Reaction with xanthates

Many diazonium solutions have been reported to react explosively with solutions of metallic polysulfides even at low temperatures.12 A violent reaction with xanthates is mentioned only in one report.3 Neither the authors nor the checkers observed any unusual reactivity during this preparation or with the procedure given for dithiosalicylic acid.4 On a large scale (100 moles of wi-toluidine) flashes of light have been occasionally observed (private communication, L. J. Roll). 

Quite frequently the natural surface of a mineral requires preliminary chemical treatment before it will form the surface film required for collection One of the commonest instances of this is with sphalerite (zinc sulphide), which does not float properly when treated with xanthates. If, however, it is given a preliminary treatment with dilute copper sulphate solution, a very small amount of copper sulphide is deposited on the surface and the ore becomes floatable, the surface being now capable of reaction with xanthates. Such treatment is usually termed activation in general, an activating solution for a sulphide mineral should contain a metallic ion whose sulphide is less soluble than that contained in the mineral for zinc sulphides, silver, copper, mercury, cadmium, and lead salts are all effective activators. 

Reaction with xanthates. The nature of the products varies according to the... 

Dithiole-2-one (60), which can be readily transformed into its thio- or seleno-carbonyl derivatives, is a key intermediate for the synthesis of tetrathiafulvalene (Scheme 13)[31]. We first anticipated that compound 57, a Michael addition product of xanthate 54 to vinyl sulfoxide, might be an ideal intermediate for the synthesis of 60 via cyclization under Pummerer rearrangement conditions. However, although Michael addition of dithiocarbamate 53 to vinyl sulfoxide proceeded smoothly to yield compound 55, the addition reaction with xanthate 54 failed. We then turned to the alkylation approach. Xanthate 54 was alkylated smoothly with 56, which served as the synthetic equivalent of the vinyl sulfoxide, in ethanol under sonication in 90% yield [32]. Cyclization of 57 under Pummerer rearrangement conditions in the presence of trifluoroacetic acid afforded 58 in 79% yield. Sodium metaperiodate oxidation gave the unstable sulfoxide 59 which underwent thermal elimination to yield 60 in refluxing benzene in moderate yield. 

A final consideration is that Z should not cause any side reactions. With xanthates (4, Z = OR ) it is important that R be a poor homolytic leaving group. Otherwise fragmentation with loss of R (irreversible chain transfer) will compete with the desired RAFT process. This requires that R be primary alkyl or aryl. Similar design consideration apply in the case of unsymmetrical trithiocarbonates (4, Z = SR )- ... 

Carbon disulfide [75-15-0] is a clear colorless liquid that boils at 46°C, and should ideally be free of hydrogen sulfide and carbonyl sulfide. The reaction with alkaU cellulose is carried out either in a few large cylindrical vessels known as wet chums, or in many smaller hexagonal vessels known as dry chums. In the fully continuous viscose process, a Continuous Belt Xanthator, first developed by Du Pont, is used (15). 

The reaction of xanthates with phosgene proceeds through the following steps (49,50) ... 

In the Leuckart thiophenol synthesis, the reaction of xanthates with dia2onium compounds may be violent. The reaction can be controlled. 

Industrially important dithiocarbonates (xanthates) result from reaction with various alcohoHc alkaHes ... 

Of great commercial significance is preparation of sodium ceUulose xanthate [9032-37-5] solution (viscose) by reaction with alkaH ceUulose ... 

Ethyl chloroformate is used in the manufacture of ore flotation agents by reaction with various xanthates (48). 

The required xanthates 1 can be prepared from alcohols 5 by reaction with carbon disulfide in the presence of sodium hydroxide and subsequent alkylation of the intermediate sodium xanthate 6. Often methyl iodide is used as the alkylating agent ... 

Diazomethane, reaction with 2,4,6-tri-nitrobenzenesulfonic acid and dimethyl ether, 46,122 Diazonium xanthates, detonation of, 47, 107... 

In (362), the cation is distorted trigonal pyramidal with the axial positions occupied by one S atom and the central P atom of the P3 ligand. In the anion the nickel center is bonded to six S-donors of three xanthate ligands. Upon reaction with dppe an approximately square planar NiS2P2 complex results.938 A similar coordination geometry is found for the two complexes (361a,b) 939,940... 

R R2CHOH -> RlR2CHCl. This transformation can be effected with retention of configuration in two steps conversion to the methyl xanthate followed by reaction with sulfuryl chloride (equation I). 

Transformation of 2-deoxysugar derivatives into glycosyl xanthates can be performed by the treatment of O-benzyl-protected hemiacetal derivative with diphe-nylphosphoryl chloride, followed by the reaction with O-ethyl potassium xanthate in the presence of a base (NaOH, PTC reaction or NaH in appropriate organic solvent). High yields and selectivities in such reactions were observed when using sodium hydride in anhydrous THF [401],... 

Metal Ion Initiation on Cellulose Xanthate. Vinyl monomers can be grafted to cellulose at high rates by reaction with cellulose xanthate using v5+, Fe + and Cr + as redox initiators l. 

The standard conversion of alcohols into their xanthate esters through reaction with carbon disulphide and an alkylating agent is improved by the addition of a quaternary ammonium salt [69]. Excellent yields (>90%) are obtained in relatively short reaction times under mild conditions. The formation over relatively short reaction times of O-glycosyl xanthates from partly protected glycosides has been described using a stoichiometric amount of the quaternary ammonium salt [70]. 

It is noteworthy that the absolute rate constants for the reaction of the benzophenone triplet with Et3SiH, n-C5HnSiH3, PhSiH3, and Cl3SiH have been measured by LFP,56 and comparison of the kinetic data with corresponding data for reactions of /-BuO radicals shows that these two transient species have a rather similar reactivity toward silanes. Furthermore, the xanthate and the p-methoxyacetophenone triplets were found to be more and less reactive, respectively, than the benzophenone triplet with Et3SiH.56 Similar behavior of excited states in reactions with tin hydrides is discussed in Section V. 

Figure 6.10 Xanthation of cellulose followed by reaction with hydrogen peroxide to generate a radical.

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. 

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