Metal xanthate

Alkali metal xanthates are prepared in high yield from reaction of amyl alcohols with alkah metal hydroxide and carbon disulfide (39—42). The xanthates are useful as collectors in the flotation of minerals and have minor uses in vulcani2ation of mbber and as herbicides (39,41). 

Table 3. Decomposition Temperatures of Alkali Metal Xanthates ...

When exposed to ait, the sodium salts tend to take up moisture and form dihydrates. The alkah metal xanthates are soluble ia water, alcohols, the lower ketones, pyridine, and acetonitrile. They are not particularly soluble ia nonpolar solvents, eg, ether or ligroin. The solubiUties of a number of these salts are Hsted ia Table 4. Potassium isopropyl xanthate is soluble ia acetone to ca 6 wt %, whereas the corresponding methyl, ethyl, / -propyl, n-huty isobutyl, isoamyl, and benzyl [2720-79-8] xanthates are soluble to more than 10 wt % (12). The solubiUties of the commercially available xanthates ia water are plotted versus temperature ia Figure 1 (14). 

The alkah metal xanthates react readily with the various alkylating reagents to form the testers ... 

Many oxidizing agents, including sodium nitrate, convert the alkaU metal xanthates to the corresponding dixanthogen ... 

In the initial formation of the cupric xanthates, soluble xanthate complexes form prior to the precipitation of the cuprous xanthate with the concurrent formation of the dixanthogen (51). The dixanthogen can be separated by virtue of its solubiUty in ether. Older samples of alkah metal xanthates contain some dixanthogen, which is thought to form by the following reaction (33) ... 

The alkali metal xanthates react with the lower alkylamines ia the presence of catalytic amounts of nickel or palladium salts to give dialkjdthionocarbamates (62) ... 

The alkah metal xanthates are generally prepared from the reaction of sodium or potassium hydroxide with an alcohol and carbon disulfide. The initial reaction is the formation of the alkoxide, which reacts with carbon disulfide to give the xanthate ... 

Many of the heavy metal xanthates have been piepaied from aqueous solutions of the alkah metal xanthates and the water-soluble compound of the heavy metal desired. 

Alkali Metal Xanthates. The commercially available xanthates are prepared from various primary or secondary alcohols. The alkyl group varies from to and the alkah metal may be sodium or potassium. Not all of the commercially available alcohols ia the range are available as... 

In addition to a continued increase in the number of use patents in these fields, a new use of xanthates as inhibitors of fertiliser nitrogen transformation in soil has been reported, as well as the use of certain metal xanthates as color developers for image-recording materials (113,114) (see Fertilizers Color photography). For several years, sodium isopropyl xanthate was used as an intermediate in the manufacture of saccharin (see... 

Many alkali-metal xanthates are formed by direct xanthation of alcohols (23), but their chemistry is still vague. Acidification of the alkali-metal salts produces the unstable xanthic acids (24). 

The adsorption of collectors on sulfide mineral occurs by two separate mechanisms chemical and electrochemical. The former results in the presence of chemisorbed metal xanthate (or other thiol collector ion) onto the mineral surface. The latter yields an oxidation product (dixanthogen if collector added is xanthate) that is the hydrophobic species adsorbed onto the mineral surface. The chemisorption mechanism is reported to occur with galena, chalcocite and sphalerite minerals, whereas electrochemical oxidation is reportedly the primary mechanism for pyrite, arsenopyrite, and pyrrhotite minerals. The mineral, chalcopyrite, is an example where both the mechanisms are known to be operative. Besides these mechanisms, the adsorption of collectors can be explained from the point of interfacial energies involved between air, mineral, and solution. 

The anionic species ROCS2 resulted from O-alkyl(aryl) esters of the hypothetical dithiocarbonic acids, ROC(S)SH, better known as xanthates, are versatile ligands and they generate an extensive coordination chemistry. The interest for metal xanthates is stimulated by their potential use as single source precursors for nanoscopic metal sulfides in photochemical or thermal vapor deposition systems under mild conditions,218 221 e.g. for Zn,222 Cd,223 In,224... 

The synthesis of alkali metal xanthates from trimethylsilyl dithiocarboxylates and alkali metal fluorides317 has been described as convenient and useful for preparative purposes of metal complexes and organometallic derivatives. 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

According to the mixed potential theory, an anodic reaction can occur only if there is a cathodic reaction proceeding at finite rate at that potential (Rand and Woods, 1984). For the flotation systems, the cathodic reaction is usually given by the reduction of oxygen. The corresponding anodic reaction involves interaction of xanthate on the sulphide minerals in various ways, including the reaction of xanthate with the sulphide mineral (MS) to form metal xanthate and the oxidation of xanthate to dixanthogen (X2) at the mineral surface. 

The mixed potential of the sulphide mineral in the flotation pulp will determine the oxidation product on its surface. If the mixed potential of the mineral in the presence of oxygen, xanthate and other reagents is above the mixed potential for the X7X2 redox couple, then the reaction will produce dixanthogen on the surface. If the mixed potential is lower than the X /Xz redox couple, metal xanthate reaction will take place rendering the surface hydrophobic. 

Epiaulfides are considered to be intermediates in the formation of trifhiocarbonateB from metallic xanthates and epoxides1 57 (Eq. 61). 

TABLE 1. SOLUBILITIES OF SOME ALKALI-METAL XANTHATES... 

The alkali metal xanthates are generally prepared from the reaction of sodium or potassium hydroxide with an alcohol and carbon disulfide. 

The alkali metal xanthates are fairly safe to handle. The standard precautions of rubber gloves, dust mask, and goggles arc sufficient when handling tile solid 01 the solution. 

The ligand field strength of the ligands is between that of the dithiocarbamates and water.49 IR studies show characteristic bands near 1250, 1100, 1020 and 550 cm-1.93 The contribution of the resonance form (85) in transition metal complexes is less than that of the analogous structure in the dithiocarbamates.60 The electron density on the metal is not very high, which accounts for the fact that abnormal high oxidation states are exceptional and a strong interaction of bases with the square planar nickel (and some other metal) xanthates is found.94... 

As very few examples of metal haloxanthates are known, the preparation of copper(II) halo-xanthates is worthy of mention.96 Pyrolytic decomposition of metal xanthates has been found to produce alkenes.97... 

Stereochemical Aspects of Metal Xanthate Complexes Molecular Structures and Supramolecular Self-Assembly... 

In this chapter, we will emphasize aspects of supramolecular self-assembly of metal xanthates, in particular for series of closely related structures. Self-assembly is a feature frequently observed in numerous xanthato complexes of soft metals, but this feature has often been ignored in the primary literature. 

There are two types of objects in supramolecular chemistry supermolecules (i.e., well-defined discrete oligomolecular species that result from the inter-molecular association of a few components), and supramolecular arrays (i.e., polymolecular entities that result from the spontaneous association of a large, undefined number of components) (4, 5). Both are observed in some metal-xanthate structures to be described herein. The most frequent intermolecular forces leading to self-assembly in metal xanthates are so-called secondary bonds . The secondary bond concept has been introduced by Nathaniel W. Alcock to describe interactions between molecules that result in interatomic distances longer than covalent bonds and shorter than the sum of van der Waals radii (6). Secondary bonds [sometimes called soft-soft interactions (7)] are typical for heavier p-block elements and play an important role as bonding motifs in supramolecular organometallic chemistry (8). Other types of intermolecular forces (e.g., Ji- -ji stacking) are also observed in the crystal structures of metal xanthates. 

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