Thiocarbonate

Thiocarbonate describes a family of anions with the general chemical formula CS_3-xO_x²⁻ (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 1.33. The state of protonation is usually not specified. These anions are good nucleophiles and good ligands.

Monothiocarbonate

Monothiocarbonate is the dianion CO₂S²⁻, which has C_2v symmetry. Monothiocarbonate arises by the hydrolysis of thiophosgene or the reaction of base with carbonyl sulfide:

COS + 2 NaOH → Na₂CO₂S + H₂O

Dithiocarbonates

Dithiocarbonate is the dianion COS₂²⁻, which has C_2v symmetry. It arises from the reaction of aqueous base with carbon disulfide:

CS₂ + 2 NaOH → Na₂COS₂ + H₂O

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.

Trithiocarbonates

Trithiocarbonate is the dianion CS₃²⁻, which has D_3h symmetry. Trithiocarbonate is derived from the reaction of sulfide sources with carbon disulfide:

CS₂ + 2 NaSH → Na₂CS₃ + H₂S

Perthiocarbonates

Addition of sulfur to trithiocarbonate gives the perthiocarbonate anion CS₄²⁻, 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.