Thiocarbonate

Thiocarbonate describes a family of anions with the general chemical formula CS
_3−xO²⁻
_x (x = 0, 1, or 2):

• for x = 2 it is monothiocarbonate ion CO₂S²⁻
• for x = 1 it is dithiocarbonate ion COS2−2
• for x = 0 it is trithiocarbonate ion CS2−3

Like the carbonate dianion, the thiocarbonate ions are trigonal planar, with carbon atom at the center of triangle, and oxygen and sulfur atoms at the peaks of the triangle. The average bond order between C and S or O is ⁠4/3⁠. The state of protonation is usually not specified. These anions are good nucleophiles and good ligands.

Thiocarbonates refer to salts of those ions as well (e.g. potassium trithiocarbonate, K₂CS₃).

Thiocarbonates refer to esters of those ions as well (e.g. dimethyl trithiocarbonate, (CH₃S)₂CS). They contain trigonal planar divalent functional groups R–CS
_3−xO
_x–R similar to these anions (x = 0, 1, or 2, R is organyl group). Esters with the formula R−O−C(=S)−S−R are also called xanthates, while esters with the formula R−S−C(=S)−S−R are also called thioxanthates.

Thiocarbonates also refer to salts of organyl thiocarbonate ions (e.g. sodium ethyl xanthate or SEX, CH₃CH₂OCS−2Na⁺). They contain R–CS
_3−xO⁻
_x anions (x = 0, 1, or 2, R is organyl group). Anions with the formula R−O−CS−2, and their salts, are also called xanthates, while salts with the formula R−S−CS−2, and their salts, are also called thioxanthates.

Monothiocarbonate

File:Methyl thiocarbonate.png

S-methyl 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

The esters of monothiocarbonic acids are called monothiocarbonates as well (e.g. O-ethyl-S-methyl monothiocarbonate CH₃CH₂OC(O)SCH₃).

Dithiocarbonates

File:Xanthate-ester-2D-general.png

A xanthate-ester

Dithiocarbonate is the dianion COS2−2, which has C_2v symmetry. It arises from the reaction of aqueous base with carbon disulfide:

CS₂ + 2 NaOH → Na₂COS₂ + H₂O

Important derivatives of dithiocarbonates are the xanthates (O-esters of dithiocarbonates), with the formula ROCS−2. These salts are typically prepared by the reaction of sodium alkoxides with carbon disulfide.

Another group of dithiocarbonates have the formula (RS)₂CO. They are often derived by hydrolysis of the corresponding trithiocarbonates (RS)₂CS. One example is tetrathiapentalenedione, a heterocycle that consists of two dithiocarbonate groups.

Trithiocarbonates

File:Dimethyl trithiocarbonate.png

Dimethyl trithiocarbonate

See also: Thiocarbonic acid and thioxanthate

Trithiocarbonate is the dianion CS2−3, which has D_3h symmetry. Trithiocarbonate is prepared by the reaction of sodium hydrosulfide (NaSH) with carbon disulfide:

CS₂ + 2 NaSH → Na₂CS₃ + H₂S

The relatively elusive trithiocarbonic acid H₂CS₃ has been characterized by X-ray crystallography.

Esters of thiocarbonic acid, such as dimethyl trithiocarbonate ((CH₃S)₂CS) are also called thioxanthate esters. Trithiocarbonate esters inhibit the enzyme carbonic anhydrase.

File:Na2dmit.svg

Sodium 1,3-dithiole-2-thione-4,5-dithiolate abbreviated Na₂dmit is one of several cyclic trithiocarbonates.

Perthiocarbonates

Addition of sulfur to trithiocarbonate gives the perthiocarbonate anion CS2−4, which contains one sulfur–sulfur bond.

Perthiocarbonic acid (or tetrathioperoxycarbonic acid / disulfanylmethanedithioic acid / CAS#13074-70-9) has never been obtained in pure form.

See also

• Trithiocarbonic acid
• Xanthate
• Thioxanthate
• Sodium ethyl xanthate (SEX)
• Potassium ethyl xanthate (KEX)
• Potassium amyl xanthate
• Potassium trithiocarbonate
• Ethyl xanthic acid