Symmetrical sulfides

Symmetrical thioethers can also be prepared by treatment of an alkyl halide with sodium sulfide.Symmetrical thioethers have also been prepared by the reaction... 

Sulfides. Symmetrical sulfides can be prepared in high yield from the reaction of alkyl halides and sodium sulfide in water with this phase-transfer catalyst. Unsymmetrical sulfides are prepared from alkyl halides and sodium mercap-tides. Secondary alkyl halides react more slowly than primary halides bromides are more reactive than chlorides. ... 

Elemental sulfur reacts with alkanes such as cyclopentane in the presence of superacidic trifluoromethanesulfonic acid to give symmetrical dialkyl sulfides in moderate yields. 

In the oxidative Eschenmoser sulfide contraction (Scheme 11), thioamide 59 is oxidized by benzoyl peroxide to give either a symmetrical disulfide or the O-benzoate of the thiolactam-S-oxide. In any event, the once-nucleophilic thioamide sulfur atom is now forced to adopt the role of electrophile a reactivity umpolung has, in effect, been achieved.13 The nucleophilic enamide 65 attacks the sulfur atom leading to the formation of sulfur-bridged intermediate 66. The action of a phosphine or a phosphite thiophile on the putative episulfide then gives vinylogous amidine 67. 

Chlorins, e.g. 14, form adducts with osmium(VIII) oxide, which can be hydrolyzed in aqueous sodium sulfide to bacteriochlorindiols, e g. 2, or isobacteriochlorindiols, e.g. 3. Thus, similar to diimide reductions of chlorins, metal-free tetraphenylchlorin 14 (M = 2H) is selectively oxidized to a corresponding bacteriochlorin 2 whereas the zinc chlorin gives an isobac-teriochlorin 3 on oxidation with osmium(VIII) oxide.40 With less symmetrical chlorins, very complex mixtures of constitutional isomers and stereoisomers are formed by /i-bishydroxyla-tion.17... 

Metzner et al. also prepared the selenium analogue 17 of their C2 symmetric chiral sulfide and tested it in epoxidation reactions (Scheme 1.6) [8]. Although good enantioselectivities were observed, and a catalytic reaction was possible without the use of iodide salts, the low diastereoselectivities obtained prevent it from being synthetically useful. 

To control the first factor, one of the two lone pairs of the sulfide must be blocked such that a single diastereomer is produced upon alkylation. For C2 symmetric sulfides this is not an issue, as a single diastereomer is necessarily fonned upon alkylation. To control the second factor, steric interactions can be used to favor one of the two possible conformations of the ylide (these are generally accepted to be the two conformers in which the electron lone pairs on sulfur and carbon are orthogonal) [14], The third factor can be controlled by sterically hinder-... 

Due to its symmetrical structure, Pentaery-thritol Tetranitrate is highly resistant to many reagents. Thus PETN differs from the majority of nitrate esters by not being readily decompd by sodium sulfide at 50°. On the other hand, it is decompd quite quickly by boiling in a ferrous... 

Salts of dithiocarbamic acid can be prepared by the addition of primary or secondary amines to carbon disulfide. This reaction is similar to 16-9. Hydrogen sulfide can be eliminated from the product, directly or indirectly, to give isothiocyanates (RNCS). Isothiocyanates can be obtained directly by the reaction of primary amines and CS2 in pyridine in the presence of DCC. ° In the presence of diphenyl phosphite and pyridine, primary amines add to CO2 and to CS2 to give, respectively, symmetrically substituted ureas and thioureas ... 

Encapsulation in Y zeohte was also the method chosen to immobihze Mn complexes of C2-symmetric tetradentate hgands (Fig. 24) [75]. These materials were used as catalysts for the enantioselective oxidation of sulfides to sulfoxides with NaOCl. The lack of activity when the larger io-dosylbenzene was used as an oxidant was interpreted as an indication that the reaction took place inside the zeolite microporous system. Both the chemo- and enantioselectivity were dependent on the structure of the sulfide. (2-Ethylbutyl)phenylsulfide led to better results than methylphenylsulfide, although in all cases the enantioselectivity was low (up to 21% ee). 

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

Zinc sulfide, ZnS, has been epitaxially deposited by the dual bath approach on Au(lll) surface and studied by STM and XPS [48]. The first complete ECALE cycle resulted in the formation of nanocrystallites of ZnS randomly distributed across Au(l 11) terraces, on account of lattice mismatch induced strain between ZnS and Au(lll) - although the mismatch is only 0.13% for ZnS/Au(lll). Atomically resolved STM images showed the ZnS/Au(lll) monolayer to be sixfold symmetric. The average diameter of the crystallites was 10 5 nm and the apparent coverage 0.38. 

Scheme 10.88 Grignard crosscoupling of 1-phenylethylmagnesium chloride and vinyl bromide with C2-symmetric macrocyclic sulfide ligands.

Cere eta/, reported that treatment of enantiopure C -symmetric polyhydroxylated thiepane 11a with trimethylsilyl iodide resulted in a polyhydroxylated tetrahydrothiopyran 13 being formed as a single diastereomer, as shown in Equation (1) <1997JOC8572>. It was proposed that transannular sulfide interaction, and displacement of the -OH... 

Chianelli, R. R., and Berhault, G., Symmetrical synergism and the role of carbon in transition metal sulfide catalytic materials. Catal. Today, 1999. 53 pp. 357-366. 

Type G syntheses are typified by the 1,3-dipolar cycloaddition reactions of nitrile sulfides with nitriles. Nitrile sulfides are reactive 1,3-dipoles and they are prepared as intermediates by the thermolysis of 5-substituted-l,3,4-oxathiazol-2-ones 102. The use of nitriles as dipolarophiles has resulted in a general method for the synthesis of 3,5-disubstituted-l,2,4-thiadiazoles 103 (Scheme 11). The thermolysis is performed at 190°C with an excess of the nitrile. The yields are moderate, but are satisfactory when aromatic nitrile sulfides interact with electrophilic nitriles. A common side reaction results from the decomposition of the nitrile sulfide to give a nitrile and sulfur. This nitrile then reacts with the nitrile sulfide to yield symmetrical 1,2,4-thiadiazoles <2004HOU277>. Excellent yields have been obtained when tosyl cyanide has been used as the acceptor molecule <1993JHC357>. 

Oae and Numata26 were the first to postulate formation of a disulfonium dication in reaction of concentrated sulfuric acid with monosulfoxide of a bis-sulfide. Later Furukawa et al.62 found that the crystalline hydrosulfate 36 can be prepared by reaction of the corresponding monosulfoxide 13 (or A-tosyli-mide 14) with concentrated sulfuric acid. Formation of a symmetric dication 38 was confirmed by isolation of 1 1 mixture of deuterated sulfoxides 37 and 39... 

If an unsaturated trapping agent is not present, however, things get really complicated. First, the sulfenic acid RSOH formed in (57) can form thiolsulfinate RS(0)SR and water (24). If the initial thiolsulfinate is an un-symmetrical one, RS(0)SR, this will mean that the symmetrical thiolsulfinate RS(0)SR will begin to appear in the reaction mixture. Second, in some way, perhaps aided by reaction of some of the water formed in (24) with thiolsulfinate, traces of acid become present in the solution. This acid catalyzes a complex disproportionation of alkyl thiolsulfinates that parallels in a number of important aspects the mechanism of the acid- and sulfide-catalyzed disproportionation of aryl thiolsulfinates already discussed. The steps that are important in this disproportionation are shown in (61)—(66). 

I. Inorganic sulfur compounds containing another (usually more electropositive) element. When the other element is an alkali or alkaline earth, the sulfide is ionic in character. Metal sulfides often have unusual stoichiometries. Examples of sulfides include H2S, Na2S, FeS, and HgS. 2. Organic sulfides are also referred to as thioethers and have the general structure R—S—R. Biochemical examples of sulfides include methionine, cystathionine, and djenkolic acid. If the two R groups are identical, the substance can be referred to as a symmetrical sulfide (biological examples of which are lanthionine and homo-lanthionine). 

At the time of the earlier review (66HC1155), it was already known that combinations of arenes with sulfur, or with sulfur mono- or dichlorides in the presence of Lewis acids (IV,B,1), or of aryl thiols, diaryl sulfides, or disulfides (IV,B,2 and 3) again heated with Lewis acid catalysts, generate thianthrenes, sometimes in acceptable preparative yields. A complimentary method is the treatment of aryl thiols with c. H2SO4. Routes from arenes and aryl thiols almost certainly involve the initial formation of diaryl sulfides. All these methods inevitably give symmetrical thianthrenes carrying identical substituents on each benzene ring (Scheme 9), unless the second sulfur is introduced in a controlled fashion into a preformed, unsymmetrical diphenyl sulfide. 

The design of a new Ci-symmetric bis-hydroxamic acid (BHA) ligand has also accomplished the successful asymmetric oxidation of unfunctionalized olefins " and sulfides (Scheme 103). 

Harris, R. K., Woplin, J. R, Murray, M., Schmutzler, R. Preparation and nuclear magnetic resonance spectra of symmetrical spin systems containing phosphorus bis(fluorophosphinothioyl) sulfides. J. Chem. Soc. Dalton 1972, 1590. 

Symmetrical dialkyl 1,2,4-trithiolanes can be prepared by reaction of di-a-chloroalkyl sulfides (145) with Na2S or ring contraction of the tetrathiepane (146) using nucleophilic reagents such as triphenylphosphine or cyanide (Scheme 41). Both methods give cisjtrans mixtures and most examples of the latter involve R = aryl <88CL1517>. 

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