Complexes disulfide, metal

AEROPHINE 3418A promoter is widely used ia North and South America, AustraHa, Europe, and Asia for the recovery of copper, lead, and ziac sulfide minerals (see Elotatton). Advantages ia comparison to other collectors (15) are said to be improved selectivity and recoveries ia the treatment of complex ores, higher recoveries of associated precious metals, and a stable grade—recovery relationship which is particularly important to the efficient operation of automated circuits. Additionally, AEROPHINE 3418A is stable and, unlike xanthates (qv), does not form hazardous decomposition products such as carbon disulfide. It is also available blended with other collectors to enhance performance characteristics. 

Carbon monosulfide [2944-05-0] CS, is an unstable gas produced by the decomposition of carbon disulfide at low pressure ia a silent electrical discharge or photolyticaHy (1 3) ia the presence or absence of sulfur (3). It decomposes with a half-life of seconds or minutes to a black soHd of uncertain composition (1—3). The monosulfide can be stabilized ia a CS2 matrix at — 196°C, and many stable coordination complexes of CS with metals have been prepared by iadirect means (8). 

SoHd lubricants ate added to help control high friction characteristics in high speed or heavy-duty appHcations where high temperatures are generated. Molybdenum disulfide [1317-33-5] M0S2, may be used alone or in a complex compound formed by grinding with fine natural graphite, and zinc sulfide [1314-98-3] ZnS. Other compounds include calcium fluoride, cryoHte [15096-52-3] Na AlF, rare-earth oxides, and metal sulfides, eg, iron, antimony, or zinc (see LUBRICATION AND LUBRICANTS). 

Other radical reactions not covered in this chapter are mentioned in the chapters that follow. These include additions to systems other than carbon-carbon double bonds [e.g. additions to aromatic systems (Section 3.4.2.2.1) and strained ring systems (Section 4.4.2)], transfer of heteroatoms [eg. chain transfer to disulfides (Section 6.2.2.2) and halocarbons (Section 6.2.2.4)] or groups of atoms [eg. in RAFT polymerization (Section 9.5.3)], and radical-radical reactions involving heteroatom-centered radicals or metal complexes [e g. in inhibition (Sections 3.5.2 and 5.3), NMP (Section 9.3.6) and ATRP (Section 9.4)]. 

This exemplified that the oxidative addition of S-S bond to a low-valent metal complex is one prototype to initiate a reaction using a disulfide. In 1987, Uemura et al. reported an analogous transformation using (PhSe)2 instead of (PhS)2 to afford the phenyl selenobenzoate 58 in up to 78% yield under 100 atm of CO in benzene at 200°C (Eq. 7.44) [50]. 

In dithiocarbamato complexes such an ambiguity can only occur when at least two dithiocarbamato ligands are bonded to a metal. In that case the question arises whether the compound is a bis (dithiocarbamato) or a thiuram disulfide complex. In these two types of complexes the oxidation number of the metal differs 2 units. 

The reaction of metallic copper with thiuram disulfides yields complexes of Cu I), which are polymeric in solution as well as in the solid state 121,122). In 123) the copper atoms are located at the corners of a slightly distorted tetrahedron with Cu—Cu distances ranging from 2.6—2.7 A. Each of the copper atoms is coordinated to three sulfur atoms in a nearly planar triangular arrangement and each sulfur atom coordinates one or two copper atoms. 

Oxidation of these complexes with halogen results in the oxidation of the ligand, yielding a thiuram disulfide complex X2M(R4tds), leaving the oxidation state of the metal unchanged (99,100,161). 

GC/FPD has been used to measure hydrogen sulfide, free disulfide, and dissolved metal sulfide complexes in water (Radford-Knoery and Cutter 1993). Hydrogen sulfide was measured in the headspace of the sample (100 mL) with a detection limit of 0.6 pmol/L. A detection limit of 0.2 pmol/L was obtained for total dissolved sulfide. This method allows for the determination of the concentration of free sulfide that is in equilibrium with hydrogen sulfide. Complexed sulfide can be estimated from the difference between total dissolved sulfide and free sulfide. 

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