Thiophosphate

For the thiophosphate esters see organothiophosphates.

A thiophosphate (or phosphorothioate) is a family of compounds and anions with the general chemical formula PS_4-xO_x^3- (x = 0, 1, 2, or 3). The state of protonation is usually not specified. They could be bound to as many as three protons for the neutral H₃PS_4-xO_x species. Two protons correspond to the related monoanions, and one proton for the dianions. The trianions are highly basic and do not exist in appreciable concentrations in solution. Thiophosphates are tetrahedral anions, with the phosphorus at the center of the tetrahedron.

Monothiophosphate

Ball-and-stick model of the monothiophosphate ion

Monothiophosphates are formally derived from the anion PO₃S^3-, which has C_3v symmetry.. A number of insecticides feature organic monothiophosphate center, including diazinon, parathion, and malathion. They have the formula (RO)₂PS(OAr), where R = methyl or ethyl and Ar = an aryl or related group. Coordination complexes of are known.^[1]

In the laboratory monothiophosphate is used as an analogue of phosphate in biochemistry. Monothiophosphate esters are biochemical reagents used in the study transcription,^[2] substitution interference assays.

Dithiophosphates

Dithiophosphates are formally derived from the anion PO₂S₂^3-, which has C_2v symmetry. This species is the major product from the reaction of base (e.g., NaOH) with phosphorus pentasulfide. The sodium salt has the nominal formula Na₃PO₂S₂, but is invariably hydrated. The main application of this dithiophosphate salt is in the purification of molybdenite ore. Organic thiophosphates feature the (RO)₂PS₂^- anion (R = alkyl, aryl). Zinc dithiophosphate, e.g., Zn(S₂P(OR)₂)₂]], are used as oil additives (R = alkyl).

Tri- and tetrathiophosphates

Trithiophosphates are formally derived from the anion POS₃^3-, which has C_3v symmetry. Tetrathiophosphate has the formula PS₄^3-. Derivatives of these two anions are less commonly encountered.

References

1. ^ Poat JC et al. (1990). "A thiophosphate bridged platinum–zinc hetero-bimetallic complex: [(Me₂PhP)₂Pt{OSP(OR)₂}₂ZnCl₂". J. Chem. Soc., Chem. Commun.: 1036–1038. http://www.rsc.org/publishing/journals/article.asp?doi=C39900001036. 
2. ^ Lorsch JR, Bartel DP, Szostak JW. (1995). "Reverse transcriptase reads through a 2'–5' linkage and a 2'-thiphosphate in a template". Nucleic Acids Res. 23 (15): 2811–2814. doi:10.1093/nar/23.15.2811. PMC 307115. PMID 7544885. http://nar.oxfordjournals.org/cgi/content/abstract/23/15/2811.