Sulfite oxidation scheme

The scheme (Fig. 15.1) thus explained the production of both sulfate and sulfur in equimolar amounts from thiosulfate oxidation. In showing adenylylsulfate as an intermediate, it also provided a feasible route for the conservation of energy from sulfite oxidation by a substrate-level phosphorylation mechanism, in which ADP sulfurylase and adenylate kinase give rise to ATP ... 

In the 1,2,3-trithiole series, 1,2,3-trithiole 2-oxide (29) was obtained in 39% yield from the reaction of 2,2-dimethyl-1,3,2-dithiagermole (112) with thionyl chloride (Equation (25)) <88RTC440>. 1,3,2-Dioxathiolane 2-oxide (8) is conveniently prepared by reaction of 1,2-dihydroxyethane with either thionyl chloride <66HC(2l-l)l> or dimethyl sulfite <76CRV747> (Scheme 26). An alternative method. 

With respect to the molybdenum center, it appears that a spectator 0x0 ligand see Spectator Ligand (Ion)) controls the electronic structure allowing the second 0x0 ligand to participate in OAT reactions with the substrate see Substrate), X = for sulfite oxidase (Scheme 3, a - b) the substrate enters the enzyme via a substrate (solvent) access channel directed toward the exchangeable 0x0 group. Egress of the oxidized substrate, XO = S04, permits the... 

The general mechanism of sulfite oxidation at the Mo active site is as described in Scheme 5.8. Sulfite attacks the equatorial oxido ligand of Mo and is incorporated into the coordination sphere as a sulfato ligand bound to Mo The two electrons on Mo are passed, one at a time, to the adjacent heme (if present), which then relays them to the terminal electron acceptor cytochrome c7 ... 

The most commonly employed routes for the preparation of the / -sulfatoethylsulfone group, which is the essential structural feature of vinylsulfone reactive dyes, are illustrated in Scheme 8.5. One method of synthesis involves, initially, the reduction of an aromatic sulfonyl chloride, for example with sodium sulfite, to the corresponding sulfinic acid. Subsequent condensation with either 2-chloroethanol or ethylene oxide gives the / -hydroxyethylsulfone, which is converted into its sulfate ester by treatment with concentrated sulfuric acid at 20 30 °C. An alternative route involves treatment of an aromatic thiol with 2-chloroethanol or ethylene oxide to give the /Miydroxyethylsulfonyl compound which may then be converted by oxidation into the /Miydroxyethylsulfone. 

The possible roles in sulfur (and sulfide or sulfane-) oxidation of a sulfur dioxygenase or of electron-transport-linked hydration/dehydrogenation are outlined above, but the fate of the sulfite product may be more complex than previously considered. Vishniac and Santer (1957) showed that S-labeled sulfide was rapidly oxidized first to thiosulfate (and polythionates) and then to sulfate by T. thioparus. This observation was incorporated into the original Peck scheme (Eqs. 15.13-15.17) by Peck and Fisher (1962), who realized that the complete oxidation of thiosulfate (after reductive scission to sulfite and sulfide Eq. 15.3) could be explained if there was recycling of sulfide to produce thiosulfate ... 

If the snlfate anion-radical is bonnd to the snrface of a catalyst (sulfated zirconia), it is capable of generating the cation-radicals of benzene and tolnene (Timoshok et al. 1996). Conversion of benzene on snlfated zirconia was narrowly stndied in a batch reactor under mild conditions (100°C, 30 min contact) (Farcasiu et al. 1996, Ghencin and Farcasin 1996a, 1996b). The proven mechanism consists of a one-electron transfer from benzene to the catalyst, with the formation of the benzene cation-radical and the sulfate radical on the catalytic snrface. This ion-radical pair combines to give a snrface combination of sulfite phenyl ester with rednced snlfated zirconia. The ester eventually gives rise to phenol (Scheme 1.45). Coking is not essential for the reaction shown in Scheme 1.45. Oxidation completely resumes the activity of the worked-out catalyst. 

The endiol-cyclic sulfite 19 obtained by oxidation of the dihydropyran 18 affords a trans-fused bipyran <99TL2235> and this system is also accessible from the sulfonyl-stabilised oxirane 20 (Scheme 6) <99TL8019>. 

Oxidation of sulfite 59 using RuCh and NaI04 yielded the cyclic sulfate 60 which is now susceptible to nucleophilic attack. Treatment of 60 with NaN3 followed by acid hydrolysis of the intermediate 2-sulfate afforded the trans-i-azido-2-hydroxy derivative 61 (Scheme 3) <1997JOC4277>. 

Cationic t 3-allyltetracarbonyliron complexes are generated by oxidative addition of allyl iodide to pentacarbonyliron followed by removal of the iodide ligand with AgBF4 under a carbon monoxide atmosphere [35]. Similarly, photolysis of vinyl epoxides or cyclic vinyl sulfites with pentacarbonyliron or nonacarbonyldiiron provides Jt-allyltricarbonyliron lactone complexes. Oxidation with CAN provides by demetallation with concomitant coupling of the iron acyl carbon to one of the termini of the coordinated allyl moiety either [3- or 8-lactones (Scheme 1.12) [36, 37]. In a related procedure, the corresponding Jt-allyltricarbonyliron lactam complexes lead to P- and 8-lactams [37]. 

Dimethylsulfonyl- and 4,5-dimethylthio-l,2,3-triazole 1-oxide 479 and 480 were reduced unselectively with sodium sulfite and nickel boride, respectively. The latter reagent also removed the N-oxygen (Scheme 140). 

Partial sulfation of sucrose can be also achieved. Thus, reaction of sucrose with SOCl2 afforded a mixture of diastereoisomeric cyclic sulfites, which are readily oxidized to sulfates. Treatment of these latter compounds with fatty acids and potassium carbonate provided the ester with the sulfate group placed on 0-4. The sulfate function can be also introduced at other positions as demonstrated by reaction of 6-<9-acyl sucrose and l -O-acylsucrose with S03-pyridine (Scheme ll).150... 

Increased reactivity toward nucleophiles may render the five-membered cyclic sulfates unstable, for instance, because of an intramolecular nucleophilic attack <1997J(P1)3173>. Thus, when the sulfate 44 is prepared by oxidation of the corresponding sulfite with ruthenium tetroxide, it undergoes a clean rearrangement at room temperature to the isomeric six-membered cyclic sulfate of 2-benzoyloxypropane-l,3-diol (Scheme 5) <1997J(P1)3173>. 

Similar elimination from 1,3,2-dioxathiolane -oxides (cyclic sulfites) has been studied and used along with an in situ trap (DBU/TMSC1) to obtain a tautomeric equivalent of a-oxocarboxylic acid ester (Scheme 14)... 

The most widely used method for the preparation of 1,3,2-dioxathiolane. Y-oxides (cyclic sulfites) 65 bearing C-linked substituents is the reaction of the corresponding 1,2-diols with thionyl chloride in presence of pyridine or Et3N (Scheme 18). More reactive 1,3,2-dioxathiolane. Y,.Y-dioxidcs (cyclic sulfates) 66 are usually obtained by oxidation of sulfites 65 with sodium periodate, which is mediated by mthenium tetroxide generated in situ from a catalytic amount of ruthenium trichloride. Numerous derivatives 65 and 66 were obtained via this approach and its modifications for further transformations, mostly as the synthetic equivalents of epoxides <1997AHC89, 2000T7051> (see also Sections 6.05.5 and 6.05.6, and Tables 1-7). 

The common feature of the thermolysis of saturated five-membered cyclic sulfites is the elimination of sulfur dioxide (Scheme 7). 4,5-Dimethyl-l,3,2-dioxathiolane 2-oxide (38) decomposes at 275 °C on calcium oxide to a mixture of 2,3-dimethyloxirane (39) and... 

The 4,5-unsubstituted 1,3,2-dioxathiolane system (7) exists only in the form of its 2-oxide and 2,2-dioxide or their derivatives. 1,3,2-Dioxathiolane 2-oxide (16) represents the parent compound of saturated five-membered cyclic sulfites. It is a colorless, distillable liquid which can be prepared according to the methods shown in Scheme 9. The most convenient laboratory technique is the reaction of ethylene glycol with thionyl chloride <66HC(2l-l)l>. Another possibility is the transesterification of dimethyl sulfite with ethylene glycol (76CRV747). The reaction of ethylene oxide with sulfur dioxide, frequently described in the patent literature (66HC(2l-l)i>, depends on the reaction conditions. It leads either directly... 

Scheme 9 Methods for preparing 1,3,2-dioxathiolane 2-oxide (ethylene sulfite)...

Alkyl-substituted 1,3,2-dioxathiolane 2,2-dioxides can be prepared in a similar manner to the parent compound, ethylene sulfate (18) (66HC(2l-l)i) (cf. Scheme 10, Section 4.33.4.2.1). The method of choice is the permanganate oxidation of the corresponding cyclic sulfites (cf. Section 4.33.3.2.3) since the direct reaction of 1,2-diols with sulfuryl chloride often proceeds less smoothly than does the reaction with thionyl chloride. 4,5-Diaryl-l,3,2-dioxathiole 2,2-dioxides of type (186) are obtained by treatment of 9,10-... 

Holm and coworkers have very recently described advanced structural models for the Mo(VI) and Mo(V) states of sulfite oxidase. Thus, the reaction sequence shown in Scheme 8 yields dioxo mono(difhiolene) complexes bearing either silyloxo or thiolate ligands. The thiolate complex, [Mo02(SC6H2 Pr3-2,4,6)(bdt)]-, exhibits a square-pyramidal (pseudotetrahedral) stracture closely related to that of oxidized sulfite oxidase (Figure 11). 

Physical studies on oxidized and reduced enzymes show that all of the enzymes studied to date possess an oxo-molybdenum center that cycles between the Mo(VI) and the Mo(IV) states during catalysis and that the Mo(V) state can be detected as a transient species by EPR spectroscopy. Scheme 3 shows a simple cycle of reactions that describes the oxidation (or in reverse, reduction) of a substrate at an oxo-molybdenum center, such as that present in sulfite oxidase. 

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