Method of removing one or more target impurities from crude fluorosulfonylimide compound

A method of at least partially removing one or more target chlorinated impurities bearing at least one —SO2Cl moiety from a crude bis(fluorosulfonyl)imide (HFSI) mixture comprising:

• (i) a compound of formula (I) F—SO2—NH—SO2—R1 (I) wherein R1 represents F or Cl;
• preferably R1 is F;
• and
• (ii) the one or more said target chlorinated impurities bearing the at least one —SO2Cl moiety, [crude mixture (C-HFSI)];
• so as to create a purified HFSI mixture [purified mixture (P-HFSI)], the method comprising:
• Step (a)—melting the crude mixture (C-HFSI) at a temperature exceeding the melting point of compound of formula (I), so as to obtain a molten mixture [molten mixture (M-FSI)];
• Step (b)—contacting the crude mixture (M-HFSI) with (b1) water or with (b2) an aqueous acidic solution comprising water and at least one mineral acid, wherein the amount of water is of at most 50 equivalent for the total equivalent of target impurities present in crude mixture (C-HFSI), so as to cause at least partial hydrolysis of the said target chlorinated impurities thereby forming hydrolysed target chlorinated impurities;
• and
• Step (c)—at least partially removing the hydrolysed target chlorinated impurities, so as to obtain a purified mixture [purified mixture (P-HFSI)].