Sodium monothiophosphate explained

Sodium monothiophosphate, or sodium phosphorothioate, is an inorganic compound with the chemical formula . It is a sodium salt of monothiophosphoric acid . Sodium monothiophosphate forms hydrates . The anhydrous form and all hydrates are white solids. The anhydrous salt (x = 0) decomposes without melting at 120-125 °C. More common is the dodecahydrate . A nonahydrate is also known .

Related salts are the sodium dithiophosphate undecahydrate, sodium trithiophosphate undecahydrate, and sodium tetrathiophosphate octahydrate .^[1]

Preparation

Sodium monothiophosphate is prepared by the base hydrolysis of thiophosphoryl chloride using aqueous sodium hydroxide:^{[2] [3]}

This reaction affords the dodecahydrate, which is easily dehydrated.

Partial dehydration over 6.5 M gives the nonahydrate. Under flowing , the anhydrous salt is formed.^[4]

Sodium monothiophosphate decomposes at neutral pH. Silicone grease catalyses the hydrolysis of the monothiophosphate ion, so it is recommended that it is not used in the glass joints.^[5]

In the anhydrous salt, the P-S bond is 211 pm and the three equivalent P-O bonds are short at 151 pm. These disparate values suggest that the P-S bond is single.^[6]

Notes and References

1. Crystallographic Data on Some Sodium Phosphorothioates. Elias, D. P.. Acta Crystallographica. 1957. 10. 9. 600. 10.1107/S0365110X57002108. free. 1957AcCry..10..600E.
2. Book: Sodium Monothiophosphate. 5. Stanley K. Yasuda . Jack L. Lambert . Inorganic Syntheses. 102–104. 1957. 10.1002/9780470132364.ch28. 978-0-470-13236-4.
3. Book: 1977. 17. 193–4. Importance of Excess Base in the Synthesis of Sodium Monothiophosphate: (Sodium Phosphorothioate). L. C. Washburn . R. L. Hayes . Inorganic Syntheses. 10.1002/9780470132487.ch53. 978-0-470-13248-7.
4. Trisodium monothiophosphate. Radiocrystallographic study. Palazzi, Marcel. Bulletin de la Société Chimique de France. 1973. 12. 3246–8.
5. Serendipitous Reactions Involving a Silicone Grease. Lucian C. Pop and M. Saito. Coordination Chemistry Reviews. 314. 64–70. 2015. 10.1016/j.ccr.2015.07.005.
6. Natriummonothiophosphat(V): Kristallstruktur und Natriumionenleitfähigkeit. Sodium monothiophosphate(V). Crystal structure and sodium ionic conductivity. 10.1002/1521-3749(200203)628:3<641::AID-ZAAC641>3.0.CO;2-8. Pompetzki, M. . Jansen, M.. Zeitschrift für Anorganische und Allgemeine Chemie. 2002. 628. 3. 641–646.