Oxidation of methyl phenyl sulfide

The oxidation of methyl phenyl sulfide using fresh PWAA gave methyl phenyl sulfone in 97% yield. In the repeated use of recovered catalyst, the yields of sulfone in runs 2 to 5 ranged from 82 to 88%. The activities of recovered catalysts were somewhat reduced. The deactivation may be caused by catalyst pulverization or degradation of the PW12O403- species. While the reusability and stability of the catalyst should be improved, this concept would be useful for the creation of sophisticated solid catalysts. After Ikegami s reports, Neumann and coworkers [140] applied this strategy to the development of alkylated polyethyleneimine/POM synzymes. 

SCHEME 102. Oxidation of methyl phenyl sulfide 22a by TADOOH 60... 

In 1997, Chmielewski and coworkers investigated the oxidation of methyl phenyl sulfide and methyl p-tolyl sulfide with chiral carbohydrate hydroperoxides, which have been... 

Oxidation of a snlfide to sulfoxide is known to be an electrophilic reaction, in contrast with nncleophUic oxidation of sulfoxide to sulfone. Since 2-nitrobenzenesulfinyl chloride/KOi oxidizes sulfides to sulfoxides selectively, intermediate 48 must be the actual active intermediate. Moreover, in the presence of l,4-diazabicyclo[2.2.2.]octane (DABCO), which is a radical capturing reagent, the oxidation of methyl phenyl sulfide to the sulfoxide was inhibited. In order to further detect the intermediate 48, pure 5,5-dimethyl-l-pyrroUne-l-oxide (DMPO) was used as a trapping reagent and spin adduct was obtained. The ESR spectrum of the DMPO spin adduct was obtained by the reaction of 02 with 2-nitrobenzenesulfinyl chloride (hyperfine coupling constants, aH = 10.0 G and aN = 12.8 G). 

The enantioselective oxidation of prochiral sulfides with DMD has been achieved by using bovine serum albumin (BSA) as the chiral inductor Moderate to good enan-tioselectivities have been reported in the presence of this protein, for which a typical example is shown in equation 22 . As yet, however, no enantioselective oxidation of a prochiral sulfide has been documented by employing an optically active dioxirane. We have tried the enantioselective oxidation of methyl phenyl sulfide with the dioxirane generated from the ketone 7 (Shi s ketone), but an ee value of only ca 5% was obtained. One major hurdle that needs to be overcome with such enantioselective dioxirane oxidations is the suppression of the background oxidation of the sulfide substrate by Caroate, an unavoidable feature of the in-situ mode. 

The structure of cytochrome P450cam (CYP101), a soluble bacterial enzyme, has been solved. This enzyme was studied for its catalytic properties in the oxidation of methyl phenyl sulfide and methyl p-tolyl sulfide [117], Molecular dynamics calculations were used to predict the absolute configuration and enantioselectivity of the reaction. 

Pasta P, Carrea G, Monzani E, Gaggero N, Colonna S (1999) Chloroperoxidase-Catalyzed Enantioselective Oxidation of Methyl Phenyl Sulfide with Dihydroxyfumaric Acid/Oxygen or Ascorbic Acid/Oxygen as Oxidants. Biotechnol Bioeng 62 489... 

The oxidation of methyl phenyl sulfide with hydrogen peroxide, in the presence of ammonium hydrogencarbonate, takes place by a mechanism involving HCO4-... 

Metallo-(salen)-catalyzed oxidation. In 1986, Pasini and co-workers62 developed chiral oxotitanium(IV)-Schiff base complex as catalyst for the oxidation of methyl phenyl sulfide. While the catalytic activity of the Pasini system was excellent (catalyst substrate ratio, 1 1000 to 1 1500), the enantioselection was unfortunately low (< 20% ee) for catalyst 31 (Fig. 4). 

In the same year, Fujita s group63 reported the asymmetric oxidation of aryl methyl sulfide by hydroperoxides (TBHP, CHP) and an optically active catalyst formed by a Schiff base-oxovanadium(IV) complex 32, giving (S)-sulfoxides in low ee (up to 40%) (Fig. 4). Later, they developed64 a more promising approach using 33, a binuclear Schiff base-titanium(IV) complex (4 mol% equiv) to catalyze the asymmetric oxidation of methyl phenyl sulfide by trityl hydroperoxide in methanol at 0 °C. The (ft)-methyl phenyl sulfoxide was obtained with 60% ee. 

Picolinic acid also accelerates the H2O2 oxidations but less efficiently than pyrazine-2-carboxylic acid. It has been demonstrated recendy that the vanadium complex with picolinic acid, VO(PA)2 , encapsulated into the NaY zeolite retains solution-like activity in the liquid-phase oxidation of hydrocarbons [16a], It is noteworthy that pyrazine-2-carboxylic acid accelerates the hydrocarbon oxidation catalyzed by CH3Re03 [25 b]. Employing a (+)-camphor derived pyrazine-2-carboxylic acid as a potential co-catalyst in the CHsReOj-catalyzed oxidation of methyl phenyl sulfide with urea-H202 adduct, the corresponding sulfoxide was obtained with an e.e. of 15% [16b]. 

Pahna C, Moreira MT, Feijoo G et al. (1997) Enhanced catalytic properties of MnP by exogenous addition of manganese and hydrogen peroxide. Biotechnol Lett 19(3) 263—267 Pasta P, Carrea G, Monzani E et til. (1999). Chloroperoxidase-catalyzed enantioselective oxidation of methyl phenyl sulfide with dihydroxyfumaric add/oxygen or ascorbic acid/oxygen as oxidants. Biotechnol Bioeng 62(4) 489-493... 

The first example of FB oxidation of sulfides dates back to 1995 dibenzothiophene and diphenyl stdfide gave the corresponding sulfones in low yields (1.4% and 10%, respectively) upon treatment with O2 at 100 °C in the presence of a not fully characterized perfluorocarbon-soluble iron—phthalocyanine [19]. Following this earlier report, Co(ll)—tetraarylporphyrin Co-5 and Co(I I [—phthalocyanine Co-12 (cf Stmcture) were tested as catalysts for the FB oxidation of methyl phenyl sulfide and para-substituted aryl methyl sulfides with O2 and a sacrificial aldehyde (Table 3) [20]. 

Jacobsen and Katsuki have both reported the use ofmanganese(III) (salen) catalysts for sulfide oxidation. These catalysts can be effective for the enantiose-lective oxidation of several aryhnethylsulfides using iodosylbenzene as the stoichiometric oxidant. Additionally, titanium(salen) complexes function as efficient catalysts in this procedure, providing up to 94% ee in the oxidation of methyl phenyl sulfide using the more economical urea hydrogen peroxide as oxidant. ... 

Pasini et al. [100] developed chiral oxotitanium(IV) complexes with Schiff bases (46) (Figure 1.4), which are highly efficient catalysts (0.1-0.07 mol%) for asymmetric oxidation of methyl phenyl sulfide by 35% H2O2 in a mixture of aqueous ethanol and dichloromethane. However, these complexes are not very enantioselective the ee remains below 20% and the corresponding sulfones are also formed. 

Preparation and application of a new class of catalytic ionic liquids containing chiral W(V1) anions has been described. The hydrophobic ionic liquid [P 6 6 6 14]2[W02(S-mandalate )2] was used to catalyse oxidation of methyl phenyl sulfide by urea-H202 in the solvent CH2Cl2 + 2% EtOH to give the sulfoxide in 53% yield with 95% selectivity and 96%... 

Titanium-catalyzed oxidations with 35% aqueous H2O2 using Schiff-base (salen) titanium 0x0 complexes as catalysts showed very high activity [28]. The oxidation of methyl phenyl sulfide required only 0.1mol% of catalyst. The use of chiral salen complexes gave low enantioselectivity (<20% ee). 

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