A NEW PROCEDURE FOR THE SYNTHESIS OF LITH IUM HEXAFLUOROPHOSPHATE

Lithium hexafluorophosphate (LiPF6) has been synthesized using commerc ial hexafluorophosphoric acid (HPF6)as starting material. The neutrali zation of this acid monitored by conductimetry by lithium hydroxide in aqueous, alcoholic and acetonitrile media gives LiPF6 with yields of 42, 35 and 61% respectively. This salt may also be prepared by neutral izing similarly lithium hydroxide (LiOH) by pyridinium hexafluorophosp hate (C5H5NHPF6) obtained by reaction from equimolar amounts of pyridi ne and HPF6 in alcoholic media (yield about 90%). From C5H5NHPF6 a new synthesis leads to LiPF6 in two steps. First the reaction of C5H5NHPF 6 with ROLi (R = CH3, C2H5) in methyl or ethyl alcohol, acetonitrile a nd tetrahydrofuran media or with RLi (R = C4H9, tert-butyl) in pentane or hexane, gives lithium pyridinium hexafluorophosphate Li(C5H5N)PF6 in about 95% yield. Heating this at 30-50 degrees C under vacuum gives LiPF6 with a purity determined by lithium titration of about 99%. (C) 1998 Elsevier Science S.A. All rights reserved.