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Sodium monothiophosphate
Chemical compound From Wikipedia, the free encyclopedia
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Sodium monothiophosphate, or sodium phosphorothioate, is an inorganic compound with the chemical formula Na3PO3S. It is a sodium salt of monothiophosphoric acid (H3PO3S). Sodium monothiophosphate forms hydrates Na3PO3S·xH2O. The anhydrous form and all hydrates are white solids. The anhydrous salt (x = 0) (Na3PO3S) decomposes without melting at 120-125 °C. More common is the dodecahydrate (Na3PO3S·12H2O). A nonahydrate is also known (Na3PO3S·9H2O).
Related salts are the sodium dithiophosphate undecahydrate Na3PO2S2·11H2O, sodium trithiophosphate undecahydrate Na3POS3·11H2O, and sodium tetrathiophosphate octahydrate Na3PS4·8H2O.[1]
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Preparation
Sodium monothiophosphate is prepared by the base hydrolysis of thiophosphoryl chloride using aqueous sodium hydroxide:[2][3]
- PSCl3 + 6 NaOH + 9 H2O → Na3PO3S·12H2O + 3 NaCl
This reaction affords the dodecahydrate, which is easily dehydrated.
Partial dehydration over 6.5 M H2SO4 gives the nonahydrate. Under flowing N2, the anhydrous salt is formed.[4]
Sodium monothiophosphate decomposes at neutral pH. Silicone grease catalyses the hydrolysis of the monothiophosphate ion PO3S3−, 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]
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References
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