Sulfones formation

The principal electrophiles to attack ring sulfur are either oxidants or alkylating reagents. Thiophene sulfoxide and sulfone formation is discussed in Section 3.02.2.6. Alkylating agents capable of forming thiophenium salts include trimethyloxonium tetrafluoroborate (MeaO BF ) and alkyl fluorosulfonates (ROSO2F). The salts e.g. 87) are conveniently isolated as hexafluorophosphates (88). 

Oxidative cleavage of oxosulfonium ylides490 as well as of sulfoximines491 leads to sulfone formation. In the course of oxidations of dialkoxy sulfuranes(IV) by hydrogen peroxide492 or f-butyl hydroperoxide493, sulfone formation takes place (equation 99). 

An interesting sulfone formation occurs when thiols are oxidized with a two-molar amount of 2-(benzenesulfonyl)-3-phenyloxaziridine497 ... 

The ion pair mechanism initially suggested by Darwish and McLaren28 (equation 2) has received further support from related studies conducted by several other investigators38-42. For example, Fava and coworkers38 have reported that during isomerization in acetic acid, optically active benzhydryl p-toluenesulfmate loses optical activity at a rate which is about two and a half times faster than the rate of sulfone formation, thus indicating that return from an ion-pair species is occurring (equation 3). 

Method for lowering content Prevention of sulfone formation by using 173... 

The reaction is highly exothermic with a AH of -170 kJ/gmol. Due to the slow second reaction aging is required to convert the formed pyrosulfonic acid with alkylate to the desired end product LAS (Table 2). There are two main side reactions anhydride formation and sulfone formation. 

Sulfones are a constituent of free oil at a level of —25-33% and cannot be eliminated by aging or any other step, i.e., sulfone competes directly with the desired main reaction. Sulfone formation is promoted by the following conditions ... 

High temperatures because the sulfone formation reaction has a higher activation energy than the main sulfonation reactions A high concentration of H+ ions (probably)... 

Anhydride and sulfone formation are not the only side reactions. Other side reactions lead to colored products (excess S03, high temperatures), traces of disulfonic acid, olefins, and oxidation products. 

A very surprising sulfone formation has been investigated by Oae and coworkers . On heating p-toluenesulfinic acid with dimethylaniline in ethanol for 15 h, the reaction mixture shown in equation 100 has been obtained. Obviously, the observed products arise from an equilibrium between the sulfinic acid and its pseudo-anhydride (disulfide trioxide), which is able to attack the amine nitrogen and degrade the tertiary amine corresponding to a Polonovsky reaction . 

Taurine is generally prepared from ox bile1 or the large muscle of the abalone.2 It has been synthesized from isethionic add through chloroethanesulfonic acid followed by the action of aqueous ammonia 3 from ethyleneimine and sulfur dioxide 4 from 2-mercaptothiazoline by oxidation with bromine water 5 from bromoethylamine and ammonium sulfite 6 and from acetaldehyde by a complex set of reactions involving sulfonation, formation of the aldehyde ammonia and the imido sulfonic add and finally reduction.7 The method given in the procedure has recently appeared in the literature.8 9... 

The first step — sulfonate formation — proceeds with retention of configuration because no bonds to the stereocenter are broken. 

Organic sulfur compounds are present in gasoline and diesel. With the increased emphasis on the requirement for more environmentally friendly transportation fuels [1], oxidative desulfurization, using H202 and redox-molecular sieves [2,5,6,7], has been studied and shown to significantly reduce the sulfur content of gasoline and diesel. The reaction of thiophene and its derivatives were successfully converted to oxidized compounds, but the identification of oxidized compounds was not simple because the concentrations of individual sulfur compounds were low. Most of the previous literature has reported sulfone formation. 

A final method of forming disulfide crosslinks between toxins and targeting molecules is the use of S-sulfonate formation using sodium sulfite (Na2SC>3) in the presence of sodium tetrathion-ate (Na2S40g). Tetrathionate reacts with sulfhydryls to form sulfenylthiosulfate intermediates (section 1.1.5.2). These derivatives are reactive toward other thiols to create disulfide linkages... 

The same combination of reagents, now with a 3 1 ratio of hydroperoxide to sulfide, gives a quantitative yield of RS(0)2R/. The reactions proceed to completion in about 2h at 323 K in chloroform. Only 0.3-0.5 mol% of 1 relative to RSR was needed. It was shown that oxidation to sulfoxide precedes sulfone formation. Again, the reaction is tolerant of many functional groups (42). 

Scheme 10 shows the course taken by these reactions. No trace was found of the 5,5-dioxide, the 5,5,10-trioxide, or the 5,5,10,10-tetraoxide. This reaffirms that sulfide oxidation precedes sulfone formation (42). 

Equilibrium constants for sulfinyl sulfone formation from aromatic sulfinic acids at 21 °C in acetic acid containing 1 to 5% H20 ... 

In the sulfoxidation, small to appreciable amounts of over oxidation with formation of undesired sulfone were observed, a result that implies that kinetic resolution may be involved in influencing the overall stereochemical result 105). This was shown to be the case. Indeed, some of the mutants are also excellent catalysts in the kinetic resolution of racemic sulfoxides such as 25 105). Directed evolution was then applied successfully to eliminate undesired sulfone formation, specifically, by going through a second cycle of epPCR 105). This is significant because it shows for the first time that an undesired side reaction can be eliminated by directed evolution. 

In 1998, Begue and coworkers reported on a very selective conversion of sulfides to sulfoxides in hexafluoro-2-propanol (HFIP) as solvent using 30% H2O2 as oxidant without the need for a catalyst (equation 54) . A variety of differently substituted acyclic sulfides and also a cyclic one could be cleanly oxidized to the sulfoxides in very good yields ranging from 82 to 99% and no sulfone formation was observed. C=C double bonds in the substrate are tolerated without being epoxidized. This excellent reactivity is explained... 

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