Temperature effect, nitrosation

N-Nitrosamine inhibitors Ascorbic acid and its derivatives, andDC-tocopherol have been widely studied as inhibitors of the N-nitrosation reactions in bacon (33,48-51). The effect of sodium ascorbate on NPYR formation is variable, complete inhibition is not achieved, and although results indicate lower levels of NPYR in ascorbate-containing bacon, there are examples of increases (52). Recently, it has been concluded (29) that the essential but probably not the only requirement for a potential anti-N-nitrosamine agent in bacon are its (a) ability to trap NO radicals, (b) lipophilicity, (c) non-steam volatility and (d) heat stability up to 174 C (maximum frying temperature). These appear important requirements since the precursors of NPYR have been associated with bacon adipose tissue (15). Consequently, ascorbyl paImitate has been found to be more effective than sodium ascorbate in reducing N-nitrosamine formation (33), while long chain acetals of ascorbic acid, when used at the 500 and lOOO mg/kg levels have been reported to be capable of reducing the formation of N-nitrosamines in the cooked-out fat by 92 and 97%, respectively (49). 

Figure 4, Effect of temperature on the initial rate of nitrosation of glyphosate at pH 3,0 (12), Initial concentrations of glyphosate and sodium nitrite, 10,5 and...

An N-nitrose compound that is unstable is obtained by the effect of dinitrogen trioxide on caproiactam at a low temperature. The compound detonates when the medium is not cooled enough. 

Fig. 2 Effect of temperature on the rate of nitrosation of morpholine with nitrite in citrate-sodium phosphate buffer for temperatures above and below the freezing temperature. (From Ref. 97.). Reproduced with the permission of the Copyright holder, the American Chemical Society, 1975.

Preussmann, R., Angew. Chem., 1963, 75, 642 Removal of the solvent carbon tetrachloride (in which nitrosation had been effected) at ambient, rather than reduced, pressure caused a violent explosion at the end of distillation. Lowest possible temperatures should be maintained in the preparation. Other precursors seem more suitable as sources of diazomethane. 

The pH of a metalworking fluid must be kept above neutrality in order to prevent acid corrosion of the metal In vitro, acid catalyzed nitrosation is optimized at pH 3.5 (4 0) however, it has been shown that In the presence of other catalysts, aqueous solutions of amines and nitrite leads to significant yields of nitrosamines at room temperature over the pH range of 6.4 to 11.0 (41). Furthermore, C-nitro-containing, formaldehyde-releasing biocides, such as bronopol or tris nitro, exert their potential catalytic effect in alkaline solution. It would thus be desirable to determine the optimum pH for a metalworking fluid that would lead to the lowest concentration of nitrosamine possible. 

Alternatively, the reaction may proceed through nitrosation by the nitrosonium ion, NO", and subsequent oxidation of the nitroso compound by nitric acid (Scheme 7.3). There is only a small concentration of NO" in dilute nitric acid and so catalytic amounts of sodium nitrite are sometimes added to increase the quantity. This technique is a useful means of effecting smooth, low-temperature nitrations. 

Andersen RA, Fleming PD, Burton HR, Hamilton-Kemp TR, Sutton TG (1991) Nitrosated, acylated and oxidized pyridine alkaloids during storage of smokeless tobaccos effects of moisture, temperature and their interactions. J Agric Food Chem... 

The keto-enol equilibrium constant of benzoylacetone in water is perturbed in the presence of -cyclodextrin, from a value of 0.62 to 5, and also in sodium dodec-yl sulfate micelles, in both cases by preferential binding of the enol tautomer. Thermodynamic parameters from temperature studies of the equilibrium give more information about the structures of the complexes for example, the enol penetrates further into the cavity of the cyclodextrin, as confirmed by H NMR spectroscopy. Nitrosation of benzoylacetone is slowed in the presence of the cyclodextrin, consistent with a protective effect arising from the strong binding to the enol. 

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