2
4
KUKHAREV et al.
0
.5
At low catalyst concentrations (k′ >> k″c
),
lead to positive entropy of activation. The low en-
thalpy of activation is consistent with the above con-
clusion, for the step characterized by the rate constant
k3 almost does not affect the order of binding of atoms.
HgX2
Eq. (8) is converted into first-order equation with re-
spect to the substrate and catalyst, while at high cata-
0
.5
lyst concentrations (k′ << k″c
), the kinetic equation
HgX2
is of first order in the substrate and of an order of 1.5
in the catalyst:
Thus the results of our kinetic study showed that
the cyclization of vinyl ethers derived from amino
alcohols into oxazolidines, catalyzed by mercury(II)
salts, is a multistep process. The first step is coordina-
tion of the mercury atom at the double C=C bond, and
next follow intramolecular cyclization (rate-determin-
ing step) and demercuration; the latter reaction occurs
both spontaneously and by the action of mercury salt
anion.
1
.5
I I
∂cII/∂τ = k′cHgX2 c ; ∂cII/∂τ = k″cHgX2c .
In all intermediate cases, taking into account the
first order of the reaction with respect to the substrate,
a linear relation should be observed between the ex-
perimental rate constant reduced to the catalyst con-
centration and cHgX2:
0
.5
k′exp/cHgX2 = k′ + k″cHgX2.
(9)
EXPERIMENTAL
In fact, the experimental rate constants determined
at 40°C for different catalyst concentrations (see table)
give excellent correlations:
Freshly distilled commercial 1-methylpyrrolidin-2-
one and 2-vinyloxy-N-phenylethanamine synthesized
according to the procedure described in [4] (with
a purity of no less than 99.3%, according to the TLC
data) were used in kinetic experiments. The purity of
the initial compounds was checked, and their iden-
tification in the reaction mixture was performed, by
gas–liquid chromatography on an LKhM-80 chroma-
tograph equipped with a thermal conductivity detector;
carrier gas helium; steel column, 3000×3 mm, packed
with 3% of OV-17 on Inerton Super (0.160–
0
.5
for Hg(OAc)
r = 0.999, s
for HgCl
r = 0.989, s
2
: k′exp/cHgX2 = 0.0062 + 0.615cHgX2;
0
= 0.03;
(10)
(11)
0
.5
2
: k′exp/cHgX2 = 0.0062 + 0.32cHgX2;
0
= 0.05.
The existence of correlations (10) and (11) confirms
the proposed mechanism for the isomerization of
aminoethyl vinyl ethers into oxazolidines.
0
.200 mm); oven temperature programming from 150
to 200°C at a rate of 4 deg/min.
Insofar as the rate of isomerization is directly pro-
Isomerization of 2-vinyloxy-N-phenylethan-
amine (I) (kinetic measurements). Samples of
a 2.34 M solution of vinyl ether I and of a 0.0936 to
portional to the rate of the first step [k , Eq. (7)], it
1
should depend on the relative stability of intermediate
cation Ia. Mercury(II) chloride is a much stronger
electron acceptor than mercury(II) acetate; therefore,
cation Ia with X = Cl should be more stable, and k1
and correspondingly kexp should be larger. This is ob-
served experimentally: at equal or similar catalyst con-
0
1
.0069 M solution of mercury(II) acetate or chloride in
-methylpyrrolidin-2-one, 5 ml in volume, were ad-
justed to 40°C and mixed. Samples of the reaction
mixture, 1 μl, were withdrawn at definite time intervals
using a microsyringe and analyzed by GLC. The con-
centration of ether I was determined by the absolute
calibration technique. The chromatographic peak areas
were calculated using an I-02 automatic digital
integrator.
centrations, the reactions catalyzed by Hg(OAc) are
2
faster by a factor of ~1.7 than those catalyzed by
HgCl (see table).
2
The temperature dependence of the isomerization
rate constant of vinyl ether I in the presence of mer-
cury(II) acetate fits the Arrhenius equation. The activa-
REFERENCES
tion parameters calculated for the temperature range
≠
4
0–70°C (see table) are ΔH = 10.7 kcal/mol and
1
. Trofimov, B.A., Geteroatomnye proizvodnye atsetilena
Heteroatom Acetylene Derivatives), Moscow: Nauka,
981, p. 8; Elderfield, R. and Short, F., Heterocyclic
≠
ΔS = – 42.9 e.u. The high negative entropy of activa-
(
1
tion indicates that the rate-determining step is intra-
molecular cyclization (k ) since the other steps either
3
Compounds, Elderfield, R., Ed., New York: Wiley, 1957,
vol. 5. Translated under the title Geterotsiklicheskie
soedineniya, Moscow: Inostrannaya Literatura, 1961,
vol. 5, p. 16.
do not involve appreciable change in the number of
degrees of freedom (k , k ) or are accompanied by
1
5
increase in the number of species (k ), which should
4
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 1 2009