The present invention relates to a solution comprising water, N,N,N, 2,2,6, 6-heptamethyl-4-piperidinaminium chloride of formula (II) and low amounts of N,N,N, 2,2,6,6-hexamethyl-4-piperidinamine of formula (I), byproducts and, N,N,1,2,2,6,6,octamethyl-4-piperidinaminium chloride of formula (III), a process for the production of this solution and the use of this solution for the production of an aqueous mixture comprising inter alia the corresponding TEMPO-derivates of formula (IV), (V) and (VI) wherein this aqueous mixture can be used as electrolyte in one chamber of a redox-flow cell for storing electrical energy.