. PMID 11878978.
  9. See Arr Oh (2013-03-03). "Secret Ingredient". Blog Syn.
  10. Frigerio, M.; Santagostino, M. (1994). "A Mild Oxidizing Reagent for Alcohols and 1,2-Diols: o-Iodoxybenzoic Acid (IBX) in DMSO". Tetrahedron Letters. 35 (43): 8019–8022. doi:10.1016/0040-4039(94)80038-3.
  11. Moorthy, J. N.; Singhal, N.; Senapati, K. (2007). "Oxidative Cleavage of Vicinal Diols: IBX can do what Dess–Martin Periodinane (DMP) can". Organic & Biomolecular Chemistry. 5 (5): 767–771. doi:10.1039/b618135j. PMID 17315062.
  12. Kirsch, S. F. (2005). "IBX-Mediated α-Hydroxylation of α-Alkynyl Carbonyl Systems. A Convenient Method for the Synthesis of Tertiary Alcohols". Journal of Organic Chemistry. 70 (24): 10210–10212. doi:10.1021/jo051898j. PMID 16292876.
  13. Kirsch, S. F.; Duschek, A. (2009). "Novel Oxygenations with IBX". Chemistry: A European Journal. 15 (41): 10713–10717. doi:10.1002/chem.200901867. PMID 19760735.
  14. Bartlett, S.L.; Beaudry, C.M. (2011). "High Yielding Oxidation of β-Hydroxyketones to β-Diketones Using o-Iodoxybenzoic Acid". Journal of Organic Chemistry. 76 (23): 9852–9855. doi:10.1021/jo201810c. PMID 22023037.
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