Thiocarbonate describes a family of anions with the general chemical formula CS
x (x = 0, 1, or 2). Organic compounds structurally related to these anions are also called thiocarbonates.
Like the carbonate dianion, the thiocarbonates are planar, with carbon at the center. The average bond order from C to S or O is 1 1⁄3. The state of protonation is usually not specified. These anions are good nucleophiles and good ligands.
Monothiocarbonate is the dianion CO2S2−, which has C2v symmetry. Monothiocarbonate arises by the hydrolysis of thiophosgene or the reaction of base with carbonyl sulfide:
COS + 2 NaOH → Na2
S + H2
Dithiocarbonate is the dianion COS2−
2, which has C2v symmetry. It arises from the reaction of aqueous base with carbon disulfide:
+ 2 NaOH → Na2
Probably the most important dithiocarbonates are the organic derivatives. The xanthates are organosulfur compounds prepared by the reaction of alkoxides with carbon disulfide. Charge-neutral organic dithiocarbonates, with the formula (RS)2CO, are also known, often being derived by hydrolysis of the corresponding organic trithiocarbonates. One example is tetrathiapentalenedione, a heterocycle that consists of two dithiocarbonate groups.
Trithiocarbonate is the dianion CS2−
3, which has D3h symmetry. Trithiocarbonate is derived from the reaction of sulfide sources with carbon disulfide:
+ 2 NaSH → Na2
Addition of sulfur to trithiocarbonate gives the perthiocarbonate anion CS2−
4, which contains one sulfur–sulfur bond.
Perthiocarbonic acid (or tetrathiocarbonic acid, CAS#13074-70-9) has never been synthesized in the pure form but only as a dark brown solution.