Benzyl sulphides, oxidation

Both of these compounds yield sulphides or thio-ethers. Thio-phenol by the diazo reaction yields di-phenyl sulphide, CeHs—S—Cell5, di-phenyl thio-ether and benzyl mercaptan yields di-benzyl sulphide, CeHs—CH2—S—CH2—CeHs, di-benzyl thio-ether. These sulphides on oxidation yield sulphones (p. 526). 

An induction period was observed in the decomposition of cumyl hydroperoxide in chlorobenzene at 70 and 110 °C in the presence of phenolic sulphides CXCVIIa,b262). This was a substantial difference with respect to the behaviour of 4,4 -thio-bis(2,6-di-tert-butylphenol) CLXVIIIb which decomposed ROOH under the same conditions without induction period. The result indicates a mechanistic distinction in the action of both types of phenolic sulphides. In the mechanism of transformations of benzyl sulphide CXCVIIb, there are assumed (Scheme 24) the formation of sulphoxide CXCVIII and the intermediary formation of CIC followed by oxidation and formation of sulphinic acid CC. Further transformation of the acid CC depends on the character of R. If R = 3,5-di-tert-butyl-4-hydroxybenzyl, as it is in the formation of CC from CXCVIIa, the total elimination of the sulphurous part of molecule may occur and the transformation products of phenolic or quinoid character may be formed 3,5-di-tert-butyl-4-hydroxybenzyl alcohol XXXI, the corresponding aldehyde XXXII, and 2,6-di-tert-butyl-l,4-benzoquinone XXII were identified. Another possible sulphurless product is 4,4 -ethylenebis(2,6-di-tert-butyl-phenol) XXVIII, which was isolated in small amounts in its oxidized form as 3,5,3 ,5 -tetra-tert-butyl-4,4 -stilbenequinone (XXIX). Quinone methide XXX formed by thermolysis of sulphoxide CXCVIII, may be also the precursor in formation of XXIX. According to66), XXX is further oxidized by hydroperoxides to XXIX... 

Oxidation of phenyl hexyl sulphide with sodium metaperiodate gave also only a trace amount of the corresponding sulphoxide72. On the other hand, Hall and coworkers73 prepared benzylpenicillin and phenoxymethyl penicillin sulphoxides from the corresponding benzyl esters by oxidation with sodium metaperiodate in dioxane solution with a phosphate buffer. A general procedure for the synthesis of penicillin sulphoxides was reported later by Essery and coworkers74 which consists in the direct oxidation of penicillins or their salts with sodium metaperiodate in aqueous solution at pH 6.5-7.0. 1-Butadienyl phenyl sulphoxide 4475 and a-phosphoryl sulphoxides 4576 were also prepared by the same procedure. 

Formation of optically active sulphoxides was found to occur during oxidation of sulphides in the presence of chiral catalysts. Thus, the oxidation of benzyl methyl sulphide... 

The oxidation of a series of cyclic and acyclic sulphides by cytochrome P 450from rabbit liver gave sulphoxides with / -configuration at sulphur. The maximum of the e.e. value (53.8%) was observed for benzyl t-butyl sulphoxide310. 

Chlorinolysis is another reaction mode observed in some sulphides, in which sulphur retains its oxidation state. For example, phenyl trityl sulphide and benzyl trityl sulphide were converted into trityl chloride and sulphenyl chlorides [26]. Thiirane and thietane reacted similarly with 3-(dichloroiodo)pyridine to afford chlorinated disulphides [25] ... 

The one-electron reduction potentials of the radical cations of thioanisole, benzyl methyl sulphide, and 2-hydroxyethyl benzyl sulfide in water and several organic solvents were investigated by cyclic voltammetry. For comparison, the one-electron oxidations in water were also measured using pulse radiolysis. ° The two methods are complementary and the reversible potentials determined by pulse radiolysis are fairly close to the peak potentials determined by cyclic voltammetry (Table 8) indicating that the peak potentials do correspond to the formation of sulfur radical cations for all three sulfides. 

Benzyl phenyl sulphide, norbornene, cw-cyclooctene, and 4-vinyl-1-cyclohexene were obtained from Aldrich and (IS)-(-)-a-pinene from Fluka. Phenyl sulphide was prepared from benzene and sulphur chloride following the literature procedure[9]. Reference samples of sulphoxides and sulphones were prepared by oxidation of sulphides with sodium periodate[10] and hydrogen peroxide[ll] respectively. Reference samples of epoxides were made by following Kaneda et al.[ 2 procedure. Metal phthalocyanines[13] were prepared from appropriate metal salt, 1,2-dicyanobenzene with ammonium molybdate as catalyst and were characterized by elemental analysis. 

Benzyl phenyl sulphide was oxidized to benzyl phenyl sulphone quantitatively in 6h with iron phthalocyanine as catalyst. Experiments were similarly carried out with other metal phthalocyanines using phenyl and benzyl phenyl sulphides. Experiments using copper phthalocyanine, nickel phthalocyanine and no catalyst, were carried out for 24 h and the products analysed by HPLC. These results are presented in Table-1. In these experiments... 

Results in Table-1 show that with iron phthalocyanine (Fe(II)Pc), manganese phthalocyanine (Mn(II)Pc) and cobalt tetrasulphonatophthalocyanine (Co(II)TSPc) as catalyst both phenyl and benzyl phenyl sulphides could be quantitatively oxidized to corresponding sulphones in 3-6 h. However, oxidation of benzyl phenyl sulphide to the corresponding sulphone with vanadyl phthalocyanine took 18h. In case of copper phthalocyanine (Cu(II)Pc) and nickel phthalocyanine (Ni(II)Pc), no sulphone formation was detected even after 24h, and the products analysis by HPLC showed the formation of 61% and 4.2% benzyl phenyl sulphoxide, respectively. The results for the oxidation of benzyl phenyl sulphide with Ni(II)Pc as catalyst and without any catalyst (entry 9, 10 Table-1) show that Ni(II)Pc rather gave negative effect in these oxidations. 

Simple optically active phosphines can be converted back into phosphonium salts without any change of configuration if benzyl or alkyl halides are used (reversal of Equation 13.57). Oxidation to phosphine oxides with hydrogen peroxide or sulphurisation to phosphine sulphides with elemental sulphur also proceeds with retention of configuration. On the other hand, racemisation or complete inversion occurs if oxidation is carried out with diethyl peroxide. Halogenation to a phosphonium compound followed by hydrolysis results in inversion (13.63). 

Epoxy alcohols are the normal products of the [VO(acac)2]+(Me2C(CN)N a -catalysed oxidation of cyclic olefins by dioxygen however, cyclo-octene is oxidized exclusively to cyclo-octene oxide. The oxidation of sulphides and alkenes by peroxides with a [V(0)(acac)2] catalyst have been compared and the nature of the monoperoxovanadium(v) intermediate investigated. Complexation of a Cr(CO)3 unit to aromatic hydrocarbons enhances the benzylic positions towards attack by superoxide ion, e.g., diphenylmethane is readily converted into benzophenone. Metal porphyrin complexes ML4 continue to attract attention both as reversible oxygen-carriers (M = Fe) and oxidation catalysts (M = Mn, Fe, or Co ). For example [Mn (=0 IPh)(TPP)Cl] is believed to be involved in the oxidation of cyclohexene to cyclohexanol by PhIO in the presence of [Mn(TPP)]+ and a ferryl intermediate [Fe (0)L4] has been proposed in the oxygenation of triphenylphosphine with iron(ii) porphyrin. [M(TPP)]X (M=Mn, X = OAc M=Fe, X=C1 M = Co, X=Br) catalyses the epoxidation of styrene and cyclohexene with NaOCl under phase-transfer conditions. ... 

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