Rate and Equilibrium Constants of Dimethylcarbamoyl Transfer between Pyridine N-Oxides

Article abstract of DOI:10.1023/A:1024974323588

Dimethylcarbamoyl transfer from N-acyloxypyridinium salts to pyridine N-oxides in acetonitrile occurs in one stage by the forced concerted SN2 mechanism. The rate and equilibrium of the reaction are fairly described by the Bronsted equation. The Marcus equation provides a much higher quality of reactivity predictions.

Full text of DOI:10.1023/A:1024974323588

Russian Journal of General Chemistry, Vol. 73, No. 3, 2003, pp. 455 462. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 3, 2003,
pp. 486 493.
Original Russian Text Copyright
2003 by Schroeder, Rybachenko, Chotii, Kovalenko, Grebenyuk, Lenska, Eitner.
Rate and Equilibrium Constants
of Dimethylcarbamoyl Transfer between Pyridine N-Oxides
G. Schroeder, V. I. Rybachenko, K. Yu. Chotii, V. V. Kovalenko,
L. V. Grebenyuk, B. Lenska, and K. Eitner
Mickiewicz University, Poznan, Poland
Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, Donetsk, Ukraine
Received February 22, 2001
Abstract Dimethylcarbamoyl transfer from N-acyloxypyridinium salts to pyridine N-oxides in acetonitrile
occurs in one stage by the forced concerted SN2 mechanism. The rate and equilibrium of the reaction are
fairly described by the Brønsted equation. The Marcus equation provides a much higher quality of reactivity
predictions.
Reactivity analysis and prediction is one of the
most actual problems of organic and bioorganic
chemistry [1, 2]. Over the past years new rigorously
physically substantiated theoretical concepts have
been developed [3], which have found wide applica-
tion (in particular, Marcus equation [4]) in analysis of
reactions whose mechanism is proved or casts no
doubts. They include hydrogen [5], methyl [6], proton
[7], or hydride transfer [8], etc. The situation with
nucleophilic substitution reactions which may involve
formation of intermediate compounds and are not
a priori one-stage, like those with carboxylic acid
derivatives [2, 9], is more intricate. A question arises
whether the analytical technique, especially new, is
suitable for a proposed mechanism which in itself is
most commonly to be diagnosed [3, 10]. At present,
no verified lines of approaching this problem are
available, which necessitates recourse to traditional
methods based, in particular, on the Brønsted equa-
tion [2, 10]. Another impediment to wide use of the
Marcus equation in organic chemistry is the shortage
or, more frequently, lack of rate and equilibrium data
for identity reactions.
Me2NCONu+i, BPh4 + Nuj
Me2NCONu+j, BPh4 + Nui,
(1)
Cl
N
N
O (Nu1), Cl
N
O (Nu2),
O (Nu4),
O (Nu ),
Me
N
3
Me
N
O (Nu6),
N
O (Nu5),
O
N
MeO
N
O (Nu7),
Me2N
N
O (Nu8),
4-ClC6H4CH=CH
PhCH=CH
N
O (Nu9),
N
O (Nu10),
O (Nu11).
4-MeOC6H4CH=CH
N
It the present work we set ourselves the task to
obtain kinetic and equilibrium characteristics of di-
methylcarbamoyl transfer reactions [scheme (1)] in
acetonitrile between acyloxypyridinium salts and
pyridine N-oxides (Nu), including identity (Nui =
Nuj), and also to establish the mechanism of these
reactions, to correlate their rates and equilibria, and to
find out the use of the Marcus equation for data
treatment.
4-Me2NC6H4CH=CH
in Table 1, together with the intrinsic barriers
{1/2(log kii + logkjj)} to the corresponding reactions
and the basicity constants of the leaving group and
nucleophile in water. With reaction nos. 1 29 (i j),
kinetic measurements were performed under pseudo-
first-order conditions in one of the reagents. Reaction
progress was followed by UV spectroscopy at optimal
wavelengths. Therewith, the rate constants of slow
reactions (nos. 8 11) were determined by the initial
All measured and calculated logarithms of the rate
and equilibrium (1) constats in acetonitrile are listed
1070-3632/03/7303-0455$25.00 2003 MAIK Nauka/Interperiodica

456
SCHROEDER et al.
Table 1. Kinetic [log kij, 1/2(log kii + log kjj)] and thermodynamic (log Kij) characteristics of reaction (1)
Reaction
no.
1/2(log kii
log kjj)
+
a
+
+
Nui
Nuj
log kij
log Kij
pKBH (Nui)
pKBH (Nuj)
1
2
3
4
5
6
7
8
9
11
11
11
11
11
11
11
2
3
4
5
10
10
10
10
10
10
9
9
9
9
9
9
8
8
8
8
8
8
2
3
4
5
6
7
8
9
10
11
2
3
4
5
2
3
4
5
2
3
4
1
2
3
4
5
3.83
3.31
2.88
2.34
1.06
0.63
1.21
1.32
1.60
1.83
2.68
2.88
2.62
1.96
0.72
0.84
1.30
2.74
2.50
1.78
0.62
0.87
1.45
2.67
2.43
1.73
0.53
0.90
1.52
1.43
1.43
1.43
1.43
1.43
1.43
1.43
0.79
1.03
1.29
2.05
1.25
1.25
1.25
1.25
1.25
1.25
1.10
1.10
1.10
1.10
1.10
1.10
1.05
1.05
1.05
1.05
1.05
1.05
0.79
1.03
1.29
2.05
3.25
3.88
1.05
1.10
1.25
1.43
0.79
1.03
1.29
2.05
0.79
1.03
1.29
2.05
0.79
1.03
1.29
2.05
0.33
0.79
1.03
1.29
2.05
3.25
3.88
1.43
1.43
1.43
1.43
0.79
1.03
1.29
2.05
3.25
3.88
0.79
1.03
1.29
2.05
3.25
3.88
0.79
1.03
1.29
2.05
3.25
3.88
0.79
1.03
1.29
2.05
3.25
3.88
1.05
1.10
1.25
1.43
1.25
1.25
1.25
1.25
1.10
1.10
1.10
1.10
1.05
1.05
1.05
1.05
1.99b
2.26
2.31
2.15
2.03
1.39
1.20
2.26
2.31
2.15
2.03
2.22
2.26
2.10
1.99
1.35
1.16
2.26
2.30
2.14
2.03
1.39
1.20
2.26
2.3
1.30, 1.28b
0.51, 0.51b
1.57, 1.62b
6
7
11
11
11
11
2
3
4
5
6
7
2
3
4
5
6
7
2
3
4
5
6
7
2
3
4
5
6
7
8
1.99b
1.30, 1.28b
0.51, 0.51b
1.57, 1.62b
1.34c
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
0.64c
0.12c
2.33c
0.90c
0.20c
0.55c
2.77c
0.76c
0.06c
0.70c
2.92c
2.14
2.03
1.39
1.20
2.31, 2.22c
2.40c
2.08c
1.85c
0.57c
0.19, 0.79c
2.20c
2.20c
2.12c
2.21c
1.74d
2.16d
2.24d
3.14d
2.03d
2.54d
2.48d
3.46d
2.10d
2.54d
2.57d
3.51d
0
0
0
0
0
0
0
0
9
10
11
10
10
10
10
9
9
9
9
8
0
0
1.34c
0.64c
0.12c
2.33c
0.90c
0.20c
0.55c
2.77c
0.76c
0.06c
0.70c
2.92c
2.22
2.26
2.10
1.99
2.26
2.3
2.14
2.03
2.26
2.3
8
8
8
2.14
2.03
5
a
b
c
d
Taken from [10]. Obtained from the equation K = k /k . Obtained from correlation equations. Obtained from k = K k .
ij
ij ji
ij
ij ji
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

RATE AND EQUILIBRIUM CONSTANTS OF DIMETHYLCARBAMOYL TRANSFER
457
Table 2. Parameters of Brønsted equations for reaction (1)a
log kij = f(pK+BH
)
Reaction no.
Int
r
S0
n
Nui
Nuj
Nu
Lg
1
2
3
4
5
6
7
8
9
8 11
8 11
8 11
8 11
8 11
8 11
8
9
10
11
2 5
2
3
4
5
6
1.64 0.25
1.15 0.10
1.60 0.18
1.33 0.20
0.68 0.16
0.81 0.11
0.92 0.31
1.22 0.13
0.02 0.22
0.87 0.24
1.63 0.20
2.35 0.14
3.64 0.18
3.72 0.18
3.87 0.20
4.32 0.11
0.47 0.04
0.977
0.992
0.989
0.979
0.946
0.981
0.994
0.994
0.993
0.997
0.999
0.07
0.03
0.05
0.06
0.05
0.03
0.22
0.22
0.24
0.17
0.03
4
4
4
4
4
4
6
6
6
7
4
0.88
1.21
0.90
1.09
1.53
1.45
0.94
0.95
0.96
1.01
1.26
7
2 7
2 7
2 7
1 7
11
1.37 0.07
1.38 0.08
1.40 0.09
1.48 0.05
10
11
1.07 0.03
a
is slope in nucleophile (Nu) or leaving group (Lg) and Int is intercept.
+
concentration technique [11] at c1 0.1 and c2
0.0001 (c1 and c2 are the initial concentrations of the
reagents. In the other cases, c1/c2 10 100, and the
apparent first-order rate constants (kapp) were calculated
by the Guggenheim method as described in [12]. Fast
reactions (nos. 6, 7, 16,17, 22, 23, 28, and 29) were
studied by the stopped-flow technique. The second-
order rate constants (k2) were calculated by the least-
squares method from the dependence of kapp on the
analytical concentration of excess reagent (3 6 points)
[Eq. (2)].
log Kij = (0 0.06) + (2.92 0.13) pKBH
r 0.994, S0 0.18, n 8.
;
(4)
+
+
+
Here pKBH = pKBH (Nui)
pKBH (Nuj).
The equilibrium constants of reaction nos. 6, 7, 16,
17, 22, 23, 28, and 29 fall far beyond the experimental
log Kij range (reaction nos. 2 5, 8 11) and are not
given in Table 1 because of the poor reliability of
predicted values. The rate constants of identity (i =
j) reactions (nos. 30 and 35) were determined in
CD3CN by IR spectroscopy using deuterated analog of
N-oxides, by the procedure described in [15]. Reaction
progress was followed by the absorbance at the hetero-
ring skeletal stretching frequency [15] (1614 and
kapp = krev + k2[Ac Nu+i, X ] or kapp = krev + k2[Nuj]. (2)
The krev values relating to reverse reactions always
met the condition krev << k2 and were not considered.
The concentrations of acyloxypyridinium salts in the
1
1642 cm for reaction nos. 30 and 35, respectively)
of the consumed salt. The rate constants of other
identity reactions (nos. 31 34 and 36 39), as well as
those of reaction nos. 30 and 35 (for the sake of
comparison) were estimated from the Brønsted
2
kinetic experiments were no higher than 2 10 M.
As shown in [13], under these considitions the salts
are almost completely dissociated into ions (electro-
+
correlations log kij = f(pKBH ). Parameters of the
lytic dissociation degree
0.8). The plots con-
corresponding equations are listed in Table 2. As seen
from data in Table 1, the rate constants of identity
reactions, obtained from the correlations, fairly fit
experimental, thus attesting the calculated values.
structed by Eqs. (2) were linear and beared no signs of
ionic dissociation and(or) hydrolysis.
The rate constants of reaction nos. 8, 11, and 30
were determined earlier [9, 14] and refined for the
latter two reactions in the present work. The rate
constants of reaction nos. 40 51 were obtained from
correlation (3).
The equilibrium constants log Kij of reaction nos.
2 5 and 8 11 (Table 1) were determined by UV spec-
troscopy in acetonitrile at 298 K. The components of
these equilibria, [4-(4-dimethylaminostyryl)pyridine
N-oxide (Nu11) (
395 nm) and its O-dimethyl-
log kij = log Kij + log kji.
(3)
carbamoyl salt ( max 510 nm)], have long-wave
max
absorption bands which do not overlap with each
other and with bands of other reagents and are very
The equilibrium constants of the same reactions,
required for the calculations, were determined from
correlation (4).
1
strong [ 36000 and 50300 l mol 1 cm , respec-
tively]. For this reason, we could measure simulta-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

458
SCHROEDER et al.
at three temperatures within the range 298 318 K.
neously two equilibrium concentrations and thus
obtain more accurate and reliable constants. It will be
emphasized that the reliability of our kinetic and
thermodynamic results is confirmed by the fact that
the log Kij values estimated from the correlation
log Kij = log kij log kji nicely fit experimental (re-
action nos. 3 5 and 9 11; Table 1). In all the other
cases, equilibrium constants were difficult to measure
for two reasons: close spectral characteristics of the
reactants and(or) long equilibration time and, a result,
uncontrolled effects of side reactions.
The following values were obtained:
H
56.7
3.0 kJ/mol, S 42.6 5.0 J mol 1 K 1 (reaction no. 6);
1
H
56.4 4.2 kJ/mol,
S
81 14 J mol 1 K (re-
action no. 8); and
H
65.6 3.6 kJ/mol,
S
67
1
12 J mol 1 K (reaction no. 11).
The heats of carbamoyl exchange-reactions be-
tween pyridine N-oxides in acetonitrile were measured
earlier [16] by calorimetric titration (Table 3, reaction
nos. 1 3). The other values in Table 3 were calculated
from the thermochemical cycle by pair summation
[schemes (5) (7)].
The activation characteristics Hij and Sij of the
carbamoyl-transfer reaction were determined from kij
(CH3)2NCO Nu+x + Nuy = (CH3)2NCO Nuy+ + Nux
(CH3)2NCO Nu+y + Nuz = (CH3)2NCO Nuz+ + Nuy
( H0xy)
( H0yz)
(5)
(6)
(CH3)2NCO Nu+x + Nuz = (CH3)2NCO Nuz+ + Nux
( H0xz)
(7)
+
As seen from data in Table 1, in response to struc-
tural factors, the equilibrium (1) constants vary
5 orders of magnitude and the rate constants, up to
7 orders of magnitude. Note for comparison that
acetyl transfer in similar conditions [9] is much faster
(rate constants are 5 7 orders of magnitude higher),
but the equilibrium constants almost coincide with
those in Table 1 for the same Nui Nuj pairs, i.e. they
are independent of the nature of the acyl fragment in
the acyloxypyridinium salt. To explain this fact is our
immediate task. The experimental rate constants of
reaction (1) correlate well with the difference in the
basicities of the nucleophile and leaving group [iden-
tity reactions were not included in correlation (8)].
H0 = ( 3.1 2.7) + (11.7 1.4) pKBH
r 0.972, S0 3.2, n 6.
;
(9)
The equilibrium rate constants [see Eq. (4)], too,
are linearly related to pKBH . This all gives us
+
grounds to believe that we deal here with an isother-
modynamic reaction series; and this, in turn, suggests
[10] identical transition states for all members of the
series and a uniform reaction mechanism. The activa-
tion parameters of reaction (1) are typical of non-
catalytic bimolecular nucleophilic substitution reac-
tions [2, 3]. Such reactions involve stable tetrahedral
transition states and feature negative activation en-
thalpies [17]. Therefore, our
H
values argue in
+
log kij = ( 2.16 0.04) + (1.40 0.03) pKBH
r 0.993, S0 0.20, n 29.
;
(8)
favor of a concerted rather than a step mechanism of
the reaction in study [1]. At the same time, the low
activation enthalpies H ( 50 kJ/mol) and entropies
A similar linear correlation was obtained for the
heat of reaction (1) [Eq. (9)].
1
S [ 60 J mol 1 K ] are indicative of an associa-
tive transition state [3, 9] with a low degree of bond
fission with the leaving group.
Table 3. Heats of dimethylcarbamoyl transfer in CH3CN
at 298 K
Let us now consider identical reactions (Table 1,
reaction nos. 30 39). As seen, their rate varies with
structure up to 2 orders of magnitude, which much
exceeds the experimental accuracy ( 0.05 log. units)
and confidence of the correlation prognosis ( 0.4 log.
units). This finding gives us grounds to state that the
reaction characteristics of the identity carbamoyl
transfer are structure-dependent. The mechanism and
transition state of these reactions were analyzed in
terms of the More O’‘Ferrall Jencks diagram [18]
Reaction no.
Nui
Nuj
H0ij, kJ/mol
1
2
3
4
5
6
2
4
5
2
4
2
7
7
7
5
5
4
30.5 2.0
29.0 1.5
22.4 2.5
8
7
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

RATE AND EQUILIBRIUM CONSTANTS OF DIMETHYLCARBAMOYL TRANSFER
(Fig. 1), whose application to nucleophilic substitu-
459
(Lg Acyl Nu)+
Lg + Nu Acyl+
tion reactions has been considered in detail in [1, 2].
It has therewith been shown that the position of the
transition state on the perpendicular diagonal of the
diagram (bond lengthening/contraction) for identity
1
5
6
reactions is determined by the
/
and(or)
Lg, and
/
(Leffler parameter [19], whereNu
are
eq
,
Lg eq
eq
the sensitivities in nucleophile, lNeuaving group, and
2 10
equilibrium, respectively). The quality of our values
9
3
1
j
+
4
(Table 2) can be tested. There are linear
pKBH
Nu
j
Nu
+
and
pKBH correlations [Eqs. (10) and (11),
respectLivgely].
7, 8
j
+
= (0.28 0.05) pKBH + (1.07 0.07);
(10)
Nu
r 0.964, S0 0.02, n 4.
i
+
= (0.25 0.08) pKBH
(1.67 0.19);
(11)
Lg
0
r 0.800, S0 0.24, n 7.
Lg Acyl+ + Nu
0
Lg + Acyl+ + Nu
1
In terms of the linear free energy approximation,
Lg
for the reaction series
Eqs. (10) and (11) we obtain
=
Lg. From this by
eq
Nu
= 2.74 0.261. The
eq
Fig. 1. More O’Ferrall Jencks diagram for dimethyl-
carbamoyl transfer between pyridine N-oxides (for reac-
tion numbering, see Table 2).
latter value is nicely consistent with an analogous but
independently obtained parameter (2.92 0.13) in Eq.
(4). On the perpendicular diagonal of the More
O’Ferrall Jencks diagram (Fig. 1) we placed points
for the reactions studied. As seen, the points locate
between the (Lg Acyl Nu)+ and (Lg + Acyl+ +
Nu) corners, i.e. the identity carbamoyl transfer be-
tween pyridine N-oxides occurs by a concerted me-
chanism as an SN2 reaction. For numerical charac-
terization of transition-state structures of identity re-
actions, Kreevoy and Lee [8] proposed the tightness
parameter [Eq. (12)] which was defined as a sum of
the forming and cleaving bond orders.
i
+
= 0.19pKBH + 0.59.
(13)
Substituting = 2, 1, and 0 into Eq. (13) we obtain
i
+
pKBH 7.4, 2.1, and 3.1. These values characterize
conditions for realization of the associative (AN + DN),
concerted (ANDN), and dissociative (DN + AN) me-
chanisms of the dimethylcarbamoyl transfer. The
i
+
pKBH values of 7.4 and 3.1 may belong to hypo-
thetical N-oxides only, and, therefore, reactions (1)
all should occur by the forced concerted mechanism
(AN DN). The concerted mechanism (ANDN) could
only be diagnosed for the identity transfer between
Nui5 (Table 1, reaction no. 33). It is interesting to cor-
relate the transition-state properties of reaction (1),
revealed in the present work and reported in the li-
= 2
/
or
= 2
/ + 2.
Lg eq
(12)
eq Nu
The values, as seen from data in Table 2, vary
from 1.53 for the most electron-donor substituent in
the reactants to 0.88 for the most electron-acceptor
substituent in the reaction series. Consequently, as the
basicity of the nucleophile and leaving group in-
creases, the transition state of reaction (1) shifts to the
(Lg Acyl Nu)+ corner of the diagram (AN + DN
mechanism), and as the basicity of the nucleophile
and leaving group decreases, to the (Lg + Acyl+ + Nu)
corner (DN + AN mechanism). Furthemore, taking into
terature. The shift of the transition state along the
i
+
perpendicular diagonal of the diagram as the pKBH of
nucleophile/leaving group charges by unit is deter-
i
+
mined as d = d /dpKBH = 2a/ eq. For reaction (1) we
have d 0.19, which is close to d 0.21, obtained in [20]
for acetyl transfer between phenolate anions.
i
+
account that = 1 +
/
= 1 + 2(apKBH + bB)/
ii eq
eq
[20] we have the following equation for characteriza-
tion of the transition state of identity carbamoyl
transfer between pyridine N-oxides [Eq. (13)].
According to [21], identity reactions should be
described by a quadratic equation like (14), whose
coefficients are determined by Eqs. (10) and (11).
1
The slopes of dependences (10) and (11) are considered equal
i
2
i
+
)
+
to each other.
log kii = a(pKBH
+ bpKBH + c.
(14)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

460
SCHROEDER et al.
log kij
log k11
35
0
0
1
2
35
27
15
34
34
0.5
21
5
8
1.0
1.5
4, 13, 18 4, 20, 26
24, 46, 50
9
40
41, 44, 48
32, 38
33
36, 37
11
2.0
2.5
43
51
39
32
3
4
10, 14, 25, 30 33,
36 39, 42, 45, 49
3, 12
2
2
47
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 pK+BH
3
2
1
0
1
2
3
log Kij
Fig. 3. Rate constants of identity dimethylcarbamoyl
transfer vs. nucleophile basicity (for reaction numbering,
see Table 1).
Fig. 2. Rate of dimethylcarbamoyl transfer vs. equilib-
rium constants (for reaction numbering, see Table 1).
Then in our case we have: a = (0.28 + 0.25)/2 =
0.27 and b = 1.07 1.67 = 0.6. Actually, as seen
from Fig. 2, the log kii values in Table 1 are readily
fitted by a parabola with the above coefficients, but
these points can also be fitted by a straight line.
log kij = 1/2(log kii + log kjj) + 1/2log Kij
(log Kij)2/16[log B
1/2(log kii + log kjj)]. (16)
Let us consider Eq. (16) and data in Table 1.
According to [22, 23], for symmetrical reactions like
(1) in acetonitrile log B
12. Simple calculations
In conclusion let us correlate the rates and equilib-
ria of reaction (1). Treatment of data in Table 1 gave
Eq. (15).
show that the maximal quadratic deviations in our
reaction series at (log Kij)2 12 and [16log B
8(log kii + log kjj)] 200 should be no larger than
0.06 log. units, which compares with experimental
uncertainty and is much smaller than the uncertainty
in estimated rate constants. Therefore, we can dwell,
like in [22], on the first two terms in Eq. (16). The
rate constants of the dimethylcarbamoyl transfer, cal-
culated without inclusion of the quadratic term, well
reproduce experimental values [Eq. (17)].
log kij
=
(2.12 0.07) + (0.50 0.05)log Kij; (15)
r 0.828, S0 0.41, n 42.
As seen from Fig. 3, the points for identity reac-
tions fall out of this dependence, and their variation
is far beyond the accuracy limits of the free term in
Eq. (15). Consequently, the whole group of reactions
cannot formally be described in terms of the Brønsted
equation. On the other hand, there are no objective
reasons why identical reactions should not be included
into correlation (15), the more so that characteristics
of such reactions form one of the key prognostic re-
activity parameters [3, 4] and a source of information
on reaction mechanisms and transition state structures
[20, 21]. In an explicit form, log kii values are used in
the Marcus equation and, in physical sence, should
relate to one-stage transformations only. The reaction
series studied meets this condition. The corresponding
Marcus equation [22] takes form (16).
log kij = (0.05 0.04) + (1.01 0.02)log kij;
r 0.995, S0 0.07, n 32.
(17)
Thus, dimethylcarbamoyl transfer between pyridine
N-oxides is controlled, along with the thermodynamic
factor, by the intrinsic [4] activation barrier
1/2(log kii + log kjj). The role and significance of
this reactivity parameter in analysis and prognosis of
reactions at the carbonyl center are far from under-
standing [1 3] and may form the subject of further
research.
=
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RATE AND EQUILIBRIUM CONSTANTS OF DIMETHYLCARBAMOYL TRANSFER
461
EXPERIMENTAL
ACKNOWLEDGMENTS
The authors are grateful to the Mianowski Science
Foundation (Poland) for financial support.
All nucleophiles were prepared and purified as
described in [9]. Acetonitrile of Acros HPLC grade
was kept over molecular sieves (3 ) before use.
REFERENCES
The rate constants of fast reactions were deter-
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device with a temperature control unit ( 0.1 K). The
rates of slow reactions were measured on an SF-26
spectrophotometer. The rates of identical reactions
were measured on a Specord IR-75 spectrophoto-
meter.
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7.97 d (2H, CH=CH, 16.4), 7.74 d (2H, Ph, 7.1),
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carbamoyl)pyridinium tetraphenylborate that was
prepared as described in [14].
All styrene derivatives were isolated from UV light.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

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