Nitrite traps

The stopping solution composition was based on experiments showing that lowering the pH from 9 to 5 to 1 reduced formation of cis-DMNM, perhaps because this prevented elution of the amine from the column, and that addition of ammonium sulfamate lowered cis-DMNM formation, relative to the situation where ascorbate alone was used as a nitrite trap. The hexane wash of the column was introduced to remove a large peak near the solvent front in the GC-TEA, perhaps due to neutral fats. Using the described procedure, the recovery of 70-160 ng NMOR added to 2 g semisynthetic diet was 92 + 19% (mean + S.D. for 13 measurements). The recovery of 227 ng NMOR from 5-8 g whole mouse homogenate using the Iqbal method was 101 + 57% for 7 measurements. 

When thiocyanate ions are added to nitrous acid in water, a pink colouration develops which is believed to be due to the formation of nitrosyl thiocyanate (equation 34), which is too unstable to be isolated but which can be used as a nitrosating agent in aqueous solution. Because the equilibrium constant for ONSCN formation81 is quite large (30 dm6mol 2) at 25 °C, thiocyanate ion is an excellent catalyst for aqueous electrophilic nitrosation. The well established82 series is Cl- < Br < SCN < (NH2)2CS. Thiocyanate ion is also a sufficiently powerful nucleophile to react in acid solution with nitrosamines in a denitrosation process (equation 35), which can only be driven to the right if the nitrosyl thiocyanate is removed by, e.g., reaction with a nitrite trap such as hydrazoic acid. 

TABLE 2. Variation of the rate constant and % rearrangement with added nitrite traps for the reaction of 95 in 3.5 M H2SO4... 

Another fluorodenitration technique features 3 mtrophthaloyl chloride in a dual role as both substrate and potassium nitrite trapping agent to give 3-fluoro phthalic anhydride in 82% yield in sulfolane at 130 °C after 1 5 h [116]... 

At higher acidities, typically 6 M HCl, complications arise the reaction loses its zero order dependence on the [nitrite trap] and the reaction rate actually decreases with increasing acidity for some of the nitrite traps (Biggs and Williams, 1976b). This can be accounted for by the extensive protonation expected for some of the nitrite traps (e.g. urea) at these acidities. 

Fluoroarenes may be prepared by fluorodenitration reactions of activated substrates by reaction with potassium fluoride in sulfolane. Here, it is necessary to add a nitrite trap so that the liberated nitrite ion does not attack the aromatic ring [236]. 

See, for example, Jacox, M.E. and Rook, F.L., Photodecomposition of methyl nitrite trapped in soKd state, /. Phys. Chem., 86, 2899, 1982... 

The efficiency of the nitrite trap HN3 increases strongly with the concentration of H and less strongly with that of the nucleophilic catalyst Br [37]. Other nucleophilic catalysts are Cl , SON", and (NH2)2CS. Their effect was attributed to the intermediate formation of NO adducts with HNO2 in the presence of acid. The results of the kinetic investigations are described in [35]. 

The influence of the nitrite trap HN3 on the Fischer-Hepp rearrangement of N-nitrosoani-line [21], on its denitrosation by an excess of a secondary amine [22], and on other reactions of the starting material [23] were investigated. 

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