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Phosphoric acid as a precursor to chemicals traditionally synthesized from white phosphorus

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Science  23 Mar 2018:
Vol. 359, Issue 6382, pp. 1383-1385
DOI: 10.1126/science.aar6620

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Silicon clears a wet path to phosphines

Phosphoric acid is produced on a massive scale for fertilizer by treating phosphate rock with sulfuric acid. In contrast, preparation of more elaborate phosphorus compounds used in chemical catalysis, pharmaceutical, and battery applications requires laborious generation and chlorination of elemental phosphorus. Geeson and Cummins now show that phosphoric acid may also be a practical source of such compounds (see the Perspective by Protasiewicz). They isolated and characterized a phosphide salt derived from treatment of dehydrated phosphoric acid with trichlorosilane, a compound already used at the commercial scale to produce high-purity silicon. The salt proved to be a versatile precursor for a range of alkylated and fluorinated phosphorus compounds.

Science, this issue p. 1383; see also p. 1333

Abstract

White phosphorus, generated in the legacy thermal process for phosphate rock upgrading, has long been the key industrial intermediate for the synthesis of phosphorus-containing chemicals, including herbicides, flame-retardants, catalyst ligands, battery electrolytes, pharmaceuticals, and detergents. In contrast, phosphate fertilizers are made on a much larger scale from phosphoric acid, obtained by treating phosphate rock with sulfuric acid. Dehydration of phosphoric acid using sodium chloride gives trimetaphosphate, and here we report that trichlorosilane, primarily used for the production of high-purity silicon, reduces trimetaphosphate to the previously unknown bis(trichlorosilyl)phosphide anion. This anion offers an entry point to value-added organophosphorus chemicals such as primary and secondary alkyl phosphines, and thus to organophosphinates, and can also be used to prepare phosphine gas and the hexafluorophosphate anion, all previously available only downstream from white phosphorus.

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