Experimental and computational study of the thermal decomposition of 3-buten-1-ol in m-xylene solution

Article abstract of DOI:10.1007/s11224-013-0234-0

An experimental study of the thermal decomposition of a β-hydroxy alkene, 3-buten-1-ol, in m-xylene solution, has been carried out at three different temperatures: 553.15, 573.15, and 593.15 K. The temperature dependence of the rate constants for the decomposition of this compound in the corresponding Arrhenius equation is given by ln k (s^-1) = (27.34 ± 1.24)-(19,328 ± 712) (kJ mol^-1) T ^-1. A computational study has been performed at the MP2/6-31+G(d) level of theory to calculate the rate constants and the activation parameters by the classical transition state theory. The Arrhenius equation obtained theoretically, ln k (s^-1) = (28.252 ± 0.025)-(19,738.0 ± 14.4) (kJ mol ^-1) T ^-1, agrees very satisfactorily with the experimental one. The bonding characteristics of reactant, transition state, and products have been investigated by the natural bond orbital analysis which provides the natural atomic charges and the Wiberg bond indices used to follow the progress of the reaction. The enthalpy of the reaction has been calculated using experimental values taken from literature and theoretic calculations. The agreement between both values is satisfactory.

Full text of DOI:10.1007/s11224-013-0234-0

Struct Chem
DOI 10.1007/s11224-013-0234-0
ORIGINAL RESEARCH
Experimental and computational study of the thermal
decomposition of 3-buten-1-ol in m-xylene solution
•
Vıctor Lopez Jairo Quijano Sofıa Luna
•
•
´
´
Pablo Ruiz Diego Rios Wilson Parra
´
•
•
•
•
Edilma Zapata Jair Gaviria Rafael Notario
•
Received: 5 February 2013 / Accepted: 8 February 2013
Ó Springer Science+Business Media New York 2013
Abstract An experimental study of the thermal decom-
position of a b-hydroxy alkene, 3-buten-1-ol, in m-xylene
solution, has been carried out at three different tempera-
tures: 553.15, 573.15, and 593.15 K. The temperature
dependence of the rate constants for the decomposition of
this compound in the corresponding Arrhenius equation is
given by ln k (s-1) = (27.34 1.24)–(19,328 712)
(kJ mol-1) T-1. A computational study has been per-
formed at the MP2/6-31?G(d) level of theory to calculate
the rate constants and the activation parameters by the
classical transition state theory. The Arrhenius equation
obtained theoretically, ln k (s-1) = (28.252 0.025)–
(19,738.0 14.4) (kJ mol-1) T-1, agrees very satisfacto-
rily with the experimental one. The bonding characteristics
of reactant, transition state, and products have been
investigated by the natural bond orbital analysis which
provides the natural atomic charges and the Wiberg bond
indices used to follow the progress of the reaction. The
enthalpy of the reaction has been calculated using experi-
mental values taken from literature and theoretic calcula-
tions. The agreement between both values is satisfactory.
Keywords b-Hydroxy alkenes ꢀ 3-Buten-1-ol ꢀ
Thermal decomposition ꢀ Reaction mechanism ꢀ
Wiberg index
Introduction
The mechanism of the thermal decomposition of
b-hydroxy alkenes in the gas phase has been previously
studied both experimentally [1–3] and theoretically [4].
They decompose thermally to give a mixture of alkenes
and carbonyl compounds, following a first order homoge-
neous unimolecular reaction [3]:
R ꢁ CH ¼ CH ꢁ CH2 ꢁ CR0 R00 OH
! R ꢁ CH2 ꢁ CH ¼ CH2 þ R0 R00 CO ð1Þ
Experimental studies [1] indicate that tertiary alcohols
decompose more readily than secondary and primary
alcohols. From a study of the products of pyrolysis,
Arnold and Smolinsky [2] proposed a mechanism via a six-
membered cyclic transition state (TS) (Fig. 1). This cyclic
TS is similar to that proposed for the thermal
decompositions of the carboxylic esters [5] and b,c-
unsatured acids [6]. Smith and Yates [1] studied the
homogeneous gas phase pyrolysis of a b-hydroxy alkene, 3-
buten-1-ol, which follows a first order law, and the data
could be fitted to the Arrhenius equation:
´
This article is dedicated to Marıa Victoria Roux on the occasion of her
retirement.
ꢀ
ꢁ
ꢀ
ꢁ
ln k sꢁ1 ¼ 25:61 ꢁ 20547 kJ molꢁ1 ꢀ Tꢁ1
ð2Þ
´
V. Lopez (&) ꢀ J. Quijano ꢀ S. Luna ꢀ P. Ruiz ꢀ D. Rios ꢀ
W. Parra ꢀ E. Zapata ꢀ J. Gaviria
A theoretic study of this reaction in the gas phase, at the
MP2/6-31G(d) and B3LYP/6-31G(d) levels, was carried
out by us [4] some years ago. We concluded that MP2
method seems to be a better choice than the DFT method to
study this reaction.
´
´
Laboratorio de Fisicoquımica Organica, Facultad de Ciencias,
Universidad Nacional de Colombia, Sede Medellın,
´
´
AP 3840 Medellın, Colombia
e-mail: valopeza@unal.edu.co
R. Notario
Instituto de Quımica Fısica Rocasolano, CSIC, Serrano 119,
We have taken up the subject carrying out an experi-
mental study of the thermal decomposition of 3-buten-1-ol
´
28006 Madrid, Spain
´
123

Struct Chem
Fig. 1 Mechanism of the thermal decomposition of b-hydroxy alkenes
in m-xylene solution within a temperature range of
553.15–593.15 K. m-Xylene has been chosen as solvent
because it is a low polar solvent adequate for carrying out
the thermolysis reaction of this type of compounds, and it
has been used previously by us in the experimental study of
the thermal decomposition of methyl b-hydroxyesters [7]
and 4-hydroxy-2-butanone [8].
determined by gas–liquid chromatography (GLC) as the
same of purity check. The rate of decomposition of
3-buten-1-ol was determined by observing the disappear-
ance rate by GLC using a DBWAX column (30 m 9
0.25 mm i.d., film thickness 0.25 lm).
A computational study was carried out at the MP2/6-
31?G(d) level to calculate the rate constants and the
activation parameters by the classical transition state theory
(TST) [7, 9, 10].
Computational details
All computational studies were performed by means of the
Gaussian 09 computational package [11] by ab initio
methods according to how they are implemented in the
computational package. The geometric parameters of the
reactant, TS, and products of the studied reaction were
fully optimized by ab initio analytical gradients post-
Hartree–Fock MP2 method [12] with the 6-31?G(d) basis
set. Each structure was characterized as a minimum or a
saddle point of first order by analytical frequency calcu-
lations. A scaling factor [13] of 0.9670 for the zero-point
vibrational energies has been used. Thermal corrections to
enthalpy and entropy values have been evaluated at the
experimental temperatures of 553.15, 573.15 and
593.15 K. To calculate enthalpy and entropy values at a
temperature T, the difference between the values at that
temperature and 0 K has been evaluated according to
standard thermodynamics [14].
This work is a contribution to the kinetic study of
b-hydroxy alkenes in solution. To our knowledge, kinetic
measurements have not been carried out for the thermal
decomposition of 3-buten-1-ol in m-xylene solution and
there are no theoretic studies on this reaction.
Experimental procedure
3-Buten-1-ol was obtained commercially (Aldrich, St.
Louis, MO, USA) distilled carefully before use and its
purity was checked by gas chromatography–mass spec-
trometry (GC–MS) using DB-WAX column (30 m 9 0.25
mm i.d., film thickness 0.25 lm), which is a polyethylene
glycol (PEG) column with high polarity.
Thermolysis was carried out in a heated aluminum
block, 60 mm length 9 60 mm diameter, insulated by
glass wool. The block was heated by resistance coil, and its
temperature was controlled to 0.2 °C by a Barber–Col-
man PID (proportional–integral–derivative) temperature
controller. The absolute temperature was checked by a
chromel–alumel thermocouple. This thermolysis was car-
ried out in a sealed glass ampoule made from carefully
washed glass tubes, having 2-mm i.d. and 500-mm length;
approximately 25 lL of a solution of 3-buten-1-ol (*4 %
v/v) and benzene as an internal standard (*1 % v/v) in
m-xylene was injected in the tube. Benzene also served as a
free radical inhibitor. The ampoule was then sealed. Six-
teen capillary tubes were placed in holes drilled in the
block, the diameter of holes was such that the tubes fitted
precisely, and at determined intervals the tubes were
withdrawn and the amount of propene produced was
Vibrational frequency calculations were carried out in
order to confirm the stationary states, including TS structure.
An IRC calculation [15] has been performed to verify that
localized TS structure connects with the corresponding min-
imum stationary points associated with reactant and products.
Energies and vibrational frequencies in solution were
computed using the integral equation formalism variant
of the polarizable continuum model (IEFPCM) [16]. To
simulate m-xylene as the solvent interacting with substrate,
a dielectric constant of 2.3478 was used [11, 17].
MP2/6-31?G(d)-calculated electronic energies, zero-
point vibrational energies, thermal corrections to enthal-
pies, and entropies, for the reactant, TS, and products,
involved in the thermal decomposition reaction of 3-buten-
1-ol in m-xylene solution, are collected in Table 1.
The bonding characteristics of reactant, TS, and prod-
ucts have been investigated by a population partition
123

Struct Chem
The activation energy, Ea, and the Arrhenius A factor
have been calculated by Eqs. 4 and 5, respectively, derived
Table 1 MP2/6-31?G(d)-calculated electronic energies Eel, zero-
point vibrational energies ZPE, and thermal corrections to enthalpies
TCH, in Hartrees, and entropies S, in cal mol-1 K-1, for the reactant,
TS, and products, involved in the thermal decomposition reaction of
3-buten-1-ol, at 553.15, 573.15, and 593.15 K, in diluted m-xylene
solution
from the TST theory:
¼
Ea ¼ DH ðTÞ þ RT
ð4Þ
ð5Þ
¼
DS ðTÞ
ekBT
R
Structure
Eelec
ZPE
A ¼
e
h
3-Buten-1-ol (R)
TS
-231.668033
-231.600935
-117.463579
-114.179792
0.115564
0.110559
0.081038
0.027287
Results and discussion
Propene (P1)
Formaldehyde (P2)
Determinations of the rate of decomposition of 3-buten-
1-ol in m-xylene solution were made at three different
temperatures: 553.15, 573.15, and 593.15 K. The reaction
was essentially homogeneous and of first order. The mea-
sured rate constants at the three temperatures are collected
in Table 1. The Arrhenius plot was linear (see Fig. 3), and
treating the data by the method of least squares gave
Ea = (160.7 5.9) kJ mol-1 and ln A = (27.34 1.24).
The enthalpies and entropies of activation calculated from
experimental data by Eqs. 4 and 5 are collected in Table 2.
Theoretical calculations at the MP2/6-31?G(d) level of
theory have been carried out to explore the nature of the
mechanism of the thermal decomposition of 3-buten-1-ol,
in m-xylene solution, the products of the reaction being
propene and formaldehyde. The mechanism proposed is
a one-step process proceeding through a six-membered
cyclic TS (Fig. 2).
T = 553.15 K
Structure TCH
T = 573.15 K
T = 593.15 K
TCH
S
TCH
S
S
R
0.134866 94.432 0.136070 95.774 0.137304 97.101
0.128332 88.791 0.129497 90.090 0.130693 91.376
0.094064 75.170 0.094843 76.038 0.095641 76.897
0.034975 58.098 0.035323 58.487 0.035678 58.868
TS
P1
P2
technique, the natural bond orbital (NBO) analysis of Read
and Weinhold [18, 19]. The NBO formalism provides the
values for the atomic natural total charges and also pro-
vides the Wiberg bond indices [20] used to follow the
progress of the reaction. The NBO analysis has been per-
formed using the NBO program [21] implemented in the
Gaussian 09 package [11] and has been carried out on the
MP2 charge densities in order to explicitly include electron
correlation effects.
The kinetic parameters for the reaction studied have
been calculated at the same temperatures used in the
experiments, 553.15, 573.15, and 593.15 K. Calculated
values of the activation parameters and the rate constants
are collected in Table 2, and compared with the experi-
mental ones. There is a very good agreement between the
experimental and the calculated values. The Arrhenius plot
obtained from theoretic data is drawn in Fig. 3, compared
with the experimental plot. As it can be observed, both
lines are almost parallel. Values of Ea = (164.11 0.12)
kJ mol-1 and ln A = (28.252 0.025) have been calcu-
lated in very good agreement with the experimental ones.
The optimized geometry for the TS in the postulated
mechanism is shown in Fig. 4. The structure consists in a
near planar six-membered ring, in which the hydrogen
We have selected the classical TST [9, 10] to calculate
the kinetic parameters. The rate constant, k(T), of the
kinetic scheme (see Fig. 2) was computed by this theory
assuming that the transmission coefficient is equal to unity,
as expressed by the following relation, known as Eyring-
Polanyi equation:
¼
RT
ꢁDG ðTÞ
kBT
h
kðTÞ ¼
e
ð3Þ
where kB, h, and R are the Boltzmann constant, the Planck
constant, and the universal gas constant, respectively.
DG=(T) is the standard-state Gibbs energy of activation, at
the absolute temperature T.
Fig. 2 Proposed mechanism for the thermal decomposition of 3-buten-1-ol
123

Struct Chem
Arrhenius plots
-4.5
-5.0
-5.5
-6.0
-6.5
-7.0
-7.5
-8.0
ln k(T
) (s-1) = (28.252 0.025) - (19738.0 14.4) (kJ mol ) T-1
-1
theoretical
k
experimental
-1
ln
k(
T
) (s-1) = (27.34 1.24) - (19328 712) (kJ mol ) T -1
0.00168 0.00170 0.00172 0.00174 0.00176 0.00178 0.00180 0.00182
1/T (K-1)
Fig. 3 Arrhenius plots obtained from experimental and calculated
data
Fig. 4 MP2/6-31?G(d)-optimized structure of the TS of the mech-
anism proposed in Fig. 2
transfer is approaching to linear angles (C1H6O5 angle of
152.08). There is one and only one imaginary vibrational
frequency in the TS, 1133.3i, in m-xylene solution, eval-
uated at the MP2/6-31?G(d) level of theory.
The Gibbs energy profile for the thermal decomposition
process of 3-buten-1-ol, at 573.15 K, is presented in Fig. 5.
To avoid the subjective aspects associated with the
geometrical analysis of the TS, the progress of the reaction
has been followed by means of the Wiberg bond indices Bi
[20]. The bond index between two atoms is a measure of
the bond order, and hence, of the bond strength between
these two atoms; thus, if the evolution of the bond indices
corresponding to the bonds being made or broken in a
chemical reaction is analyzed along the reaction path, a
very precise image of the timing and extent of the bond-
breaking and bond-forming processes at every point can be
achieved.
Fig. 5 Gibbs energy profile at 573.15 K, evaluated at the MP2/6-
31?G(d) level, for the thermal decomposition of 3-buten-1-ol
The Wiberg bond indices, corresponding to the bonds
involved in the reaction center of the mechanism for all the
reactant, TS, and products, are shown in Table 3.
Moyano et al. [22] have defined a relative variation of
the bond index at the TS, dBi, for every bond i, involved in
a chemical reaction as
where the superscripts R, TS, and P refer to reactant, TS,
and product, respectively. The calculated percentages of
evolution (%EV = 100 dBi) of the bonds involved in the
reaction center are shown in Table 2. As it can be seen, the
breaking of the C1–C2 double bond (72.7 %) is the most
advanced process and the H6 displacement from O5 to C1 is
very advanced, the O5–H6 bond is almost broken (69.3 %),
while the H6–C1 bond is less advanced (58.5 %).
ðBTi S ꢁ BRi Þ
dBi ¼
ð6Þ
ðBPi ꢁ BRi Þ
Table 2 Experimental and calculateda rate constants and activation parameters of the thermolysis of 3-buten-1-ol in m-xylene solution
ꢁ1
ꢁ1
ꢁ1
DS ðJ mol Kꢁ1
Þ
DH ðkJ mol
Exp.
Þ
DG ðkJ mol
Exp.
Þ
¼
¼
¼
T (K)
103 k (s-1
)
Exp.
Calc.
Exp.
Calc.
Calc.
Calc.
553.15
573.15
593.15
a
0.51
1.60
5.40
0.59
2.05
6.56
-31.06
-31.36
-31.64
-23.60
-23.78
-25.95
156.10
155.93
155.77
159.44
159.34
159.24
173.28
173.90
174.54
172.50
172.97
173.45
At the MP2/6-31?G(d) level of theory
123

Struct Chem
Table 3 Wiberg bond indices (Bi), of reactant (R), transition state
(TS) and products (P)
Table 4 NBO charges, calculated at the MP2/6-31?G(d) level, at the
atoms involved in the reaction
C1–C2
C2–C3
C3–C4
C4–O5
O5–H6
C1–H6
C1
C2
C3
C4
O5
H6
biR
bTi S
biP
1.985
1.299
1.042
72.7
1.026
1.395
1.987
38.4
1.003
0.569
0.000
43.3
0.912
0.723
0.222
0.000
69.3
0.004
0.549
0.936
58.5
R
-0.441
-0.771
-0.224
-0.501
-0.581
-0.047
-0.837
-0.838
0.507
0.406
1.263
TS
0.043
0.105
1.834
%EV
38.1
on the atoms) of the atoms involved in the reaction center
of the postulated mechanism for the reaction (see Fig. 2).
There is an important positive charge developed on H6
(?0.507 in the reactant, and ?0.406 in the TS), whereas
the electronic excess is supported by the O atom and the C1
and C3 carbon atoms. The strong negative character of C1
atom (-0.441 in the reactant, and -0.771 in the TS) allows
it to attract the H6 atom in the TS.
dbav = 0.53
Sy = 0.85
The lengthening of the C1–C2 bond with the initial
migration of the H6 atom from O5 to C1 can be seen as the
driving force for the studied reaction.
The average value, dBav, is calculated as [22]
X
1
Some years ago, we measured [23] the enthalpy of for-
mation in the gas phase of 3-buten-1-ol. Using this value,
-(147.3 1.8) kJ mol-1, and the experimental enthalpies
of formation of propene and formaldehyde, taken from lit-
dBav
¼
dBi
ð7Þ
n
with n being the number of bonds involved in the reaction
and it measures the degree of advancement of the TS along
the reaction path. Calculated dBav value for the mechanism
of the studied reaction is shown in Table 2. The dBav
values calculated, 0.53, shows that the TS is slightly
‘‘advanced,’’ nearer to the products than to the reactants.
The synchronicity, Sy, of a chemical reaction can be
calculated as
erature [24], (20.0 0.7) and -(108.6 0.5) kJ mol-1
,
respectively, a value of (58.7 2.0) kJ mol-1 is calculated
for the enthalpy of decomposition reaction of 3-buten-1-ol in
the gas phase. By means of the theoretical calculations at the
MP2/6-31?G(d) level a value of 52.0 kJ mol-1 is obtained
in a reasonable agreement with the experimental one.
Sy ¼ 1 ꢁ A
ð8Þ
A being the asynchronicity calculated by the expression
Summary
proposed by Moyano et al. [22]:
X
1
jdBi ꢁ dBavj
dBav
The thermal decomposition of 3-buten-1-ol has been theo-
retically studied at the MP2/6-31?G(d) level of theory. The
mechanism proposed is a one-step process proceeding
through a six-membered cyclic TS. The agreement between
experimental and calculated kinetic parameters is reasonable.
The progress of the reactions has been followed by
means of the Wiberg bond indices. The lengthening of the
C1–C2 bond with the initial migration of the H6 atom from
O5 to C1 can be seen as the driving force for the studied
reaction. Calculated synchronicity value indicates that the
mechanism does not correspond to a concerted and highly
synchronous process. The TS is slightly ‘‘advanced,’’
nearer to the products than to the reactants.
A ¼
ð9Þ
ð2n ꢁ 2Þ
Synchronicities vary between 0 and 1, which is the case
when all of the bonds implicated in the reaction center have
broken or formed at exactly the same extent in the TS. The
Sy values obtained in this way are, in principle,
independent of the degree of advancement of the TS. The
Sy value calculated for the reaction studied is shown in
Table 2. Calculated synchronicity value (0.85) is not very
high, indicating that the mechanism does not correspond to
a concerted and highly synchronous process.
Another aspect to be taken into account is the relative
asynchronicity of the bond-breaking and bond-forming
processes that measures the bond deficiency along the
reaction path. In the studied reaction, the bond-breaking
processes are more advanced (an average value of ca.
62 %) than the bond-forming processes (an average value
of ca. 45 %), indicating a bond deficiency in the TS.
The trend in the degree of bond lengthening is mirrored
in the NBO atomic charges. In Table 4, we have collected
the natural atomic charges (the nuclear charges minus the
summed natural populations of the natural atomic orbitals
The enthalpy of the reaction studied has been calculated
using experimental values taken from literature and theoretical
calculations. The agreement between both values is satisfactory.
Acknowledgments This study is supported by the research funds
provided by Universidad Nacional de Colombia, Project
‘‘201010011033’’, ‘‘Estudio Computacional y Experimental de la
´
Eliminacion de 3-Metil-3-buten-1-ol en Solucion de m-Xileno,’’
DIME 2012, Modalidad 2.’’ R.N. thanks the financial support of the
´
´
Spanish Ministerio de Economıa y Competitividad under Project
CTQ2010-16402.
123

Struct Chem
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