Effect of the reactants molar ratio on the kinetics of cycloaddition of 2,3-dimethylbuta-1,3-diene to allyl methacrylate

Article abstract of DOI:10.1134/S1070363212120109

The cycloaddition reaction between 2,3-dimethylbuta-1,3-diene and allyl methacrylate proceeds by the second order kinetics. The rate constants increase with the increase in the excess of one of the reactants. The change in the effective rate constants is

Full text of DOI:10.1134/S1070363212120109

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ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 12, pp. 1970–1974. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © I.S. Polevaya, G.G. Makitra, G.A. Marshalok, Ya.P. Kovalskyi, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 12,
pp. 2016–2020.
Effect of the Reactants Molar Ratio on the Kinetics
of Cycloaddition of 2,3-Dimethylbuta-1,3-diene
to Allyl Methacrylate
I. S. Polevayaa, G. G. Makitrab, G. A. Marshaloka, and Ya. P. Kovalskyia
a National University “Lviv Polytechnic,” ul. Bandery 12, Lviv, 79013 Ukraine
e-mail: polyova.ira@gmail.com
b Institute of Geology and Geochemistry of Fossil Fuels, National Academy of Sciences of Ukraine, Lviv, Ukraine
Received October 11, 2011
Abstract—The cycloaddition reaction between 2,3-dimethylbuta-1,3-diene and allyl methacrylate proceeds by
the second order kinetics. The rate constants increase with the increase in the excess of one of the reactants.
The change in the effective rate constants is described by the Michaelis–Menten equation indicating that the
reaction proceeds through the initial equilibrium stage of formation of an intermediate complex which then
transforms into the product. The effective rate constants, the equilibrium constants of formation of the
intermediate complex, and the rate constant of its transformation into the reaction product were determined, as
well as the thermodynamic parameters of the formation of the intermediate complex and the activation
parameters of the transformation of the intermediate complex into the product. The limiting stage of the
reaction is established and its mechanism is suggested.
DOI: 10.1134/S1070363212120109
Alkylcyclohexene carboxylates are starting materials
for drugs, as well as modifiers, plasticizers, epoxy
resins, and co-monomers [1]. They are used to create
lotions, body emulsions, shampoos, day and night
creams, perfumes, and food flavors [2].
moved from the thermostat, quickly cooled, opened,
and the reaction mixture was analyzed by gas–liquid
chromatography on a SELMI CHROM-1 apparatus.
The quantitative analysis was performed with internal
normalization. The accuracy of chromatographic
analysis in multiple parallel determinations did not
exceed 3% [4].
In this work we studied the kinetics of interaction
between 2,3-dimethylbuta-1,3-diene and allyl metha-
crylate to optimize the process of producing allyl
1,3,4-trimethylcyclohex-3-ene-1-carboxylate (I).
The investigated reaction proceeds according to the
second-order kinetics. The values of effective rate
constants are listed in Table 1.
O
We found that the values of the effective second-
order constants increase with the increasing ratio 2,3-
dimethylbuta-1,3-diene:allyl methacrylate. The difference
is more pronounced at higher temperatures. It was
appropriate to examine in more detail the mechanism
of this reaction. Note that the mechanism of the [4+2]
cycloaddition reaction today is still controversial [5].
Two concerted mechanism are suggested: a single-step
(sinchronous) and a two-step, in which the first step is
the limiting one [6].
C
H3C
O
C
CH2CH CH2
CH3
CH2
H3C
I
Kinetic studies were performed in temperature-
controlled sealed glass ampules according to the
method described in [3], in the temperature range 130–
160°C. To the 10 cm3 ampules were charged allyl
methacrylate and 2,3-dimethylbuta-1,3-diene in the
molar ratios from 1:1 to 1:1.75 and some hydro-
quinone, the ampules were sealed and placed in a
thermostat. At regular intervals, an ampule was re-
The Arrhenius equation described satisfactorily the
dependence of the effective rate constants on
temperature for different ratios (Fig. 1), which allowed
1970

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EFFECT OF THE REACTANTS MOLAR RATIO ON THE KINETICS OF CYCLOADDITION
1971
Table 1. Effective rate constants and activation parameters of the cycloaddition reaction between 2,3-dimethylbuta-1,3-diene
and allyl methacrylate
(kef±Δk)×106, l mol–1 s–1
Allyl methacrylate:2,3-dimethylbuta-1,3-diene
(mol)
Еef,
ΔНef,
ΔSef,
kJ mol–1
kJ mol–1
J mol–1 K–1
130°C
2.0±0.1
2.4±0.1
2.7±0.1
3.0±0.1
3.4±0.1
4.2±0.1
140°C
3.6±0.1
4.6±0.1
5.8±0.2
150°C
160°C
1:1
5.6±0.2
8.9±0.3
71.4
71.5
73.2
76.2
77.9
82.7
74.4
74.9
76.6
79.6
81.3
86.1
–188
–185
–180
–171
–166
–153
1:1.25
1:1.4
1:1.5
1:1.6
1:1.75
7.3±0.2 10.6±0.3
8.9±0.3 12.5±0.4
6.7±0.2 10.9±0.3 14.7±0.5
7.9±0.2 12.6±0.4 17.3±0.5
9.9±0.3 16.5±0.5 23.5±0.7
us the calculation of the formal activation energy and
other activation parameters of the overall process
(Table 1). The correlation coefficient was satisfactory
in all cases (R2 > 0.95). The analysis of the parameters
made it possible to establish that upon increase in the
2,3-dimethylbuta-1,3-diene excess and the accom-
panying increase in the values of kef a systematic
increase was observed in the effective energy (ΔEef)
and the effective activation enthalpy (ΔHef).
Simultaneously, the value of the effective activation
entropy (–ΔSef) also increased.
0.99) between the effective entropy and enthalpy of
reaction, which allowed the calculation of the
isokinetic temperature Tiso = 65°C (Fig. 2) that was far
from the investigated temperature range.
The increase in Eef and ΔHef with increasing excess
of 2,3-dimethylbuta-1,3-diene and a simultaneous
increase in ΔSef indicate the increasing steric hind-
rances in the reaction course. This finding suggests
also that the reaction mechanism is unique in the
studied range of the reagents ratio.
Such a systematic change in the rate constants with
an increase in excess of one of the reactants is typical
of the reactions that include the formation of the
charge transfer complex (CTC by the reagents) [7, 8].
A similar reaction course has been proved also for
several cases, including the alcoholysis of alcohols [9,
10], where the formation of charge-transfer complexes
was confirmed by the methods of physicochemical and
spectral analyses.
For all ratios of reagents an isokinetic relationship
was observed with a high degree of correlation (R2 =
For these reactions the effective second-order rate
constant does not remain constant at the change in the
reagent ratio, and the kinetics of the process is
described by the Michaelis–Menten equation:
6
5
4
3
y = –338.5x + 137.65
2
1
1/T, K–1
Fig. 1. Dependence of the effective rate constant of cyclo-
addition between 2,3-dimethylbuta-1,3-diene and allyl
methacrylate on temperature for different ratios of reac-
tants: 2,3-dimethylbuta-1,3-diene: allyl methacrylate =
(1) 1:1, (2) 1.25:1, (3) 1.4:1, (4) 1.5:1, (5) 1.6:1, and
(6) 1.75:1.
–ΔSef, J mol–1 K–1
Fig. 2. Dependence of the effective activation entropy on
the effective activation enthalpy of the cycloaddition of
2,3-dimethylbuta-1,3-diene to allyl methacrylate.
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1972
POLEVAYA et al.
In our case, the change in the effective rate
constants of the 2,3-dimethylbuta-1,3-diene cyclo-
addition to allyl methacrylate as a dependence on the
ratio of reactants is also satisfactorily described by the
Michaelis–Menten equation (2). This fact suggests that
the cycloaddition reaction between 2,3-dimethylbuta-
1,3-diene and allyl methacrylate proceeds through a
stage of equilibrium with the formation of an inter-
mediate complex followed by its conversion into the
reaction product [Eq. (3)].
Keq
kconv
А + В ⇄ [A:B] → Reaction product,
1/kef = 1/kconv + (KeqcA)/(kconv),
(1)
(2)
where kef is experimentally determined effective
second order rate constant (l mol–1 s–1) for each reagent
ratio, Keq is the equilibrium constant (l mol–1) for the
intermediate complex formation, kconv is the rate
constant (s–1) of the intermediate complex conversion
into the reaction product, cA is the molar concentration
(M) of the substance taken in excess.
O
H3C
CH2
C
C
C
+
O
CH3
CH CH2
CH2
C
H3C
O
CH2
H2C
O
O
C
C
Keq
H3C
H3C
kconv
H3C
H3C
O
C
C
CH2CH CH2
CH2CH CH2
(3)
CH3
CH3
CH2
CH2
150°C: 1/kef = –161490CA +338760, (R2 = 0.994), (6)
160°C: 1/kef = –94241CA +209279, (R2 = 0.992).
(7)
The slope of the obtained straight lines gives the
From the dependences shown in Fig. 3 for four
temperatures, we obtained the following linear equations:
130°C: 1/kef = –340146CA +838510, (R2 = 0.998), (4)
140°C: 1/kef = –244294CA +520041, (R2 = 0.991), (5)
rate constants of the conversion of the intermediate
complex in the reaction product (kconv). The values of
the intercepts on the ordinate axis give the equilibrium
constants of the complex formation (Table 2)
according to the expression Keq = 1/(kef kconv).
1/kef
The dependence of the equilibrium constant (Keq) of
the intermediate complex formation is described by the
isobar (Fig. 4, R2 = 0.993). The dependence of the rate
constants of conversion (kconv) on temperature is
described by the Arrhenius equation (Fig. 5, R2 =
0.999), which allows the calculation of the activation
parameters of the intermediate complex conversion in
the reaction product (Table 2).
The found positive ΔGeq and negative ΔSeq values
indicate the energy advantage of the intermediate
complex formation. At the same time a relatively fast
decomposition of the intermediate complex suggests
that its formation is the limiting stage of the process.
2,3-dimethylbuta-1,3-diene:allyl methacrylate, mol
Fig. 3. Dependence of the effective rate constant of cyclo-
addition between 2,3-dimethylbuta-1,3-diene and allyl
methacrylate on the molar ratio of reagents in the tem-
perature range 130–160ºC.
Thus, we established for the first time that the
kinetics of the investigated process obeyed Michaelis–
Menten equation, which was valid in the case of the
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EFFECT OF THE REACTANTS MOLAR RATIO ON THE KINETICS OF CYCLOADDITION
1973
Table 2. Equilibrium constants (Keq) and thermodynamic parameters of formation of the intermediate complex, the rate
constants (kconv) and activation parameters of its transformation into a product of the reaction
ΔН, kJ mol–1
ΔS, J mol–1 K–1
ΔG, kJ mol–1
Constants
130°С
140°С
150°С
160°С
Keq×1011, l mol–1
2.85
1.27
0.54
0.19
8.5
–250
96
kconv×106, s–1
1.19
1.92
2.95
4.78
70.1
–204
66.7а
а Econv
.
reaction course through the stage of the associative
equilibrium . It is an argument in favor of this reaction
to proceed by the mechanism of concerted
cycloaddition. However, the nature of the interaction
of the components should be studied in more detail. It
is known that the addition of a diene molecule to the
dienophile double bond originates from a certain
deficiency of the electron density on this double bond
due to its interactions with the other active groups, and
the stronger conjugation with them, the easier the
diene addition. Indeed, while kef. of 2,3-dimethylbuta-
1,3-diene interaction with allyl methacrylate at 80ºC is
0.74××10–6 mol l–1 s–1 (determined graphically), the kef
for the interaction of 2,3-dimethylbuta-1,3-diene with
1,4-naphthoquinone, where the π-bond interacts with
two C=O groups, is 0.14×10–5 mol l–1 s–1 (in hexane)
[11], and with its 5-substituted derivatives it is even
two orders of magnitude higher, 1.5×10–3 mol l–1 s–1
[12]. The accelerating effect of electronegative
substituents, like cyano group or halogen, on the
cycloaddition reaction is even more pronounced. Thus,
in the interaction of cyclopentadiene with methyl
acrylate at 30ºC in dioxane kef is 2.8×10–5 mol l–1 s–1,
with fumaric acid dinitrile, 155×10–5 mol l–1 s–1, and
with tetracyanoethylene, 10200×10–5 mol l–1 s–1. In
such cases it is reasonable to assume that a relatively
strong donor–acceptor bond arises between the
reagents [13].
The results of the study of kinetic regularities in the
process of synthesis of allyl 1,3,4-trimethylcyclohexa-
3-ene-1-carboxylate and the study of the mechanism of
this reaction showing its corresondence to the
Michaelis–Menten equation confirm the formation of
an intermediate complex between the reagents, 2,3-
dimethylbuta-1,3-diene and allyl methacrylate. The
study of thermodynamic parameters of formation of
the intermediate complex suggests that the limiting
stage is the slow formation of an intermediate
complex, the activation parameters of the
transformation of the intermediate complex in the
product indicate that the conversion of the intermediate
complex in the product occurs rapidly and
spontaneously.
ln kconv
ln Keq
1/T, K–1
1/T, K–1
Fig. 5. Dependence of the rate constants of conversion of
the intermediate complex in the reaction product on the
temperature.
Fig. 4. Dependence of the equilibrium constant of the
formation of intermediate complex on the temperature.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 12 2012