Frémy's salt is prepared from hydroxylaminedisulfonic acid. Oxidation of the conjugate base gives the purple dianion:
:HON(SOH) → [HON(SO)] + 2 H
:2 [HON(SO)] + PbO → 2 [ON(SO)] + PbO + HO
The synthesis can be performed by combining nitrite and bisulfite to give the hydroxylaminedisulfonate. Oxidation is typically conducted at low-temperature, either chemically or by electrolysis.
Other reactions:
: HNO + 2  →  + HO
: 3  +  + H  →  3  + MnO + 2 HO
: 2  + 4 K → K[ON(SO)]