e salts can be added in solid form or in aqueous solution or in mixtures of water and water-miscible organic solvents, e.g. methanol, ethanol, isopropanol, acetone, tetrahydrofuran and DMSO.The formation of the salts of the formula I is carried out at temperatures between -10.degree. and +60 C., preferably between +5.degree. and +30.degree.