Synthesis and Characterization of Alkylammonium Hyponitrites and Base-Stabilized Hyponitrous Acid Salts

A number of alkylammonium and bipyridinium salts of hyponitrous acid, namely, N, N, N ‘, N ‘-tetraethylethylenediammonium ( 3 and 4 ), N, N, N ‘, N ‘-tetramethylethylenediammonium ( 5 ), triethylenediammonium ( 6 ), diquinuclidinium ( 7 ), 2,2‘-bipyridinium ( 8 ), 4,4‘-bipyridinium ( 9 ), 4,4‘-trimethylenebis(1-methylpiperidinium) ( 10 ), 4,4‘-trimethylenepiperidinium ( 11 ), and bis(triethylammonium) ( 12 ) hyponitrite salts, have been synthesized by the reaction of the corresponding amine in either anhydrous diethyl ether or absolute ethanol with hyponitrous acid solution in anhydrous diethyl ether. Single-crystal X-ray crystallographic data were obtained for sodium hyponitrite ( 1 ), and the thermal decomposition behavior of the salt was examined. The new salts were characterized by IR and Raman spectroscopic data and elemental analyses. Compounds 4 and 7 − 9 were also characterized by single-crystal X-ray crystallography. The hyponitrite anions in 1 and 7 − 9 exhibit similar structural features. The anions are planar with average N N and N−O bond distances of 1.237 and 1.380 Å, respectively. The monoprotonated hyponitrite anion and solvated hyponitrous acid molecules present in 4 also exhibit close structural similarity to the dianion in the crystals of 1 and 7 − 9 . Most of these salts are soluble in organic solvents. The UV−vis spectra of the sodium and alkylammonium salts ( 1, 3 − 7, and 10 − 12 ) in aqueous 0.1 M NaOH exhibit an absorption peak at 248 nm (λ max ) with a molar extinction coefficient of 7033 ± 153 M - 1 cm - 1 . Differential scanning calorimetric data for the salts reveal exothermic decomposition of the hyponitrite species. Significantly, the pentahydrate and anhydrous forms of Na 2 N 2 O 2 exhibit distinct thermal decomposition behavior. The thermogram of the pentahydrate exhibits two exotherms at ca. 96 and 382 °C, whereas that of the anhydrous Na 2 N 2 O 2 exhibits a single exotherm at ca. 382 °C. The exotherm at 96 °C observed for the pentahydrate is explained in terms of a coupled phase transition−dehydration process. The alkylammonium and bipyridinium salts undergo exothermic decomposition at a considerably lower temperature in the range 67−170 °C. Electrochemistry of the salts in acetonitrile solvent reveal an irreversible oxidation at ∼1.80 V vs an Ag/AgCl reference electrode.