Nitrito compounds

Nitrito- Compounds. Organic compds containing one or several —O.N 0 groups which are called oxynitroso radicals. These compds are also known as organic nitrites. Some are expl, as, for example, Methyl Nitrite, CHj.O.NO (see in this Vol). They are not as stable as the corresponding nitrates and nitrocompds Ref Hackh s (1972), 457... 

Metal nitrites and nitrito compounds. Until recently the only stable simple metal nitrites known were those of the alkali and alkaline-earth metals, Zn, Cd, Ag(i), and Hg(i). The alkali nitrites decompose at red heat, the others at progressively lower temperatures. The ionic nitrites of the more electropositive metals contain the NOJ ion which in NaN02 has the following configuration ONO, 1154°, and N-0, 1-236 A. It may be of interest to summarize here the structural data for the unique series NOj, NO2, and NO2 with respectively 16,17, and 18 valence electrons ... 

In contrast to Ni(tu)4Cl2, which forms finite molecules in which there is an (unexplained) asymmetry (the lengths of the two trans Ni-Cl bonds being 2-40 and 2-52 A),the thiocyanate Ni(tu)2(NCS)2 consists of infinite chains of edgesharing octahedra, (e) in contrast to Ni(en)2(NCS)2, type (b), the nitrito compound Ni(en)20N0 is built of chains of vertex-sharing octahedra, (f). ... 

As shown in Figure 3 (A) and (B), good correspondences exist between the decrease of the band at 1558 cm l and the increase of N2, N2O, and CO2. By contrast, the correlations were not found for the bands at 1658 cm (nitrito-compound), 2266 and 2241 cm (NCO), or 1724 cm"l (carbonyl). The doublet at around 1400 cm" (nitrate) also decreased. However, the relative change of the band intensity was smaller than that of the band at 1558 cm and moreover it was confirmed by a separate experiment that N2 was not produced by thermal desorption of nitrate species which was formed only from NO2. Therefore, it is unlikely that N2 observed in the above experiment was produced from nitrate. Thus, N2, N20> and CO2 were most probably produced by the decomposition of the nitro-compounds formed during the NO2-C3H6-O2 reaction. 

It may also be possible that a part of the nitro-compounds are transformed to N2 via isocyanate species (and/or cyanide), since the band at 2241 cm"l also slowly decreased in NO 2- On the contrary, it is unlikely that nitrito-compounds participate in the formation of N2. Slight increase of the bands at around 1700 cm"l (Figure 3 (B)) suggests the possibility of the formation of carbonyl species from the nitrocompounds as intermediates. However, the detailed mechanism subsequent to the formation of the nitro-compounds is not very clear yet. 

A detailed mechanistic study of the interactions of NO and N02 with MbFeIV = 0 (an analog of compound II above) was recently conducted by Herold and Rehmann (141). These authors demonstrated that MbFeIV= 0 reacts rapidly with NO to form an intermediate possessing a characteristics spectrum, consistent with the formation of the ferric nitrito complex MbFem(ONO). This reaction has analogy with the reactions of NO with the CrIV = O complex described above (112). 

In this paper author reported the reactivity of newly synthesized Co(III)-nitrosyls complexes with superoxide radical to follow nitric oxide dioxygenation. Two new Co(III)-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(12-TMC)-Com(NO)]2+ (1) and [(13-TMC)Coin(NO)]2+ (2), were synthesized via [(TMC)Con(CH3CN)]2+ + NO(g) reactions. Spectroscopic and structural characterization showed that these compounds bind the nitrosyl moiety in a bent end-on fashion. Complexes 1 and 2 reacted with K02/2.2.2-ciyptand to produce [(12-TMC)Con(N02)]+ (3) and [(13-TMC)Con(N02)]+ (4), respectively these possess 0,0 -chelated nitrito ligands. 

Nitroprusside reacts with hydroxide to yield the corresponding nitro complex. The rate is first order in both reactants and probably involves nucleophilic attack by OH on the NO followed by proton ionization. Infrared studies on 0-labeled compounds indicate the NOJ to be bound as nitro (-NO2) rather than as nitrito (-ONO) [3, 116]. 

Cr(XH3)s(XO.,)]R .—These salts were discovered by Christensen in 1SS1. It is still doubtful whether the salts are true nitrito-salts with the group O—NO in the nucleus, or whether they are nitro-compounds they are yellow in colour, which points to the possibility that they are nitro-eompounds. Only one series is known, whereas in the eobalt-ammino-compounds both nitro- and nitrito-salts have been isolated (see p. 144). 

As an example of this, consider the three compounds obtained from hexammino-eobaltie chloride by replacing ammonia by nitrito-groups. The same total number of acidic radicles is retained in the molecule, but the derivatives differ in electrical conductivity in equivalent solutions. The molecular conductivity of hexammino-eobaltie chloride at 25° C. and 1000 litres dilution is 431-6 of the mononitrito-derivative, [Co(NH3)5(N02)]C12, is 246-4 of the di-derivative, [Co(NH3)4(N02)2]C1, is 98-83 and of the trinitrito-derivative, [Co(NH3)3(N02)3], is zero, this being a non-electrolyte. Further substitution transforms the complex from cation to anion thus [Co(NH3).2(N02)4]K. 

Werner knew of two other examples of linkage isomerism, both nitro-nitrito isomers, and they underwent the same period of skepticism and confirmation as the compounds discussed above although considerably less work was done with diem. A period of more than 50 years passed before Basolo and coworkers attacked the problem with rather amazing results.w Linkage isomerism, once relegated to a few lines as an "exceptional" situation in discussions of isomerism, now boasts an extensive chemistry which continues to develop. The first new linkage isomers prepared were mtro-nitnto isomers of Cr lII), Rh(lll), Ir(lll), and Pt(lV). In all cases except Cr(lll), the nitrito isomer converts readily to the more stable nitro isomer... 

On the basis of these observations and conclusions it was suggested that the cobalt complexes described above might follow a related pathway. Here, however, it can be argued that the presence of base in, e.g. the reactions of Co(dmgH)2NO, leads initially to the quantitative formation of Co,(dmgH)2(NO)B. In this case attack of 02 leads first to the peroxy compounds and then, because of the absence of a suitable NO+ compound, rearrangement occurs to give the nitrito derivative. Clearly whether or not nitro or nitrato compounds are produced would depend on the concentration of base B. In some cases it is possible to obtain mixtures of such products. These oxidations are also observed for other metals, e.g. equations (37) and (38). 

Contrary to previous indications, a recent study320 of the products of various synthetic routes to [Co(phen)2(N02)2]+ and [Co(bipy)2(N02)2]+ has shown that only the cis-nitro-isomers can be isolated. Although different crystalline forms of several compounds containing these cations were recognized, a thorough search did not reveal any trans-isomers or nitrito co-ordination. 

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