Disulfides aliphatic

3 Aliphatic Disulfides The molecular ion peak, at least up to C10 disulfides, is strong. 

As required by Table 2.3, the M + 2 peak in the spectrum of p-chlorobenzophenone (Fig. 2.12) is about one-third the intensity of the molecular ion peak (m/z 218). As mentioned earlier, the chlorine-containing fragments (m/z 141 and 113) show (fragment + 2) peaks of the proper intensity. 

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Aliphatic disulfides 4 are not particularly reactive in chain transfer towards MMA and S (Table 6.3). However, they appear to be ideal transfer agents (Cu 1.0) for VAc polymerizations. 

Aliphatic disulfides are not thought to be effective as initiators in this context. However, Endo et a . K have described the use of the cyclic 1,2-disulfides 11 and 12 as initiators in a controlled radical polymerization. Polymerization of S at 120 °C gave a linear increase in molecular weight with conversion and the PS formed was used as a macroinitiator to form PS-6/oet-PMMA. The precise mechanism of the process has not been elucidated. 

Addition of diphenyl disulfide (PhS)2 to terminal alkynes is catalyzed by palladium complexes to give l,2-bis(phe-nylthio)alkenes (Table 3)168-172 The reaction is stereoselective, affording the (Z)-adducts as the major isomer. A rhodium(i) catalyst system works well for less reactive aliphatic disulfides.173 Bis(triisopropylsilyl) disulfide adds to alkynes to give (Z)-l,2-bis(silylsulfanyl)alkenes, which allows further transformations of the silyl group to occur with various electrophiles.174,175 Diphenyl diselenide also undergoes the 1,2-addition to terminal alkynes in the presence of palladium catalysts.176... 

Cyclic peptides, self-assembly of, 24 59-60 Cyclic peroxides, 18 436, 447-448, 459 Cyclic poly(aliphatic disulfide)s, 23 712 Cyclic poly(disulfide)s, available information related to, 23 713 Cyclic polyethers, 12 658 chelating agents, 5 710 Cyclic reforming operations, 25 166 Cyclic sesquiterpenoids, biosynthetic routes to, 24 472 Cyclic siloxanes... 

This procedure affords a one-step synthesis of aromatic sul-finic esters from readily available starting materials. It is successful with a variety of types of aromatic sulfinic esters.6 The method is rather unattractive for aliphatic disulfides, however, because the nature of by-products formed makes rigorous purification of the sulfinic esters impracticable.8... 

OwenTC, Ellis DR (1973) Radiation-induced mixed-disulfide formation from cystamine and aliphatic disulfides in aqueous solution. Radiat Res 53 24-32... 

As a combined reaction of (3-cleavage of a cyclopropylcarbinyl radical and intermolecular addition, treatment of vinylcyclopropane (266) and activated alkyne in the presence of PhSSPh and AIBN forms a cyclopentene skeleton (267), through the initial addition of a thiyl radical to the vinyl group, P-cleavage of the cyclopropylcarbinyl radical, addition of the carbon-centered radical to the alkyne, ring closure of a vinyl radical via 5-exo-trig manner, and finally subsequent P-elimination of the thiyl radical, as shown in eq. 3.107 [272-276]. Here, PhSSPh acts as a catalyst, since the thiyl radical is regenerated. Aliphatic disulfides such as... 

Of the compounds (1-4) above, only the ion (4) possesses cyclic delocalization and is aromatic. Compound (1) reacts mainly as an aliphatic disulfide, while compounds (2) and (3a-d) may have intermediate properties. 

Alkyl sulfides and thiols. Some alkyl thiols and sulfides, notably those from commonly ingested Allium sativum (garlic) and Allium cepa (onion) (Alliaceae), are variously bioactive as odorants and antimicrobials. Propanethial S-oxide (CH3-CH2-CH=S=0) is a lachrymatory irritant principle of onion. Allicin (S-oxodiallydisulfide CH2=CH—CH2-SO-S-CH2— CH=CH2), diallyldisulfide (CH2=CH-CH2-S-S-CH2-CH=CH2) and diallylsulfide (CH2=CH—CH2—S—CH2-CH=CH2) are major odorants of garlic that are reactive and irritant because of the allyl groups. Dimethyl disulfide (CH3—S—S-CH3), dipropyl disulfide (CH3-CH2-CH2-S-S-CH2-CH2-CH3), methyl allyl disulfide (CH3-S-S-CH2-CH=CH2) and propane-1-thiol (CH3-CH2—CH2—SH) are further Allium odorants. Methane thiol (methyl mercaptan CH3—SH) is a widespread plant volatile and notably derives from anaerobic bacterial degradation of cysteine as in human flatus and bad mouth odour. The aliphatic disulfides allicin and ajoene inhibit proinflammatory expression of iNOS. 

Perfluoroalkyl halides can be converted into phenyl sulfides by treatment with aromatic or aliphatic disulfides under reductive conditions involving the presence of various precursors of the SO/ radical anion. ... 

Most of the studies concerning the formation and decay mechanisms of (RS.-. SR)- radical anions have been performed on aliphatic disulfides in aqueous solutions. Since the solubility of aromatic disulfides (ArS-SAr) is very poor in water, their radical anions (ArS.-. SAr)- can be easily investigated in organic solvents. A dissociation mechanism of the S-S bond in the a,a -dinapthyl disulfide radical anion (NpS.. SNp)" in dimethylformamide (DMF) solutions was investigated by pulse radiolysis and in methyltetrahydrofuran (MTHF) rigid glasses by y-radiolysis. ... 

A number of simple aliphatic disulfides were photolyzed in organic matrices at 77 °K and the spectral changes occurring during the photolysis were recorded . For primary and secondary disulfides the rates of decay of the substrate and the rate of appearance of product followed first-order kinetics and it was concluded that thiyl radicals are initially produced, viz. 

They are used the most. The first investigitions were carried out by Costanza and Pierson [68, 76] on styrene with aromatic disulfides especially. These authors showed that the aliphatic disulfides are not very reactive even though the aliphatic R—SH thiols are very good transfer agents. For instance, the transfer constant of Bu—S—S— Bu is 1.54x 10" at 55 °C [77] and 6.80x 10 at 99 °C [78]. 

More recently, the oxidation of aliphatic disulfides could be modulated (one-electron or two-electron process) according to the applied potential [295,296] and has afforded (Scheme 64) a convenient synthesis of amides. 

The alkyl groups of aliphatic disulfides are chlorinated particularly easily by elemental chlorine. For example, although dimethyl disulfide affords methanesulfenyl chloride670 at —15° to —20°, chloromethanesulfenyl chloride is formed even at 0° ... 

In the presence of aromatic hydrocarbons, primary aliphatic disulfides are cleaved under Friedel-Crafts conditions to alkyl aryl sulfides 674... 

A new easier approach to cyclic poly(aliphatic disulfide)s by catal3d ic transformation of thiiranes by (thiirane)W(CO)5 complexes has been studied (85,86). For this purpose, the new thiirane complexes such as W(CO)5(thiirane) (cl), W(CO)5(cis-dimethylthiirane) (c2), and W(CO)5(frans-dimethylthiirane) (c3) were prepared and characterized. It was found that cl, as W(CO)5(NCMe) (87) used earlier, transforms free thiirane (thiacyclopropane, ethylene sulfide) [420-12-2] (28) into a mixture of cyclic poly(disulfide)s (29), and ethylene, catalytically the compound (29a) was the major product ( 66%). Also, cis- and traras-dimethylthiirane were catalytically transformed hy c2 and c3 with the formation of small amounts of cyclic disulfides. The mechanism of these reactions has heen proposed. 

Ion series In saturated aliphatic disulfides, H2S2 and its alkyl homologues are characteristic (m/z 66, 80, 94,...). 

Formation of the (RSSR) radical cations can be achieved by oxidation of disulfides with OH radicals [157, 158]. As already indicated in Section 1.1 on thiyl radicals, this reaction enters into at least two different pathways. In the case of simple aliphatic disulfides the yields of (RSSR) amount to about 50% but appear to drop for more functionalized disulfides such as cysteine, cysteamine, and others. First, these lower yields may not be the true yields since buffer effects could have distorted the time-resolved conductivity signals by which these yields have been determined. But more importantly, additional reaction pathways may be entered. For several of these compounds weak absorptions at 374 nm have been observed indicating the possible formation of perthiyl radicals [159]. This is corroborated by the fact that the decay of this presumed RSS absorption is not accelerated by OH" addition as is the case for the (RSSR) band. 

This disulfide offers a straightforward entry to Z-l,2-bis-alkyl-sulfanyl-alkenes, which are not available in satisfying yields from aliphatic disulfides. As shown in eq 12, the protected disulfide first adds to the triple bond via a cross-coupling reaction catalyzed by Pd°. The adduct is converted through deprotection with TBAF to the bis-vinyl thiolate, which reacts with methyl iodide to give the corresponding bis-alkylsulfide (eq 12). ... 

The selective oxidation of disulfides to their mono-oxides has been achieved using Oxone and the Shi ketone catalyst 5 (Figure 19.1). The results show promising levels of enantioselectivity, but suffer from limited scope (Figure 19.13). The oxidation of aliphatic disulfides proceeded in up to 75% ee [122], and the oxidation of more stericaUy hindered hydroxyl disulfides with up to 96% ee [123],... 

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