Inhibition of nitrosation of amines by thiols, alcohols and carbohydrates.

The addition of a number of simple alcohols and carbohydrates to reactions of nitrous acid with amines in dilute acid solution resulted in a reduction in the overall rate constant for N-nitrosation. The effects were not very large and complete suppression of nitrosation was not achieved. The results are all consistent with the rapid equilibrium formation of the corresponding alkyl nitrite which is virtually inactive as a direct nitrosating agent itself. Addition of the two thiols L-cysteine and N-acetylpenicillamine, however, had a much more marked effect and it was possible to prevent nitrosation of the amine completely in both cases. This findings was no doubt due to competition from the irreversible S-nitrosation. On the other hand the effect of S-methyl-L-cysteine and L-methionine was rather small. The results are all discussed in terms of the likely reaction mechanisms.