Ene Reaction of β-Pinene with 4-Phenyl-3H-1,2,4-triazole-3,5(4H)-dione: Effects of Temperature, High Pressure, and Solvent Nature

Article abstract of DOI:10.1134/S1070428018070187

The effects of temperature, solvent nature, and high hydrostatic pressure on the rate of the ene reaction of 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione with β-pinene have been studied. The reaction gives only one product and is accompanied by a large heat effect. Comparison of the activation and reaction volumes indicates cyclic structure of the transition state. The reaction rate changes by a factor of 200 in the series of nine examined solvents, but this variation is not determined by solvent polarity.

Full text of DOI:10.1134/S1070428018070187

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2018, Vol. 54, No. 7, pp. 1080–1084. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © V.D. Kiselev, D.A. Kornilov, O.V. Anikin, V.V. Plemenkov, A.I. Konovalov, 2018, published in Zhurnal Organicheskoi Khimii, 2018,
Vol. 54, No. 7, pp. 1073–1077.
Ene Reaction of β-Pinene with 4-Phenyl-3H-1,2,4-triazole-
3
,5(4H)-dione: Effects of Temperature, High Pressure,
and Solvent Nature
a
a
a
a
b
V. D. Kiselev ,* D. A. Kornilov , O. V. Anikin , V. V. Plemenkov , and A. I. Konovalov
a
Butlerov Institute of Chemistry, Kazan Federal University, ul. Kremlevskaya 18, Kazan, 420008 Tatarstan, Russia
e-mail: vkiselev.ksu@gmail.com
*
b
Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
Received May 23, 2017
Abstract—The effects of temperature, solvent nature, and high hydrostatic pressure on the rate of the ene
reaction of 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione with β-pinene have been studied. The reaction gives only
one product and is accompanied by a large heat effect. Comparison of the activation and reaction volumes
indicates cyclic structure of the transition state. The reaction rate changes by a factor of 200 in the series of nine
examined solvents, but this variation is not determined by solvent polarity.
DOI: 10.1134/S1070428018070187
Among alkenes and cycloalkenes studied in ene
reactions with 4-phenyl-3H-1,2,4-triazole-3,5(4H)-di-
one (1), the highest activity was observed for 2,3-di-
quantitative parameters of this ene reaction. In the
present work we have determined rate constants of the
reaction 1 + 2 → 3 (Scheme 1) in nine solvents at 20,
30, and 40°C and reaction enthalpy, estimated pressure
effect on the reaction rate, calculated the activation and
reaction volumes, and compared the obtained data with
the corresponding parameters of some other ene reac-
tions with compound 1 (Table 1).
–
1
–1
methylbut-2-ene (k = 200 L mol s in toluene at
2
2
0°C) [1]. Compound 1 showed enhanced reactivity in
[4+2]- and [2+2]-cycloadditions and ene reactions in
comparison to other dienophiles, including tetracyano-
ethylene which is the strongest π-acceptor dienophile
[
9
(
1–7]. Triazole 1 reacted at a moderate rate with
,10-diphenylanthracene in which the reaction centers
C and C ) are completely shielded due to almost
The reaction rate in polar solvents such as DMF
and acetonitrile was significantly lower than in weakly
polar media. The entropy of activation of the reaction
9
10
orthogonal orientation of the phenyl rings with respect
to the plane of the tricyclic fragment [8]. This Diels–
Alder reaction proceeds fairly readily, but it involves
accessible 1,4-positions [8] rather than 9,10 as pre-
sumed previously [9].
1
+ 2 → 3 was close to the entropy of activation of
other ene reactions, as well as of [4+2]-cycloaddition,
but considerably lower than of [2+2]-cycloaddition
reactions (Table 2, Scheme 2).
The ene reaction of 1 with 7 involving C=C bond
migration to the bridgehead carbon atom of 7 is
forbidden by Bredt’s rule due to high strain energy;
β-Pinene 2 reacts with triazole 1 to give adduct 3 as
the only product [10]. However, there are no data on
Scheme 1.
Me
Me
N
N
O
Me
Me
HN
O
O
+
N
N
Ph
Ph
H C
2
O
1
2
3
1
080

ENE REACTION OF β-PINENE WITH 4-PHENYL-3H-1,2,4-TRIAZOLE-3,5(4H)-DIONE:
1081
Table 1. Rate constants and enthalpies, entropies, and Gibbs energies of activation of the ene reaction 1 + 2 → 3
–
1 –1
≠
≠
≠
k
2
, L mol s
∆
H (25°C), –∆S (25°C), ∆G (25°C),
Solvent
ε [11]
–1
–1
kJ/mol
J mol K
kJ/mol
2
0°C
30°C
40°C
a
DMF
36.7
20.7
06.0
02.2
37.5
02.3
02.3
10.3
04.6
0.0347
0.0506
0.0518
0.0990
0.2560
0.3740
0.5630
2.4400
7.5500
0.0667
0.0912
0.0941
0.1770
0.4230
0.6060
0.9170
3.3800
10.00000
0.1226
0.1530
0.1560
0.2660
0.6370
0.9450
1.3600
4.6400
–
45.7
39.8
39.6
35.3
32.4
32.9
31.3
22.2
20.7
117
134
134
144
146
141
143
161
157
80.0
79.1
78.9
77.5
75.2
74.2
73.2
69.4
66.7
a
Acetone
Ethyl acetate
,4-Dioxane
1
Acetonitrile
Toluene
Benzene
1
,2-Dichloroethane
Chloroform
a
Calculated with a correction for side reaction of 1 with the solvent.
however, the [2+2]-cycloaddition reaction turned out
to be less favorable than Wagner–Meerwein rearrange-
ment [5, 13]. The enhanced reactivity of compound 1
as acceptor, even in comparison to tetracyanoethylene,
as well as increased stability of adducts obtained from
[4+2]-cycloaddition of 1 to 9,10-diphenylanthracene
11 with sterically inaccessible positions 9 and 10.
Nevertheless, the reaction 1 + 11 does occur but at the
accessible atoms in positions 1 and 4 of 11 [8, 16].
The smallest difference between the energies of
bond cleavage an bond formation, which is reflected in
1
in all the examined reactions (Table 2), enabled
Scheme 2.
O
N
N
O
1
1
N
Ph
N
N
N
Ph
5
4
O
O
O
Ph
1
1
N
N
N
N
N
O
O
O
N
6
7
Ph
Ph
N
Ph
N
O
O
O
O
1
N
N
1
N
NH
8
9
H C
2
Ph
Ph
Ph
O
Me
NH
Me
Me
Me
Me
Me
1
1
N
N
Ph
N
N
Me
O
O
N
O
Ph
Ph
1
0
11
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018

1
082
KISELEV et al.
≠
≠
≠
Table 2. Rate constants, enthalpies (∆H ), entropies (∆S ), and volumes of activation (∆V ), and volumes (∆V
r
) and enthalpies
(
∆Hr.) of some reactions with 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (1) at 25°C
≠
≠
≠
–1
–1
∆H ,
–∆S ,
–∆V /–∆V
r
,
Reaction
+2, ene
Solvent
k
2
, L mol s
–1
–1
3
–∆H
r
, kJ/mol
kJ/mol J mol K
cm /mol
1
Ethyl acetate
0.070
39.8
134
36.0/30.4
159.1,
dichloroethane
134 [6]
5
1
1
1
+4, [4π+2π]
Toluene
Toluene
Toluene
1.6×10 [6]
–
–
–
+5, [2π+2σ+2σ]
+6, [2π+2π+2π]
0.282 [11]
39.6
50.9
123
121
25.4/20.9 [11]
25.1/30.9 [12]
255 [11]
–3
3.95×10 [12],
dichloroethane
218 [12]
–
4
1
1
+7, with Wagner–
Toluene
Toluene
Toluene
1.28×10
[5, 13]
55.3
24.0
134
198
26.6/24.6
[5, 13]
170 [5, 13],
dichloroethane
Meerwein rearrangement
+8, [2π+2π]
0.0175 [14]
50.8/37.6 [14]
86.4 [14],
dichloroethane
1
1
1
+9, ene
0.027 [15]
46.0
20.0
58.6
125
144
097
27.6/20.6 [15]
–
172 [15]
150 [1]
+10, ene
Dichloroethane 335 [1]
–3
+11, [4π+2π]
Toluene
2.74×10
8, 16]
17.5/15.4
50.2 [8, 16]
[
the reaction, was observed for the reactions 1 + 8 and
+ 11, and the largest reaction enthalpies were found
Experimental) was measured two times (c01
c = 5.00 mM).
=
1
0
–
2
for the reaction 1 + 6 with non-conjugated norbornadi-
ene, as well as for the reaction 1 + 5 involving two
cyclopropane rings of 5. However, the data in Table 2
show that high exothermicity is not the main factor
determining the reaction rate.
1
d = –(0.0346118±0.00039) c
3
+ (1.1178038±0.00000087),
2
3
R = 0.9979; ∆V
r
= –30.9±0.5 cm /mol;
–1
d = –(0.0331679±0.000279)c
3
+
(1.1177995±0.00000066),
2
3
The enthalpy of the reaction 1 + 2 → 3 was deter-
mined from the data of three successive dissolutions
of a crystalline sample of 1 in a solution of donor 2
in 1,2-dichloroethane at 25°C. With correction for
the heat of dissolution of 1 in 1,2-dichloroethane
R = 0.9985; ∆V
= V – V – V
–30.65 cm /mol;
r
= –(29.8±0.3) cm /mol;
∆
V
r
3
1
2
= 257.17 – 128.98 – 158.84
3
=
3
∆
V
r
(av.) = –(30.4±0.5) cm /mol.
(
21.9 kJ/mol), we obtained the following heats of the
≠
The ratio ∆V /∆V is equal to 1.18. All studied ene
cor
r
reaction: –157.5, –160.5, and –159.4 kJ/mol, the aver-
≠
reactions are characterized by a ∆V /∆V ratio of
cor
r
age value being ∆H (av.) = –(159.1±1.1 kJ/mol. The
r
larger than unity [1, 6, 15]. This may be rationalized
assuming cyclic structure of the transition state which
is thus more compact than the acyclic adduct [17].
high exothermicity of the reaction 1 + 2 → 3 makes it
almost irreversible.
The activation volume of the reaction 1 + 2 → 3
was determined in ethyl acetate at 25°C on the basis of
the rate constants under normal pressure (1 bar) and at
a pressure of 1000 bar [Eqs. (9, 10); see Experimental).
From the ratio k1000 bar/k1 bar = 3.92 we calculated the
In the examined solvent series (Table 1) the reac-
tion rate changes by two orders of magnitude; how-
ever, the differences are not related to the solvent
polarity. Analogous activation of dienophiles in
proton-donor media is well known for other reaction
types. We previously [11, 14] examined solvent effect
on the rate of a number of reactions with dienophile 1.
These data allowed us to consider solvent effect on the
rate of the ene reaction 1 + 2 → 3 in comparison with
the [2π+2σ+2σ] reaction of 1 with quadricyclane 5
[11], ene reaction with 2-methylbut-2-ene 12 [18],
[2π +2π] cycloaddition with 2-chloroethyl vinyl ether
≠
3
value ∆V = –39.0±1.5 cm /mol. With account taken
exp
of variation of the reactant concentration due to com-
pressibility of the solvent, the corrected activation
≠
cor
3
volume was ∆V = –(36.0±1.5) cm /mol.
The reaction volume ∆V was determined in two
r
ways. The dependence of the density of the reaction
mixture on the concentration of adduct 3 [Eq. (11); see
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018

ENE REACTION OF β-PINENE WITH 4-PHENYL-3H-1,2,4-TRIAZOLE-3,5(4H)-DIONE:
1083
1
3 [19], addition and rearrangement in the reaction
increased steric hindrances and is characterized by
with norbornene 7 [5, 13], ene reaction with trans-hex-
lower exothermicity than the other reactions (Table 2).
3
1
-ene 14 [7], [4π+2π]-cycloaddition with anthracene
5 [1], [2π+2π] reaction with biadamantylidene 8 [14]
It is known [21] that the heat effect in the hydro-
genation of 1-methylcyclohexene is smaller by
with account taken of the enthalpy of dissolution (∆Hr)
of compound 1 in the given solvents [20]:
1
9 kJ/mol than in the hydrogenation of methylidene-
cyclohexane. Therefore, it may be presumed that the
exocyclic C=C double bond in β-pinene 1 should be
more reactive than the endocyclic double bond in
α-pinene. In fact, the rate constant of the reaction 1+2
in 1,4-dioxane at 25°C is higher by a factor of 26.5
than that of the reaction of 1 with α-pinene.
lnk1+5 = (0.8192±0.1397)lnk1+2 + (0.1293±0.2856); (1)
2
R = 0.8515, N = 8;
lnk1+12 = (0.9912±0.0272)lnk1+2 + (0.6748±0.0590); (2)
2
R = 0.9912, N = 9;
lnk1+13 = (0.5192±0.0345)lnk1+2 + (2.6474±0.0763); (3)
EXPERIMENTAL
2
R = 0.9869, N = 5;
Commercial β-pinene (2, 6,6-dimethyl-2-methyli-
denebicyclo[3.1.1]heptane; 99%, Sigma–Aldrich) was
used without additional purification. 4-Phenyl-3H-
lnk1+7 = (0.4592±0.0069)lnk1+2 – (6.7253±0.0137); (4)
2
R = 0.9995, N = 4;
lnk1+14 = (0.8764±0.1816)lnk1+2 – (2.5507±0.3543); (5)
1
,2,4-triazole-3,5(4H)-dione (1; 97%, Aldrich) was
2
R = 0.9588, N = 3;
additionally purified by sublimation at 100°C under
reduced pressure (100 Pa), mp 165–170°C (decomp.)
[2]. The purity of 1 was checked by UV spectro-
photometry with account taken of the reported molar
absorption coefficient [6]. Adduct 3 was obtained in
quantitative yield and was recrystallized from hexane–
ethanol (5:1), mp 136–137°C; published data [10]:
lnk1+15 = (0.8848±0.03561)lnk1+2 – (0.1990±0.0633); (6)
2
R = 0.9919, N = 7;
lnk1+8 = (1.0730±0.2603)lnk1+2 – (2.2136±0.5648); (7)
2
R = 0.7081, N = 9;
lnk1+2 = (0.2632±0.0423)∆Hsol 1 – (5.1619±0.7499); (8)
2
1
13
R = 0.8854, N = 7.
mp 137–139°C. The H and C NMR spectra of 3
completely coincided with those given in [10]. All
solvents were purified by known methods [22].
A significant difference in the solvent effect on the
reaction rate was observed only with the [2π+2π]-
Kinetic measurements under atmospheric pres-
sure. The reaction rate was monitored by spectropho-
tometry, following the absorbance of alkene 2 in the
region λ 530–550 nm with a Hitachi U-2900 spectro-
photometer. The temperature of the reaction solution in
a quartz cell capped with a ground stopper was
maintained with an accuracy of ±0.1°C. The stability
of triazole 1 in all solvents used was checked by
measuring its absorbance over a period corresponding
to the reaction time. The relative standard error in the
determination of the rate constants was ±3%, and the
enthalpies and entropies of activation were determined
2
cycloaddition of 1 with biadamantylidene (1+8, R =
0
.7081. A high degree of proportionality was found
with the ene reactions 1+12 and 1+14 and Diels–
Alder reaction 1+15, and the slope is close to unity.
Similarity in the solvent effects on different reac-
tions implies a small difference in the effect of the
medium on the transition state level. The reaction 1+7
accompanied by Wagner–Meerwein rearrangement
cannot be regarded as a concerted one-step process [5].
The formation of intermediate aziridinium imide com-
plex was proved experimentally [3–5]. It follows from
correlations (1)–(8) that assumingly dipolar or diradi-
cal nature of this intermediate should be low sensitive
to the solvent polarity. The available data allow us to
conclude that new bonds are formed most rapidly and
easily in the Diels–Alder reactions of 1 with 1,3-di-
enes; next follow ene reactions, including that accom-
panied by Wagner–Meerwein rearangement, and
–
1
–1
with accuracies of ±2 kJ/mol and ±6 J mol K ,
respectively.
Kinetic measurements at elevated pressure. The
effect of pressure on the rate of the reaction 1 + 2 → 3
was studied in ethyl acetate at 25°C with the aid of
an HP-500 pressure multiplier, a PCI-500 variable-
volume quartz cell, and a programmed SCINCO spec-
≠
exp
[
2+2]-cycloadditions are least favorable. There are no
trophotometer. The observed activation volume ∆V
other more favorable versions of the addition of 1 to
biadamantylidene; therefore, the formation of cyclo-
butane adduct in the [2+2]-cycloaddition 1+8 involves
for the reaction 1 + 2 → 3 was calculated from the rate
constants at 1 and 1000 bar using correlation (9) pro-
posed in [23]:
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018

1
084
∂lnk
KISELEV et al.
–
3
(
p
/∂p)1 bar = (1.15±0.03)×10 ln(k1000 bar/k1 bar). (9)
4. Cheng, C.C., Seymour, C.A., Petti, M.A., Green, F.D.,
and Blount, J.F., J. Org. Chem., 1984, vol. 49, p. 2910.
5. Adam, W. and Carballeira, N., J. Am. Chem. Soc., 1984,
≠
The ∆V value was corrected for the compressi-
exp
bility of the solvent:
vol. 106, p. 2874.
6
. Kiselev, V.D., Kornilov, D.A., and Konovalov, A.I., Int.
J. Chem. Kinet., 2017, vol. 49, p. 562.
≠
≠
∆V
cor = ∆Vexp + β
T
RT,
(10)
–
4
–1
7. Ohashi, S. and Butler, G.B., J. Org. Chem., 1980,
where β = 1.20× 10 bar is the isothermal com-
T
vol. 45, p. 3472.
pressibility coefficient of ethyl acetate [24].
8
9
. Kiselev, V.D., Shakirova, I.I., Kashaeva, H.A., Potapo-
va, L.N., Kornilov, D.A., Krivolapov, D.B., and Kono-
valov, A.I., Mendeleev Commun., 2013, vol. 23, p. 235.
Reaction volume. The reaction volume (∆V ) was
r.
determined in two ways. The kinetic method allows
determination of reaction volume from correlation (11)
between the density of the reaction solution and
concentration of adduct 3. Reaction volume can also
be determined from the difference in the partial molar
volumes of the product and initial reactants [Eq. (12)]:
. Roy, N. and Lehn, J.-M., Chem. Asian J., 2011, vol. 6,
p. 2419.
1
0. Adam, W., De Lucchi, O., and Hill, K., Chem. Ber.,
1982, vol. 115, p. 1982.
1. Kiselev, V.D., Kornilov, D.A., Anikin, O.V., Latypo-
1
va, L.I., Bermeshev, M.V., Chapala, P.P., and Konova-
lov, A.I., Russ. J. Org. Chem., 2016, vol. 52, p. 777.
12. Kiselev, V.D., Shakirova, I.I., Kornilov, D.A., Kashae-
va, H.A., Potapova, L.N., and Konovalov, A.I., J. Phys.
Org. Chem., 2013, vol. 26, p. 47.
1
/d
τ
= 1/d
0
+ c3,τ ∆V
r
/1000d
0
;
(11)
(12)
∆V
r
= V
3
– V
2
1
– V .
Here, d and d are, respectively, the densities of the
0
τ
reaction solution at the initial moment and at a time τ;
c3 is the current concentration of adduct 3; and V , V ,
1
3. Kiselev, V.D., Kornilov, D.A., Kashaeva, E.A., Potapo-
va, L.N., Sedov, I.A., and Konovalov, A.I., Russ. J. Org.
Chem., 2015, vol. 51, p. 387.
,τ
1
2
and V are the partial molar volumes of compounds
3
1
–3, respectively. The current concentration of 3 was
14. Kiselev, V.D., Kornilov, D.A., Anikin, O.V., Sedov, I.A.,
and Konovalov, A.I., Russ. J. Org. Chem., 2017, vol. 53,
p. 1864.
calculated from the kinetic data. The density of the
reaction mixtures was measured at 25±0.002°C with
an Anton Paar DSA 5000M precision densitometer
with an accuracy of ±2×10 g/cm . The V , V , and V
values were calculated from the densities of solutions
and the solvent.
15. Kiselev, V.D., Kornilov, D.A., Lekomtseva, I.I., Reshet-
–
6
3
nikova, O.Y., and Konovalov, A.I., Russ. J. Org. Chem.,
1
2
3
2
015, vol. 51, p. 382.
1
1
1
6. Kiselev, V.D., Kornilov, D.A., Kashaeva, E.A., Potapo-
va, L.N., Krivolapov, D.B., Litvinov, I.A., and Konova-
lov, A.I., Russ. J. Phys. Chem. A, 2014, vol. 88, p. 2073.
7. High Pressure Chemistry: Synthetic, Mechanistic, and
Supercritical Applications, Van Eldik, R. and
Klärner, F.-G., Eds., Weinheim: Wiley-VCH, 2002.
Heat of reaction. The enthalpy of the reaction
+ 2 → 3 was determined in 1,2-dichloroethane at
5°C using a differential calorimeter according to the
1
2
procedure described in [1, 6]. A weighted amount of
crystalline compound 1 was added to a solution of
β-pinene taken in excess.
8. Desimoni, G., Faita, G., Righetti, P.P., Sfulcini, A., and
Tsyganov, D., Tetrahedron, 1994, vol. 50, p. 1821.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
nos. 16-03-00071, 18-33-00063) and by the Ministry
of Education and Science of the Russian Federation
19. Hall, J.H. and Jones, M.L., J. Org. Chem., 1983, vol. 48,
p. 822.
20. Konovalov, A.I., Breus, I.P., Sharagin, I.A., and Kise-
lev, V.D., Zh. Org. Khim., 1979, vol. 15, p. 361.
(
project no. 4.6223.2017/9.10).
21. Cox, J.D. and Pilcher, G., Thermochemistry of Organic
and Organometallic Compounds, London: Academic,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018