We report the results of a kinetic study of the reactions of a number of ni
trogen nucleophiles with the nitrosothiol S-nitrosopenicillamine (SPEN). Th
e range of nucleophiles includes primary, secondary and tertiary aliphatic
amines, together with hydrazine, hydroxylamine, azide ion, ammonia, semicar
bazide, thiomorpholine and S-methylcysteine. Secondary amines form N-nitros
amines quantitatively. As expected, reaction occurs via the free base forms
of the nucleophiles and consequently most of the reactions take place read
ily only at relatively high pH. Experiments were carried out with [nucleoph
ile] much greater than [RSNO], and for many reactions, plots of the first o
rder rate constant vs. [nucleophile] were linear. For ammonia and the prima
ry amines, however, this plot tended to level off at high [nucleophile] and
an explanation is offered involving the reversible formation of an inactiv
e RSNO-amine complex, for which there is spectral evidence, in parallel wit
h the main reaction. For the secondary amines there is a reasonably good Br
onsted plot with a beta value of approximate to 0.2. The much greater react
ivities of S-methylcysteine and thiomorpholine, compared to those of primar
y amines and morpholine respectively are consistent with initial attack at
the sulfur atom, followed by an internal rearrangement. Over the whole rang
e of nucleophiles studied there is a reasonable correlation with the Ritchi
e N+ parameter, and not with the Pearson n scale. Comparisons are made with
the corresponding reactions of alkyl nitrites and N-methyl-N-nitrosotoluen
e-p-sulfonamide (MNTS).