Dithiocarbamates, electrochemistry

Zinc dithiocarbamates have been used for many years as antioxidants/antiabrasives in motor oils and as vulcanization accelerators in rubber. The crystal structure of bis[A, A-di- -propyldithio-carbamato]zinc shows identical coordination of the two zinc atoms by five sulfur donors in a trigonal-bipyramidal environment with a zinc-zinc distance of 3.786 A.5 5 The electrochemistry of a range of dialkylthiocarbamate zinc complexes was studied at platinum and mercury electrodes. An exchange reaction was observed with mercury of the electrode.556 Different structural types have been identified by variation of the nitrogen donor in the pyridine and N,N,N, N -tetra-methylenediamine adducts of bis[7V,7V-di- .vo-propyldithiocarbamato]zinc. The pyridine shows a 1 1 complex and the TMEDA gives an unusual bridging coordination mode.557 The anionic complexes of zinc tris( V, V-dialkyldithiocarbamates) can be synthesized and have been spectroscopically characterized.558... 

Figure 7.16 is the polarization curves of the pyrite electrode in dithiocarbamate solution at different concentration for dipping for 48 hours. Electrochemistry parameters determined by the computer PARcal are listed in Table 7.3. It can be seen from Fig. 7.16 and Table 7.3 that the corrosive potential of pyrite electrode decreases gradually from 187 to 160 mV and the corrosive current decreases from 10.78 to 6.01 xA/cm without or with the DDTC addition of 5 x 10 mol/L, while polarization resistance increases from 6.2 to 10.1 kfl with the increase of dithiocarbamate concentration. It indicates the formation of surface oxidation products. Comparing with xanthate, DDTC has less effect on corrosive potential, current and polarization resistance. It indicates that collector function of DDTC on pyrite is less than that of xanthate. 

Figure 7.41 is the polarization curves of sphalerite-carbon combination electrode in different collector solution at natural pH. The corrosive electrochemistry parameters are listed in Table 7.8. These results show that xanthate and dithiocarbamate have distinctly different effects on sphalerite. The corrosive potential and current of sphalerite electrode are, respectively, 42 mV and 0.13 pA/cm at natural pH in the absence of collector, -7 mV and 0.01 pA/cm in the presence of xanthate, and 32 mV and 0.12 pA/cm in the presence of dithiocarbamate. The corrosive potential and current decrease sharply with xanthate as a collector, indicating that the electrode surface has been totally covered by the collector film from the electrode reaction. Xanthate has big inhibiting corrosive efficiency and stronger action on sphalerite. However, the corrosive potential and current of sphalerite electrode have small change with dithiocarbamate as a collector, indicating that DDTC exhibits a weak action on sphalerite. 

There have been two books that contain compilations of the electrochemistry of Os (572,573). There have also been reviews that cover the electrochemistry of certain classes of complexes with ligands such as porphyrins (142), dithiocarbamates (463), and macrocyclic complexes (39, 93). The purpose of this section is not to provide a comprehensive review of electrochemical studies over recent years, but rather to give some insight into the factors that affect the redox potentials and their use in obtaining information about 7r bonding and backbonding. Particular emphasis is placed on the similarities and differences between analogous Os and Ru complexes. 

The rednctive electrochemistry of several Ni complexes of unsaturated dithiolate ligands has been examined. On the basis of the electrochemical redox potentials, EPR spectral evidence, and SCF calculations, these rednction products are best formulated as Ni complexes for dithiocarbamate and 1,2-dithiolene hgands, and as Ni stabihzed ligand-radical anions for dithiodiketonate species. It is often difficnlt to assign electron-density distributions within a molecnle, particnlarly with delocahzed hgands such as dithiolenes. 

Chen, W., Ghosh, D., Sun, J., Tong, M. C., Deng, F. J., Chen, S. W. Dithiocarbamate-protected ruthenium nanoparticles Synthesis, spectroscopy, electrochemistry and STM studies. Electrochim Acta 2007, 53, 1150-1156. 

In very recent work, Lieder (165) calculated standard potentials of the dithiocarbamate-thiuram disulfide redox system via thermochemical cycles and computational electrochemistry. A pathway proceeding via a single electron detachment is predicted to be the most favorable mechanism for dithiocarbamate oxidation, while thiuram disulfide reduction can proceed via two pathways. In the gas phase, reduction followed by sulfur-sulfur bond cleavage is energetically preferred, while in solution a concerted bond-breaking electron-transfer mechanism is predicted to be equally probable. 

Beer and co-workers (1468) studied the electrochemistry of a number of zinc bis(dithiocarbamate) complexes, including ferrocene derivatives 479-481 (Fig. 255). The xylyl-bridged macrocycle 480 exhibits a single reversible oxidation wave for all four ferrocene groups ( ]/2 = 0.25 V), and the ferrocene spacer groups in 479 are also oxidized reversibly in a single step ( 1/2 = 0.26 V). In contrast, 481 shows two oxidation waves (as expected), but only a single return reduction wave—the reason is as yet unknown. 

The electrochemistry of [Hg(S2CNR2)2] at mercury electrodes has been probed, with dithiocarbamate exchange occurring upon reduction (163, 607, 1891). Interestingly, two reversible one-electron oxidation processes are observed and this is believed to be associated with the oxidation of the mercury electrode producing cationic multinuclear mercury dithiocarbamate complexes... 

Electrochemistry of copper dithiocarbamate complexes in a conventional electrochemical cell... 

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