Trans-nitrous acid

The cis and trans forms differ greatly in energy and the cis form, being generally less stable, is readily converted into the trans form in presence of suitable reagents like halogens, halogen acids or nitrous acid e.g.,... 

Bongartz, A., J. Karnes, F. Welter, and U. Schurath, Near-UV Absorption Cross Sections and Trans/Cis Equilibrium of Nitrous Acid, . /. Phys. Chem., 95, 1076-1082 (1991). 

Aziridines not substituted on the nitrogen atom react with nitrous acid to produce olefins.324 An N-nitroso compound is an intermediate (2-51) other reagents that produce such intermediates also give olefins. The reaction is stereospecific cis aziridines give cis olefins and trans aziridines give trans olefins.325 Aziridines carrying N-alkyl substituents can be converted to olefins by treatment with ferrous iodide326 or with m-chloroperbenzoic acid.327 An N-oxide intermediate (9-28) is presumably involved in the latter case. 

Thiochroman-4-ones are reduced to thiochroman-4-ols by sodium borohydride6 and lithium aluminum hydride.50 Lithium aluminum hydride reduction of thiofiavan-4-ones (27) forms the 2,4-ws-thiofiavan-4-ols (28) as in Eq. (8). By contrast, deamination of 2,4-cis-4-aminothio-flavans (29) with nitrous acid produced the trans- alcohol (30) as shown in Eq. (9).50 The alcohols obtained by the hydride reductions have... 

The ground state nitrous acid exists in planar cis and trans forms of comparable stability, the trans form being lower in energy by about 0.5 kcal mol D0(HO—NO) = 2.09 0.03 eV, D0(H—ONO) = 3.36 0.03 eV. 

In 1875, 0. W. Gibbs made a series of dinitritotetrammines under the name croceo-salts and S. M. Jorgensen, in 1894 , made a series of isomeric dinitritotetrammines which he called flavosalts. A. Werner showed that the two series of salts are probably structurally alike, and are probably analogous to the cis- and trans- forms of nitrous acid. The solubilities of several of these salts were by J. N. Bronsted and A. Petersen, by V. K. la Mer and C. F. Mason, and by F. Ephraim. 

A more striking example of the influence of conformation on the reaction outcome is seen in the nitrous acid deamination of 2-aminocyclohexanols which takes place by rearrangement of a group on the carbinol carbon that is anti to the developing carbocation. The deamination reaction is very fast and the products reflect the population of the chair conformers. The trans isomer exists mainly in the diequatorial conformer thus the only group anti to the amino... 

Although nitrous acid has never been isolated as a pure compound, its aqueous solution is a widely used reagent. Nitrous acid is a moderately weak acid with p/fa = 3.35 at 291 K. In the gaseous state, it adopts the trans-planar structure, as shown in Fig. 15.2.2(c). 

When oxides of nitrogen come in contact with water, both nitrous and nitric acids are formed (18) (Table IV). Toxic reactions may result from pH decrease. Other toxic reactions may be a consequence of deamination reactions with amino acids and nucleic acid bases. Another consideration is the reactions of oxides of nitrogen with double bonds (Table IV). The cis-trans isomerization of oleic acid exposed to nitrous acid has been reported (19). Furthermore, the reaction of nitrogen dioxide with unsaturated compounds has resulted in the formation of both transient and stable free radical products (20, 21) (Table V). A further possibility has been raised in that nitrite can react with secondary amines to form nitrosamines which have carcinogenic properties (22). Thus, the possible modes of toxicity for oxides of nitrogen are numerous and are not exhausted by this short list. 

It appears that the NO+ group can be transferred directly only to those species which can behave as reasonably powerful nucleophiles in moderately acid solution. This is undoubtedly the reason why species such as azide ion and amines do not appear to act in this way since they are very extensively protonated in these solutions. Azide ion catalysis has been reported in one case, however (Meyer and Williams, to be published) the denitrosation of N-acetyl-N-nitrosotryptophan, which reacts very rapidly, has been examined at pH 6 where a substantial quantity of free azide ion exists. Presumably the same would be true for some amines at these very low acidities. However, there is experimental evidence from two independent groups which shows that a direct (sometimes called trans-) nitrosation by nitrosamines can occur with aromatic amines. The reactions of N-nitrosodiphenylamine in aqueous acid solution were studied in this context (Challis and Osborne, 1973). The reaction was acid-catalysed for all the substrates studied and was believed to involve the protonated form of the nitrosamine (here written as PhjNNO, H" ). Two separate pathways were detected (a) a direct reaction with N-methylaniline (without the formation of free nitrous acid or a derivative of nitrous acid) as outlined in Scheme 20 and b) an indirect reaction with... 

A cis and a trans form are possible for HNOO. However, only one form, probably the trans form, was detected in the matrix-isolation experiments. Imine peroxide isomerizes to nitrous acid upon irradiation with UV or IR light. 

Reaction of iodine with trans -hyponitrous acid yields nitrous acid and nitric acid ... 

Planar nitrous acid forms two isomers (Scheme 30). The trans form (77) (ATff = -80.18 kJmol , d(N=0) 117.7 pm,... 

As shown in Table I, a concentration of 20% or more crude trans--gyplure in formulations of cis-gyplurt is sufficient to cause inactivation the mechanism of this inactivation is not known. The trans- form was prepared by elaidinization of the cis isomer with nitrous acid. The propyl and butyl analogs of w-gyplure were completely devoid of activity in field tests. These results show that a cis double bond and an acetoxy group are necessary for activity (27). 

Niobiun bromide (NbBrg) BrgNb (g) 527 Nitrous acid, trans (MONO) HiNiOgCg) 1239 ... 

Jefferson DA (2000) The surface activity of ultrafine particles. Phil Trans Roy Soc Lond A 358 2683-2692 Jose-Yacamai M (1998) The role of nanosized particles. A frontier in modem materials science, from nanoelectronics to environmental problems. Metall Mater Trans A 29 713-725 Kalberer M, Ammann M, Arens F, Gaggeler HW, Baltensperger U (1999) Heterogeneous formation of nitrous acid (HONO) on soot aerosol particles. J Geophys Res 104 13825-13832 Kamm S, Mohler O, Naumann KH, Saathoff H, Schurath U (1999) The heterogeneous reaction of ozone with soot aerosol. Atmos Environ 33 4651-4661... 

Nitrous acid. Only dilute solutions of nitrous acid have been prepared, and these rapidly decompose, evolving oxides of nitrogen. Two structures can be envisaged for the molecule of nitrous acid, the second of which could exist in cis and trans forms ... 

This tautomerism is suggested by the fact that by the interaction of metal nitrites with alkyl halides two series of compounds are obtained, the nitrites-in which the NO2 group is attached to carbon through an O atom—and the nitro compounds, in which there is a direct N—C link. From i.r. studies of nitrous acid gas it is concluded that there is no evidence for the existence of form (a) and that the two isomers of (b) exist in comparable amounts, the trans isomer being rather more stable. The structure (c) has been assigned to the trans isomer. 

Treatment of A-nitroso-iV-(cr5-2-phenylcyclopropyl)urea with excess sodium formate in methanol at 25 "C for 15 hours affords ( )-3-methoxy-l-phenylprop-l-ene (25%) and 3-methoxy-3-phenylprop-l-ene (60%, Table 15, entry 7). An almost identical result is obtained when the tran -isomer is used as substrate. Formation of the 2-phenylcyclopropyldiazonium ion, decomposition with loss of nitrogen to the 2-phenylcyclopropyl cation, followed by ring opening to form the phenylallyl cation, can explain the result. When [l- Hi]aminocyclopropane is subjected to deamination with nitrous acid in water at 0°C (Table 15, entry 8), allyl alcohol is obtained, which is isolated as the 4-(phenylazo)benzoate derivative in 44% yield. In this case, the deuterium is only located at the C2 allyl position. ... 

NDMA is not an industrially or commercially important chemical nevertheless, it can be released into the environment from a wide variety of manmade sources. This is due to the inadvertent formation of NDMA in industrial situations when alkylamines, mainly dimethylamine and trimethylamine, come in contact and react with nitrogen oxides, nitrous acid, or nitrite salts, or when trans-nitrosation via nitro or nitroso compounds occurs. Thus, potential exists for release into the environment from industries such as tanneries, pesticide manufacturing plants, rubber and tire manufacturers, alkylamine manufacture/use sites, fish processing industries, foundries and dye manufacturers. At this time, NDMA has been found in at least 1 out of 1177 hazardous waste sites on the National Priorities List (NPL) in the United States (VIEW Database 1989). 

The base-catalysed addition of acetone to trans-aziridines (368) affords oxazolidines (369). The complex reaction of 2-aminoethanol with nitrous acid results in the nitroso-compound (370). °... 

Aniline and substituted-anilines react with nitrous acid to form arenediazonium salts a diazonium group can be displaced by a nucleophile. Arenediazonium ions can be used as electrophiles with highly activated benzene rings to form azo compounds that can exist in cis and trans forms. Secondary amines react with nitrous acid to form nitrosamines. 

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