Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

Article abstract of DOI:10.1134/S0036024414120152

The Diels-Alder reaction between substituted anthracenes 1a-1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ? 3a in toluene at 25°C: K_eq = 2120 M^-1, ΔH_f^≠ = 58.6 kJ/mol, ΔS_f^≠ = -97 J/(mol K), ΔV_f^≠ = -17.2 cm³/mol, ΔH_b ^≠ = 108.8 kJ/mol, ΔS_b^≠ = 7.3 J/(mol K), ΔV_b^≠ = -0.8 cm³/mol, ΔH_r-n = -50.2 kJ/mol, ΔS_r-n = -104.3 J/(mol K), ΔV_r-n = -15.6 cm³/mol. It is concluded that the values of equilibrium constants of the reactions 1a-1j + 2 ? 3a-3j vary within 4 × 10¹-10¹¹ M^-1.

Full text of DOI:10.1134/S0036024414120152

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2014, Vol. 88, No. 12, pp. 2073–2080. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © V.D. Kiselev, D.A. Kornilov, E.A. Kashaeva, L.N. Potapova, D.B. Krivolapov, I.A. Litvinov, A.I. Konovalov, 2014, published in Zhurnal Fizicheskoi Khimii,
2014, Vol. 88, No. 12, pp. 1914–1921.
CHEMICAL KINETICS
AND CATALYSIS
Features of the Diels–Alder Reaction
between 9,10ꢀDiphenylanthracene
and 4ꢀPhenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione
V. D. Kiseleva, D. A. Kornilova, E. A. Kashaevaa, L. N. Potapovaa,
D. B. Krivolapovb, I. A. Litvinovb, and A. I. Konovalovb
a Butlerov Institute of Chemistry, Kazan Federal University, 420008 Russia
b Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, 420088 Russia
eꢀmail: vkiselev.ksu@gmail.com
Received February 4, 2014
Abstract—The Diels–Alder reaction between substituted anthracenes 1a–1j and 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ
3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10ꢀatoms of substituted
anthracenes. The orthogonality of the two phenyl groups at the 9,10ꢀposition of diene 1a is found to shield
9,10ꢀreactive centers. No dienophiles with C=C bonds are shown to participate in the Diels–Alder reaction
with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ
3,5ꢀdione. It is shown that attachment occurs on the less active but sterically accessible 1,4ꢀreactive center of
diene 1a. The structure of adduct 3a is proved by 1
H
and 13C NMR spectroscopy and Xꢀray diffraction analꢀ
ysis. The following parameters are obtained for reaction 1a + 2
3a in toluene at 25°C: K
eq = 2120 M–1,
≠
≠
≠
≠
≠
Δ
Hf = 58.6 kJ/mol,
Δ
Sf = –97 J/(mol K),
Hr–n = –50.2 kJ/mol,
15.6 cm3/mol. It is concluded that the values of equilibrium constants of the reactions 1a–1j + 2
3j vary within
101–1011 M–1
Δ
Vf = –17.2 cm3/mol,
Δ
Hb = 108.8 kJ/mol,
Δ
Sb
=
=
≠
7.3 J/(mol K),
Δ
Vb = –0.8 cm3/mol,
Δ
Δ
Sr–n = –104.3 J/(mol K),
Δ
Vr–n
⎯
3a–
4
×
.
Keywords: 9,10ꢀdiphenylanthracene, 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione, Diels–Alder reaction, regioseꢀ
lectivity, high pressure
DOI: 10.1134/S0036024414120152
INTRODUCTION
and 9,10ꢀatoms of anthracenes is 65 8 kJ/mol [5–7].
This allows us to estimate the ratio of reaction rate
constants on the 9,10ꢀ and 1,4ꢀreactive centers of
anthracenes: k(9,10)/k(1,4) = 3200. Theoretical calculaꢀ
tions for the activity of different cycles of anthracenes
in the Diels–Alder reaction yield a similar ratio:
All dienophiles attach themselves to 9,10ꢀreactive
centers of substituted anthracenes in the Diels–Alder
reaction. The overlapping of the 1,8ꢀhydrogen atoms
of anthracene fragments and 2,6ꢀhydrogen atoms of
the phenyl group of 9ꢀphenylanthracene 1d results in
k(9,10)
dienophile
/
k(1,4) = 3500 [8]. The Diels–Alder reaction of
with substituted anthracenes 1b–1j proꢀ
a dihedron of ~60° [1]. This creates strong shielding
2
for the Cꢀ9 of diene 1d. Nevertheless, the reaction
with 9ꢀphenylanthracene proceeds at the 9,10ꢀreacꢀ
tive position, although it is slower than for molecules
without such steric hindrances [2, 3]. The Diels–
Alder reaction between substituted anthracenes 1а–1j
and 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione
Scheme 1.
ceed at the sterically accessible and more active
9,10ꢀposition of these dienes to produce 3b–3j [9–
1
13
13]. The H and C NMR spectra (see below) are in
accordance with the structure of adducts 3b–3j. The
Diels–Alder reaction of diene 1а does not proceed for
any known dienophile with C=C bonds under normal
conditions.
2 is shown in
An almost orthogonal positioning of the planes of
both phenyl groups to anthracenes plane is observed
There are a number of works dedicated to studying
for 9,10ꢀdiphenylanthracene 1а [4]. This prevents a the behavior of 4ꢀsubstituted 1,2,4ꢀtriazolineꢀ3,5ꢀ
dienophile from approaching the most active 9,10ꢀ diones in thermal and photochemical reactions
reactive center of diene 1а. The relative activity of [4+2]ꢀ, [3+2]ꢀ, [2+2]ꢀcycloaddition and enone synꢀ
9,10ꢀ and 1,4ꢀreactive centers of anthracenes, thesis [9–21]. Studies were conducted earlier on
k(9,10)
/
k(1,4), can be estimated when there are no steric adduct structure, reaction rate, and effect of the solꢀ
hindrances in the Diels–Alder reaction [3]. The difꢀ vent on the [4+2]ꢀcycloaddition of
2
to various 1,3ꢀ
ference between the hydrogenation energy of the 1,4ꢀ dienes [9–13]. 4ꢀPhenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione
2
2073

2074
KISELEV et al.
R1
O
N
N
+
N Ph
O
O
R2
(1a–1j)
O
(2)
N Ph
O
N Ph
O
N
N
N
Ph
N
R1
R2
(3b–3j)
Ph
(3a)
1, 3
a
b
с
d
e
f
g
h
i
j
R1
R2
Ph
Ph
H
H
H
H
Me Cl OMe
H
H
H
Cl
Ph Me Me Cl OMe NO2 CN
Scheme 1.
have high activity in all reactions leading to attachꢀ limated prior to measurements at 100
°
C
and a presꢀ
(dec). The absorption of
in toluene did not change over long
periods of time either in the closed system at room
temperature or in the dark. The purity of was verified
ment along N=N bonds. The lower energy of N=N
bonds (418) relative to C=C bonds (611 kJ/bond) is
assumed to be the main reason for the lower activation
energy in all reactions along N=N bonds.
sure of 100 Pa.
a solution of
Tm was 170°C
2
2
via spectrophotometric titration of its solution with
It has been shown that the reactivity of dienoꢀ
phile 2 is sufficiently high even at room temperature
known concentrations of diene 1f, which reacts rapꢀ
at the uncommon 1,4ꢀreactive center in reaction idly with
2 (k
2 = 12200 М–1 s–1), and quantitatively
(K
eq > 106 М–1,
Δ
Hr–n = –117.8 kJ/mol) at 25°C [13].
1a
+
2
3a
(k
2 = 2.7 °С).
10ꢀ3 M–1 s–1; toluene, 25
×
All solvents were purified and dried according to the
standard procedures in [22].
The rate constants and enthalpies for the Diels–Alder
reaction of 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione, tetꢀ
racyanoethylene, and maleic anhydride with 15 cyclic
and acyclic dienes were compared in [13]. It follows
from these data that the activity of 4ꢀphenylꢀ1,2,4ꢀtriꢀ
azolineꢀ3,5ꢀdione in the Diels–Alder reaction is 5–
6 orders of magnitude higher than that of maleic anhyꢀ
dride. We are now finally able to study and compare
the parameters of the Diels–Alder reaction on the
9ꢀ,10ꢀ, and 1,4ꢀatoms of diene 1a–1j. In this work, we
studied the effect of temperature and pressure on the
rate and equilibrium of the Diels–Alder reactions of
Adduct 3a, 3,10,15ꢀtriphenylꢀ13,15,17ꢀtriazaꢀ
pentacycloꢀ[10.5.2.02,11.04.9.013,17]ꢀnonadecaꢀ
2,4(9),5,7,10,18ꢀhexaeneꢀ14,16ꢀdione (3a) decomꢀ
poses at 210–220°C. Elemental analysis,%: C, 80.42,
80.52; H, 4.49, 4.43; N, 7.90, 7.84. Calc.,
1
C34H23O2N3: C, 80.78; H, 4.59; N, 8.31%. NMR H
(400 MHz), CDCl3, 25
3.5 Hz, C(1)H, C(12) ), 6.87 (t,
C(19) ), 7.3–8.0 (aromatics, 19H); δC (100 MHz,
CDCl3, 25 C) 54.73 (C(1), C(12)), 125.26 (C(18), C(19)),
°
C, δH, ppm: 5.92 (t,
J =
H
J
= 3.5 Hz, C(18)H,
H
°
4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione 2 with series 1а–
1j of substituted anthracenes.
126.73–136.11 (aromatics), 155.61 (C=O) (the numꢀ
bering of atoms is similar to that in Fig. 1).
For adduct 3d, δH: 6.46 (s, C(9)H, methine group),
EXPERIMENTAL
7.0–8.0 (m, aromatics, 18H); δC: 62.70 (C(9), methine
group), 72.74 (C(10), tert), 123.93–139.25 (aromatics),
156.61 (C=O), 157.38 (C=O) (the carbon numbering
is similar to that of diene 1d).
All of the substituted anthracenes (Sigma Aldrich)
with 99% purity (except for 1i and 1j) were used withꢀ
out prior purification. Dienes 1i 1j (97%) were puriꢀ
≥
,
fied via column chromatography on silica gel. The eluꢀ
ent was benzene : hexane (1 : 2). The optical purity of
the dienes was measured in the range of 390–405 nm
after reacting with purified maleic anhydride of known
For adduct 3f, δH: 2.75 (s, methyl, 6H), 7.2–7.6
(m, aromatics, 13H); δC: 14.74 (methyl), 63.29 (C(9),
C(10)), 121.20–140.34 (aromatics), 152.15 (C=O)
concentration. Dienophile 2 (Aldrich, 97%) was subꢀ (carbon numbering is similar to that of diene 1f).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 88
No. 12 2014

FEATURES OF THE DIELS–ALDER REACTION
2075
Adducts 3b, 3f, 3h were synthesized in [12]. The 1H
NMR spectra of 3a 3b 3e 3f, and 3g in CDCl3 in the
presence of 1a 1b 1e 1f, and 1g are given in [23].
,
,
,
,
,
,
HITACHI Uꢀ2900 and UNICOꢀ2800 spectrophoꢀ
tometers were used for kinetic measurements at atmoꢀ
spheric pressure. The rate of direct reaction 1 + 2
3
was studied quantitatively from the disappearance of
the band of the absorption of dienophile in
toluene (λmax = 540 nm, ε2, max = 245 M–1 cm–1). For
slow and equilibrium reactions 1a + 2 3a, 1g +
3g, 1i + 2 3i, and 1j + 2 3j, the initial
concentrations of dienes were 15–40 times higher
C5
n
π*
2
C3
C1
C4
C9
C2
N17
N13
C16
C6
C7
C18
C19
2
N15
C14
than that of dienophile
retro reaction 3a
2
[(4–5)
×
10–3 M]. The rate of
C11
C10
C12
1a + 2 was studied under condiꢀ
C8
tions preventing equilibrium. 3а was decomposed in
the presence of trans transꢀ1,4ꢀdiphenylbutadieneꢀ
1,3, which rapidly (k2 = 6.2 М–1 s–1, 30
) and irreꢀ
versibly ( Hr–n = –142 kJ/mol) reacted with dienoꢀ
phile forming during the decomposition of 3а (toluꢀ
ene, 25–50
,
°C
Δ
2
°C). The initial concentration of 3a was
(4–5)
(1–2)
×
10⎯4 M; that of 1,4ꢀdiphenylbutadieneꢀ1,3 was
×
10–3 M. It was shown that increasing the conꢀ
Fig. 1. Xꢀray structure of (3,10,15ꢀtriphenylꢀ13,15,17ꢀ
centration of 1,4ꢀdiphenylbutadieneꢀ1,3 does not
affect the rate of 3a decomposition. The reaction rate
was measured for the increased absorption of diene 1a
2,11 4.9 13,17
triazapantacycloꢀ[10.5.2.0 .0 .0
]ꢀnonadecaꢀ
2,4(9),5,7,10,18ꢀhexaeneꢀ14,16ꢀdione) 3a
.
(
Dt,1а) at 395 nm. Observance of the Beer law had
tion of
5000 M vibration densitometer was used to measure
the density at 25 0.002 C.
3
; and Vr–n is the reaction volume. A DSA
Δ
already been verified. Absorption coefficient ε1a in tolꢀ
uene at 395 nm was 14600 M–1 s–1. Rate coefficient k1
of the decomposition of 3а was calculated as
°
k1t = ln[C0,
where Dmax
/
Ct,3a] = ln[Dmax,1a/(Dmax,
is optical density of absorption of
–
Dt,1a)], (1)
3a
1a
The Xꢀray data of crystal 3a were obtained on a
Brucker Smart Apex II CCD diffractometer at 20
using Mo radiation (0.71073 Å) with graphite monoꢀ
,
°C
1a
K
diene 1a after the full decomposition of 3a
С0,3a ε1а; and Dt,1a is the current absorption of diene 1a
The reaction rate of 1a + 2 3a at high pressure was
followed by changes in the optical density of dienoꢀ
phile at 540–550 nm, where other reagents were
transparent. The details of operating high pressure
equipment were described in [24]. The С0, С0,2 ratio
; Dmax, =
α
1a
.
chromator. Crystals of 3а, C34H23O2N3, are monoclinic:
a
= 11.139(5) Å,
119.93 (3);
= 2489.9(17) Å3;
1.349 g/cm3; space group, P21
b
= 22.304(8) Å,
c
= 11.564(4) Å,
β
=
=
°
V
Z
= 4 dcryst
;
2
/c
. The parameters of a
cell and the intensity of 5989 independent reflections,
2442 of which had , were measured in the scanꢀ
ning regime of θ ≤ 28.00 Rinr = 0.1720). No adjustment
was made for absorption (
Mo = 0.85 cm–1). Structures
/
1a
I
≥
2
σ
ω
was
~0.007 M. The rate of 3a
high pressure at 45 in the presence 1,4ꢀdiphenylbꢀ
∼10–15, where the initial concentration С0, was
2
°
(
1a + 2 decomposition at
μ
°C
were resolved directly and refined with the full matrix of
least squares using SHELX [26]. All nonꢀhydrogen
atoms were refined anisotropically. Hydrogen atoms are
considered to be rigid atoms. The final differences were
Rob = 0.0869 and Rwob = 0.1789. The images were
indexed, integrated, and scaled using the APEX2 packꢀ
age for treating data [27]. All of the figures were produced
with the ORTEP program [28]. The main geometric
parameters were C1–C2, 1.521 Å; C2–C3, 1.382 Å;
C3⎯C4, 1.445 Å; C4–C5, 1.419 Å; C5–C6, 1.365 Å;
C6⎯C7, 1.398 Å; C7⎯C8, 1.354 Å; C8–C9, 1.418 Å;
C9⎯C10, 1.440 Å; C10–C11, 1.371 Å; C11–C12, 1.515 Å;
C12–N13, 1.485 Å; N13–C14, 1.367 Å; C14–O14, 1.217 Å;
C14–N15, 1.398 Å; N15–C16, 1.401 Å; C16–O16, 1.219 Å;
C16–N17, 1.357 Å; N17–C1, 1.480 Å; C1–C18, 1.517 Å;
utadieneꢀ1,3 was measured from increasing optical
density Dt,1а of diene 1a at a wavelength of 395 nm over
time. The bathochromic shift of the absorption band
of diene 1a occurred at a higher pressure, so the presꢀ
sure dependence of the extinction coefficient of 1a was
studied to calculate the rate constant.
≠
The apparent volume of activation
lated using the dependence of lnkp on
reaction rate constant at pressure . The reaction volꢀ
ΔV
was calcuꢀ
p, where kp is the
p
ume is normally determined from the differences
between the partial molar volumes of the adducts and
reagents with an error of 1–2 cm3/mol. We used a
more precise method for determining
ΔVr–n [25]:
1/ t = 1/dt Ct,3aΔ r–n/(1000dt = 0),
= 0
d
+
V
(2)
where dt = 0 and dt are the initial and current densities
of the reaction mixture; Ct,3 is the current concentraꢀ
C18–C19, 1.320 Å; C12–C19, 1.520 Å; C2C1C18, 106.16°;
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 88
No. 12 2014

2076
KISELEV et al.
N17C1C18, 104.98
°
; C1N17C16, 128.37
°
; C11C12C19,
The pressure dependence of the reaction rate
(Fig. 2) is described by second order polynomial and
logarithmic equations
107.00 ; N13C12C19, 103.84
°
°; C12N13C14, 127.67°.
ln(k2,p/k2,p=1) = −0.0040
(4)
RESULTS AND DISCUSSIONS
The reaction rate constant for and 9,10ꢀdiphenylꢀ
= 7.84 ×10−4 p − 9.10 ×10−8 p2, R = 0.9990,
2
anthracene 1a + 2 3a in toluene at 25 C (2.7
10–3 М–1 s–1; Table 1) was considerably lower than the
ones for the reactions of and 9,10ꢀdiphenylanꢀ
°
×
ln(kp/kp=1
= 2.070ln[(2540 + p)/2540]; R = 0.9980.
According to (4), the experimental value of activation
)
(5)
2
thracene 1f (12200), 9ꢀmethylanthracene 1е (84.0),
anthracenes 1b (0.33), and 9ꢀphenylanthracene
(0.40 M–1 s–1) [13]. The ratio of the rate constants
≠
volume
Δ
Vapp is –19.4 1.2 cm3/mol. The adjusted
≠
(12200/2.7
×
10⎯3) was 4.5
×
106 at equal ionization
value of
Δ
Vcorr was calculated using Eq. (3) and toluꢀ
10–6 bar–1
[30]: –17.2 1.2 cm3/mol. From Eq. (5), we find that
potentials of 9,10ꢀdimethylanthracene 1f (7.11 eV)
and 9,10ꢀdiphenylanthracene 1a (7.10 eV) [29]. This
indicates that the phenyl substituents in 1a can parꢀ
tially shield even 1,4ꢀreactive centers. As was shown
above, reducing the activity due to steric hindrances by
more than a factor of 3200–3500 should change the
ene compressibility coefficient βT = 90
×
≠
≠
Δ
Vapp and
Δ
Vcorr are –20.1
1.2 and –17.9
1.2 cm3/mol, respectively. Ratio (4) has better correꢀ
lation coefficient than (5). Nevertheless, Eq. (4), in
regioselectivity of reaction 1a
+
2
3a. A similar
contrast to (5), assumes there is a false peak at
4300 bar, so reaction rate [ln(kp kp ] at higher presꢀ
sures cannot be predicted. It should be noted that the
p =
comparison allows us to predict 1,4ꢀadditions during
the reaction of 9,10ꢀdiphenylanthracene and maleic
anhydride, and to estimate the constant of this reacꢀ
/
)
= 1
≠
difference between the two values of V at p = 1 lies
Δ
tion rate at 25°C
with 10–9 М–1 s–1, making it imposꢀ
within the experimental error. Equation (5) can be
used to determine the activation volume at any presꢀ
sure, and to predict the reaction rate under pressure.
The effect pressure has on the rate of decomposition
sible to study at room temperature.
The NMR spectrum of adduct 3a (see above) difꢀ
fers considerably from the spectra of 3d and 3f. The
presence of protons on the saturated tertial carbon
atoms and in the ethylene fragment corresponds to the
formation of 1,4ꢀadduct 3a. These signals are missing
from the reactions with the accessible 9,10ꢀreactive
3a
1a
+
2
is minimal (Table 2, Fig. 2):
ln(k1, p/k1, p =1
= 0.00046 + 3.1×10−5 p − 2.80 ×10−8 p2,
where correction member –1)RTβT is equal to 0
corr = –0.8 0.8 cm3/mol.
The difference between activation volumes
)
(6)
centers; e.g., 1f
of crystal 3а corresponds to the formation of an exo
+
2
3f. Xꢀray diffraction analysis
(n
ꢀ
≠
≠
(
n
= 1), so
Δ
Vexp
=
Δ
V
conformation of adduct 3а (Fig. 1).
The kinetic data for direct reaction 1a
and retro reaction 3a 1a allow us to calculate
equilibrium constants (Keq), enthalpies (
+
2
3a
≠
≠
{
Δ
Vcorr
(
1a
+
2
3a) –
Δ
Vcorr
(3a
1a + 2) =
→
+ 2
≠
⎯
16.4 2.0 cm3 /mol} should be equal to the value
ΔH
), entroꢀ
Sr–n).
dramatically
reduce the activity of dienes 1g, 1i, 1j and the stability
≠
of reaction volume
Δ
Vr–n. This value (–15.6
pies (ΔS
) of activation and reaction (
ΔHr–n
,
Δ
0.3 cm3/mol, Fig. 3) is also determined ((2), Fig. 3)
from three independent measurements and agrees
with the difference between the activation volumes
Electronꢀacceptor
substituents
of their adducts (Table 1).
(
⎯
16.4 2.0 cm3/mol) of the direct (1a
+
2
3a)
As was shown in [25], the adjusted value of activaꢀ and retro (3a
1a
Vr–n is 1.10 0.10. The resulting
values for the enthalpy, entropy, and activation and
+ 2) processes.
≠
≠
tion volume ΔVcorr requires that we consider the corꢀ
Ratio
Δ
Vcorr
/
Δ
rection for solution compression,
reaction volumes of 1a 3a with 1,4ꢀatoms of
+
2
→
≠
Δ
Vcorr = –RT
∂ln(kp)/
∂P
+ (
n
– 1)RTβT
,
(3)
diene were compared to the parameters of several
reactions with 9,10ꢀatoms of substituted anthracenes
1f and 1d and maleic anhydride (Table 3). The close
values of the entropy and activation and reaction volꢀ
umes of both the 1,4ꢀ and 9,10ꢀatoms of anthracenes
are remarkable.
where kp is the rate constant under pressure, calculated
without adjusting for concentration ( ) under
pressure , ( – 1)RTβT is a correction for compressꢀ
ibility, where is the order of the reaction and βT
ln( )/ is the coefficient of solvent compressibility.
m, c, x
p
n
n
=
∂
d
∂p
Special attention was given to determining the
Data on the effect pressure has on the rate constants of equilibrium parameters, due to the dramatic differꢀ
direct reaction 1a 3a and retro reaction 3a ences between the data obtained via UV monitoring of
1a are presented in Table 2 and in Fig. 2. the absorption of in the reaction mixture (Table 1)
+
2
+
2
2
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FEATURES OF THE DIELS–ALDER REACTION
2077
≠
≠
Table 1. Rate constants (
stants (
eq, M–1), enthalpies (
anthracenes 1a–1j with dienophile
k
2, M–1 s–1), enthalpies (
r–n, kJ/mol), and volumes (
in toluene
Δ
H
, kJ/mol), entropy (
Δ
S
, kJ/mol/K) of activation, equilibrium conꢀ
K
Δ
H
Δ
V
r–n, cm3/mol) for the Diels–Alder reactions of substituted
2
k2
Keq
Δ
H
Δ
S
Δ
Vr–n
Δ
Hr–n
1a
58.6
+
2
→
3a
0.00110 (15°C
0.00272 (25°C
0.00276 (25°C
0.00573 (35°C
)
)
)
)
2120 (25°C
)
–97
–15.9b
–15.5b
–14.9c
–15.2c
–15.4
–50.2d
[–16.7]a
[57 (25°C)]a
1410 (30°C
1120 (35°C
)
)
0.0125 (45°C
)
776 (40°C
534 (45°C
443 (50°C
)
)
)
3a
108.8
→
1a
+
2
1.29
2.81
5.12
1.11
2.34
4.02
×
×
×
×
×
×
10–6 (25°C
10–6 (30°C
10–6 (35°C
10–5 (40°C
10–5 (45°C
10–5 (50°C
)
)
)
)
)
)
7.3
15.4
50.2
1b
–
+
+
2
→
3b
3c
e
0.33 (25°C
)
106–109 (25°C
[328 (25°C)]a
)
–
–
–96.7e
[–44.0)]a
1c
47.3
2
2
→
0.0645 (15°C
)
1.5
×
105 (25°C
)
–99.6
–18.5c
–19.0b
–18.6b
–18.7
–83.1d
0.130 (25°C
0.185 (30°C
)
)
51800 (35°C
11200 (50°C
)
)
4160 (60°C
)
1d
41.4
+
→
3d
0.218 (15°C
0.291 (20°C
0.297 (20°C
0.402 (25°C
0.397 (25°C
)
)
)
)
)
6.3
×
104 (25°C
)
–113.8
–21.2 b
–22.1 b
–20.8 b
–21.4 b
–21.4
–73.2f
–70.8f
–72.5f
–72.2
1e
–
+
+
+
2
2
2
→
→
→
3e
3f
e
84 (25°C
)
106–1010 (25°C
[115 (25°C)]a
)
–
–
–
–
–
–
–101.9e
[–52.9)]a
1f
–
e
12180 (25°C
)
106–1012 (25°C
[101 (25°C)]a
)
–117.8e
[–35.6)]a
1g
–
3g
0.0031 (25°C
)
40
–
[28 (25°C)]a
[–40.2]a
1h
–
1i
58.6
+
+
2
2
→
→
3h
3i
e
13750 (25°C
)
>107
–
–
–
–87.9f; –91.7g
–
1.04
1.67
2.53
5.30
2.19
×
×
×
×
×
10–4 (20°C
10–4 (25°C
10–4 (30°C
10–4 (40°C
10–3 (60°C
)
)
)
)
)
–120.5
–18.6c
1j
–
+
2
→
3j
5.55
5.70
×
×
10–4 (25°C
10–4 (25°C
)
)
160 (25°C
)
–
–15.8c
–16.1b
–15.9
–
a
b
c
Data of [23]. Reaction volume was determined according to Eq. (2) using adduct concentrations calculated from kinetic data. Adduct conꢀ
centrations were calculated using measurements of the absorption of dienophile 2 during the reaction. The enthalpy of reaction was calcuꢀ
lated from the difference between the enthalpies of activation for the direct and reverse reactions. Data of [13]. Data from calorimetric meaꢀ
d
e
f
g
surements of the reaction heat in toluene at 25°C. Data from calorimetric measurements of the reaction heat in 1,2ꢀdichloroethane at 25°C.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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2078
KISELEV et al.
Table 2. Effect of pressure (
P
2
, bar) on the rate constants of the direct reaction (1a
+
2
→
3a
,
k
2, M–1 s–1) at 25°C and the
ln(k2, k2,
reverse reaction (3a
→
1a
+
,
k
1, s–1) at 45
°C in toluene
p
k2,
/
k2,
ln(k2, /k2,
p
)
p
k2,
/k2,
/
)
= 1
p
p
= 1
p
= 1
p
p
= 1
p
p
1a
+
2
→
3a
3a
→
1a + 2
1
298
1
0
1
1
0
1.23
1.51
1.81
2.48
2.81
3.07
3.60
0.207
0.412
0.593
0.908
1.033
1.122
1.281
567
1012
1402
2110
1.005
1.019
0.975
0.945
0.005
563
0.0188
–0.025
–0.056
820
1381
1624
1918
2126
≠
≠
≠
Table 3. Comparison of enthalpy (
Δ
H
, kJ/mol), entropy (
Δ
S
, J/mol/K), volume of activation (
Δ
, cm3/mol), and
Vcorr
volume of the series of reactions (
Δ
V
r–n, cm3/mol) in toluene at 25
°C
≠
≠
≠
≠
Δ
Vr–n
Reaction (reactive center)
(1,4)a
9,10ꢀDimethylanthracene + MA (9,10)b
9ꢀPhenylanthracene + MA (9,10)b
2ꢀMethylꢀ1,3ꢀbutadiene + MAd
Δ
H
–ΔS
/ΔVr–n
Vcorr
Vcorr
9,10ꢀDiphenylanthracene +
2
58.6
40.2
68.0
59.0
97
–17.2
–21.7
–23.2c
–34.8e
–15.6
–18.9
–27.3
–34.5
1.10
1.15
0.85
1.01
150
140
149
a
b
c
d
e
Data of this work. Reaction with maleic anhydride (MA) according to the data of [30]. At 60°C. According to [31]. At 35°C.
8000 M–1 s–1). Allowing for the final absorption of
D2 = 0.010, 0.2% of equilibrium dienophile
= 0.216, 0.1% of equilibrium diene 1b),
2
2)
and while monitoring the concentration of diene 1a by
means of H NMR [23]. We repeatedly studied reacꢀ
1
(
∼
,t
=
∞
tion 1b + 2
dienophile
3b (35 mM of diene 1b and 35 mM of
in chloroform at 25 as in [23]) using
and 1b
(
D1b
∼
,
t
=
∞
2
°C
the equilibrium constant of reaction 1b + 2
3b is
more than 107 M–1, which is considerably higher than
vacuumꢀdried 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione
with UV monitoring of its concentration. We calcuꢀ
lated the values for the initial absorption of dienophile
the value (328 M–1) given in [23]. This can be
explained by the low purity of the dienophile
2 used in
2
(
D2 = 6.2;
λ
= 540 nm; ε2, 540 nm = 177 M–1 s–1)
[23] without purification, and by lack of the signals in
,calc
1
and diene 1b
(
D1b,calc = ~280;
λ
= 378 nm; ε1b, 378 nm
=
the H NMR spectrum of dienophile
monitor it. The level of conversion for equimolar conꢀ
centrations of dienes 1f 1b 1e and dienophile was
found to be very high in toluene at 25 , preventing us
2 needed to
,
,
2
°C
ln(kp/kp )
=1
1.3
from determining the equilibrium constants with a
high degree of accuracy. These evaluations were based
on data for the initial (D0, = 1.777, 540 nm; ε2
=
2
245 M–1 s–1, C0,2 = 7.253
×
10–3 M) and final absorpꢀ
0.9
0.5
0.1
0.3
tion ( = 0.002, 0.005, and 0.002) with equimolar
concentrations of dienes 1f, 1b, 1e, respectively. It folꢀ
lows that equilibrium constants Keq of these reactions
are higher than 106 M–1. Keq can be calculated using
data on the enthalpies of these reactions in solution
D
∞
1
2
1000
2000
(Table 1) if we use an entropy of
equilibrium constants of reactions
more than by 10 orders of magnitude (Table 1).
⎯
150 kJ/(mol K). The
p, bar
1
+
2
3
differ
−
The high values of Keq agree with observations of
the full decoloration of equimolar concentrations of
Fig. 2. Pressure (bar) dependence of ln(
k
/
k
) for direct
= 1
p
p
1b and
2
in toluene (Table 1) and dichloromethane
in benzene and 1,4ꢀ
reaction 1a
3a 1a
+
+
2
2
3a
) at 45
(
°
1
C
) at 25
in toluene.
°C and for reverse reaction
(2
[12], and of solutions of 1h and 2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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FEATURES OF THE DIELS–ALDER REACTION
1.14740
2079
1.1446
1
1.14736
1.14732
1.14728
3
1.1444
1.1442
1.1440
2
0
0.01
C3a, mol/L
0.02
Fig. 3. Reaction volume of 1a
+
2
3a, determined from the dependence of specific volume 1/
d
on adduct concentration
) 1/ = –0.017319
(C
) in solution: ( ) 1/ 0.018353
1
d
=
–
C
+ 1.144711, = 0.9999, = 0.1131 M, = 0.02328 M,
R
C
C
0,2
(2
d
t,3a
t,3a
0,1a
C
+ 1.144342,
R
= 0.9997,
C
= 0.1174 M,
C
= 0.02294 M,
(
3) 1/
d
=
–
0.017909
C
+ 1.147418;
R
= 0.9995;
C
=
t,3a
0,1a
0,2
t,3a
0,1a
3
0.09873 M;
C
= 0.00898 M;
Δ
V = –16.0 (
1
), –15.1 (
2
), –15.6 cm /mol (
3).
0,2
r–n
dioxane at room temperature [9]. The equilibrium 1a and tetracyanoethylene is lower than that for the
constants of reaction 1a + 2
calculated using the ratio Keq
3a in toluene were
k2 k1. For reactions
1j + 2 3j, they were noethylene is therefore very low under ordinary condiꢀ
calculated from the initial and equilibrium absorption tions; i.e., it is not possible for thermodynamic reaꢀ
of dienophile . For reactions 1j + 2 3j and 1k + sons. The entropy and volume parameters of reaction
3k, time needed to attain equilibrium was ~10– 1a
3a on the 1,4ꢀatoms of diene do not differ
20 h at 25
reaction of 1a and
2
by a factor of 103–105 [13]. The
=
/
level of conversion for the reaction of 1a and tetracyaꢀ
1c + 2
3c,
1g + 2
3g,
2
2
+ 2
°
C.
appreciably from those of ordinary
tions on 9,10ꢀreactive centers.
1
+
2
3 reacꢀ
CONCLUSIONS
ACKNOWLEDGMENTS
The reaction of 9,10ꢀdiphenylanthracene 1a and
This work was financially supported by the Russian
Foundation for Basic Research, grant no. 12ꢀ03ꢀ
00029.
highly active dienophile proceeds with changing
2
regioselectivity. The shielding of active 9,10ꢀreactive
centers of 1a excludes the common path of the Diels–
Alder reaction with any dienophile. Only the high
Crystallographic data for the structure of 3a are on
file at the Cambridge Crystallographic Data Centre
(CCDC number 922287) and can be accessed over the
activity of dienophile 2 is sufficient for reactions along
the less active and more accessible 1,4ꢀpath. Direct
spectrophotometric measurements of the equilibrium
parameters corresponded to the high stability of
internet
at
http://www.ccdc.cam.ac.uk/
data_request/cif.
adducts 3b–3е and 3h in the reaction of
on the 9,10ꢀatoms of dienes. However, adducts 3g
2
attachment
3j
,
with acceptor substituents in diene have low stability.
The resistance to the decomposition of the adducts
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