ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2014, Vol. 88, No. 5, pp. 890–892. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © V.D. Kiselev, D.A. Kornilov, L.N. Potapova, H.A. Kashaeva, A.I. Konovalov, 2014, published in Zhurnal Fizicheskoi Khimii, 2014, Vol. 88, No. 5, pp. 899–901.
SHORT
COMMUNICATIONS
Enthalpy and Entropy of Activation and the Heat Effect
of the Ene Reaction between 4ꢀPhenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione
and 2,3ꢀDimethylꢀ2ꢀbutene in Solution
V. D. Kiseleva, D. A. Kornilova, L. N. Potapovaa, H. A. Kashaevaa, and A. I. Konovalovb
a Butlerov Institute of Chemistry, Kazan Federal University, Kazan, 420008 Russia
b Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center,
Russian Academy of Sciences, Kazan, 420008 Russia
eꢀmail: vkiselev.ksu@gmail.com
Received June 5, 2013
Abstract—The rate of the fastest ene reaction between 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione (
1) and 2,3ꢀ
dimethylꢀ2ꢀbutene ( ) is studied by means of stopped flow in solutions of benzene ( 2 = 55.6 0.5 and 90.5
2
k
1.3 L mol–1 s–1 at 23.3 and 40°C) and 1,2ꢀdichloroethane (335 9 L mol–1 s–1 at 23.5°C). The enthalpy of
reaction (–139.2 0.6 kJ/mol in toluene and –150.2 1.4 kJ/mol in 1,2ꢀdichloroethane) and the enthalpy
1
(20.0 0.5 kJ/mol) and entropy (144 2 J mol–1 K⎯ ) of activation are determined. A clear correlation is
observed between the reaction rate and ionization potential in a series of ene reactions of 4ꢀphenylꢀ1,2,4ꢀtriꢀ
azolineꢀ3,5ꢀdione with acyclic alkenes.
Keywords: ene synthesis, 4ꢀphenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione, 2,3ꢀdimethylꢀ2ꢀbutene, thermochemistry,
kinetics.
DOI: 10.1134/S0036024414050136
INTRODUCTION
the reactants. In this work, the rate of reaction 1 + 2
→
3
was measured using the stoppedꢀflow approach, and
4ꢀPhenylꢀ1,2,4ꢀtriazolineꢀ3,5ꢀdione (1) actively
participates in (4 + 2)ꢀ, (2 + 2)ꢀ reactions of cycloadꢀ
dition and ene reactions of addition along N=N bonds
the parameters of activation and the heat effect of the
reaction were determined. Possible reasons for the
high rate of reaction between
ene were discussed.
1 and tetramethylethylꢀ
[1]. The enhanced activity of
reaction relative to the C=C analog
1
in the Diels–Alder
ꢀphenylmaleimꢀ
N
ide is explained by the easier rupturing of N=N bonds
(418 kJ/mol) relative to C=C bond (611 kJ/mol) [2].
Alkenes, which have an allylic proton and the ability to
shift C=C bonds, readily participate in ene reactions.
There are data on the rate of the reaction between
EXPERIMENTAL
4ꢀPhenylꢀ1,2ꢀ4ꢀtriazolineꢀ3,5ꢀdione
(Aldrich,
Germany; 97%) was sublimed prior to measurements
at 100 and 100 Pa. The purity of triazolinedione
was verified using the familiar absorption coefficient
ε532 = 171 in 1,4ꢀdioxane at 25 [3]), and by its titraꢀ
tion with 9,10ꢀdimethylanthracene, which reacts with
rapidly, quantitatively and irreversibly [2]. 2,3ꢀ
°C
1
active enophile
reaction between
1
and a wide range of alkenes. In the
and 2,3ꢀdimethylꢀ2ꢀbutene ( ),
1
2
(
°C
only product (
3
) is formed. Its structure was deterꢀ
mined in [1]:
1
Dimethylꢀ2ꢀbutene (SigmaꢀAldrich, >98%) was
used for our measurements without further purificaꢀ
tion. Solvents were purified using the procedures
described in [4].
Ph
Ph
N
N
H3C CH3
O
O
O
O
+
Conventional methods for monitoring the rate of
N
NH
H3C CH3
CH2
reaction 1 + 2
→
3 proved to be unsuitable, due to its
N
N
H3C
completion while mixing the reagent solutions. The
reaction rate was then measured using the stoppedꢀ
flow approach on a Cary 50 Bio spectrophotometer
equipped with an RX 2000 unit (step, 12.5 ms) in benꢀ
(1
)
(2)
CH3
CH3
(3)
The reaction product is formed in considerable zene at 23.3 and 40.1°C, and in 1,2ꢀdichloroethane at
amounts during the mixing of even dilute solutions of 23.5°C. The progress of the reaction was monitored
890