Sulphoxides oxidation

Nitric acid is one of the most common, and cheaper, oxidants used in organic chemistry. It will oxidize sulphoxides to sulphones in good yields if heated under reflux for several... 

Hydrogen peroxide was used to oxidize sulphoxides to sulphones at an early stage in the development of organosulphur chemistry28 and has remained the reagent of choice for everyday laboratory oxidations of this type. Typically, an excess of 30% hydrogen peroxide in water is employed at room temperature, often with a co-solvent such as an alcohol or acetone. 

Peracetic acid can be used to preferentially oxidize sulphoxides to sulphones in the presence of hydroxyl groups41, whilst attempted peracid oxidation of 2,6-diiodoaryl sulphoxides was not successful42. 

Peroxomonophosphoric acid and peroxodiphosphoric acid have both been used to oxidize sulphoxides to sulphones. 

Peroxomonosulphate and peroxodisulphate have also been used to oxidize sulphoxides to sulphones in good yields at room temperature. Potassium persulphate (KHS05) readily oxidizes a range of sulphoxides to sulphones at 0°C in yields greater than 90%, in the presence of hydroxy, keto and alkene groups82-84. The mechanism is similar to that observed for other peroxy species, as discussed above. Peroxomonosulphate oxidation has been used as an analytical procedure for the estimation of dimethyl sulphoxide84. 

Potassium peroxodisulphate (K2S2Og) also oxidizes sulphoxides to sulphones in high yield, either by catalysis with silver(I) or copper(II) salts at room temperature85 or in pH 8 buffer at 60-80 °c86-88. The latter conditions have been the subject of a kinetic study, and of the five mechanisms suggested, one has been shown to fit the experimental data best. Thus, the reaction involves the heterolytic cleavage of the peroxodisulphate to sulphur... 

V-chloro compounds have also been used for the preparation of sulphones from sulphoxides. /V-chlorosuccinimide(NCS) oxidizes sulphoxides in aqueous acetic acid and acetic acid-perchloric acid mixtures. In purely aqueous media, the reaction is very slow and marked decomposition of the NCS occurs with no oxidation being evident105. 

Osmium(VIII) will also oxidize sulphoxides to sulphones146 although this is usually accomplished in alkaline media in contrast to other transition-metal oxidations described above. The reaction may also be carried out in the presence of potassium... 

Carbonyl oxides (formed by the reaction of diazo compounds with singlet oxygen) may also be used to oxidize sulphoxides ". The corresponding sulphone is formed in reasonable yields and the reaction may be carried out in the presence of the sulphide functionality. The reaction proceeds as shown in equation (21) and involves initial nucleophilic attack by the carbonyl oxide on the sulphoxide sulphur atom followed by the facile departure of the carbonyl compound yielding the required sulphone. 

As with chlorine-containing oxidants, JV-bromo species have been used to oxidize sulphoxides to sulphones (with no bromine incorporation) through the initial formation of a bromosulphonium ion, by nucleophilic attack of the sulphoxide sulphur atom on the electrophilic halogen atom. Such reactions involve JV-bromosuccinimide ° bromamine-T, iV-bromoacetamide ° and iV-bromobenzenesulphonamide. All reported studies were of a kinetic nature and yields were not quoted. In acid solution all oxidations occurred at or around room temperature with the nucleophilic attack on the electrophilic bromine atom being the rate-limiting step. In alkaline solution a catalyst such as osmium tetroxide is required for the reaction to proceed . ... 

Hydrophilic molecules are composed of ions (such as sulphonate, sulphate, carboxylate, phosphate and quaternary ammonium), polar groups (such as primary amines, amine oxides, sulphoxides and phosphine oxide) and non-polar groups with electronegative atoms (such as oxygen atom in ethers, aldehydes, amides, esters and ketones and nitrogen atoms in amides, nitroalkanes and amines). These molecules associate with the hydrogen bonding network in water. 

Phosphines react with the oxygen atom in amine oxides, sulphoxides and in other compounds (6.68). These reactions indicate that P forms stronger bonds to oxygen than do N, As, S or Cl. 

Some cycloeliminations use a ring of five atoms instead of six but still involve six electrons. This is no longer a retro ene reaction but it is still a retro group transfer and is allowed in the all-suprafacial mode. Some common examples of such reactions are pyrolysis of amine oxides, sulphoxides, and selenoxides. All these reactions are syn stereospecific. 

---