Dithiocarbonic acids

The xanthates react with alkyl halides to give the di-esters of dithiocarbonic acid 0=C(SH)2 S=C(SH)0H, for example ... 

Thioacids have a most disagreeable odour and slowly decompose in air. Their boiling points are lower than those of the coiTcsponding oxygen counterparts and they are less soluble in water, but soluble in most organic solvents. An important dithioacid is dithiocarbonic acid (HO—CS2H). Whilst the free acid is unknown, many derivatives have been prepared such as potassium xanthate giving a yellow precipitate of copper xanthate with copper salts ... 

Ditluokohlensaure, /, (either) dithiocarbonic acid specif., dithiolcarbonic acid (HSCOSH), ditluonig, a. dithioncus, (less desirably) hypo-sulfurous. 

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... 

Unlike the inorganic salts of the azido-dithiocarbonic acid, the org derivs are not particularly expl. They puff midly when held in a flame or when heated rapidly on a hot plate. On exposure to light they show no photosensitivity and undergo no coloration... 

Their sensitivities to friction and their brisanee increase with increasing atomic wt. The Amm, K, Rb Cs salts are characterized by their peculiar sensitivity to light. All change color when exposed to sunlight. The Cs salt may even decomp violently during the process of crystn from aq soln. The alkali salts, especially Na, can be used to prepare the heavy metal salts, such as Pb(SCSN3)2, and the alkyl or aryl derivatives of azido-dithiocarbonic acid... 

Free xanthic acids (83), also referred to as O-alkyl- and O-aryl-dithiocarbonic acids, are not well-characterized compounds. They are strong acids and stable only in an extremely pure state. The isomeric acids (84) are unknown. 

CHAN-SCSNj, mw 192.32, N 29.13 wh crystalline tablets (from w), mp 95-8° (with color change to dk grn and then dec) very sol in w, sol in MeOH or acet si sol in eth and insol in CC14, CS, chlf. It can be prepd by three methods a)neutraIization of azido-dithiocarbonic acid with aq tetramethylam-monium hydroxide b)double decompn of Ba azidodithiocarbonate and tetramethylammonium sulfate and c)digestion of aq tetramethyl-ammonium izid with 9 si 3fc ss of CS as reqd by the equation... 

Pilcher73 has recently reviewed the experimental data for a variety of carbonyl and thio-carbonyl compounds. Enthalpies of formation for dithiocarbonic acids, R2N—C(=S)SH, thioamides and thioureas were determined by standard calorimetric methods. For an important, older review on the thermochemistry and thermochemical kinetics of sulfur-containing compounds, see work of Benson74. 

Fig. 4.14. The Chugaev reaction for the dehydration of alcohols. (The decomposition of dithiocarbonic acid methylester—here given in brackets—to form carbon oxy-sulfide and methane thiol is outlined in Section 8.1 near Figure 8.4.)...

In the presence of potassium hydroxide, cellulose adds to carbon disulfide (Figure 8.4). In this way potassium xanthate A is produced. It is soluble in water, but restores the water-insoluble cellulose upon addition of acid. The primary protonation product is the dithiocarbonic acid O-cellulose ester B. B reacts just like the unstable carbonic acid derivatives in Figure 8.3, namely via a zwitterion (C) and its decomposition into cellulose (a heteroatom nucleophile)... 

In Figure 4.14, we learned about the Chugaev elimination in connection with the synthesis of alkenes. The second (primary) product of this reaction is the dithiocarbonic acid 5-methyl ester (A). It equilibrates with the zwitterion B, which decomposes into carbon oxysulfide (a heterocumulene) and methanethiol (a heteroatom nucleophile). 

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. 

The mixed esters of carbonic acid [see Table I, type (a)] were formerly designated carboalkyloxy, but this term is now avoided, since it was often confused with carboxyalkyl [—(CHj) —CO2H]. A, the mixed esters of dithiocarbonic acid [see Table I (e) R = alkyl] have been termed alkyl xanthogenates or alkyl xanthates, thus relating them to the corresponding acid dithiocarbonates (R = metal), industrially called xanthates, but more precisely termed 0-(/Si-metal thiolthiocarbonyl) derivatives. Of the mixed-ester types and acid types indicated in Table I, examples of (a), (b), (e), (f), and (g) of the former, and (a), (b), and (e) of the latter have so far been reported. For intermolecular esters, examples of (i) and (k), and, for cyclic esters, examples of (0) and (t), have been described. 

CHF,0,S, Methanesulfonic acid, trifluoro-, iridium, manganese, and rhenium complexes, 26 114, 115, 120 platinum complex, 26 126 CHOSj, Dithiocarbonic acid, 27 287 CH, Methylene, osmium complex, 27 206 CHiOj, Formic acid, rhenium complex, 26 112... 

OPSi2C,H27, Phosphine, [2,2-dimethyl-1-(trimethylsiloxy)propylidene](tri-methylsilyl)-, 27 250 OS2CH, Dithiocarbonic acid, 27 287 OSiC4H 2, Silane, methoxytrimethyl-,... 

S2OCH, Dithiocarbonic acid, 27 287 S2O3OSJC, Osmium, nonacarbonyl-)ji3-thio-tri-, 26 306... 

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