Rhodium-catalyzed thiophosphinylation and phosphinylation reactions of disulfides and diselenides

Alkyl and aryl dithiophosphinates were synthesized by the reaction of disulfides with biphosphine disulfides in the presence of RhH(PPh₃)₄ and 1,2-diphenylphosphinoethane (dppe). The catalyst also promoted synthesis of thiophosphinates and selenothiophosphinates from disulfides and diselenides.     

Oxidation/reduction interconversion of thiols and disulfides using hydrogen and oxygen catalyzed by a rhodium complex

RhH(PPh₃)₄ catalyzes reduction of disulfides to thiols by hydrogen and RhH(PPh₃)₄/1,4-bis(diphenylphosphino)butane (dppb) catalyzes oxidation of thiols to disulfides by oxygen.     

Preparation of unsymmetrical disulfides by using sulfines1

Acidolytic cleavage of unsymmetrically substituted dithioacetal monoxides, ArCH(SR)S(O)Me has been used to prepare linear unsymmetrical disulfides RSSMe. Disproportionation was suppressed by the addition of a small amount of benzyl mercaptan. The required starting materials were conveniently obtained from appropriately substituted sulfines ArC(=SO)SR and methyl lithium. The following disulfides were prepared: R =n-C₄H₉ (73.5%), n-C₇H₁₅ (78%), Ph (77.3%), AcO(CH₂)₁₀ (81.5%).The unsymmetrical dithioacetal PhCH(SEt)SC₇H₁₅-n gave upon oxidation with one equivalent of peracid a mixture of two dithioacetal monoxides which on treatment with HClO₄ led to three disulfides. This result is discussed in term of the mechanism of acidolysis.     

Photoelectron spectra of powder and single crystalline chromium-copper disulfides

2p _3/2,1/2 Photoelectron spectra of single crystalline specimens of chromium-copper disulfides CuCrS₂ and CuCr_0.85V_0.15S₂ are studied. It is shown that the spectra of single crystalline specimens substantially differ from the corresponding spectra of chromium-copper disulfides in the powder state.     

Oxidation of Thiols Using K 2 S 2 O 8 in Ionic Liquid

A green, straightforward, and novel method for oxidation of thiols to the corresponding disulfides is reported using K ₂ S ₂ O₈ in the ionic liquid 1-butyl-3-methylimidazolium bromide [(bmim)Br] at 65–70°C. The corresponding disulfides were obtained in excellent yield and short reaction time.     

Solvent free,palladium catalyzed highly facile synthesis of diaryl disulfides from aryl thiols

An efficient solvent free Pd(pCH₂S)₂dba catalyzed green-chemical strategy for the synthesis of diaryl disulfides from aryl thiols in moderate to excellent yield is reported. Variety of diaryl disulfides were synthesized. The catalyst is recyclable up to four cycles.     

A Convenient Method for the Aerobic Oxidation of Thiols to Disulfides

Thiols are oxidized to the corresponding disulfides using K⁺/CH ₃ CN system under ambient conditions in the presence of air. This system provides a convenient, rapid, and efficient aerobic oxidative for the syntheses of symmetrical disulfides.     

Perfluoroalkylation of 2-Thiopyrimidine Derivatives

The method of perfluoroalkylation of heterocyclic thiols and disulfides by thermolytic reaction with xenon(II) bisperfluoroalkylcarboxylates has been extended to sulfur-containing pyrimidines, including 2-mercaptopyrimidines, symmetrical disulfides, and S-trifluoroacetyl derivatives obtained from the corresponding thiols. The main reaction products are 2-SC_nF_2n+1 (n = 1, 2)-substituted pyrimidines. Their formation proceeds only via disulfides into which the initial thiols and S-trifluoroacetyl derivatives are converted in the reaction medium. Side reactions occurred in the case of trifluoromethylation linked with the perfluoroalkylation of the pyrimidine nucleus at the free 5 position (in the case of the 4,6-dimethyl derivative), or at position 4 or 4 and 5 (for unsubstituted pyrimidine). In addition, the introduction of the CF₃ group at one of the methyl substituents was confirmed by the formation of CH₂CF₃ fragment.     

Simultaneous determination of thiols and disulfides by high-performance liquid chromatography with fluorescence detection

The proposed simultaneous determination of thiols and disulfides requires 4- (aminosulfonyl)- 7-fluor-2,1,3,-benzoxadiazole (ABD-F) as the pre-column derivatization reagent for thiols and ammonium 7-fluoro-2,1,3,-benzoxadiazole-4-sulfonate (SBD-F) for disulfides followed by chromatography. The thiols and disulfides in solution are treated with ABD-F at 60°C for 5 min in pH 9.3 borate buffer containing 1 nM disodium-EDTA. After removal of excess of ABD-F with ethyl acetate, the remaining disulfides in the aqueous phase are treated with SBD-F at 60°C for 20 min in the presence of tri-n-butylphosphine, a reducing agent. The ABD-thiols and SBD-thiols thus produced are separated by reversed-phase chromatography and detected by fluorimetry (380- nm excitation, 510 - nm emission). SBD-cystein, SBD-homocystein, ABD-homocysteine, ABD-cysteine, SBD-glu- tathione, ABD-homocystein, SBD-N-acetylcystein, ABD-glutatione and ABD-N-acetylcysteine are well separated by linear gradient elution from 0.15 M H₃PO₄/CH₃CN (96:4) to 0.15 M H₃PO₄/CH₃CN (85:15) over 30 min followed by isocratic elution with 0.15 M H₃PO₄/CH₃CN (85:15) fro 10 min. The detection limits for the derivatives are in the range 0.09–0.9 pmol. When the method was applied to the determination of thiols and disulfides in rat tissues, cystein (0.75 μmol g^-1) and cystine (0.62 μmol g^-1) were obtained in kidney and reduced glutathione (1.4–3.4 μmol g^-1) was observed in liver, spleen, heart and testicle.     

Reactions of thiols and organic disulfides with iron and its oxides

The influence of O₂ and H₂O on the formation of iron dithiolates (IDTs) by the reactions of thiols and organic disulfides with the iron powder was studied under the static (without mechanical activation of the reaction) and dynamic (with mechanical activation of the reaction) conditions. Under the static conditions in the absence of O₂ or H₂O, only BnSH and PhSH give IDTs, whereas DdSH (Dd is dodecyl) produces IDTs in the presence of O₂ or H₂O. For the mechanical activation of the reactions of organic disulfides with the iron powder, the formation of IDTs is possible if the reaction mixture contains H₂O. On the interaction with iron oxides excess thiols are oxidized to organic disulfides and also afford IDTs. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1383–1386, August, 2006.     

Magnetic iron oxide nanoparticles/K<Subscript>2</Subscript>S: a simple and scale-up method for the direct synthesis of symmetrical disulfides from aryl halides

A simple, one-pot, efficient and novel protocol has been developed for direct synthesis of symmetrical organic disulfides by domino reaction of aryl halides and K₂S in the presence of magnetic Fe₃O₄ nanoparticles as a readily available, highly efficient and recyclable catalyst. A variety of diaryl disulfides can be obtained in good-to-excellent yields up to 98%.     

Base-free oxidation of thiols to disulfides using selenium ionic liquid

We present here the results on the use of 1-n-butyl-3-methylimidazolium methylselenite, [bmim][SeO₂(OCH₃)], in the synthesis of symmetrical disulfides starting from thiols. This efficient and improved method is general for aromatic, aliphatic, and functionalized thiols affording the disulfides in good to excellent yields after easy work up. The use of a microwave accelerates the reaction and the [bmim][SeO₂(OCH₃)] was reused for further oxidation reactions.     

Transition-metal-free trifluoromethylthiolation and difluoromethylthiolation of thiols with trifluoromethanesulfonyl chloride and difluoromethanesulfonyl chloride

Triphenylphosphine-mediated metal-free trifluoromethylthiolation and difluoromethylthiolation of thiols by CF₃SO₂Cl and CHF₂SO₂Cl to synthesize trifluoromethyl disulfides and difluoromethyl disulfides, respectively, was achieved at room temperature. Iodine generated in situ from iodide facilitated this reaction via the formation of iodotriphenylphosphonium iodide which could serve as a reducing agent in this transformation. Readily available reagents and mild reaction conditions without transition-metals allow this protocol to be more practical than traditional methods.     

On the Reaction of Triaryl Trithioarsenites, (ArS)3As,with Octasulfur

para‐Substituted with electron donating or electron withdrawing groups triphenyl trithioarsenites, (ArS)₃As, and octasulfur in refluxing carbon disulfide or chloroform do not give the triaryl tetrathioarsenates, (ArS)₃As=S, as was claimed in the literature for tris(4‐methylphenyl) tetrathioarsenate. In some cases oxidative decomposition to As₂O₃ and disulfides ArSSAr was found. When equivalent amounts of the same esters and octasulfur were heated at 105 or 150 °C no As^V compound was detected or isolated and again some esters decomposed to As₂O₃ and disulfides. These experiments demonstrated that the aromatic trithioarsenites do not react with octasulfur, probably because they cannot open the octasulfur ring. These esters in solution react with octasulfur in the presence of a catalytic (10—20 mol%) amount of triethylamine giving disulfides, As₂O₃ and colored solids which could not be characterized.     

Phosphine-free cationic rhodium(I) complex-catalyzed disulfide exchange reaction: convenient synthesis of unsymmetrical disulfides

A phosphine-free cationic rhodium(I) complex, [Rh(cod)₂]BF₄, is an effective catalyst for disulfide exchange reaction of symmetrical disulfides to unsymmetrical disulfides under inert atmosphere. This reaction could be carried out using unpurified commercial grade solvents under air without decrease of yields and reaction rates.     

Visible-light-mediated facile synthesis of disulfides using reusable TiO2/MoS2 nanocomposite photocatalyst

A nontoxic and inexpensive TiO₂/MoS₂ nanocomposite was prepared and employed as an efficient photocatalyst for the synthesis of symmetrical disulfides under visible light irradiation at room temperature. Both aryl and alkyl thiols survived the reaction conditions, affording the corresponding disulfides in good to excellent yields. The photocatalyst could be easily recovered by simple centrifugation and filtration and reused several times without significant loss in its activity.     

XPS spectra of vanadium-doped disulfides CuCrS<Subscript>2</Subscript>

The charged state of atoms in layered cation-substituted disulfides CuCr_1?x V _x S₂ (x = 0?0.4) was studied using X-ray photoelectron spectroscopy. The study was performed with polycrystalline powder and ceramic samples of chromium-copper disulfides. CuCr_1?x V _x S₂ samples were shown to comprise differently charged atoms of chromium, copper and vanadium, the charged state of which varies with the concentration of vanadium cations (x).     

OXIDATION OF ORGANIC SULFUR COMPOUNDS WITH DINITROGEN TETROXIDE

Abstract

Symmetrical disulfides were known to be oxidized with excess N₂O₄ to the corresponding sulfonic anhydride in good yields. We have found that the oxidation of methyl phenyl disufide or an intermediate, phenyl methanethiolsulfinate undergoes via forming the unstable intermediate, i.e. the thionitrite, which are derived by the cleavage of sulfur-sulfur bond of the subsrates. The oxidation products were symmetrical disulfides, thiolsulfonates, and sulfonic acids which were undoubtedly derived from the scission of sulfur-sulfur bond.     

Copper-catalyzed direct thiolation of xanthines and related heterocycles with disulfides

A novel copper-catalyzed, base-free direct thiolation of xanthines and related heterocycles is described, featuring the use of inexpensive Cu(OAc)₂·H₂O as the catalyst, O₂ as a clean and cheap oxidant, and easy-to-handle disulfides as the thiolation reagents. It works well for both aryl and alkyl disulfides. Moreover, the resultant products can be converted into 8-(hetero)aryl- or alkenyl-substituted xanthines in good yields via the Liebeskind–Srogl coupling reaction.     

General, fast, and high yield oxidation of thiols and disulfides to sulfonic and sulfinic acids using HOF·CH3CN

Thiols and disulfides are oxidized to the corresponding sulfonic and sulfinic acids using HOF·CH₃CN. This oxidation is suitable for a variety of thiols and disulfides and proceeds under mild conditions, in short reaction times and with high yields.