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.[1][2]
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
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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 → Na2CO2S + H2O
The esters of monothiocarbonic acids are called monothiocarbonates as well (e.g. O-ethyl-S-methyl monothiocarbonate CH3CH2OC(O)SCH3).
Dithiocarbonates
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Dithiocarbonate is the dianion COS2−2, which has C2v 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.[3] 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
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Trithiocarbonate is the dianion CS2−3, which has D3h symmetry. Trithiocarbonate is prepared by the reaction of sodium hydrosulfide (NaSH) with carbon disulfide:[4]
- CS2 + 2 NaSH → Na2CS3 + H2S
The relatively elusive trithiocarbonic acid H2CS3 has been characterized by X-ray crystallography.[5]
Esters of thiocarbonic acid, such as Dimethyl trithiocarbonate ((CH3S)2CS) are typically called thioxanthates instead.
Perthiocarbonates
editAddition of sulfur to trithiocarbonate gives the perthiocarbonate anion CS2−4, which contains one sulfur–sulfur bond.[6]
Perthiocarbonic acid (or tetrathioperoxycarbonic acid / disulfanylmethanedithioic acid / CAS#13074-70-9[7]) has never been obtained in pure form.[8]
See also
editReferences
edit- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5
- ^ Gattow, Gerhard; Behrendt, Werner (1977). Carbon Sulfides and their Inorganic and Complex Chemistry. Stuttgart: Georg Thieme. ISBN 3-13-526201-4.
- ^ Perumalreddy Chandrasekaran; James P. Donahue (2009). "Synthesis of 4,5-Dimethyl-1,3-dithiol-2-one". Org. Synth. 86: 333. doi:10.15227/orgsyn.086.0333.
- ^ R. E. Strube (1959). "Trithiocarbodiglycolic Acid". Org. Synth. 39: 967. doi:10.15227/orgsyn.039.0077.(a procedure for synthesis of K2CS3
- ^ Krebs, Β.; Henkel, G.; Dinglinger, H.-J.; Stehmeier, G. (1980). "Neubestimmung der Kristallstruktur von Trithiokohlensäure α-H2CS3 bei 140 Κ". Z. Kristallogr. 153 (1–4): 285–296. doi:10.1524/zkri.1980.153.14.285. S2CID 201671683.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Sodium tetrathiocarbonate from PubChem
- ^ Tetrathioperoxycarbonic acid from PubChem
- ^ A Text-book of Inorganic Chemistry, Volume 7, Issue 2, 1931, p. 269