Sodium monothiophosphate, or sodium phosphorothioate, is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemi ...
with the molecular formula Na
3PO
3S(H
2O)
x. All are white solids. The anhydrous material (x = 0) decomposes without melting at 120-125 °C. More common is the dodecahydrate. A nonahydrate is also known.
Related salts are the ''di''thiophosphate Na
3PS
2O
2.11H
2O, ''tri''thiophosphate Na
3PS
3O
.11H
2O, and ''tetra''thiophosphate Na
3PS
4.8H
2O.
Preparation
Sodium monothiophosphate is prepared by the base hydrolysis of
thiophosphoryl chloride using aqueous
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkal ...
:
:PSCl
3 + 6 NaOH + 9 H
2O → Na
3PO
3S
.(H
2O)
12 + 3 NaCl
This reaction affords the dodecahydrate, which is easily dehydrated.
Partial dehydration over 6.5 M H
2SO
4 gives the nonahydrate. Under flowing N2, the anhydrous salt is formed.
Sodium phosphorothiolate decomposes at neutral
pH.
Silicone grease
Silicone grease, sometimes called dielectric grease, is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane (PDMS) and the thickener is amorphous fumed silica. Using thi ...
catalyses the hydrolysis of the phosphorothioate ion, so it is recommended that it is not used in the glass joints.
In the anhydrous material, 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.
References
Sodium compounds
Phosphorothioates
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