Kinetics and mechanisms of gas-phase decarbonylation of α-methyl-trans-cinamaldehyde and E-2-methyl-2-pentenal under homogeneous catalysis of hydrogen chloride

Article abstract of DOI:10.1002/poc.3282

The kinetics of the gas-phase elimination of α-methyl-trans- cinamaldehyde catalyzed by HCl in the temperature range of 399.0-438.7 °C, and the pressure range of 38-165 Torr is a homogeneous, molecular, pseudo first-order process and undergoing a parallel reaction to produce via (A) α-methylstyrene and CO gas and via (B) β-methylstyrene and CO gas. The decomposition of substrate E-2-methyl-2-pentenal was performed in the temperature range of 370.0-410.0 °C and the pressure range of 44-150 Torr also undergoing a molecular, pseudo first-order reaction gives E-2-pentene and CO gas. These reactions were carried out in a static system seasoned reactions vessels and in the presence of toluene free radical inhibitor. The rate coefficients are given by the following Arrhenius expressions: Products formation from α-methyl-trans-cinamaldehyde α-methylstyrene: logk1′s-1lmol-1=12.67±0.02-183.3±0.31kJmol-12.303RT-1 β-methylstyrene: logk1′s-1lmol-1=13.19±0.03-183.0±0. 45kJmol-12.303RT-1 Products formation from E-2-methyl-2-pentenal E-2-pentene: logk1′s-1lmol-1=12.79±0.06-174.5±0.80kJmol-12.303RT-1 The kinetic and thermodynamic parameters for the thermal decomposition of α-methyl-trans-cinamaldehyde suggest that via (A) proceeds through a bicyclic transition state type of mechanism to yield α-methylstyrene and carbon monoxide, whereas via (B) through a five-membered cyclic transition state to give β-methylstyrene and carbon monoxide. However, the elimination of E-2-methyl-2-pentenal occurs by way of a concerted cyclic five-membered transition state mechanism producing E-2-pentene and carbon monoxide. The present results support that uncatalyzed α-β-unsaturated aldehydes decarbonylate through a three-membered cyclic transition state type of mechanism. Copyright

Full text of DOI:10.1002/poc.3282

Research Article
Received: 4 October 2013,
Revised: 5 December 2013,
Accepted: 18 December 2013,
Published online in Wiley Online Library: 5 February 2014
(wileyonlinelibrary.com) DOI: 10.1002/poc.3282
Kinetics and mechanisms of gas-phase
decarbonylation of α-methyl-trans-
cinamaldehyde and E-2-methyl-2-pentenal
under homogeneous catalysis of hydrogen
chloride
Libia L. Julioa, Jesus Lezamaa, Alexis Maldonadoa, José R. Moraa
and Gabriel Chuchania*
The kinetics of the gas-phase elimination of α-methyl-trans-cinamaldehyde catalyzed by HCl in the temperature range of
399.0–438.7 °C, and the pressure range of 38–165 Torr is a homogeneous, molecular, pseudo first-order process and
undergoing a parallel reaction to produce via (A) α-methylstyrene and CO gas and via (B) β-methylstyrene and CO gas. The
decomposition of substrate E-2-methyl-2-pentenal was performed in the temperature range of 370.0–410.0 °C and the
pressure range of 44–150 Torr also undergoing a molecular, pseudo first-order reaction gives E-2-pentene and CO gas. These
reactions were carried out in a static system seasoned reactions vessels and in the presence of toluene free radical inhibitor.
The rate coefficients are given by the following Arrhenius expressions:
Products formation from α-methyl-trans-cinamaldehyde
À
Á
α-methylstyrene:logk1′
s
s
ꢀ1lmolꢀꢀ11 ¼ ð12:67 0:02Þ ꢀ ð183:3 0:31ÞkJmolꢀ1ð2:303RTÞꢀꢀ11
À
Á
β-methylstyrene:logk1′
ꢀ1lmol
¼ ð13:19 0:03Þ ꢀ ð183:0 0:45ÞkJmolꢀ1ð2:303RTÞ
Products formation from E-2-methyl-2-pentenal
À
Á
E-2-pentene:logk1′
s
ꢀ1lmolꢀ1 ¼ ð12:79 0:06Þ ꢀ ð174:5 0:80ÞkJmolꢀ1ð2:303RTÞꢀ1
The kinetic and thermodynamic parameters for the thermal decomposition of α-methyl-trans-cinamaldehyde suggest that via
(A) proceeds through a bicyclic transition state type of mechanism to yield α-methylstyrene and carbon monoxide, whereas via
(B) through a five-membered cyclic transition state to give β-methylstyrene and carbon monoxide. However, the elimination of
E-2-methyl-2-pentenal occurs by way of a concerted cyclic five-membered transition state mechanism producing E-2-pentene
and carbon monoxide. The present results support that uncatalyzed α-β-unsaturated aldehydes decarbonylate through a
three-membered cyclic transition state type of mechanism. Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: kinetics; gas-phase elimination; α-methyl-trans-cinamaldehyde; E-2-methyl-2-pentenal
hydrogen migrated during the slow step of the reaction. These
results imply a unimolecular reaction and obeying a first-order
INTRODUCTION
Aldehydes are organic molecules difficult to study in homoge-
neous, unimolecular gas-phase thermal decomposition kinetics
in the gas phase. This type of compounds are liable to be oxidized
in the presence of oxigene and to undergo a complex free radical
reactions.[1] In this sense, the thermal decomposition of low molec-
ular saturated aldehydes, formaldehyde,[2–4] acetaldehyde,[5–20]
propionaldehyde,[21–27] and at temperatures above 450 °C, have
shown to undergo complex free radical processes. However, the
aromatic aldehyde, benzaldehyde[28–32] at 550–1400°C decomposed
via a radical reaction yielding benzene and CO gas, and small
amounts of biphenyl and hydrogen gas.
2,2-Dimethyl-3-butenal, the only β-γ-unsaturated aldehyde,
studied in gas-phase kinetic decomposition[33] (282–302 °C),
was found to produce 2-methyl-2-butene and carbon monoxide.
The kinetic isotope effect of this reaction gave a kH/kD = 2.8 at
296.9 °C (i.e., 7.2 at 25 °C), suggesting that the aldehyde
rate law, thus suggesting a five-membered cyclic transition state
type of mechanism as described in reaction (1).
(1)
* Correspondence to: Gabriel Chuchani, Centro de Química, Instituto Venezolano
de Investigaciones Científicas, Apartado 21827, Caracas, Venezuela.
E-mail: chuchani@ivic.gob.ve
a L. L. Julio, J. Lezama, A. Maldonado, J. R. Mora, G. Chuchani
Centro de Química, Instituto Venezolano de Investigaciones Científicas,
Apartado, 21827, Caracas, Venezuela
J. Phys. Org. Chem. 2014, 27 450–455
Copyright © 2014 John Wiley & Sons, Ltd.

GAS-PHASE DECOMPOSITION OF UNSATURATED ALDEHYDES CATALYZED BY HCL
Grela and Colussi[32], besides reporting the pyrolysis kinetic
of benzaldehyde in a flow system, included in the work the
thermal decomposition of 2-furaldehyde and 2-butenal. The 2-
furaldehyde gave a biradical mechanism, whereas 2-butenal
proved to be a molecular process. The evaluation of the
mechanism of 2-butenal was performed by a copyrolysis of 2-
butenal in a 1:3 mixture of normal and 2-butenal-O-d, where it
was found a nearly the same ratio in the products C3H5D and
C3H6, with a negligible kinetic isotope effect of 0.97 0.1. Based
from this result, it was proposed the mechanism of 2-butenal to
proceed through a tight concerted three-membered cyclic
Kinetics
The thermal decomposition experiments were performed in cylindrical
vessels seasoned or deactivated by the products of decomposition of
allyl bromide in a static system,[35–37] and the rate coefficients were
determined manometrically (mercury manometer). The temperature
was controlled within
0.2 °C with a SHINKO DIC-PS (Shinko,
Senbahigashi, Osaka, Japan) 23TR resistance thermometer controller with
a calibrated Iron Constantan thermocouple. The temperature reading
was measured within 0.1 °C with the Iron-Constantan thermocouple at-
tached to a Digital Multimeter Omega 3465B. The reaction vessel showed
no temperature gradient at different points, and the substrates were
injected directly into the reaction vessel through a silicone rubber
septum. HCl gas was added into the reaction vessel to an amount
measured manometrically from a reservoir of the system. The volume
of substrate used for each reaction was ≈0.05–0.1 ml.
transition state structure with an A factor of 1013.5
in reaction (2).
s
ꢀ1 as depicted
(2)
RESULTS AND DISCUSSION
The elimination reaction of α-methyl-trans-cinamaldehyde and
E-2-methyl-2-pentenal catalyzed by HCl gas, in
a static
Chuchani and collaborators[34] studied the gas-phase thermal
decarbonylation of two α-β-unsaturated aldehydes: E-2-butenal
and E-3-phenyl-methylpropenal. The kinetics was determined
in a static reaction system at the temperature range of 430–
480 °C (703.15–753.15 K). These reactions showed to be homoge-
neous, unimolecular, and followed a first-order law. The
decomposition products of 2-butenal are propene and CO gas,
whereas 3-phenyl-2-methylpropenal yielded α-methylstyrene,
cis-trans-β-methylstyrene, indan, and CO gas. The reported
kinetics and thermodynamics data suggested these elimination
reactions to proceed through a three-membered cyclic transition
state type of mechanisms, thus supporting the proposal of Grela
and Colussi[32] for α-β-unsaturated aldehydes decomposition.
However, a two-steps mechanism for the formation of a carbene
type of intermediate through a four-membered cyclic transition
structure was not contemplated.
deactivated reaction vessel with allyl bromide decomposition
and in the presence of toluene free radical suppressor, produces
CO gas and the corresponding olefin as described in reaction (3)
and (4):
(3)
The proposed three-membered cyclic transition state type of
mechanism from few works in gas-phase thermal decomposition
of α-β-unsaturated aldehydes appears to require verification or
support of this type of transition state by using a catalysis such
as hydrogen chloride. In this respect, undertaking an experimen-
tal task of decarbonylation of α-β-unsaturated aldehydes by
incorporating the effect of a catalyst such as HCl gas under
homogeneous conditions is a challenge. Consequently, the
present work aimed at examining the gas-phase elimination kinet-
ics of α-methyl-trans-cinamaldehyde and E-2-methyl-2-pentenal
catalyzed by HCl gas.
(4)
The experimental stoichiometry for reactions (3) and (4) was
checked by carrying out the decomposition process until no fur-
ther pressure increase was observed. These stoichiometries for
product formations requires that, for long reaction times, Pf = 2
P0, where Pf and P0 are the final and initial pressure, respectively.
The average experimental results for Pf/P0 values at five different
temperatures and 10 half-lives were 1.95 for α-methyl-trans-
cinamaldehyde and 1.90 for E-2-methyl-2-pentenal (Table 1).
The stoichiometries of (3) and (4) are shown in Table 2. For
both unsaturated aldehydes, up to about 40% reaction, there is
a reasonable agreement between the extents of decomposition
of the substrate as predicted from pressure measurements and
form the chromatographic analyses of products formation.
Product distributions in the thermal decomposition of α-
methyl-trans-cinamaldehyde as described in reaction (3) at 40%
reaction at 420 °C and at different temperatures are specified in
Tables 3 and 4. The quantitative chromatographic analysis of
the styrene products indicates a kinetic control in the process
of elimination. The ratio %β-methylstyrene/%α-methylstyrene
shows a ratio kβ/kα of 3.54 in the temperature range, where β-
methylstyrene is favored by the kinetic control and the more
thermodynamic stable isomer.
EXPERIMENTAL SECTION
The starting materials α-methyl-trans-cinamaldehyde (99.1%) and E-2-
methyl-2-pentenal (98.0%) were acquired from Aldrich. The purity
of the substrates and products were determined by GC/MS/MS (Saturn
2000, Varian). Capillary column DB – 5MS, 30 × 0.250 mm. id. 0.25 μm.
The quantitative chromatographic analyses of α-methylstyrene, β-
methylstyrene, and E-2-pentene were determined by using a gas
chromatograph Hewlett Packard 5710-A with
a Chromosorb 103,
80–100 mesh 1 m and internal diameter of 2 mm. The identification of
the products was made by comparing chromatogram of the reaction
products with true authentic samples bought from Aldrich and in a
GC–MS (Saturn 2000, Varian 3600X with a DB-5MS capillary column
30 × 0.25 mm. i.d. and 0.25 μm).
J. Phys. Org. Chem. 2014, 27 450–455
Copyright © 2014 John Wiley & Sons, Ltd.
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L. L. JULIO ET AL.
Table 1. Ratio of final (Pf) to initial pressure (P0)a
α-methyl-trans-cinamaldehyde
Table 4. Olefin distribution at different temperatures of α-
methyl-trans – cinamaldehyde at 35% decomposition
Temperature (°C)
% α-Methylstyrene % β-Methylstyrene
Temperature
P0(Torr)
Pf(Torr)
Pf/P0
Average
410.0
420.0
430.0
22.2
22.0
21.9
77.8
78.0
78.1
399.2
410.2
421.0
430.0
437.4
53
65
47
48
84
104
124
92
95
165
1.96
1.91
1.97
1.97
1.96
1.95 0.02
Seasoned vessel with presence of twofold toluene inhibitor
and threefold of HCl gas with respect to the substrate.
E-2-methyl-2- pentenal
371.1
380.7
390.6
399.6
409.3
64
60
59
74
76
121
113
111
140
149
1.90
1.88
1.88
1.89
1.96
1.90 0.03
significant effect on the rates. However, when the packed and
unpacked vessels are seasoned or deactivated with allyl bromide
decomposition products, no effect on the rate coefficients was
obtained (Table 5). These results suggest that the polymeric layer
formed in the thermal decomposition of allyl bromide does not
affect the rate coefficient, and consequently, the homogeneity
is confirmed.
aSeasoned vessel with presence of toluene inhibitor of ≈2P0
and threefold of HCl gas with respect to the substrate.
Table 5. Homogeneity of the reaction
a
Table 2. Stoichiometry of the reactions
S/V (cmꢀ1
)
106 k1(Torrꢀ1 sꢀ1 (a)
)
106 k1(Torrꢀ1 sꢀ1 (b)
)
Substrate
Temperature Time
%
% Reaction
α-Methyl-trans-cinamaldehyde at 420.0 °C
(°C)
(min) Productb (pressure)
(GC)
1.0
6.0
9.90 5.30
12.80 7.00
7.80 0.23
7.84 0.10
α-methyl-trans-
cinamaldehyde
420.0 °C
4
5
7
10
4
6
7.8
12.7
22.5
36.1
14.3
21.3
32.0
42.9
8.0
13.5
23.7
37.0
13.0
20.0
31.0
43.0
E-2-methyl-2-pentenal at 391.7 °C
1.0
6.0
7.56 4.50
9.70 8.70
2.85 0.97
2.88 1.90
E-2-methyl-2-
pentenal
390.7 ° C
S, surface; V, volume.
Presence of twofold toluene inhibitor, and threefold of HCl
gas with respect to the substrate
10
15
aClean Pyrex vessel.
bVessel deactivated with allyl bromide.
aSeasoned vessel with presence of twofold toluene inhibitor,
and threefold of HCl gas with respect to the substrate.
bThese values are the total percentage of products.
Table 6. Effect of toluene inhibitor on rates
P0
(Torr)
Pi
(Torr)
Pi/P0
106 k1
k1
Table 3. Olefin distribution of α-methyl-trans-cinamaldehyde
decomposition at different % reaction.
(Torrꢀ1 sꢀ1
)
(cm3molꢀ1 sꢀ1
)
α-Methyl-trans-cinamaldehyde at 420.0 °C
Time
(min)
%
% α-Methyl-
styrene
% β-Methyl-
styrene
61
55
41
46
27
—
56
60
92
62
—
6.90 0.20
7.40 0.01
7.79 0.01
7.79 0.36
7.80 0.20
298.53 8.65
320.16 0.43
337.20 0.43
337.10 15.57
337.46 8.65
Reaction
1.02
1.46
2.00
2.30
4
5
7
10
7.8
12.7
22.5
37.0
22.1
22.0
21.8
22.0
77.9
78.0
78.2
78.0
E-2-methyl-2-pentenal at 389.7 °C
47
73
74
56
50
—
85
112
114
120
—
2.64 0.07
2.76 0.05
2.87 0.06
2.87 0.10
2.87 0.10
109.19 2.89
114.16 2.06
118.70 2.50
118.50 4.13
118.20 4.13
Temperature 420.0 °C.
Seasoned vessel with presence of twofold toluene inhibitor
and threefold of HCl gas with respect to the substrate.
1.16
1.51
2.04
2.40
The homogeneity of these elimination reactions, in the pres-
ence of the chain inhibitor toluene, was examined by carrying
out several runs in a vessel with a surface-to-volume ratio of
about 6.0 relative to that of the normal vessel, which is equal
to one. The packed and unpacked clean Pyrex vessel gave a
P0, pressure of the substrate; Pi, pressure of the inhibitor
toluene inhibitor of ≈2P0.
Vessel deactivated with allyl bromide. Presence of threefold
of HCl gas with respect to the substrate.
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J. Phys. Org. Chem. 2014, 27 450–455

GAS-PHASE DECOMPOSITION OF UNSATURATED ALDEHYDES CATALYZED BY HCL
The kinetic runs of these substrates were performed in the
presence of at least twice the amount of the radical chain
suppressor toluene in order to inhibit any possible radical
chain reactions. The effect of different proportions of toluene
in the process is shown in Table 6. The absence of toluene in-
hibitor yields a small decrease in the rate coefficient with
values of 6.90 × 10ꢀ6 (Torrꢀ1 sꢀ1) and 2.64 × 10ꢀ6 (Torrꢀ1 sꢀ1
)
for α-methyl-trans-cinamaldehyde and E-2-methyl-2-pentenal
elimination, respectively. When the reaction is carried out in
the presence of toluene in ratios Pi/P0 from 1.0 to 2.6, the rate
coefficient is constant, and any radical chain reaction is
suppressed.
In the pseudo first-order rate law described in Equation (1), the
rate coefficient kobs is not independent of the catalyst HCl pres-
sure, which indicates that the variation of PHCl gives different
values of kobs-values. Therefore, the second-order rate coeffi-
cient is obtained by dividing kobs into PHCl. Thus, Equation (1)
changes into Equation (2). In Table 7 are shown the values of
the kobs with different values of PHCl from 74 to 249 Torr
Table 7. Effect of HCl gas catalyst on the rate of decarbonylation
P
HCl(Torr)
104kobs(sꢀ1
)
106 k1(Torrꢀ1 sꢀ1
)
α-Methyl-trans-cinamaldehyde at 420.2 °C
219
110
100
85
17.00 0.70
8.60 0.30
7.80 0.40
6.60 0.30
5.70 0.85
7.76 0.31
7.82 0.27
7.80 0.40
7.76 0.35
7.70 0.11
74
E-2-methyl-2-pentenal at 390.5 °C
249
229
207
191
175
7.10 0.07
6.60 0.05
5.90 0.10
5.50 0.05
5.00 0.07
2.85 0.03
2.88 0.02
2.85 0.05
2.88 0.03
2.86 0.04
Seasoned vessel with presence of twofold of toluene
inhibitor. P0 substrate ≈ 45.0 Torr
Table 8. Invariability of rate coefficient with initial pressure
of the substrate
P0(Torr)
106 k1(Torrꢀ1 sꢀ1
)
k1(cm3molꢀ1 sꢀ1
)
α-Methyl-trans-cinamaldehyde at 429.8 °C
60
57
48
46
11.51 0.03
11.58 0.02
11.56 0.05
11.62 0.06
504.88 1.32
508.00 0.88
507.07 2.19
509.70 2.63
E-2-methyl-2-pentenal at 371.1 °C
65
61
57
44
1.05 0.04
1.03 0.03
1.08 0.10
1.06 0.02
42.50 1.61
41.40 1.21
43.41 4.02
42.50 0.80
Seasoned vessel with presence of twofold of toluene
inhibitor and threefold of HCl gas with respect to the
substrate
J. Phys. Org. Chem. 2014, 27 450–455
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L. L. JULIO ET AL.
obtained by the fitting of PT = P0[2-exp(ꢀkobst)] by using
OriginPro 8.0 program (Origin Lab Co., Northhampton, MA, USA),
and it was observed a constant value in the second-order rate
constant in agreement with the predicted by the Equation (2).
of the decomposition through via B, the formation of β-methyl
styrene and CO gas appears to be the result of a concerted
five-membered cyclic transition state type of mechanism
(reaction 5 (via B)). As previously described, these two parallel
reactions proceed through different transition states and
therefore distinct values in the activation entropy. This differ-
ence in rate coefficients of these two parallel processes is
dominated by the entropic effects. The α-methyl styrene
(Table 10) shows log A = 12.67 and a more negative value
in activation entropy of ꢀ25.5 Jmolꢀ1 Kꢀ1. This transition state
is more rigid and presents a major lost in translational,
rotational and vibrational degrees of freedom when com-
pared with the transition state involved in the β-methyl
styrene formation.
With regard to E-2-methyl-2-pentenal elimination reaction, the
formation of E-2-pentene implies a mechanism similar to the
process of β-methyl styrene formation from the α-methyl-trans-
cinamaldehyde (reaction 5, via B). This means a concerted five-
membered cyclic transition state (reaction 6). When via B of α-
methyl-trans-cinamaldehyde elimination (β-methyl styrene
formation) is compared with that of E-2-methyl-2-pentenal, a
small difference in the activation enthalpy is found. This
difference is due to the stabilization of the partial negative carbon
atom formed in the rate determining factor Cδꢀ–Hδ+. This fact
infers an impediment for electron delocalization in the transition
state due to the steric interaction between the methyl group and
the aromatic nuclei (reaction 5). Hence, the sequence in rates is
E-2-methyl-2-pentenal> α-methyl-trans-cinamaldehyde.
P0
kobs ¼ PHCIk1 ¼ ð1=tÞ ln
k1 ¼ ð1=tÞð1=PHCIÞ ln
(1)
(2)
ð2P0 ꢀ PTÞ
P0
ð2P0 ꢀ PTÞ
The rate coefficient of these decarbonylation reactions, at
constant HCl gas pressure, was found to be independent of the
initial pressures (Table 8). The second-order rate coefficient was
estimated from Equation (2).
To propose an elimination mechanism and discuss the
observed difference in the reactivity of these two compounds
(Tables 6–8), it was considered the variation of the rate coeffi-
cients with temperatures. For the decomposition of α-methyl-
trans-cinamaldehyde (PHCl/P0 = 3.7) and E-2-methyl-2-pentenal
(PHCl/P0 = 4.0), the results are given in Table 9. This table leads,
by using the least-squares procedure and 90% confidence limits,
to obtain the Arrhenius equations of each reaction.
According to the results of Table 9, the activation energy for
the formation of α-methyl styrene and β-methyl styrene is similar
(183.0 kJmolꢀ1), yet the isomer β-methyl styrene is kinetically
favored because log A value is greater than the value of the α-
methyl styrene formation. Therefore, these parallel reactions
proceed through different transition states. The activation energy
of E-2-methyl-2-pentenal decomposition was 174.5kJmolꢀ1
,
which is a lower value when compared with that obtained for
the elimination of α-methyl-trans-cinamaldehyde. Combining the
Arrhenius expression with the Eyring equation, it is possible to
obtain the thermodynamic parameters of activation as ΔS‡, ΔH‡,
and ΔG‡. In Table 10, the kinetic and thermodynamic activation
parameters for the elimination process studied in the present work
are listed.
(5)
The kinetic and thermodynamic parameters of Table 10 reveal
the homogeneous molecular nature of the gas-phase thermal
decomposition of α-methyl-trans-cinamaldehyde and E-2-methyl-
2-pentenal catalyzed by HCl gas. According to products formation
of α-methyl-trans-cinamaldehyde, a parallel elimination takes
place. Via A proceeds through a concerted bicyclic transition
state type of mechanism (ΔS≠ = ꢀ25.5 Jmolꢀ1 Kꢀ1). In this
respect, the polarization of the Cδꢀ–Hδ+ bond of the CHO
group is the limiting factor. This way a phenyl group may
undergo through an intramolecular Wagner–Meerwein type
of rearrangement. Because of this, the partial positive charge
at the Cα atom is then stabilized (reaction 5 (via A)). In the case
(6)
Table 10. Kinetic and thermodynamic activation parameters at 410.0 °C (683.15 K)
Product
log A
Ea
ΔS‡
ΔH‡
ΔG‡
(kJmolꢀ1
)
(Jmolꢀ1 Kꢀ1
)
(kJmolꢀ1
)
(kJmolꢀ1
)
α-methyl-trans-cinamaldehyde
β-methyl styrene
α-methyl styrene
13.19 0.03
12.67 0.02
183.0 0.31
183.3 0.45
ꢀ15.4
ꢀ25.5
172.3
172.6
182.2
189.0
E-2-methyl-2-pentenal
E-2-pentene
12.79 0.06
174.5 0.80
ꢀ23.1
163.7
178.6
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GAS-PHASE DECOMPOSITION OF UNSATURATED ALDEHYDES CATALYZED BY HCL
[15] N. Imai, O. Toyama, Bull. Chem. Soc. Japan. 1967, 40, 81.
[16] K. J. Laidler, M. T. H. Lui, Proc. Roy. Soc. Lond. Ser. A, 1967, 297, 365.
[17] M. T. H. Liu, Can. J. Chem. 1968, 46, 479.
[18] I. Bardi, F. Márta, Acta Phys. Chem. 1973, 19, 227
[19] I. Bardi, F. Márta, Acta Phys. Chem. 1974, 20, 47.
[20] P. F. Knewstubb, J. Chem. Soc. Faraday Trans. 2 1989, 85, 671.
[21] C. N. Hinshelwood, H. W. Thompsom, Proc. Roy. Soc. Lond. Ser. A
1926, 113, 221.
The consideration of these mechanisms (reactions 5 and 6) in-
sinuates that uncatalyzed α-β-unsaturated aldehydes may well
decarbonylate through a three-membered cyclic transition state
type of mechanism. Consequently, the present results appear to
support the mechanisms of thermal decomposition of α-β-unsat-
urated aldehydes in the gas phase reported in the literature.[32,34]
[22] C. A. Winkler, C. J. M. Fletcher, C. N. Hinshelwood, Proc. Roy. Soc.
Lond. Ser. A 1934, 146, 345.
[23] J. R. E. Smith, C. N. Hinshelwood, Proc. Roy. Soc. Lond. Ser. A, 1942,
180, 237.
REFERENCES
[1] F. A. Carey, R. J. Sundberg, Advanced Organic Chemistry. Part A:
Structure and Mechanism, 4th Edition. Kluwer Academic/Plenum
Publishers, New York, 2000, p. 202.
[2] R. Klein, M. D. Scheer, L. J. Schoen, J. Am. Chem. Soc. 1956, 78, 50.
[3] H. G. Schecker, W. Jost, Ber. Bunsenges. Phys. Chem. 1969, 73, 521.
[4] C. J. Chen, D. J. McKenney, Can. J. Chem. 1972, 50, 992.
[5] L. S. Kassel, J. Phys. Chem. 1930, 34, 1166.
[24] T. J. Sworski, M. Burton, J. Am. Chem. Soc. 1951, 73, 3194.
[25] Z. G. Szabó, F. Márta, J. Am. Chem. Soc. 1961, 83, 768.
[26] D. H. Volman, R. K. Brinton, J. Chem. Phys. 1954, 22, 929.
[27] K. J. Laidler, M. Eusuf, Can. J. Chem. 1965, 43, 268.
[28] R. E. Smith, C. N. Hinshelwood, Proc. Roy. Soc. Lond. Ser. A, 1940, 175, 131.
[29] R. E. Smith, C. N. Hinshelwood, Proc. Roy. Soc. Lond. Ser. A, 1942, 180,
253.
[30] K. U. Ingold, F. P. Lossing, Can. J. Chem. 1953, 31, 30.
[31] R. E. Smith, Trans. Faraday Soc. 2 1940, 36, 983.
[32] M. A. Grela, A. J. Colussi, J. Phys. Chem. 1986, 90, 434.
[33] R. J. Crawford, S. Lutener, H. Tokunaga, Can. J. Chem. 1977, 55, 3951
[34] O. Y. Chabán, R. M. Domínguez, A. Herize, M. Tosta, A. Cuenca, G.
Chuchani, J. Phys. Org. Chem. 2007, 20, 307.
[6] C. J. M. Fletcher, C. N. Hinshelwood, Proc. Roy. Soc. Lond. Ser. A, 1933, 141,
41.
[7] F. O. Rice, K. F. Herzfeld, J. Am. Chem. Soc. 1934, 56, 284.
[8] C. A. Winkler, C. N. Hinshelwood, Proc. Roy. Soc. Lond. Ser. A, 1935, 149, 355.
[9] E. Leifer, H. C. Urey, J. Am. Chem. Soc. 1942, 64, 994.
[10] J. R. Freeman, J. C. Danby, C. N. Hinshelwood, Proc. Roy. Soc. Lond.
Ser. A, 1958, 245, 456.
[11] S. K. Ho, Proc. Roy. Soc. Lond. Ser. A 1963, 276, 278.
[12] A. B. Trenwith, J. Chem. Soc. 1963, 4426.
[13] R. W. Dexter, A. B. Trenwith, J. Chem. Soc. 1964, 5459.
[14] M. Eusuf, K. J. Laidler, Can. J. Chem. 1964, 42, 1851.
[35] A. Maccoll, J. Chem. Soc. 1955, 965.
[36] E. S. Swinbourne, Aust. J. Chem. 1958, 11, 314.
[37] R. M. Dominguez, A. Herize, A. Rotinov, A. Alvarez-Aular, G. Visbal, G.
Chuchani, J. Phys. Org. Chem. 2004, 17, 399.
J. Phys. Org. Chem. 2014, 27 450–455
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