Sodium hyponitrite

The trans isomer is colorless and soluble in water and insoluble in ethanol and ether. :2 NaNO2 + 4 Na(Hg) + 2 H2O → Na2N2O2 + 4 NaOH + 4 Hg Sodium hyponitrite (trans) was prepared in 1927 by A. W. Scott by reacting alkyl nitrites, hydroxylammonium chloride, and sodium ethoxide : RONO + NH2OH + 2 EtONa → Na2N2O2 + ROH + 2 EtOH An earlier method, published by D. Mendenhall in 1974, reacted gaseous nitric oxide () with sodium metal in 1,2-dimethoxyethane, toluene, and benzophenone. The salt was then extracted with water. The method was later modified to use pyridine. Other methods included oxidation of a concentrated solution of hydroxylamine with sodium nitrite in an alkaline medium:NH2OH (conc.) + NaNO2 + NaOH → Na2N2O2 + 2H2O; or electrolysis of sodium nitrite. Hydrates A variety of hydrates ()x of the trans isomer have been reported, with x including 2, 3.5, 4, 5, 6, 7, 8, and 9; but there is some dispute. The hydration water seems to be just trapped in the crystal lattice rather than coordinated to the ions. Liquid N2O4 oxidises sodium hyponitrite (trans) to give sodium peroxohyponitrite [ON=NOO]2−). ==Cis isomer==

The cis isomer of sodium hyponitrite is a white crystalline solid, insoluble in aprotic solvents, and (unlike the trans isomer) decomposed by water and other protic solvents. It was also obtained in 2021 by Carl Hoff and co-workers by ball milling (mechano-chemistry) sodium oxide sodium oxide with 30 psi of nitrous oxide for 4 hours at room temperature. Properties and reactions The anhydrous cis salt is stable up to 325 °C, when it disproportionates to nitrogen and sodium orthonitrite: : 3 → 2 + 2 It is generally more reactive than the trans isomer. ==See also==