110
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
Petrov et al.
[1]•10, [12]•102/mol L–1
[11]•103/mol L–1
hyde 12 and thus decreasing their concentration. The
problem is new and interesting, and its study requires
special efforts.
24
6
5
4
3
2
1
Ternary system 1—2—amine is complicated for invesꢀ
tigation, and it is impossible to propose a specific mechaꢀ
nism for oxidation on the basis of the obtained results.
Literature data cannot help: in a huge number of works on
acidꢀ and baseꢀcatalyzed transformations of epoxides, the
authors operate only with concepts in the framework of
heterolysis. In addition mixing of Hꢀacid and base, as it
was done in our work, seems unreasonable from the viewꢀ
points of concepts on the mechanisms of reactions of
epoxides and the practice of using epoxides, for example,
via catalyzed solidification. A similar case was described
earlier8: the acidꢀcatalyzed oxidation of the BS and deꢀ
composition of hydroperoxide in the TS accelerated with
an increase in the alcohol concentration in the solution
accompanied by a decrease in the acidity. We believe that
the interaction of positively charged protonated particles
with neutral particles resulting in the formation of an
intermediate complex that transforms via parallel heteroꢀ
lytic (A) and homolytic (B) routes (Scheme 2) can be
accepted to be the basis of the scheme of the mechanism
of oxidation of TS amine—epoxide—acid.
20
16
3
1
1
2
12
2´
8
4
1´
3´
3
2
600
1200
1800
2400 t/s
Fig. 3. Kinetic curves of consumption of epoxide 1 (1—3, circles)
and accumulation of benzaldehyde 11 (1´—3´, triangles)
and aldehyde 12 (1—3, rhombi) in a MeCN solution, [1]0
= 0.52 mol L–1, [2] = 0.034 mol L–1, 343 K: oxidation of BS 1—2,
light points (1, 1´, 1); oxidation of TS 1—2—7, [7] = 0.25 mol L–1
=
,
black points (2, 2´, 2); oxidation of the BS in the presence of
pyridine 10, [10] = 0.41 mol L–1, black—white points (3, 3´, 3).
Scheme 1
SEH+ + NB
NBH+ + SE
Scheme 2
SE is styrene epoxide, NB is nitrous base.
ence of all nitrogen bases tested by us (see Figs 2 and 3). The
detailed mechanism of formation of aldehyde 12 in soluꢀ
tions of Hꢀacids from compound 1 is unknown; however,
the protonation of epoxide as a necessary prerequisite for
the formation of aldehyde 12 is always postulated.6 Thereꢀ
fore, it is quite unexpected that aldehyde 12 is nearly comꢀ
pletely absent from the oxidates of manometric experiꢀ
ments with all amines tested in this work. Pyridine 10 is
Am is amine.
i. Oxidation.
The inhibition ability of amines seems to be insignifiꢀ
cant: strictly speaking, compound 7 is not inhibitor, unꢀ
like 3, but, as it is clear from the results of our work, the
acceleration effect of these amines is comparable. A simiꢀ
lar acceleration of BS oxidation involving phenols was
found only in experiments with hydroquinone. Probably,
the acceleration of oxidation of BS 1—2 is related to the
oxidation of amines in TS amine—1—2. The following
variants of the mechanism are possible:
(1) amines are oxidized with participation of the deꢀ
sired quasiꢀradical particle that appears in the BS;
(2) the oxidation of TS amine—1—acid proceeds via
different mechanism that the oxidation of BS 1—acid;
(3) amines are oxidized by accumulated H2O2.9
It is difficult to elucidate each contribution because of
a complicated experiment: it is impossible to iodometriꢀ
cally monitor the hydrogen peroxide concentration in
brightly colored oxidates of the TS. The study of the naꢀ
ture of colored products is promising: the color appears
only in an oxygen atmosphere.
a stronger base than compound 7, pKPyH+ = 5.21, pK7H
=
+
= 4.62 (H2O, 298 K).7 If the accumulation of aldehyde 12
at unchanged concentrations of compounds 1 and 2 would
be determined by the protonated epoxide content only,
pyridine 10 should more strongly suppress the accumulaꢀ
tion of aldehyde 12. However, aldehyde 12 is nearly absent
in all oxidates of experiments with amines (see Fig. 2,
curves 1 and 2). In the case of pyridine 10, aldehyde 12 is
accumulated in measurable amounts even at high [Py] (see
Fig. 2, curve 4, cf. curves 2 and 3 in Fig. 3). The sharp
decrease (by one—two orders of magnitude) in the conꢀ
centration of aldehyde 12 in the presence of amines is
explicitly caused not only by proton—acceptor properꢀ
ties of these bases. Possibly, the route of oxidation of
TS 1—2—amine proceeds through the same intermediate
compounds of particles that precede the formation of aldeꢀ
hyde 12. Possibly, amines themselves, regardless of their
relation to oxidation, block the formation of aldehyde 12
interacting with particleꢀprecursors of formation of aldeꢀ