SomeoneSomewhere
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Phosphorous Acid
Is there any route to the synthesis of phosphorous acid (H3PO3) besides using P4O6,PCl3,and potassium phosphite (They are unavailable where I live
 )?
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diddi
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try your local auto store for mag wheel cleaner. there are often OTC solutions to your supply problems
Beginning construction of periodic table display
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SomeoneSomewhere
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Quote: Originally posted by diddi  | try your local auto store for mag wheel cleaner. there are often OTC solutions to your supply problems
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I think you are talking about PhosphorIC acid(H3PO4),not phosphorous (H3PO3).
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woelen
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Reducing phosphate is not an option. The only viable way to phosphite is from the element.
Can you obtain red P? From red P and chlorine you can make PCl3. With Br2 you can make PBr3. You can prepare these chemicals in solution (e.g. CHCl3
or CH2Cl2) to make the reaction less violent. Addition of water then makes H3PO3 and HCl/HBr. Purification of the H3PO3 is not that difficult, simply
heating drives off the solvent and trapped HCl/HBr. The last percent or so of chloride/bromide is not easy to remove, but for many applications this
is not a real issue.
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Mesa
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Yates Anti-Rot is an aqueous solution containing the mixed potassium salts of phosphorous acid. The free acid can be prepared by addition of HCl,
boiling off excess water, and filtering the KCl byproduct as it precipitates.
Keep an eye on the temperature as you near the end of the evaporation. H3PO3 decomposes at around 180*C to H3PO4 and PH3. PH3(Phosphine) is very
dangerous stuff.
Adding methanol or ethanol helps to remove the last fractions of water without overheating. This eventually yields the solid acid as white,
translucent flakes. It's very hygroscopic.
Further purification can be done by forming the calcium salt of the H3PO3 and isolating, then reacting with dilute H2SO4 and filtering out insoluble
CaSO4.
[Edited on 5-1-2016 by Mesa]
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