Xanthates, thermal decomposition

The heavy metal salts, ia contrast to the alkah metal salts, have lower melting points and are more soluble ia organic solvents, eg, methylene chloride, chloroform, tetrahydrofiiran, and benzene. They are slightly soluble ia water, alcohol, ahphatic hydrocarbons, and ethyl ether (18). Their thermal decompositions have been extensively studied by dta and tga (thermal gravimetric analysis) methods. They decompose to the metal sulfides and gaseous products, which are primarily carbonyl sulfide and carbon disulfide ia varying ratios. In some cases, the dialkyl xanthate forms. Solvent extraction studies of a large number of elements as their xanthate salts have been reported (19). 

The Chugaev reaction, or thermal decomposition of the substituted esters of the xanthates, gives olefins without rearrangement (35,36). For example ... 

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... 

Unsaturated derivatives of cellulose containing double bonds directly in the pyranose ring have b n synthesized by the thermal decomposition of cellulose methylxanthate or bis-xanthate (39,40), which proceeds as follows ... 

Alkenes are formed by the thermal decomposition of esters, xanthates, amine oxides, sulfoxides, and selenoxides that contain at least one (3-hydrogen atom. These elimination reactions require a cw-configuration of the eliminated group and hydrogen and proceed by a concerted process. If more than one (3-hydrogen is present, mixtures of alkenes are generally formed. Since these reactions proceed via cyclic transition states, conformational effects play an important role in determining the composition of the alkene product. 

The xanthates are stable in the solid state, but in acidic aqueous solutions they are readily decomposed into the starting materials. The thermal decomposition of xanthates can be a useful route to metal sulfides,197 e.g., using the CVD technique.198 Nickel xanthates serve as precursors for photochemical (laser) and thermal vapor deposition of metal sulfide films.199... 

Reactions of diaryliodonium salts with various organochalcogen anions led to the arylchalcogen derivatives. (Table 5.7) The anions of sulfur compounds afford generally the 5-aryl derivatives. Sometimes the intermediate iodanes can be isolated. Examples are the reaction of dithiocarbamate and xanthate salts with diaryliodonium. Upon heating, the dithiocarbamate derived iodane afforded the aryldithiocarbamates.133 Thermal decomposition of the xanthate derived iodanes gave mixtures of arylxanthates and diaryldisulfides. ... 

Hill and co-workers studied the thermal decomposition of a large number of metal complexes of various alkyl derivatives of xanthic and dithiocarbamic acids. The complexes were studied by using TG. DSC. and other TA techniques. Compounds investigated included Nil IB alkyl xanthates (79), Cu(II) dithiocarbamate complexes (80), dihalotin (IV) bisdiethyldithio-carbamates (81), bisldiethyldithiocarbamatoi diphenyl tin (IV) (82), tetrakis-(diethyldithiocarbamatoi tin(lV) (83, 84), and bisidieihyldithiocarbamato) tin(IV) (85). 

The modification of cellulose with alkaline carbon disulfide to introduce xanthate groups has been extensively exploited in the industrial production of viscose. Early work on the preparation and properties of starch xanthate has been discussed. Xanthate derivatives of cellulose and starch have been discussed with respect to general xanthate chemistry, and the xanthation of cellulose in homogeneous medium is known to be a second-order reaction. Cellulose xanthate shows some potential as a matrix for enzyme insolubilization, " and stable derivatives of this xanthate may be prepared by transesterification. Thermal decomposition of cellulose allyl- and benzyl-xanthates gives 5,6-cellulosene. Some thiocarbonyl derivatives of polysaccharides have been prepared. "... 

The complexes NiLX2(L = bipyorphen X = Cl or Br) have been prepared and [Ni(phen)3](xanthate)2 has been isolated from the reaction of potassium xanthate with NiC and phen in aqueous solution. D.t.a. studies on optically active [Ni(phen)3]X2 complexes show specific endothermic peaks in the cases of X = I or CIO4 which are attributed to the racemization process, and [Ni(phen)2X2] complexes have been isolated from the thermal decomposition of [Ni(phen)3X2] (X = Cl, Br, I, or SCN). ... 

Glucopyranosyl xanthates of general formula (27) have been prepared by reaction of 2,3,4,6-tetra-0-acetyl-o -D-glucopyranosyl chloride with potassium alkyl xanthates o.r.d., c.d., u.v., and n.m.r. spectra of the products were examined and the effect of solvents on the Cotton effect curve was studied. The thermal decomposition of the dixanthates (28) and (29), prepared... 

Other literature methods not described in detail here, utilise glycosyl sulfenate [41], thiopseudourea [42], xanthate [42, 43], thiocyanate [44, 45] and dithioacetal [44, 46] intermediates or rely on radical addition to thiohemiacetals [47, 48] or thermal decomposition of diazo compounds prepared by reacting 1-thioaldoses and aryl diazonium salts [44]. Some of these procedures have specific advantage in some specific cases, e.g. the dithioacetal to thioglycoside route is valuable for preparing 1-thio-hexofuranosides [46, 49]. 

Several carboxylates have been prepared, either during separations of An + ions or for thermal decomposition as a route to the dioxides. Most of the actinide carboxylates can be prepared as hydrates by dissolving the appropriate oxide and hydroxide in carboxylic acid. Formates, acetates, oxalates, xanthates, and carbamates are also known. 

A minor amount of Pb(C2H5)4 is produced during the room temperature decomposition of (C2H5)2PbBr2 [178]. Thermal decomposition of (C2H5)3pb-xanthate [714, 718],... 

Thermal decomposition single source precursor Cd-xanthates, thiocarbonates, thiophosphates hexadecylamine HDA 5.60-3.71 [187]... 

Esters derived from the primary alcohols are the most stable and those derived from the tertiary alcohols are the least stable. The decomposition temperature is lower in polar solvents, eg, dimethyl sulfoxide (DMSO), with decomposition occurring at 20°C for esters derived from the tertiary alcohols (38). Esters of benzyl xanthic acid yield stilbenes on heating, and those from neopentyl alcohols thermally rearrange to the corresponding dithiol esters (39,40). The dialkyl xanthate esters catalytically rearrange to the dithiol esters with conventional Lewis acids or trifluoroacetic acid (41,42). The esters are also catalytically rearranged to the dithiolesters by pyridine Ai-oxide catalysts (43) ... 

Very little information is available concerning the thermal stability of the metallic salts of the acid carbonates and thiocarbonates. Calcium glyc-eritol dicarbonate [C3H60H(C0s )2Ca ], although very unstable in solution, could be stored at room temperature in an anhydrous state for a short period of time. On being strongly heated it charred, with the evolution of acrolein. A hydrated 0-(sodium thiocarbonyl) derivative of cellulose became insoluble in alkali within 24 hours at room temperature, due to decomposition. On the other hand, many metal xanthates, particularly the insoluble copper salts, which are readily obtained in a pure, anhydrous state, appear to be reasonably stable at about 20°. This very limited evi-... 

Even with no unpaired electrons present, even-electron ions can undergo reactions thought to be characteristic of a radical site, even at sites remote from the charge (Gross 1988). Note that similar reactions occur in organic chemistry y-H/)9-cleavage rearrangements of neutral molecules take place in both closed-shell (retro-ene reaction) and open-shell (Norrish II process) systems, while these and p-H decompositions occur thermally in esters, xanthates, sulfoxides, and carbamates. For the EE" ions of Equation 8.35 (Kraft and Spiteller 1967),... 

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