Nitroxyls

Nitroxylic acid, HiNO . Yellow NajNOa formed by electrolysis NaN02 in NHj. Structure unknown free acid unknown. Nitramide, H2NNO2. A weak acid. 

H2NO2 nitroxylic acid H2SO2 sulfoxylic acid... 

Eor antioxidant activity, the reaction of aminyl radicals with peroxy radicals is very beneficial. The nitroxyl radicals formed in this reaction are extremely effective oxidation inhibitors. Nitroxides function by trapping chain-propagating alkyl radicals to give hydroxylamine ethers. These ethers, in turn, quench chain propagating peroxy radicals and in the process regenerate the original nitroxides. The cycHc nature of this process accounts for the superlative antioxidant activity of nitroxides (see Antioxidants). Thus, antioxidant activity improves with an increase in stabiUty of the aminyl and nitroxyl radicals. Consequendy, commercial DPA antioxidants are alkylated in the ortho and para positions to prevent undesirable coupling reactions. 

Nitroxyl radicals of diarylamines can also be obtained on oxidation with hydrogen peroxide in the presence of vanadium ions. Resonance helps stabili2e these radicals. Eor example, the nitroxide from 4,4 -dimethoxydiphenylainine [63619-50-1] is stable for years, whereas the radical from the unsubstituted diphenylamine caimot be isolated. Substitution in the ortho and para positions also increases the stabiUties of these nitroxides by inhibiting coupling reactions at these sites. However, they are not as stable as the stericaHy hindered tetramethylpiperidyl radical. 

The 9,9-dimethylacridan formed ia the reactioa betweea diphenylamine and acetone, besides functioning as an antioxidant, also improves the flex fife of mbber vulcani2ates siace it forms a more stable nitroxyl radical than the alkylated diphenylamiaes. 

E. G. Rozantsev, Free Nitroxyl Radicals, Plenum Press, New York, 1970. 

According to this mechanism, hindered-amiae derivatives terminate propagatiag reactioas (eqs. 5 and 6) by trappiag both the alkyl and peroxy radicals. In effect, NO competes with O2, and NOR competes with RH. Siace the nitroxyl radicals are not consumed ia the overall reactioas, they are effective at low coaceatratioas. 

Oxidation of 7V-hydroxyazoles can give cyclic nitroxyls (e.g. 571-573) (79AHC(25)205). 

Dinitro-l, 3,5-trimethylbenzene Di-(p-nitroxyethyl) ammonium nitrate a, a -Di-(nitroxyl) methylether... 

HNO Nitroxyl Reactive intermediate (p. 461), salts are known (see also p. 453). 

H4N2O4 Nitroxylic (hydronitrous) acid Explosive sodium salt known Na4[02NN02] ... 

ISodium nitroxylate can he prepared as a yellow solid hy reduction of sodium nitrite with Na/NH3(liq.) ... 

The reaction is based on an early observation by Angeli and Ahrens that Piloty s acid converted aldehydes to hydroxamic acids, and this has formed the basis of the Angeli-Rimini aldehyde test. Di Maio and Tardella propose the above reaction sequence, consistent with the observed second-order kinetics. The possibility that benzenesulfon-hydroxamic acid would decompose in alkali to give nitroxyl (HNO)... 

Fig. 1. Electi onic absorption spectra of the nitroxyl radicals 101 and 102 in benzene.

The g-factors of radicals 101 and 102 are 2.0065 and 2.0059, respectively. The pyrazolylnitroxides have effective magnetic moments at room temperature corresponding to the standard values for one unpaired electron per molecule (1.71 0.05 B.M.). The values of effective magnetic moments of the nitroxyls practically do not change in the temperature range 5-300K. 

Nitroxylgruppe, /. nitroxyl group (nitryl group, NCh, nitro group). 

The early recognition of the role of stable nitroxyl free radicals, e.g., 2,2,6,6-tetramethyl-4-oxopiperidine, and their hindered amine precursors, in polymer stabilization soon led to the development of the hindered amine light stabilizer (HALS) class of photoantioxidants. The first HALS, Tinuvin 770, AO-33, (commercialized in 1974) proved to offer much higher UV-stabil-ity to polymers than any conventional UV-stabilizer available at the time such as UV-absorbers, nickel compounds and benzoates. Table 3). 

Irg 1076, AO-3 (CB), are used in combination with metal dithiolates, e.g., NiDEC, AO-30 (PD), due to the sensitized photoxidation of dithiolates by the oxidation products of phenols, particularly stilbenequinones (SQ, see reaction 9C) (Table 3). Hindered piperidines exhibit a complex behavior when present in combination with other antioxidants and stabilizers they have to be oxidized initially to the corresponding nitroxyl radical before becoming effective. Consequently, both CB-D and PD antioxidants, which remove alkyl peroxyl radicals and hydroperoxides, respectively, antagonise the UV stabilizing action of this class of compounds (e.g.. Table 3, NiDEC 4- Tin 770). However, since the hindered piperidines themselves are neither melt- nor heat-stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. 

Nitryl Perchlorate (Nitroxyl Perchlorate). N02C104, mw 145.47, white cryst mp, decomps rapidly at 120° deflagrates on rapid heating Can be prepd by the action of cone nitric acid on perchloric acid ... 

Nitryl Perchlorate (Nitroxyl Perchlorate, Ni-tronium Perchlorate). N02C104, mw 161.45, OB +29.7% colorl monoclinic hygr ciysts mp decomps above 135° without explg CA Registry No 17495-81-7 1... 

So laBt sich das Perchlor-triphenylmethyl-Radikal in 97%iger Ausbeute zu Tris- pen-tachlor-phenyl]-methan reduziercn2 Nitroxyl-Radikale reagierenzu Hydroxylaminen3 ... 

Grustacean chitins were submitted to regiospeciUc oxidation at G-6 with NaOGl in the presence of the stable nitroxyl radical 2,2,6,6-tetramethyl-l-... 

These additives are thus able to trap both alkyl and peroxy radicals. In this way they interfere with the propagating steps of the degradation process. Since overall the nitroxyl radicals are not consumed in this mechanism these additives are effective at low concentrations in the polymer. 

This highly conjugated molecule was stabilised with nitroxyl biradical side chains. The resulting material had sufficient ferromagnetism that a usable compass needle could be made from it. Despite the success of this demonstration, organic ferromagnetism remains a curiosity. Such polymers are not likely to replace conventional ferromagnetic metals in any application within the foreseeable future. 

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