Thiuram disulfides, synthesis

I) Simple Monomeric Molybdenum Complexes. The first report on the synthesis of simple Mo dithio complexes appeared in 1971 when Mo(IV)(R2Dtc)4 complexes were obtained by CS2 insertion into Mo(NR2)4 complexes (68). Shortly after this report, the synthesis of these complexes from MoC14 and NaR2Dtc in acetonitrile was reported (88). A variety of tetrakis R2Dtc complexes of Mo(IV) also were obtained by the oxidative decarbonyla-tion of Mo(CO)6 with tetraalkyl thiuram disulfide (481,482, 609). 

These are easily prepared by the reaction of amines with carbon disulfide (1) in the presence of alkali (Scheme 17).2 The synthesis of dithiocarba mates (4) was first reported by Debus in 1850. Dithiocarba mates (4) form metal chelates, and sodium dimethyl dithiocarbamate is used in quantitative inorganic analysis for the estimation of metals, e.g. copper and zinc. Dithiocarba mates are also employed as vulcanisation accelerators and antioxidants in the rubber industry, and as agricultural fungicides.3 The parent dithiocarbamic acids are unstable, decomposing to thiocyanic acid and hydrogen sulfide however, the salts and esters are stable compounds. Dithiocarba mates (4) are oxidised by mild oxidants to the thiuram disulfides (38) (Scheme 17). 

Electrochemical oxidation and reduction of het-ero atom compounds, such as N, S, and P compounds, has been intensively studied and utilized for synthesis of many fine chemicals [1-4]. Electrooxidative S-S, S-N, S-P, and N-P bond formation is performed successfully by electrolysis of thiols, disulfide/amine, disulfide/phosphate, amine/ phosphate, and so on, affording useful chemicals, e.g., thiuram disulfide [17], sulfenamide [18], sulfenimides [19], phosphorothiolates [20], phosphoramidate [21], and so on. For instance, cross-coupling of phthalimide and dicyclohexy disulfide is performed by electrolysis in acetonitrile containing a catalytic amount of sodium bromide under a ccaistant apphed voltage (3 V, 0.7-0.9 V vs. SCE) to afford N-(cyclohexylthio)phthalimide, an important prevulcanization inhibitor in the rubber industry, in quantitative yield [19] (Fig. 4). 

Although bis(disubstitutedthiocarbamoyl) disulfides (thiuram disulfides) have been known for some time, the synthesis of the titled disulfides have never been reported. In 1977 D Amico and Morlta (60) reported that the reaction of thiocarbamoylsulfenamides (61-62) with carbon disulfide in methyl alcohol afforded either the symmetrical or previously unknown asymmetrical thiuram disulfides in 87 to 98% yield. The thiocarbamoylsulfenamides (61-62) were prepared by the oxidative condensation of a salt of a dlsubstituteddithiocarbamic acid and a secondary amine or by the reaction of the above salt with a N-chloro secondary amine. 

Thiuram disulfides, described above as photoiniferters, can also act as thermal iniferters. The mechanism of the polymerization is the same and polymer chains are invariably end-capped at both ends with iniferter segments. The use of thiurams as thermal or photoiniferters for the preparation of block copolymers greatly depends on the quantum yield of dissociation. The synthesis of dithiocarbamate functional polymers by direct photolysis of the iniferters is limited due to the low quantum yield of dissociation, especially in the case of the thiuram disulfide (e.g., the quantum yield of dissociation (rf) of TD is 0.0025 in cyclohexane [81]). This very low value makes the photochemical dissociation much less attractive than the thermal one. It was suggested that better dithiocarbamate functionalization can be achieved by either thermal initiation with TD at 95°C or polymerization in the presence of AIBN as a thermal initiator and TD as a chain transfer agent. In the latter case, monofunctional or bifunctional TD-PSt were formed, depending on the mole ratio AIBN/TD. Interestingly, the quantum yield of BDC was found to be 0.06, which is 24 times higher than that of TD. Thus, BDC can be used both as a thermal initiator and as a photoiniferter [81]. 

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