Appearance colorless ChemSpider ID 146330 | Pubchem 167254 | |
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Thiophosphoric acid is a chemical compound. Structurally, it is the acid derived from phosphoric acid with one extra sulfur atom, although it cannot be prepared from phosphoric acid. It is a colorless compound that is rarely isolated in pure form, but rather as a solution. The structure of the compound has not been reported, but two tautomers are reasonable: SP(OH)3 and OP(OH)2SH.
Preparation
The compound has been prepared in a multistep process starting with the base hydrolysis of phosphorus pentasulfide to give dithiophosphate, which is isolated as its barium salt:
P2S5 + 6 NaOH → 2 Na3PO2S2 + H2S + 2 H2O2 Na3PO2S2 + 3 BaCl2 → 2 Ba3(PO2S2)2 + 6 NaClIn a second stage, the barium salt is decomposed with sulfuric acid, precipitating barium sulfate and liberating free dithiophosphoric acid:
Ba3(PO2S2)2 + 3 H2SO4 → BaSO4 + 2 H3PO2S2Under controlled conditions, dithiophosphoric acid hydrolyses to give the monothioderivative: H3PO2S2 + H2O → H3PO3S + H2S