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Solutions in difluorophosphoric acid Reed, William

Abstract

The physical and inorganic chemistry of solutions in difluorophosphoric acid, HPO₂F₂, has been studied, as part of a general study of solutions in non-aqueous protonic solvents. Difluorophosphoric acid is a colourless, associated liquid which might be expected to have solvent properties similar to those of other protonic systems such as H₂O, H₂SO₄ and HSO₃F. However, electrical conductivity studies of solutions of various electrolytes and nuclear magnetic resonance studies of solutions of alkali metal difluorophosphates indicate that the acid is a poor solvent for electrolytes and that ion-pairing is probably extensive. Acid-base behaviour in HPO₂F₂ has been extensively investigated. Compounds which behave as bases in this system include metal difluorophosphates, chlorides, nitrates and carbonates, organic amines, and some organic nitro-compounds and carboxylic acids. Inorganic molecules such as H₂SO₄, HSO₃F and SbF₅ behave as acids. Reaction between an acid and a base in HPO₂F₂ commonly result in the formation of an insoluble salt. The reaction between KPO₂F₂ and SbF₅, for example, has been used to prepare the new compound KSbF₅PO₂F₂. To further investigate the factors affecting acid strengths, cryoscopic and electrical conductivity studies of various inorganic oxy-acids were carried out in nitrobenzene, as solvent. The acids H₂SO₄, HSO₃F and HPO₂F₂ appeared to be virtual non-electrolytes in nitrobenzene, with H₂SO₄ apparently exhibiting some polymerization.

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