Alkali metal xanthates

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 ...

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

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... 

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 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. 

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. 

Many of the heavy metal xanthates have been prepared from aqueous solutions of the alkali metal xanthates and the water-soluble compound of tlie heavy metal desired. 

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. 

Carbon disulfide is the dithio derivative of C02. It is only a weak electrophile. Actually, it is so unreactive that in many reactions it can be used as a solvent. Consequently, only good nucleophiles can add to the C—S double bond of carbon disulfide. For example, alkali metal alkoxides add to carbon disulfide forming alkali metal xan-thates A (Figure 7.4). If one were to protonate this compound this would provide compound B, which is a derivative of free dithiocarbonic acid. It is unstable in the condensed phase in pure form, just as free carbonic acid and the unsubstituted carbamic acid (Formula B in Figure 7.3) are unstable. Compound B would therefore decompose spontaneously into ROH and CS2. Stable derivatives of alkali metal xanthates A are their esters C. They are referred to as xanthic add esters or xanthates. They are obtained by an alkylation (almost always by a methylation) of the alkali metal xanthates A. You have already learned about synthesis applications of xanthic acid esters in Figures 1.32, 4.13, and 4.14. 

When exposed to air, the sodium salts tend to take up moisture and form dihydrates. The alkali metal xanthates are soluble in water, alcohols, the lower ketones, pyridine, and acetonitrile. They are not particularly soluble in nonpolar solvents, eg, ether or hgroin. The solubiHties of a number of these salts are Hsted in Table 4. Potassium isopropyl xanthate is soluble in acetone to ca 6 wt %, whereas the corresponding methyl, ethyl, -propyl, -butyl, isobutyl, isoamyl, and ben2yl [2720-79-8] xanthates are soluble to more than 10 wt % (12). The solubiHties of the commercially available xanthates in water are plotted versus temperature in Figure 1 (14). 

The alkali metal xanthates react readily with the various alkylating reagents to form the i -esters ... 

Many oxidizing agents, including sodium nitrate, convert the alkali 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 solubility in ether. Older samples of alkali metal xanthates contain some dixanthogen, which is thought to form by the following reaction (33) ... 

The alkali 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 ... 

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