Sodium monothiophosphate

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).

Sodium monothiophosphate

Molecular model of sodium monothiophosphate
Names
IUPAC name Sodium monothiophosphate
Identifiers
CAS Number	10101-88-9 (anhydrous) Y (nonahydrate): 51674-18-1 (dodecahydrate): 51674-17-0 Y
3D model (JSmol)	Interactive image (nonahydrate): Interactive image (dodecahydrate): Interactive image
ChemSpider	8053214 (dodecahydrate): 23499061
ECHA InfoCard	100.030.224
EC Number	233-261-6
PubChem CID	6913045 (nonahydrate): 165360175 (dodecahydrate): 45052183
UNII	AN1017219I Y (dodecahydrate): 4VBT402QNM Y
CompTox Dashboard (EPA)	DTXSID30889527 (nonahydrate): DTXSID401336664 (dodecahydrate): DTXSID501336667
InChI InChI=1S/3Na.H3O3PS/c;;;1-4(2,3)5/h;;;(H3,1,2,3,5) Key: RZLYVIFNQHQSQM-UHFFFAOYSA-N (nonahydrate): InChI=1S/3Na.H3O3PS.9H2O/c;;;1-4(2,3)5;;;;;;;;;/h;;;(H3,1,2,3,5);9*1H2/q3*+1;;;;;;;;;;/p-3 Key: KGZBZRPZTFGJAF-UHFFFAOYSA-K (dodecahydrate): InChI=1S/3Na.H3O3PS.12H2O/c;;;1-4(2,3)5;;;;;;;;;;;;/h;;;(H3,1,2,3,5);12*1H2/q3*+1;;;;;;;;;;;;;/p-3 Key: AALQBIFJJJPDHJ-UHFFFAOYSA-K
SMILES [O-]P(=S)([O-])[O-].[Na+].[Na+].[Na+] (nonahydrate): O.O.O.O.O.O.O.O.O.[O-]P(=S)([O-])[O-].[Na+].[Na+].[Na+] (dodecahydrate): O.O.O.O.O.O.O.O.O.O.O.O.[O-]P(=S)([O-])[O-].[Na+].[Na+].[Na+]
Properties
Chemical formula	Na3PO3S
Molar mass	180.00 g·mol−1
Appearance	White solid
Density	1.58 g/cm3 (dodecahydrate) 2.40 g/cm3 (anhydrous)
Melting point	120 to 125 °C (248 to 257 °F; 393 to 398 K) (decomposition)
Solubility in water	soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Related salts are the sodium dithiophosphate undecahydrate Na₃PO₂S₂·11H₂O, sodium trithiophosphate undecahydrate Na₃POS₃·11H₂O, and sodium tetrathiophosphate octahydrate Na₃PS₄·8H₂O.^[1]

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]