Methyl phenyl sulfoxide, oxidations

However, the (M)-phenyl methyl sulfoxide has the opposite configuration to (Mi-styrene oxide (Fig. 8, inset) (49). A possible structural difference between styrene and thioanisole is the fact that the ethylene group in styrene is in the plane of the phenyl ring while the S-methyl group in thioanisole is perpendicular to the phenyl group. If the Mb mutants discriminate this steric difference, one could expect (S)-sulfoxide formation if cyclic sulfides are employed as substrates, since the cyclic sulfides should have planar structures (Fig. 8c) similar to styrene. Table III lists representative results of cyclic and acyclic sulfide... 

When 2 equivalents of hydrogen peroxide are used, the submitters report that 0-2% of the sulfone is obtained. When phenyl methyl sulfoxide is oxidized under similar conditions, no sulfone is observed, even after 24 hr. 

The submitters report that oxidation of phenyl methyl sulfide to phenyl methyl sulfoxide also can be achieved selectively by using hexafluoroisopropyl alcohol (HFIP) as the solvent the reaction is complete after 10 min. 

Rosini adapted the reaction conditions developed by Uemura and reported on a system using 10 mol % of (S,S)-l,2-diphenylethane-l,2-diol (12) as chiralHgand and tert-butyl hydroperoxide as the terminal oxidant. After optimization of the process, phenyl methyl sulfoxide was obtained in 60% yield with an ee of 80% [24]. 

Phenyl methyl sulfoxide and benzoic anhydride heated 8 hrs. at 120° under Ng benzoyloxymethyl phenyl sulfide. Y 81%.—Similarly Tetrahydrothio-phene 1-oxide and acetic anhydride 3 hrs. at 80° -> 2-acetoxytetrahydrothiophene. Y 84%. F. e. s. L. Horner and P. Kaiser, A. 626, 19 (1959). 

It was reported earher that the oxidation of a sulfoxide to a sulfone involves either an initial nucleophihc attack of the nucleophilic oxidant or an electrophihc attack by an electrophilic oxidant. It is noteworthy that the oxidation of p-tolyl methyl, phenyl methyl and p-chlorophenyl methyl sulfoxides to the sulfones using the sulfonylperoxy intermediate 51 appears to be electrophihc, namely the relative reactivity order was p-tolyl methyl > phenyl methyl > p-chlorophenyl methyl sulfoxide based on competitive oxidations. 

Determination of dimethyldioxirane concentration by the GLC method is as follows A standard solution of thioanisole (phenyl methyl sulfide) is prepared. The solution is usually 0.2 M in acetone, but other concentrations may be used. It is important to keep the sulfide in excess so that oxidation by the dioxirane will produce largely or exclusively the sulfoxide and not the sulfone. 

Chiral sulfoxides. The Sharpless reagent lor asymmetric epoxidation also effects asymmetric oxidation of prochiral sulfides to sulfoxides. The most satisfactory results are obtained for the stoichiometry Ti(0-(-Pr)4/L DET/H20/(CH,),C00H = 1 2 1 2 for I equiv. of sulfide. In the series of alkyl p-tolyl sulfides, the (R)-sulfoxide is obtained in 41-90% ee the enantioselectivity is highest when the alkyl group is methyl. Methyl phenyl sulfide is oxidized to the (R)-sulfoxide in 81% ee. Even optically active dialkyl sulfoxides can be prepared in 50-71% ee the enantioselectivity is highest for methyl octyl sulfoxide. 

Previously, Pasini [27] and Colonna [28] had described the use chiral titani-um-Schiff base complexes in asymmetric sulfide oxidations, but only low selec-tivities were observed. Fujita then employed a related chiral salen-titanium complex and was more successful. Starting from titanium tetrachloride, reaction with the optically active C2-symmetrical salen 15 led to a (salen)titani-um(IV) dichloride complex which underwent partial hydrolysis to generate the t]-0x0-bridged bis[(salen)titanium(IV)] catalyst 16 whose structure was confirmed by X-ray analysis. Oxidation of phenyl methyl sulfide with trityl hydroperoxide in the presence of 4 mol % of 16 gave the corresponding sulfoxide with 53% ee [29]. 

A highly selective oxidation of sulfides to sulfoxides takes place by 30% aqueous H2O2 in phenol at room temperature [18]. Methyl phenyl sulfide was oxidized to the sulfoxide within 0.5 minutes in 99% yield. No sulfone could be detected. In a control experiment methyl phenyl sulfoxide was allowed to react for 14 h with 30% aqueous H2O2 in phenol at room temperature the sulfoxide was recovered unchanged. 

Phenyl methyl and benzyl sulfides have been catalytically oxidized to corresponding sulfoxides (>80%) and sulfones (<10%) using lutidine N-oxide as oxidant in the presence of Ru(TMP)(0)2 the reaction takes days at ambient conditions, and depends especially on the coordination ability of the sulfide and sulfoxide . Considering the non-reactivity of aryl sulfides toward the dioxo species, the amine oxide may well play a role as an axial ligand in these systems (see Sections 3.3 and 3.4). 

Hydrogen peroxide is frequently used as an oxidizing agent in organic chemistry. One application is for the oxidation of thioethers to sulfoxides. For example, methyl phenyl sulfide was oxidized to methyl phenyl sulfoxide in 99% yield in methanol in 18 hours (or 20 minutes using a TiCls catalyst) ... 

---