Patent ID: 7989635

Claim:
A method for producing a purified particulate solid (II) of a salt represented by formula (1), which comprises: suspending a particulate solid (I) of a salt in a solvent comprising an etheric oxygen atom-containing compound, separating the solvent by filtration, and recovering particulate solid (II) of said salt; wherein particulate solids (I) and (II) of a salt are represented by the formula: [HNR 3 ] + [Q 1 -SO 2 —N—SO 2 —Q 2 ] − (1) wherein each of R's which may be the same or different, is a hydrogen atom or a C 1-10 alkyl group, and each of Q 1 and Q 2 which are independent of each other, is a monovalent fluoroalkyl group, or Q 1 and Q 2 together form a bivalent fluoroorganic group which are 4, 5 or 6-membered rings; wherein particulate solid (I) has a purity ranging from 80 mol. % to 99 mol. % as measured by NMR (nuclear magnetic resonance); and wherein particular solid (II) has a purity of 90 mol. % or higher as measured by NMR (nuclear magnetic resonance), and wherein the purity of particular solid (II) is higher than the purity of particular solid (I).