Solvent effect on the volume of the DielsAlder reaction between tetracyanoethylene and trans,trans-1,4-diphenyl-1,3-butadiene

Article abstract of DOI:10.1023/A:1015456003857

From the partial molar volumes of tetracyanoethylene, trans,trans-1,4-diphenyl-1,3-butadiene, and their Diels-Alder adduct, the volumes of the reaction in a series of solvents at 25°C (cm³ mol^-1) were calculated: in dioxane, -26.4; in chloroform, -34.9; in ethyl acetate, -34.5; in acetonitrile, -4.4; in cyclohexanone, -34.0; in 1,2-dichloroethane, -31.8; in benzene, -26.9; in toluene, -24.5; in o-xylene, -21.1; and in mesitylene, -16.9. The solvent effects on the activation and reaction volumes and on the partial molar volumes of the reactants, activated complex, and adduct were discussed.

Full text of DOI:10.1023/A:1015456003857

Russian Journal of General Chemistry, Vol. 72, No. 3, 2002, pp. 432 435. Translated from Zhurnal Obshchei Khimii, Vol. 72, No. 3, 2002,
pp. 465 468.
Original Russian Text Copyright
2002 by Kiselev, Medvedeva, Kashaeva, Shikhaab, Iskhakova, Konovalov.
Solvent Effect on the Volume
of the Diels Alder Reaction between Tetracyanoethylene
and trans,trans-1,4-Diphenyl-1,3-butadiene
V. D. Kiselev, M. D. Medvedeva, E. A. Kashaeva,
M. S. Shikhaab, G. G. Iskhakova, and A. I. Konovalov
Butlerov Research Chemical Institute, Kazan State University, Kazan, Tatarstan, Russia
Received June 4, 2000
Abstract From the partial molar volumes of tetracyanoethylene, trans,trans-1,4-diphenyl-1,3-butadiene,
1
and their Diels Alder adduct, the volumes of the reaction in a series of solvents at 25 C (cm3 mol ) were
calculated: in dioxane, 26.4; in chloroform, 34.9; in ethyl acetate, 34.5; in acetonitrile, 4.4; in cyclo-
hexanone, 34.0; in 1,2-dichloroethane, 31.8; in benzene, 26.9; in toluene, 24.5; in o-xylene, 21.1; and in
mesitylene, 16.9. The solvent effects on the activation and reaction volumes and on the partial molar
volumes of the reactants, activated complex, and adduct were discussed.
Studies of how the elevated pressure affects the
rates and equilibria of chemical and biochemical proc-
esses furnish additional information on their mechan-
isms [1 3]. The activation volume is an important
additional activation parameter allowing calculation
of the partial molar volume of the activated complex.
The foundations for using the activation volume as an
additional characteristic of the activated complex were
laid in [4, 5]. By now, apparatus have been developed
for studying reactions at elevated pressure with direct
monitoring by various methods, including NMR, IR,
and UV spectroscopy [1 3]. Barostats with direct
monitoring are especially convenient for determining
the volume characteristics of fast and/or reversible
reactions.
the reaction volume can be also determined directly,
as the difference between the molar volumes of the
products and reactants, and compared with the value
obtained from the pressure dependence of the equilib-
rium constant [Eq. (2)]. For the reversible Diels Alder
reaction of tetracyanoethylene with 9-chloroanthra-
cene in 1,2-dichloroethane, determinations of the re-
action volume by independent measurements of the
activation volumes of the direct and reverse reactions,
by examination of the pressure dependence of the
equilibrium constants, and by direct measurements of
the apparent molar volumes gave similar results [6].
It is known that for reactions with significant
charge separation in the activated complex the activa-
tion volume strongly depends on the solvent polarity
[1 3]. We suggested that the solvent effect on the
volume characteristics should be significant for any
reactions in which one of the states is capable of
strong specific interaction with the solvent [7, 8]. It
was shown recently that for such a strong acceptor
as tetracyanoethylene the volumes of the reversible
reaction with 9-chloroanthracene [9] and irreversible
reaction with cyclopentadiene [10] and the activation
volume in the irreversible reaction with trans,trans-
1,4-diphenyl-1,3-butadiene [11] in aromatic solvents
depend on the -donor power of the solvent. With the
majority of dienes tetracyanoethylene reacts very fast
or reversibly, so that measurements at elevated pres-
sure in common barostats without direct monitoring
of the concentration variation are inefficient. The
reaction with trans,trans-1,4-diphenyl-1,3-butadiene
The activation volume is the difference between the
partial molar volumes of the activated complex and
reactants in the given solvent; it can be calculated
from the pressure dependence of the rate constant:
( lnk/ P)T
=
(
G / P)T/RT =
V /RT.
(1)
The reaction volume can be determined from the
pressure dependence of the equilibrium constant:
( lnk/ P)T
=
(
G/ P)T/RT =
Vr/RT.
(2)
Precision measurements of the density of dilute
solutions allow determination of the apparent molar
volumes and calculation of the partial molar volumes
of the reactants and reaction products at infinite dilu-
tion. Therefore, in contrast to the activation volume,
1070-3632/02/7203-0432$27.00 2002 MAIK Nauka/Interperiodica

SOLVENT EFFECT ON THE VOLUME
433
Partial molar volumes of trans,trans-1,4-diphenyl-1,3-butadiene (VI), tetracyanoethylene (VII), adduct (VIII), and activated
complex (VIV), reaction volume ( Vr), and activation volumes of the direct ( V1) and reverse ( V ) reactions in a series
1
1
of solvents at 25 C, cm3 mol
No.
Solvent
VI
VII
VIII
VIV
Vr
V 1
V
1
1
2
3
4
5
6
7
8
9
1,4-Dioxane
Ethyl acetate
Acetonitrile
Cyclohexanone
1,2-Dichloroethane 202.7 0.4
Dichloromethane
Chloroform
Chlorobenzene
Benzene
200.4 0.2
195.2 0.3
200.0 0.3
201.7 0.3
105.7 0.2
112.1 0.1
110.0 0.1
110.4 0.4
107.8 0.2
107.8 0.2a
108.9 0.1
109.2 0.1
108.4 0.3
104.6 0.4
102.1 0.3
98.1 0.1
279.8 0.1
272.8 0.3
275.5 0.1
278.1 0.3
278.8 0.2
26.3 0.5
34.5 0.6
34.5 0.5
34.0 0.9
31.7 0.8
276.9 0.7
278.0 1.2
278.8 0.9
33.1 0.3
34.1 0.5
31.7 0.3
1.4 0.8
0.1 1.4
0.0 1.1
199.8 0.1
273.8 0.1
34.9 0.3
199.3 0.3
199.8 0.2
199.8 0.1
199.8 0.1
280.8 0.2
279.9 0.3
280.7 0.4
281.0 0.2
275.0 1.0
274.8 1.0
275.0 0.7
274.7 0.8
26.9 0.6
24.5 0.9
21.2 0.8
16.9 0.4
32.7 0.4
29.6 0.4
26.9 0.3
23.2 0.6
5.8 1.0
5.1 1.3
5.7 1.1
6.3 1.0
10 Toluene
11 o-Xylene
12 Mesitylene
a
According to [12].
(see scheme) appeared to be convenient for determina-
tion of the activation and reaction volumes.
ined solvent series, except ethyl acetate in which the
packing of these compounds is closer than in the other
examined solvents. The partial volumes of diene I and
dienophile II in chloroform suggest lack of strong
hydrogen bonding of chloroform with these reactants.
NC
NC
CN
CN
+
Variation of the reaction and activation volumes in
aromatic solvents correlates with variation of the par-
tial molar volume of tetracyanoethylene (see figure).
For the activation volume, the correlation for aromatic
and nonaromatic solvents is common (curve 1):
I
II
CN
CN
NC
NC
V
=
0.8593VII + 60.83; R 0.9952, N 7. (3)
IV
The correlation with the reaction volume for aro-
matic solvents (nos. 9 12, curve 2)
NC CN
NC CN
Vr = 0.9918VII + 80.08; R 0.9904, N 4. (4)
does not include data for nonaromatic solvents.
III
In the group of solvents nos. 1 5 and 7, the pack-
ing features of diene I and adduct III noticeably differ
from those in aromatic solvents (nos. 9 12), which
results in more negative reaction volumes in the non-
aromatic solvents (curve 2). Dioxane with respect to
the capability for complexation with tetracyanoethyl-
ene occupies an intermediate position between ben-
zene and toluene.
Comparison of the activation and reaction volumes
in a series of solvents gives insight into the structure
of the transition state. In this work we determined the
partial molar volumes of reactants I and II and adduct
III in ten - and n-donor solvents and calculated the
reaction volumes (see table).
The decisive effect of the specific interactions of
aromatic solvents with tetracyanoethylene on the free
energy of formation of , complexes, activation free
energy in the Diels Alder reaction, enthalpy of solu-
tion, and partial molar volume was discussed in [7, 8].
The partial molar volumes of diene I and adduct III
(VI, VIII, see table) vary insignificantly in the exam-
It should be noted that the reaction and activation
1
volumes appreciably change (by 17 and 11 cm3 mol ,
respectively) in going from inert solvents to mesityl-
ene, which is the strongest donor among the sol-
vents examined. The slope of 0.86 of relationship (3)
suggests that in the activated complex the -acceptor
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 3 2002

434
V, cm3 mol
KISELEV et al.
(149 150 C [14]). Tetracyanoethylene (Merck) was
1
sublimed in a vacuum ( 50 Pa) at 110 C. The melting
point of the white crystalline substance was 200
201 C (201 202 C [15]). Adduct III was prepared
from equimolar solutions of I and II in 1,2-dichloro-
ethane with subsequent recrystallization from benzene,
mp 211 212 C (211 212 C [16]). All the solvents
were purified by common procedures [17].
11
11
12
20
25
1
2
9
12
10
1
30
35
3
7
5
9
4
2
5
3
10
40
45
4
96 98 100 102 104 106 108 110 112VII, cm3 mol
1
The apparent molar volumes ( ) were calculated
from the relationship
= (1/d
1/d0) 1000/m +
Comparison of the solvent effects on the (1) activation
volume and (2) reaction volume, plotted vs. the partial
M/d, where d and d0 are the densities of the solution
and solvent, m is the molal concentration, and M is
the molecular weight of the solute. In all the solutions
the apparent molar volumes ( ) of I III in the concen-
molar volume of tetracyanoethylene (V ). The point nos.
II
correspond to the solvent nos. in the table. The points
corresponding to the activation volumes are shifted along
1
tration range 0.01 0.04 mol kg were independent
3
1
the ordinate by 5 cm mol
.
of the concentration and therefore could be considered
as partial molar volumes (V). The densities of solu-
tions and solvents were determined from the vibration
frequency of the vibrating tube of a DMA-602 den-
simeter at 25 0.001 C. The temperature was main-
tained with a three-step cascade of thermostats con-
taining 20 l of water each, kept at 21.0, 24.3, and
25 C. In the last thermostat, the heater power was
decreased to 16 W. The densimeter was arranged in a
glove box with a constant temperature (25 0.2 C).
The measurement procedure is described elsewhere
[6, 10]. For each solution, 4 5 measurements were
performed. In the check measurements of the apparent
molar volumes of I III performed after a 3-month
period in freshly purified dioxane, the results given in
the table were fully reproduced.
power of tetracyanoethylene is preserved to only 14%,
and in going to the adduct [Eq. (4)] its -acceptor
power is fully lost.
The data obtained allow calculation of the partial
molar volume of the activatied complex (VIV) and the
activation volume of the reverse reaction ( V ) from
the relationships VIV = (VI + VII
+
V11) and
V
= V1 Vr = VIV VIII. The results (see table)
1
show that the partial molar volumes of the activated
complex and adduct in nonaromatic solvents (nos. 3 5)
are constant and equal to each other. In the aromatic
solvents (nos. 9 12), the partial molar volumes of the
activated complex and adduct are also constant, but
the molar volume of the transition state is smaller by
1
5 6 cm3 mol than that of the adduct. Therefore, the
ACKNOWLEDGMENTS
activation volume of the retro reaction is close to zero
in the first group of solvents and negative in aromatic
solvents. The negative activation volume for the
adduct decomposition was noted in numerous papers
[6, 13]. The more compact structure of the activated
complex as compared to the adduct of the Diels Alder
reaction was tentatively attributed to secondary inter-
actions of the unsaturated fragments [13]. Another
explanation is associated with the possible increase in
the fraction of voids inaccessible for the solvent in the
adduct, as compared to the structure of the activated
complex which is more accessible for solvation [6].
The study was financially supported by the Russian
Foundation for Basic Research (project no. 98-03-
33053a).
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