NOVELTY - Tetra-alkyl-dimethyl guanidinium compounds containing organic or inorganic anion, are new.    USE - The compounds are useful as solvents, in supported liquid membranes providing selective transport of organic molecules (such as alcohols, amines, esters, carboxylic acids), peptides, amino acids, sugars, anthocyanines, nucleic acids and other compounds with chemical, biochemical or pharmacological properties; in pervaporation processes (involving a separation process based on the molecular interaction between the feed components and a dense non-porous membrane polymer; in which any solute diffused towards the membrane downstream surface is instantaneously desorbed and subsequently removed from the downstream side of the membrane, by either application of vacuum (vacuum pervaporation) or by passing an inert gas over the membrane downstream surface (sweeping-gas pervaporation); in biphasic extraction; in dissolution of carbohydrates (such as cellulose, glucose, maltose and dextrose), carbon nanotubes, metals, metal salts, metal nanoparticles, supercritical CO2 and other compounds with chemical, biochemical or pharmacological properties; and in synthetic transformations (such as chemical catalysis, biocatalysis and chiral auxiliaries) and electrochemical transformation (such as, as an electrolyte and/or in fuel cells) (claimed).    ADVANTAGE - The compounds are present is liquid states at (-50 - 150, preferably 0 - 80) degrees Centigrade. The compounds provide a recyclable and environmentally benign ionic medium, compared to the traditional solvents having risks for environment and public health, are needed in smaller amounts compared to the traditional solvents, are no volatile and thus provide easier containment, storage and reutilization.    DETAILED DESCRIPTION - Tetra-alkyl-dimethyl guanidinium compounds containing organic or inorganic anion of formula (CH3)2N+=C(NR1R2)2.X- (I), are new. (I) are chiral or achiral.    R1 and R2 = T1, T2 or T3;    T1 = 1-30C hydrocarbyl (optionally containing double or triple bonds, and optionally saturated aromatic rings) (preferably 1-30C hydrocarbyl having 1 - 15 CH2 units replaced by di-radicals selected from O, NR3, S, SO, SO2, CO, SiR3R4 or P(O)R3; or 1-30C hydrocarbyl having 1 - 15 CH2 units replaced by tri-radicals selected from N, SiR5 or PO) (all having at least one H replaced by F, Cl, Br, I, OH, SH or NH2), H, F, Cl, OH, SH or NH2;    T2 = (thio)imide, sulfonimide, N-acyl-sulfonamide, N-acyl-phosphoramide or other anion of formula (R1-Z-)2N-;    T3 = ascorbate, isocyanurate, barbiturate, ferrocenecarboxylate, methanefullerenecarboxylate or T1 and/or T2;    a pair of R1 and/or R2 = at least one ring; including aromatic ring, bonded together by at least one single, double or triple bond;    X- = phosphite, phosphonate (PF6-, H2PO2-, H2PO4-, PO3-), borate (BF4-, BO2-, BO3-), nitrile, nitrate (NO2-, NO3-), sulfate (HSO4-), cyanide, cyanate (CN-, SCN-, CNO-), dicyanamide ((CN)2N-), azide (N3-), carbonate (HCO3-), bromate (BrO3-), iodate (IO3-, IO4-), chlorite, chlorate (ClO-, ClO2-, ClO3-, ClO4-), halide, metal halide anion, anions containing group Ib - VIIb, group IIIa - VIa, or group VIII elements, (thio)carboxylate, carbamate, dithiocarbamate, xanthate, sulfonate, organo-sulfate, organo-sulfamate, organo-phosphate, (thio)phsophonate or other anion of formula R1-Z-Y;    Z = SO2, P(Y)R2, As(Y)R2 or CY;    Y = O or S;    R3-R5 = no defined.    An INDEPENDENT CLAIM is included for preparation of (I).