Nitrosation processing

The formation of the Wheland intermediate from the ion-radical pair as the critical reactive intermediate is common in both nitration and nitrosation processes. However, the contrasting reactivity trend in various nitrosation reactions with NO + (as well as the observation of substantial kinetic deuterium isotope effects) is ascribed to a rate-limiting deprotonation of the reversibly formed Wheland intermediate. In the case of aromatic nitration with NO, deprotonation is fast and occurs with no kinetic (deuterium) isotope effect. However, the nitrosoarenes (unlike their nitro counterparts) are excellent electron donors as judged by their low oxidation potentials as compared to parent arene.246 As a result, nitrosoarenes are also much better Bronsted bases249 than the corresponding nitro derivatives, and this marked distinction readily accounts for the large differentiation in the deprotonation rates of their respective conjugate acids (i.e., Wheland intermediates). 

Formation of the Wheland intermediate from the ion-radical pair as the critical reactive intermediate is common to both nitration and nitrosation processes. The nitrosoarenes (unlike their nitro counterparts) are excellent electron donors, as judged by their low Eox° as... 

The photolysis of nitrate in surface waters and of nitrite in atmospheric hydrometeors is a relevant source of hydroxyl, while the assessment of the environmental importance of nitration and nitrosation processes needs further studies. Recent results, however, indicate that photonitration and photonitro-sation might play a more important role in the environment than previously suspected [144], All such processes are influenced by substrate and ion concentration and in some cases by the amount of dissolved organic matter. 

J. (1995). Partial replacement of sodium chloride with potassium chloride in dry fermented sausages Influence on carbohydrate fermentation and the nitrosation process. Meat Sci. 40,45. 

We have to assume that the nitrosatable amino groups of the five drugs are not located in the cavity of the CD ring. Because of the location outside of the cavity the nitrosation process can proceed in presence of CDs. 

These systems nitrate aromatie eompounds by a proeess of electro-philie substitution, the eharacter of whieh is now understood in some detail ( 6.1). It should be noted, however, that some of them ean eause nitration and various other reactions by less well understood processes. Among sueh nitrations that of nitration via nitrosation is especially important when the aromatic substrate is a reactive one ( 4.3). In reaetion with lithium nitrate in aeetie anhydride, or with fuming nitrie aeid, quinoline gives a small yield of 3-nitroquinoline this untypieal orientation (ef. 10.4.2 ) may be a eonsequenee of nitration following nucleophilic addition. ... 

Under the same conditions the even more reactive compounds 1,6-dimethylnaphthalene, phenol, and wt-cresol were nitrated very rapidly by an autocatalytic process [nitrous acid being generated in the way already discussed ( 4.3.3)]. However, by adding urea to the solutions the autocatalytic reaction could be suppressed, and 1,6-dimethyl-naphthalene and phenol were found to be nitrated about 700 times faster than benzene. Again, the barrier of the encounter rate of reaction with nitronium ions was broken, and the occurrence of nitration by the special mechanism, via nitrosation, demonstrated. 

The evidence outlined strongly suggests that nitration via nitrosation accompanies the general mechanism of nitration in these media in the reactions of very reactive compounds.i Proof that phenol, even in solutions prepared from pure nitric acid, underwent nitration by a special mechanism came from examining rates of reaction of phenol and mesi-tylene under zeroth-order conditions. The variation in the initial rates with the concentration of aromatic (fig. 5.2) shows that mesitylene (o-2-0 4 mol 1 ) reacts at the zeroth-order rate, whereas phenol is nitrated considerably faster by a process which is first order in the concentration of aromatic. It is noteworthy that in these solutions the concentration of nitrous acid was below the level of detection (< c. 5 X mol... 

Again the uncertainty about the proportion of an observed result which is due to nitration and the proportion which is due to nitrosation exists. Thus, in expt. 11 phenol was being nitrated above the encounter rate and the observed isomer distribution could arise from a combination of nitration by whatever is the usual electrophile with nitration by a new, less reactive electrophile, or with nitrosation, or all three processes could be at work. 

Sodium Bisulfite. Sodium bisulfite [7631-90-5] NaHSO, is occasionally used to perform simultaneous reduction of a nitro group to an amine and the addition of a sulfonic acid group. For example, 4-amino-3-hydroxyl-l-naphthalenesulfonic acid [116-63-2] C qH NO S, is manufactured from 2-naphthol in a process which uses sodium bisulfite (59). The process involves nitrosation of 2-naphthol in aqueous medium, followed by addition of sodium bisulfite and acidification with sulfuric acid. 

The NO nitrosating agents present in the atmosphere are often due to air poUution. High surface area fillers such as carbon black absorb NO and Hberate it during the vulcanization process. Of course, this is the process where NO is most likely to be in contact with the various accelerators. 

Caprolactam was first successfully polymerized to Pedon in 1938 by I. G. Farben and the associated technology was acquired as a part of postwar reparations by the Western AUies and the former USSR (1). By 1965 other countries, eg, Italy and Japan, had developed their own caprolactam processes, each involving nitrosation of an aUphatic ring. 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

The nitrosation of pyrroles and indoles is not a simple process. The 3-nitroso derivatives (84) obtained from indoles exist largely in oximino forms (85) (80IJC(B)767). Nitrosation of pyrrole or alkylpyrroles may result in ring opening or oxidation of the ring and removal of the alkyl groups. This is illustrated by the formation of the maleimide (86) from 2,3,4 -trime thylpyrrole. 

Nitrose, /. (Sulfuric Acid) a solution of nitro-sylsulfuric acid in sulfuric acid, formed in the lead-chamber process. 

Some time ago Tedder (1957) recommended a process which he called direct introduction of the diazonium group , because it replaces the steps of nitration, reduction, and diazotization of an aromatic compound by a one-pot operation with three equivalents of a nitrosating reagent in acidic solution. The first step (Scheme 2-35) is a C-nitrosation and the following steps (Scheme 2-36) are the reduction of the nitroso-arene. 

Research into the mechanism of diazotization was based on Bamberger s supposition (1894 b) that the reaction corresponds to the formation of A-nitroso-A-alkyl-arylamines. The TV-nitrosation of secondary amines finishes at the nitrosoamine stage (because protolysis is not possible), but primary nitrosoamines are quickly transformed into diazo compounds in a moderately to strongly acidic medium. The process probably takes place by a prototropic rearrangement to the diazohydroxide, which is then attacked by a hydroxonium ion to yield the diazonium salt (Scheme 3-1 see also Sec. 3.4). 

It has already been pointed out that nitrosation is probably the first step in diazotization. Ingold (1952) describes the reaction as N-nitrosation and classifies it as an electrophilic substitution, together with related processes such as the formation of 4-nitrosophenol, an example of a C-nitrosation. It was probably Adamson and Kenner (1934) who first applied these ideas to diazotization and realized that in aniline itself the electron density at the nitrogen atom is greater than in the anilinium ion, so that the base is more reactive. On the other hand, the nitrosoacidium ion (3.1), the addition product of nitrous acid and a proton, is a more powerful electrophilic reagent than the HN02 molecule. They therefore represented the first step of diazotization as in Scheme 3-5. 

How proline is converted to NPYR has not yet been fully elucidated and could conceivably occur by either of two pathways (29, ). One pathway involves the initial N-nitrosation of proline, followed by decarboxylation, while in the other, proline is first decarboxylated to pyrrolidine followed by N-nitrosation to NPYR. Since the conversion of N-nitrosoproline (NPRO) to NPYR occurs at a much lower temperature than the transformation of proline to pyrrolidine, the pathway involving intermediacy of NPRO is thus the more likely route ( ). It has been reported that preformed NPRO in raw bacon is not the primary precursor of NPYR in cooked bacon (29,33-5), as shown by the fact that ascorbyl paImitate, when added to bacon, inhibits the formation of NPYR (33). However, this by no means rules out the intermediacy of NPRO which could be formed at the higher temperatures attained during the frying process (29,36). 

Smoking. The effects of smoking on the formation of N-nitros-amines in bacon has been investigated recently by Bharucha et al. ( ). They reported that unsmoked bacon samples generally tended to contain more N-nitrosamines, presumably because of their higher nitrite content at the time of frying. Sink and Hsu (55) showed a lowering of residual nitrite in a liquid smoke dip process for frankfurters when the pH also was lowered. The effects of smoke seem to be a combination of pH decrease and direct C-nitrosation of phenolic compounds to lower the residual nitrite in the product (56). This is an area which requires further study since certain C-nitrosophenols have been shown to catalytically transnitrosate amines in model systems (57). 

We thus assume, that the biochemical processes during tobacco curing may be different from the ui vitro N-nitrosation of secondary and tertiary amines (30). 

The fact that nitrite reacts with the iron of the heme compound was described earlier. Because such a large number of metal ions are present in meat, and because some occur in relatively high concentration, there has been considerable interest in them. For the most part, studies have dealt with how metal ions influence reactions of nitrite. The role of sodium chloride (which is used extensively in meat processing) must also be recognized both in terms of its functional role in making reactants in the meat more or less available, and in terms of reports that it directly influences nitrosation reactions (50). Ando (51) studied the effect of several metal ions on decomposition of nitrite, and in the absence of ascorbate, only Fe++ caused a loss of nitrite but in its presence, the effect of Fe " was more pronounced and Fe+++, Mg++, Ca++ and Zn++ showed similar effects. Lee e al. 

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