Xanthates mercaptans

In recent studies, a new line of PGM collectors had been developed [13] known as the PM series. These collectors are an ester-modified mixture of xanthate + mercaptan. The reaction product forms an oily greenish-coloured liquid. The results obtained using the PM series of collectors are shown in Table 18.5. High PGM recovery was obtained using a combination of sodium amyl xanthate plus collector PM301. 

Solubility products of collector-metallic ion compounds (see Appendix C) suggest that the sulfide mineral collectors such as xanthates, mercaptans and thiophosphates containing sulfur bonding atom in the minerophilic group can form compounds of low solubility products with ions of elements with affinity for copper(II). They can not form insoluble... 

The described method of preparation of w-nitrophenyl disulfide is essentially that of Foss and co-workers and is a modification of that reported by Ekbom. The disulfide has been prepared by reaction of potassium ethyl xanthate with w-nitrobenzenedi-azonium chloride solution, followed by hydrolysis to yield the mercaptan, which is subsequently oxidized with potassium ferro-cyanide or dilute nitric acid to the disulfide. ... 

Xanthates (e.g. EtOCSSK) discovered by W. C. Zeise who also prepared the first mercaptan (EtSH) in 1834 (see also p. 930). 

All reactions of benzotriazole derivatives of the type Bt-CR RbS discussed above are based on electrophilic or nucleophilic substitutions at the ot-carbon, but radical reactions are also possible. Thus, the first report on unsubstituted carbon-centered (benzotriazol-l-yl)methyl radical 841 involves derivatives of (benzotriazol-l-yl)methyl mercaptan. 3 -(Benzotriazol-l-yl)methyl-0-ethyl xanthate 840 is readily prepared in a reaction of l-(chloromethyl)-benzotriazole with commercially available potassium 0-ethyl xanthate. Upon treatment with radical initiators (lauroyl peroxide), the C-S bond is cleaved to generate radical 841 that can be trapped by alkenes to generate new radicals 842. By taking the xanthate moiety from the starting material, radicals 842 are converted to final products 843 with regeneration of radicals 841 allowing repetition of the process (Scheme 134). Maleinimides are also satisfactorily used as radical traps in these reactions <2001H(54)301>. 

The primary collector used in PGM flotation is xanthate. As a choice of secondary collectors, dithiophosphates and mercaptans are used in some operating plants. 

The highest PGM recovery was achieved using sodium amyl and sodium isobutyl xanthate. Using a mercaptan collector alone gave poor PGM recovery. However, when using xanthate with mercaptan, substantial improvement in PGM recoveries was achieved. 

The reagent scheme generally used in these concentrators is presented in Table 19.9. Sodium silicate is used as the common depressant, and also acts as a dispersant together with the soda ash. In the majority of operating plants, Na2S 9H20 is used as the principal activator. Some operating plants in Zambia use NaHS as a sulphidizer. Sodium or potassium xanthates are the principal collectors used, where mercaptans are used as secondary collectors. 

During oxide lead flotation, the choice of collector is rather limited to xanthates, which are used in operating plants. Dithiophosphates and mercaptans are used as secondary collectors. This is due to the fact that natural ores contain a variety of floatable gangues, for which the anionic flotation process is not applicable. The use of chelating agents as flotation collectors for oxide lead flotation have been extensively examined [5,6], Oximes/fuel oil... 

In plant practice, lead oxide minerals are recovered using a sulphidization method with xanthate as the primary collector and mercaptans as the secondary collector. 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

Amphipathic substances such as we have discussed throughout this chapter are used as collectors. Alkyl compounds with C8 to C18 chains are widely used with carboxylate, sulfate, or amine polar heads. For sulfide minerals, sulfur-containing compounds such as mercaptans, monothiocarbonates, and dithiophosphates are used as collectors. The most important collectors for sulfides are xanthates, the general formula for which is... 

The Leuckart Thiophenol Reaction allows the preparation of thiophenols and corresponding thioethers from anilines or their corresponding diazonium salts. The first step is the reaction of an aryl diazonium salt with a potassium alkyl xanthate to give an aryl xanthate, which affords an aryl mercaptan upon basic hydrolysis or an aryl thioether upon warming. 

Thermal decomposition of methyl xanthates is similar to the pyrolysis of acetates for the formation of the double bond. Olefins are obtained from primary, secondary, and tertiary alcohols without extensive isomerization or structural rearrangement. The other products of the pyrolysis of the methyl xanthates are methyl mercaptan and carbon oxy-sulfide. The xanthates prepared from primary alcohols are more difficult to decompose than those prepared from secondary and tertiary alcohols. Over-all yields of 22-51% have been obtained for a number of tertiary alkyl derivatives of ethylene. Originally the xanthates were made by successive treatment of the alcohol with sodium or potassium, carbon disulfide, and methyl iodide. In a modification of this procedure sodium... 

The kinetic isotope effects in the gas phase which could distinguish between mechanisms 1 and II have not been measured. However, solution xanthate decompositions, when performed with labeled sulfur and carbon atoms, support mechanism I. These decompositions, which give mercaptan, olefin and COS, are completely analogous to carbonate decomposition. 

Since alkyl halides can be converted to mercaptans, thioethers, xanthates, or thiouronium compounds, the ready removal of these groups offers another... 

Halide ions, S , mercaptans Halide ions, xanthate Metal ions... 

Ammonium Sulfate Amoxicillin Butyl Mercaptan Calcium Sulfate Cellulose Xanthate Copper(II) Sulfate Magnesium Sulfate Mercury(II) Sulfide Methyl Mercaptan Penicillin... 

Mercaptans — Sulpho compounds — Sodium isethionate — Methyl-sulphuric acid—Potassium-trichlorrmethyl sulphate — Potassium-trichlor-methyl sulphonate — Ethyl-sulphuric acid—Potassium-isoamyl sulphate—Potassium xanthate—Dimethyl-dithiocarbamic acid.47 49... 

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