TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Claimed): Preparation of (I) comprises preparing an N-substituted sulfonimide compound (II) of formula RSO2N(R3a)SO2R1a using a sulfur compound of formula R-SO2F and subjecting (II) for a nucleophilic substitution reaction on the substituent.R3a = benzyl or trimethylsilyl.Preferred Process: The process is carried out reacting R-SO2F with excess bezylamine, followed by the neutralization with hydrogen chloride to give a N-benzyl-sulfimide compound (III) of formula RSO2N(Bn)H and reacting (III) with an anhydride compound of formula (R1aSO2)2O in the presence of tertiary amine to give a N-benzyl-sulfimide compound of formula RSO2N(Bn)R1a. The R-SO2F compound is reacted with a salt of hexamethyldisilazane of formula ((CH3)3Si)2N-A+ to obtain a compound formula RSO2N((CH3)3Si)R1a. The process is carried out using an alkaline(earth)metal hydroxide or halide in the presence of ethanol to obtain metallic sulfonimide; ammonium hydroxide or halide to obtain ammonium sulfonimide; secondary amine to obtain tertiary ammonium sulfonimide; or using tertiary amine to obtain quaternary ammonium sulfonimide. Preferred Definitions:    M = Ca2+ or Mg2+;    Ar = phenyl (optionally substituted) or aromatic heterocyclic ring; and    z = 1.    SPECIFIC COMPOUNDS - 5 Compounds (I) are specifically disclosed e.g. lithium 2-(phenylsulfanyl)-1,1,2,2-tetrafluoro-N- ( trifluoromethylsulfonyl)ethanesulfonimide of formula (Ia), lithium    difluoro-phenylsulfanyl-N-(trifluoromethanesulfonyl)methanesulfonamide, lithium 2- (phenylsulfonyl)-1,1,2,2-tetrafluoro-N-(trifluoromethanesulfonyl)-ethanesulfonamide, lithium 2-(phenylsulfanyl)-1,1,2,2-tetrafluoro-N- (2-(phenyl    sulfanyl)- 1,1,2,2-tetrafluoroethanesulfonyl)-ethanesulfonamide and    triethylammonium 2-(phenylsulfanyl)-1,1,2,2 -tetrafluoro-N-(trifluoromethanesulfonyl)-ethanesulfonamide.    EXAMPLE - ((Bromodifluoromethyl) sulfanyl)benzene (4.8 g) was added to a suspension of magnesium (960 mg), trimethylsilyl chloride (10.2 ml) and anhydrous tetrahydrofuran (50 ml) at 0?oC. The obtained reaction mixture was agitated at 0?oC for 1 hour and at ambient temperature for 1 hour. The obtained crude product was worked up to give difluoro(phenylsulfanyl)methyl trimethylsilane. A solution of sulfur dioxide was treated with difluoro(phenylsulfanyl)methyl trimethylsilane (4.3 g) under an inert atmosphere at ambient temperature over a night. The obtained reaction mixture was worked up to give difluoro-(phenylsulfanyl)methanesulfonyl fluoride. A solution of difluoro-(phenylsulfanyl)methanesulfonyl fluoride (2.09 g) in dichloromethane (20 ml) was treated with fresh distilled benzylamine (4 ml). The obtained mixture was shaken and heated at 50?oC for 20 hours. The obtained crude product was worked up to give N-benzyl-2-(phenylsulfanyl)-1,1,2,2-tetrafluoroethanesulfonamide. A solution of N-benzyl-2-(phenylsulfanyl)-1,1,2,2-tetrafluoroethanesulfonamide (750 mg) in dichloromethane (10 ml) was treated with diisopropylethylamine (420 ~ml) and triflic anhydride (510 ~ml) at 0?oC to ambient temperature for 1.3 hours. The obtained reaction mixture was worked up to give N-benzyl-2-(phenylsulfanyl)-1,1,2,2-tetrafluoro-N-(trifluoromethylsulfonyl)-ethanesulfonamide. A solution of the obtained compound (510 mg) was treated with lithium hydroxide dehydrate (42 mg) at ambient temperature for 8 hours. The obtained reaction mixture was worked up to give lithium 2-(phenylsulfanyl)-1,1,2,2-tetrafluoro-N-( trifluoromethylsulfonyl)ethanesulfonimide.