1911 Encyclopædia Britannica/Xanthic Acid

XANTHIC ACID (xanthogenic acid), C₂H₅O⋅CS⋅SH, an organic acid named from the Greek ξανθός, yellow, in allusion to the bright yellow colour of its copper salt. The salts of this acid are formed by the action of carbon bisulphide on the alcoholates, or on alcoholic solutions of the caustic alkalis. They react with the alkyl iodides to form dialkyl esters of the dithio-carbonic acid, which readily decompose into mercaptans and thiocarbamic esters on treatment with ammonia: C₂H₅O⋅CS⋅SR₁+NH₃ = C₂H₅O⋅CS⋅NH₂+R₁⋅SH; with the alkali alcoholates they give salts of the alkyl thiocarbonic acids: C₂H₅O⋅CS⋅SR+CH₃OK+H₂O = CH₃O⋅CO⋅SK+C₂H₅OH+R⋅SH. Ethyl xanthic acid, C₂H₅O⋅CS⋅SH, is obtained by the action of dilute sulphuric acid on the potassium salt at 0° C. (Zeise, Berz. Jahresb., 3, p. 83). It is a colourless oil which is very unstable, decomposing at 25° C. into carbon bisulphide and alcohol. The potassium salt crystallizes in colourless needles and is formed by shaking carbon bisulphide with a solution of caustic potash in absolute alcohol. On the addition of cupric sulphate to its aqueous solution it yields a yellow precipitate of cupric xanthate. Potassium xanthate is used in indigo printing and also as an antidote for phylloxera. Tschugaeff (Ber., 1899, 32, p. 3332) has used the xanthic ester formation for the preparation of various terpenes, the methyl ester when distilled under slightly diminished pressure decomposing, in the sense of the equation, C_nH_2n-1⋅O.CS⋅SCH₃ = C_nH_2n-2+COS+CH₃SH. According to the author molecular change in the hydrocarbon is prevented, since no acid agent is used.