2- Iodobenzoic acid, oxidation

Potassium persulfate, reagent for oxidation of o-iodobenzoic acid, 46, 107... 

Efficient new methods for oxidation are always welcome. The Dess-Martin periodinane has become the workhorse for alcohol to aldehyde or ketone conversion in organic research labs around the world. Viktor V. Zhdankin of the University of Minnesota, Duluth has described (Chem. Commun. 2004, 106) a complementary family of reagents. Oxidation of an ester I of o-iodobenzoic acid with NaOCl delivers 2. Depending on the ester, the reagent 2 is soluble and an effective oxidant, with KBr catalysis, in a wide range of organic solvents. Presumably, the spent oxidant can be recovered and recycled. 

A. 1 -Hydroxy-1,2-benziodoxol-3(1 H)-one 1-oxide (1). A 2-L, three-necked, round-bottomed flask, fitted with a mechanical stirrer, condenser, and an immersion thermometer is charged with 80.0 g (0.48 mol) of potassium bromate (KB1O3) and 750 mL of 2.0 M sulfuric acid (Notes 1-3). The resulting clear solution is heated to 60°C in an oil bath and 80.0 g of finely powdered 2-iodobenzoic acid (0.323 mol) is added in... 

Use of higher concentration sulfuric acid ( 2.0 M) than traditionally employed is crucial to allow complete conversion of the 2-iodobenzoic acid to 1.2 In the submitters hands, use of lower concentrations ( 0.5 M) of sulfuric acid at 60°C led to exclusive formation of 1-hydroxy-1,2-benziodoxol-3(1 H)-one. When lower concentrations of sulfuric acid are employed, higher temperatures are required to effect oxidation, as judged by the initiation of bromine evolution. One of the factors leading to the lack of reproducibility in the preparation of 2 results from incomplete conversion to 1. 

Iodobenzoic acid has been prepared by the oxidation of -iodotoluene with chromic acid mixture 1 and with nitric acid 2 from the nitrile obtained from -iodonitrobenzene and potassium cyanide 3 and from / -aminobenzoic acid by diazotization.4... 

The closely related o-iodylbenzoic acid (IBX) and Dess-Martin oxidations have proved to be effective methods for the synthesis of peptide aldehydes (Table 7, Scheme 6) 9 38 39] 2-Iodobenzoic acid is oxidized by potassium bromate to form 2-iodylbenzoic acid (IBX), which can be used directly for IBX oxidation. IBX can be further treated with acetic anhydride and TosOH at 100 °C for 40 minutes to form the more stable Dess-Martin periodinane reagent 45 46]... 

The Dess-Manin periodinane ( DMP ) reagent, l,l,l-tris(acetyloxy)-l,l-dihydro-l,2-benziodoxol-3(lff)-one, has also been used in several complex syntheses for the oxidation of primary or secondary alcohols to aldehydes or ketones, respectively (e.g., M. Nakatsuka, 1990). It is prepared from 2-iodobenzoic acid by oxidation with bromic acid and acetylation (D. B. Dess, 1983). 

The o-iodosobenzoic or o-iodobenzoic acids, recovered from the work-up of oxidations with Dess-Martin periodinane, can be recycled back to this oxidant by oxidation to IBX, followed by transformation of IBX into Dess-Martin periodinane.2... 

In this work-up, the periodinane species 38s, resulting from the reduction of Dess-Martin periodinane, is further reduced with sodium thiosulfate to o-iodobenzoic acidh that is removed with a sodium bicarbonate aqueous solution. The treatment with sodium thiosulfate is normally made in the presence of sodium bicarbonate as buffer. This is the most common work-up because it is done under almost neutral conditions and the organic periodinane 38 is destroyed thus, avoiding a possible difficult chromatographic separation from the product. The o-iodobenzoic acid can be recycled back to Dess-Martin periodinane by oxidation. 

The o-iodoxybenzoic acid (37) (p. 181) commonly known as IBX was prepared for the first time more than a century ago by Hartman and Meyer by oxidation of o-iodobenzoic acid with KBrC>3.4 This compound was not explored in organic synthesis for a long time because it was wrongly supposed that its virtual lack of solubility in common organic solvents would preclude any synthetic usefulness. IBX came to the attention of the organic... 

Two polyvalent iodine compounds arising from o-iodobenzoic acid have been found to be useful synthetic reagents. Thus oxidation of the iodo acid (7) with potassium persulphate, followed by the addition of benzene and treatment with potassium iodide gives the iodonium iodide (8) which is converted into diphenyliodonium-2-carboxylate [DPIC (9)] with aqueous alkali (Expt 6.35).16... 

The periodinane (10) may also be prepared from o-iodobenzoic acid by oxidation with potassium bromate and then treatment with acetic anhydride18 (see Expt 6.36 for detailed formulation). It should be noted that the organic derivatives of pentacoordinate iodine(v) are termed periodinanes.18b This compound (the systematic name is l,l,l-triacetoxy-2,l-benzoxiodol-3(3//)-one) has found use as an oxidant of primary alcohols to aldehydes and alicyclic ketones to secondary alcohols it is claimed to have advantages over the chromium-based oxidation reagents. 

Dehydrogenation of 3-kelo steroids. The dehydrogenation of 3-keto steroids to l,4-diene-3-ones with benzeneseleninic anhydride (8, 31) can be carried out in comparable yield by use of a process in which the benzeneseleninic anhydride is used in catalytic amounts and is continuously regenerated from diphenyl diselenide by oxidation with iodylbenzene. In practice, m-iodylbenzoic acid is a more convenient reagent, since m-iodobenzoic acid is easily recovered. 12-Keto and 12-hydroxy steroids arc oxidized by the catalytic system to A9(1 - -keto steroids in high yield. In fact, methyl desoxycholate (1) can be oxidized in this way directly to the trienedione 2 in 64% yield.1... 

Many of these iodanes are formed by oxidation of ortho-iodobenzoic acids or certain orf/zo-iodophenylated alcohols with Cl2, AcOOH, f-BuOCl, CF3OF or magnesium monoperoxyphthalate. Among A3-iodanes more important are those derived from o-iodosobenzoic acid which is obtained from the mild oxidation of o-iodobenzoic acid. An improved yield for o-iodosobenzoic acid was obtained by hydrolysis of its acetyl derivative which in turn was prepared from o-iodobenzoic acid and acetyl nitrate in acetic anhydride, at room temperature (Scheme 14) [52]. 

The oxidation of ortho-iodobenzoic acid to give the Dess-Martin reagent is shown in Figure 17.39. This oxidation is a synthetically important oxidation of an iodine atom. The mechanism of the oxidation is not yet understood. 

Iodonium salts with a hydroxyl or a carboxyl group are readily converted into their inner salts, i.e. zwitterionic compounds of various types. 2-(Phenyliodonio) benzoate, whose structure may be cyclic, belongs to this category it is prepared from o-iodobenzoic acid upon oxidation and coupling with benzene (or arenes) [51], On strong heating, iodobenzene and carbon dioxide are eliminated, with formation of benzyne ... 

Diphenyliadoniiiin-2-carboxylate monohydrate (4), m.p. 220-222° (dec ), first described by Lc Goff, can be prepared in yields of 72-79 % by oxidation of o-iodobenzoic acid with potassium persulfate in sulfuric acid to the iodonium salt (2) and Fricdel-... 

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