Disulfides from alkyl halides

Thiol (s), 652, 667-668 disulfides from, 668 electrostatic potential map of, 75 from alkyl halides, 667 hybridization of, 20 naming, 667 odor of, 667 oxidation of, 668 pKa of, 604... 

Silver salts are also utilized to perform nucleophilic additions to disulfide bonds to yield sulfenamides (146). If alkyl halides are treated with stoichiometric AgBF4 in dimethyl sulfoxide solvent (DMSO, solvent), the corresponding aldehydes/ ketones will form in good yields. This reaction is an alternative to the well-known Swern oxidation (147). In addition, silver can drive the formation of dialkylper-oxonium ions from alkyl halides, which then oxidizes sulfoxides or sulfides (148,149). In the presence of AgN03, sulfides can be oxidized into a-chloro sulfoxides by SO2CI2 (Fig. 36) (150). 

Pyrrolethiols, readily obtained from the corresponding thiocyanates by reduction or treatment with alkali, rapidly oxidize to the corresponding disulfides. They are converted into thioethers by reaction with alkyl halides in the presence of base. Both furan- and thiophene-thiols exist predominantly as such rather than in tautomeric thione forms. 

The stannylenes from either source will insert into the Sn- Sn, Sn-R, or Sn-H bonds of organotin compounds, and react with alkyl halides, disulfides, or peroxides as shown in the reaction scheme below, but only the stannylenes that are generated photolytically will react with carbonyl compounds, and it appears that the stannylenes may exist in two forms, perhaps related as singlet and triplet, or a com-plexed and uncomplexed species. 

Strong caustic solutions penetrate the crystal lattice of alpha cellulose and produce an alkoxide called alkali, or soda, cellulose. Mercerized cotton is produced by aqueous extraction of the sodium hydroxide from alkali cellulose fibers. Cellulose ethers and cellulose xanthate are produced by reactions of alkyl halides or carbon disulfide, respectively, with the alkali cellulose. 

Alkylation of an ethanolic solution of sodium sulfide containing an equivalent amount of dissolved sulfur produces disulfides in 60-80% yields from alkyl" or o- and p-nitrophenyl halides." Cyclic disulfides are prepared by alkylation with 1,3-dihalides." Hydroxyl" and nitro" groups do not interfere. Alkylation of a solution of sodium sulfide containing 2-5 equivalents of sulfur produces polysulfides. 

Sodium thiosulfate reacts with alkyl halides to form salts of the type RSSOjNa (Bunte salts). Alkyl disulfides may be obtained from these salts by pyrolysis or reaction with iodine or hydrogen peroxide. The yields range from 47% to 6S>%. Cyano and carboxyl groups do not interfere. Benzoylation of sodium thiosulfate produces benzoyl disulfide in 58% yield. ... 

Symmetrical disulfides (73) may be prepared by reaction of alkyl halides with disodium disulfide (Scheme 43). The product is contaminated with triand polysulfides owing to the presence of impurities in the disodium disulfide however, lower members of the series of dialkyl disulfides may be purified by fractional distillation. Disulfides can also be obtained from thiols by mild oxidation, e.g. by treatment with iodine or dimethyl sulfoxide (DMSO) (Scheme 44). In the reaction with iodine, the hydriodic acid formed must be removed, otherwise the disulfide is largely reduced back to the thiol by hydriodic acid which is a powerful reducing agent. Pure unsymmetrical disulfides are more difficult to prepare owing to their tendency to undergo disproportionation they can, however, be synthesised from thiols by treatment with imides (see p. 59) or sulfenyl halides (51) (Scheme 45). 

Alkyldithio carbamates are prepared from the acid chloride (EtsN, EtOAc, 0°C) and amino acid, either free or as the O-silyl derivatives (70-88% yield). They may also be prepared by the addition of carbon disulfide to the amine which can then be alkylated with an alkyl halide using CS2CO2 as the base. The A-(i-propyldithio) carbamate has been used in the protection of proline during peptide synthesis. Alkyldithio carbamates can be cleaved with thiols, NaOH, PhsP/TsOH. They are stable to acid. Cleavage rates are a function of the size of the alkyl group as illustrated in the table below. 

Dipotassium cyanodithioimidocarbonate (269) is readily produced from cyanamide and carbon disulfide in alkali, and affords the S-alkyl derivatives (280) in good yield upon treatment with a variety of primary and secondary alkyl halides.219,220 The action of chlorine converts the parent salt (269) to 3-chloro-l,2,4-thiadiazole-5-sulfenyl chloride(282,85-100%), and the bromo analog is similarly accessible.209,221,222 Dipotassium perthiocyanate (270, obtained from 269 and sulfur209) is chlorinated to the stable bissulfenyl... 

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