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ChemicalBook CAS DataBase List Phosphorous acid
13598-36-2

Phosphorous acid synthesis

3synthesis methods
Phosphorus acid can be prepared by the reaction of phosphorus trichloride with water:
PCl3 + 3H2O → H3PO4 + 3HCl
The reaction is violent. Addition of PCl3 should be extremely cautious and slow. The addition can be carried out safely in the presence of concentrated HCl. Alternatively, a stream of air containing PCl3 vapor is passed into icecold water and solid crystals of H3PO4 form.
Alternatively, phosphorus acid can be prepared by adding phosphorus trichloride to anhydrous oxalic acid:
PCl3 + 3(COOH）2 → H3PO3 + 3CO + 3CO2 + 3HCl
In this reaction, all products except H3PO3 escape as gases leaving the liquid acid.
Dissolution of phosphorus sesquioxide in water also forms phosphorus acid. When shaken with ice water, phosphorus acid is the only product .
P4O6 + 6H2O → 4H3PO3
However, in hot water part of the phosphorus acid disproportionates to phosphoric acid and phosphorus or phosphine.
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Yield:13598-36-2 84%

Reaction Conditions:

with Ni-doped silica for 18 h;Reflux;

Steps:



0056] Phosphorous acid: (Table 2, entry 12). After concentration of water, 1.72 g (84%) of clear liquid was obtained. 1H NMR (400 MHz, CDCl3) δ 6.72 (d, 1JHP=663.2 Hz, 1H); 31P NMR (161.97 MHz, CDCl3) δ 4.37 (d, JPH=664 Hz).

References:

US2014/303394,2014,A1 Location in patent:Paragraph 0036; 0056

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