Decomposition of 2-methylfuran. Experimental and modeling study

Article abstract of DOI:10.1021/jp962646c

The thermal reactions of 2-methylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1100-1400 K and with overall densities of approx. 3 × 10^-5 mol/cm³. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. The unimolecular decomposition is initiated by two parallel channels: (1) 1,2-hydrogen atom migration from C(5) to C(4) and (2) a methyl group migration from C(2) to C(3) in the ring. Each channel is followed by two parallel modes of ring cleavage. In the first channel, breaking the O - C(2) and the C(4) - C(5) bonds in the ring yields CO and different isomers of C₄H₆, whereas breaking of the O - C(2) and the C(3) - C(4) bonds yields CH₂CO and two isomers C₃H₄. In the second channel, breaking the O - C(5), and C(2) - C(3) bonds in the ring yields again CO and isomers of C₄H₆, whereas in the second mode O - C(5), C(2) - C(3), and C(3) - C(4) are broken to yield CO, C₂H₂, and C₂H₄. The four C₄H₆ isomers in decreasing order of abundance were 1,3-butadiene, 1-butyne, 1,2-butadiene, and 2-butyne. The major decomposition product is carbon monoxide. The rate constant for its overall formation is estimated to be k_CO = 10^15.88 exp(-78.3 × 10³/RT) s^-1, where R is expressed in units of cal/(K mol). Other products that were found in the postshock samples in decreasing order of abundance were C₄H₄, C₂H₂, CH₄, p-C₃H₄, C₂H₆, C₂H₄, a-C₃H₄, C₆H₆, C₄H₄O, C₃H₆, and C₄H₂. The total decomposition of 2-methylfuran in terms of a first order rate constant is given by k_total = 10^14.78 exp(-71.8 × 10³/RT) s^-1. This rate and the production rate of carbon monoxide are slightly higher than the ones found in the decomposition of furan. An oxygen-carbon mass balance among the decomposition products was obtained. A reaction scheme composed of 36 species and some 100 elementary reactions accounts for the product distribution over the temperature range covered in this study. First order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity analysis are shown. Differences and similarities in the reactions of furan and 2-methylfuran are discussed.

Full text of DOI:10.1021/jp962646c

1018
J. Phys. Chem. A 1997, 101, 1018-1029
Decomposition of 2-Methylfuran. Experimental and Modeling Study
Assa Lifshitz,* Carmen Tamburu, and Ronen Shashua
Department of Physical Chemistry, The Hebrew UniVersity, Jerusalem 91904, Israel
ReceiVed: August 30, 1996; In Final Form: NoVember 7, 1996X
The thermal reactions of 2-methylfuran were studied behind reflected shock waves in a pressurized driver
single pulse shock tube over the temperature range 1100-1400 K and with overall densities of ∼3 × 10-5
mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free
radical reactions were obtained under shock heating. The unimolecular decomposition is initiated by two
parallel channels: (1) 1,2-hydrogen atom migration from C(5) to C(4) and (2) a methyl group migration
from C(2) to C(3) in the ring. Each channel is followed by two parallel modes of ring cleavage. In the first
channel, breaking the OsC(2) and the C(4)sC(5) bonds in the ring yields CO and different isomers of C4H6,
whereas breaking of the OsC(2) and the C(3)sC(4) bonds yields CH2CO and two isomers C3H4. In the
second channel, breaking the OsC(5), and C(2)sC(3) bonds in the ring yields again CO and isomers of
C4H6, whereas in the second mode OsC(5), C(2)sC(3), and C(3)sC(4) are broken to yield CO, C2H2, and
C2H4. The four C4H6 isomers in decreasing order of abundance were 1,3-butadiene, 1-butyne, 1,2-butadiene,
and 2-butyne. The major decomposition product is carbon monoxide. The rate constant for its overall formation
is estimated to be kCO ) 1015.88 exp(-78.3 × 103/RT) s-1, where R is expressed in units of cal/(K mol).
Other products that were found in the postshock samples in decreasing order of abundance were C4H4, C2H2,
CH4, p-C3H4, C2H6, C2H4, a-C3H4, C6H6, C4H4O, C3H6, and C4H2. The total decomposition of 2-methylfuran
in terms of a first order rate constant is given by ktotal ) 1014.78 exp(-71.8 × 103/RT) s-1. This rate and the
production rate of carbon monoxide are slightly higher than the ones found in the decomposition of furan.
An oxygen-carbon mass balance among the decomposition products was obtained. A reaction scheme
composed of 36 species and some 100 elementary reactions accounts for the product distribution over the
temperature range covered in this study. First order Arrhenius rate parameters for the formation of the various
reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity
analysis are shown. Differences and similarities in the reactions of furan and 2-methylfuran are discussed.
I. Introduction
where only overall decomposition rates were determined from
which high-pressure-limit rate constants were evaluated.
In this investigation we present data on the product distribu-
tion in shock heated mixtures of 2-methylfuran with a special
emphasis on the C4H6 isomers, a detailed mechanism is sug-
gested, a reaction scheme is constructed, and computer simula-
tion including unimolecular decompositions, isomerization, and
free radical reactions is performed.
We have recently published a detailed investigation of the
thermal decomposition of furan in a single pulse shock tube
over the temperature range 1060-1260 K and at overall
densities of ∼3 × 10-5 mol/cm3.1 It was shown that the main
thermal reaction of furan is a 1,2 H atom migration from C(5)
to C(4) followed by CO elimination and formation of C3H4:
(3)
(2)
(4)
(5)
CH3C CH + CO
II. Experimental Section
O
(1)
a. Apparatus. The thermal reactions of 2-methylfuran were
studied behind reflected shocks in a pressurized driver, 52 mm
i.d. single pulse shock tube. The tube and its mode of operation
have been described in an earlier publication4 and will be given
here very briefly.
The driven section was 4 m long and was divided in the
middle by a 52 mm i.d. ball valve. The driver had a variable
length up to a maximum of 2.7 m and could be varied in small
steps in order to obtain the most rapid cooling conditions. A
36 L dump tank was connected to the driven section at a 45°
angle near the diaphragm holder in order to prevent reflection
of transmitted shocks. The driven section was separated from
the driver by “Mylar” polyester film of various thickness,
depending upon the desired shock strength.
After pumping down the tube to approximately 10-5 Torr,
the reaction mixture was introduced into the section between
the 52 mm i.d. ball valve and the end plate, and pure argon,
into the section between the diaphragm and the valve, including
the dump tank. Gas samples were collected from the tube
through an outlet in the driven section (near the end plate) in
The rate constant obtained for this process was kCO ) 1015.25
exp(-77.5 × 103/RT) s-1. Another unimolecular cleavage of
the ring produced ketene and acetylene at a rate approximately
3.5 times slower than the production rate of CO and C3H4.
In a more recent study we investigated the thermal reactions
of 2-furonitrile2 and found that similar unimolecular ring
cleavage takes place where the main products are CH3CtCCN
and CO and to a lesser extent CHtCCN and CH2CO. A
computer modeling of the overall decomposition of 2-furonitrile,
based on a reaction scheme in which these two reactions and a
•
dissociation of the main product, CH3CtCCN f CH2 CtCCN
+ H•, were the major reactions, gave a very good agreement
with the experimental results.
We are not aware of any detailed investigations involving
other substituted furans such as mono- and dimethylfuran. We
are aware, however, of one VLPP study of these molecules3
X Abstract published in AdVance ACS Abstracts, January 1, 1997.
S1089-5639(96)02646-1 CCC: $14.00 © 1997 American Chemical Society

Decomposition of 2-Methylfuran
J. Phys. Chem. A, Vol. 101, No. 6, 1997 1019
Figure 1. Gas chromatogram of a postshock mixture of 0.5%
2-methylfuran in argon heated to 1319 K.
150 cm3 glass bulbs and were then analyzed on a Carlo-Erba
Model VEGA-2000 gas chromatograph using a flame ionization
detector.
Reflected shock temperatures were calculated from the extent
of decomposition of 1,1,1-trifluoroethane which was added in
small quantities to the reaction mixture and served as an internal
standard. Its decomposition to CH2dCF2+HF is a first order
unimolecular reaction with a rate constant5 of k1st ) 1014.51 exp
(-72.6 × 103/RT) s-1
.
Reflected shock temperatures were calculated from the
relation
Figure 2. GC/MS chromatograms of the four C4H6 isomers at 1170
and 1296 K, respectively. The peaks of 1,2-butadiene and 1-butyne
are not separated from the GC peak of C4H4.
1
At
T ) -(E/R)/ ln - ln(1 - ø)
(I)
[
{
}
]
where t is the reaction dwell time and ø is the extent of
decomposition defined as
ø ) [CH2CF2]t/([CF2CH2]t + [CH3CF3]t)
(II)
The additional reflected shock parameters were calculated
from the measured incident shock velocities using the three con-
servation equations and the ideal gas equation of state. Dwell
times of approximately 1.8 ms were measured with an accuracy
of ∼5%. Cooling rates were approximately 5 × 105 K/s.
b. Materials and Analysis. Reaction mixtures containing
0.5% 2-methylfuran in argon were prepared manometrically and
stored in 12 L glass bulbs at 700 Torr. Both the bulbs and the
line were pumped down to ∼10-5 Torr before the preparation
of the mixtures. 2-Methylfuran was obtained from Aldrich
Chemical Co. and showed only one GC peak. The argon used
was Matheson ultrahigh purity grade, listed as 99.9995%, and
the helium was Matheson pure grade, listed as 99.999%. All
of the materials were used without further purification.
The gas chromatographic analyses of the postshock mixtures
were performed on two columns with flame ionization detectors.
The analyses of all of the products except for CO were
performed on a 2 m Porapak N column. Its initial temperature
of 35 °C was gradually elevated to 190 °C in an analysis which
lasted about 40 min. A typical chromatogram of 0.5% 2-
methylfuran in argon shock heated to 1319 K is shown in Figure
1.
We could not separate the peaks of 1-butyne and 1,2-
butadiene from the large peak of C4H4. These two C4H6 isomers
were discovered in an additional series of experiments using
GC-MS. In Figure 2 we can see two such chromatograms at
1170 and 1296 K, where m/z 54, 39, 53, and 27 which are
characteristic of the C4H6 isomers, and m/z 52, characteristic
of C4H4, are shown. As can be seen there are two peaks, slightly
separated, of C4H6 hidden behind the large peak of C4H4. These
two peaks were identified as 1,2-butadiene, the first peak, and
1-butyne, the second peak. The identification was based on
Figure 3. Relative abundance of the four C4H6 isomers plotted as a
function of temperature.
the relative heights of m/z 39 and 54 which differ considerably
in these two isomers.6 Figure 3 shows an estimated relative
abundance of the four C4H6 isomers calculated from the sum
of the integrated peak areas of m/z 54, 39, 53, and 27.
In order to incorporate the GC-MS data into the first series
of experiments, we first fitted second order polynomials as a
function of T5 to the GC-MS data points in Figure 3 (shown as
lines on the figure) and then used these polynomials to calculate
the ratio of the four C4H6 isomers in the first series of
experiments on the basis of their shock temperature. By using
the obtained ratio and knowing the mole percent of 1,3-
butadiene, we could calculate the mole percents of 1,2-butadiene
and 1-butyne.
We have also carried out another series of experiments in
order to verify the presence or absence of ketene and/or
methylketene in the postshock mixtures, as these two molecules
can be formed in unimolecular decompositions of the ring.

1020 J. Phys. Chem. A, Vol. 101, No. 6, 1997
Lifshitz et al.
Ketene and methylketene tend to react with small quantities of
water absorbed in various locations on the way to the GC and
produce acetic and propionic acids, which are also absorbed
and hard to analyze. When the postshock mixture is collected
in a bulb containing a small quantity of methyl alcohol, methyl
acetate is formed from ketene and methyl propionate is formed
from methylketene. The latter can be relatively easily, at least
qualitatively, analyzed.
We did not identify any methyl propionate (methylketene)
in the postshock mixtures, but methyl acetate (ketene) was
clearly found. The concentration of ketene, which could not
be determined quantitatively, was taken as being equal to the
sum of allene and propyne, assuming that both molecules are
formed with ketene in the same unimolecular process as will
be discussed later.
Carbon monoxide was analyzed on a 2 m molecular sieve
5A column at 35 °C. It was reduced at 400 °C to methane
prior to its detection using a Chrompak methanyzer with a carrier
composed of 50% hydrogen and 50% argon. These analyses
gave the ratio [CO]/[CH4]. From these ratios and the known
methane concentration obtained in the Porapak N analyses, the
concentration of CO could be calculated for each run. The ratio
[CO]/[CH4] in a standard mixture of methane and carbon
monoxide was determined periodically in order to verify a
complete conversion of the latter to methane in the methanyzer.
The concentrations of the reaction products C5(pr)i were
calculated from their GC peak areas from the following
relations.7
Figure 4. Oxygen-carbon mass balance among the decomposition
products.
C5(pri) )
A(pri)t/S(pri){C5(2-methylfuran)0/A(2-methylfuran)0} (III)
C5(2-methylfuran)0 )
{p1(%(2-methylfuran))F5/F1}/(100RT1) (IV)
A(2-methylfuran)0 )
A(2-methylfuran) + 1/ N(pr ) × A(pr ) /S(pr ) (V)
∑
t
5
i
i t
i
In these relations C5(2-methylfuran)0 is the concentration of
2-methylfuran behind the reflected shock prior to decomposition
and A(2-methylfuran)0 is the calculated GC peak area of
2-methylfuran prior to decomposition (eq V), where A(pri)t is
the peak area of a product i in the shocked sample, S(pri) is its
sensitivity relative to 2-methylfuran, and N(pri) is the number
of its carbon atoms. F5/F1 is the compression behind the
reflected shock, and T1 is room temperature.
The identification of the reaction products was based on their
GC retention times and was also assisted by a Hewlett-Packard
Model 5970 mass selective detector. The sensitivities of the
various products to the FID were determined relative to
2-methylfuran from standard mixtures. The areas under the GC
peaks were integrated with a Spectra Physics Model SP4200
computing integrator and were transferred after each analysis
to a PC for data reduction and graphical presentation.
Figure 5. Arrhenius plot of the first order rate constant for the overall
decomposition of 2-methylfuran. The rate constant is calculated from
the relation ktotal ) -ln{[2-methylfuran]t/[2-methylfuran]0}/t. The value
obtained is ktotal ) 1014.77 exp(-71.8 × 103/RT) s-1
. The total
decomposition of furan is also shown for comparison.
mixture (not including Ar and H2) and irrespective of the number
of its carbon atoms.
The balance of oxygen vs carbon among the decomposition
products is shown in Figure 4. The concentrations of carbon
monoxide, ketene, and furan are plotted against one-fifth of the
sum of the concentrations of all of the decomposition products
(including the oxygen containing species), each multiplied by
the number of its carbon atoms. One-fifth is the ratio of oxygen
to carbon in the reactant molecule. The 45° line in the figure
represents a complete mass balance. As can be seen there is
no major deviation from an oxygen-carbon balance over the
temperature range of the investigation.
III. Results
Figure 5 shows the rate constant for the overall decomposi-
tions of 2-methylfuran, calculated as a first order rate constant
from the relation:
In order to determine the distribution of reaction products,
some 40 tests were run with mixtures containing 0.5% 2-
methylfuran in argon, covering the temperature range 1100-
1400 K. Extents of pyrolysis as low as a few hundredths of
1% were determined. Details of the experimental conditions
and the distribution of reaction products are given in Table 1.
The percent of a given product in the total sample, as shown in
the table, corresponds to its mole fraction in the postshock
ktotal ) -ln{[2-methylfuran]t / [2-methylfuran]0}/t (VI)
The value obtained is ktotal ) 1014.78 exp(-71.8 × 103/RT) s-1
,
where R is expressed in units of cal/(K mol). The rate constant
for the total decomposition of furan is also shown on the graph

Decomposition of 2-Methylfuran
J. Phys. Chem. A, Vol. 101, No. 6, 1997 1021

1022 J. Phys. Chem. A, Vol. 101, No. 6, 1997
Lifshitz et al.
Figure 8. Arrhenius plot of the rate of the production acetylene.
Figure 6. Arrhenius plot of the first order production of carbon
monoxide. The rate constant is calculated from the relation kproduct
)
TABLE 2: Arrhenius Parameters for Production Rates
ktotal × [product]t/([2-methylfuran]0 - [2-methylfuran]t). The production
compound
log{A, s-1
}
E, kcal/mol
rate of carbon monoxide in furan is also shown for comparison.
total decomposn
CO
CH4
C2H4
C2H6
C2H2
C3H6
CH2dCdCH2
CH3CtCH
CH2dCHCHdCH2
CH2dCdCHCH3
CHtCCH2CH3
CH3CtCCH3
C4H4
C4H2
C4H4O
C6H6
CH2dCO
14.78
15.88
13.95
15.50
15.49
15.70
10.69
17.10
15.39
13.74
15.11
12.10
15.46
16.38
20.72
6.41
71.8
78.3
71.6
82.2
82.5
80.6
59.9
93.1
80.5
70.3
81.6
62.0
86.3
84.6
120
33.7
96.4
82.8
17.56
15.91
of 2-methylfuran under the conditions of the present experiment
is a simple unimolecular process. As will be discussed later,
the decomposition is composed of a large number of elementary
steps involving unimolecular and free radical reactions.
Figure 7. Arrhenius plots of the rate of the production of ethylene.
for comparison. The overall decomposition of 2-methylfuran
is somewhat faster owing to faster initiation of free radical
reactions due to the existence of a methyl group in the molecule.
Figures 6-8 show Arrhenius plots of the first order production
rate of CO and of two other decomposition products, calculated
from the relation
IV. Discussion
a. Unimolecular Processes. It has recently been shown1
that the major unimolecular channel in the decomposition of
furan is a 1,2 H-atom migration from C(5) to C(4) in the ring,
followed by elimination of carbon monoxide and formation of
C3H4 (Scheme 1). The large preexponential factor and activa-
tion energy of this reaction, as obtained from the production
[product]t
kproduct
)
ktotal (VII)
rate of CO1, k(furanfC H +CO) ) 1015.25 exp(-77.5 × 103/RT) s-1
,
[2-methylfuran]0 - [2-methylfuran]t
3
4
clearly point to the existence of a biradical mechanism where
the O(1)sC(2) bond in the ring must be almost completely
broken prior to the rearrangements in the open ring structure
and elimination of CO.
Figure 6 shows also the production rate of CO in furan for
comparison. The rate in 2-methylfuran is slightly higher owing
to an additional channel in its production. This will be discussed
later.
The formation of a stable C3H4 molecule which follows the
ring opening requires an H-atom migration from C(3) to either
C(4) or C(2). A migration to C(4) leads to the formation of
methylacetylene, and a migration to C(2), to the formation
allene. Both structural isomers were found in mixtures of shock
heated furan.
The ratio [methylacetylene]/[allene] was around 10 at low
temperatures. Owing to allene f methylacetylene isomerization
(kisomerization ) 1013.17 exp[-60.4 × 103/RT] s-1)8, it approached
a value of ∼3 at high temperatures, which is roughly the
equilibrium ratio.9 It is thus obvious that the preferred H-atom
Values of E obtained from the slopes of the lines and their
corresponding preexponential factors are summarized in Table
2. It should be mentioned that the parameters for the decom-
position products do not represent elementary unimolecular
reactions. Moreover, even for true unimolecular decompositions
such as the formation of the various C4H6 isomers the rates are
not the true unimolecular formation rates because of the further
decomposition of these compounds at higher temperatures. This
presentation simply provides a way of summarizing general
rates. Also, it does not imply that the overall decomposition

Decomposition of 2-Methylfuran
J. Phys. Chem. A, Vol. 101, No. 6, 1997 1023
SCHEME 1
SCHEME 3
SCHEME 2
SCHEME 4
migration is a migration from C(3) to C(4), even beyond the
thermal stability of these two isomers.
The results obtained in the study of 2-methylfuran show that
CO elimination from the ring in 2-methylfuran follows a pattern
similar to that of furan. However, the loss of symmetry in
2-methylfuran opens additional channels. The process thus
starts in 2-methylfuran by a 1,2 H-atom migration from C(5)
to C(4) but can also take place by a 1,2 methyl group migration
from C(2) to C(3) (Scheme 2). The question of whether the
latter does indeed exist will be dealt with after the results of
the computer simulation are described.
In addition to CO, both channels lead also to the production
of C4H6 intermediates. In order to obtain stable C4H6 molecules,
additional rearrangements must take place in the remaining open
from this intermediate by a simple rearrangement. We have
thus assumed that it is not formed in the 1,2 H-atom migration
channel.
There are two possibilities for stabilizing the second
intermediate, C(5)H•dC(4)HsC(3)(‚‚‚CO)H•sC(6)H3, by
additional 1,2 H-atom migrations (Scheme 4).
•
ring structures. These structures are CO‚‚‚C(4)H2 sC(3)Hd
C(2)•sC(6)H3, in the first channel (H-atom migration), and
C(5)H•dC(4)HsC(3)(‚‚‚CO)H•sC(6)H3, in the second chan-
nel (methyl group migration).
There are three possibilities for rearranging and stabilizing
•
the first intermediate, CO‚‚‚C(4)H2 sC(3)HdC(2)•sC(6)H3, by
Migration from
additional 1,2 H-atom migrations (Scheme 3).
Migration from
(1) C(4) to C(3) yields CO + CHtCCH2CH3
1-butyne
(1) C(6) to C(2) yields CO + CH2dCHCHdCH2
1,3-butadiene
(2) C(4) to C(5) yields CO + CH2dCdCHCH3
(2) C(3) to C(4) yields CO + CH3CtCCH3 2-butyne
1,2-butadiene
(3) C(3) to C(2) yields CO + CH2dCdCHCH3
Similarly, we cannot see how 1,3-butadiene, CH2dCHCHd
CH2, and 2-butyne, CH3CtCCH3, can be formed from this
intermediate by simple rearrangements.
1,2-butadiene
We cannot visualize a production of 1-butyne, CHtCCH2CH3,

1024 J. Phys. Chem. A, Vol. 101, No. 6, 1997
Lifshitz et al.
TABLE 3: Reaction Scheme for the Decomposition of 2-Methylfurana
reaction
A
n
E
kf(1250 K)
kr(1250 K) ∆Sr°(1250 K) ∆Hr°(1250 K)
ref
1. 2-mf f CH3CtCCH3 + CO
2. 2-mf f CH2dCHCHdCH2 + CO
3. 2-mf f CH2dCdCHsCH3 + CO
4. 2-mf f CHtCsCH2CH3 + CO
5. 2-mf f p-C3H4 + CH2CO
2.25 × 1015
3.50 × 1015
4.50 × 1015
2.80 × 1015
5.75 × 1015
1.70 × 1015
4.00 × 1016
4.00 × 1016
1.60 × 1016
3.00 × 1014
1.50 × 1012
8.00 × 1011
8.00 × 1011
8.00 × 1011
8.00 × 1011
5.00 × 1014
1.78 × 1015
5.01 × 1014
4.00 × 1016
4.00 × 1015
2.25 × 1015
2.25 × 1015
2.25 × 1015
3.29 × 1015
3.00 × 1013
3.00 × 1013
3.00 × 1013
6.00 × 1015
4.00 × 1015
2.00 × 1015
1.00 × 1015
3.00 × 1015
2.00 × 1015
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
85.1
79.5
85.1
79.5
82.9
79.5
90.5
106.0
86.0
2.98
4.16
42.0
43.9
45.5
45.2
46.3
76.7
52.7
51.8
32.8
24.7
16.8
29.6
30.3
49.5
57.2
94.5
110.7
90.5
-16.4
-17.3
-2.58
-1.12
0.116
-16.9
-9.84
25.5
50.8
101
30.
37.9
this work
this work
this work
this work
this work
this work
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
1
1
estd
estd
estd
estd
estd
estd
17
17
17
4.42 × 10
9.68 × 10-1
1.02 × 10
9.88 × 10
6.62 × 104
4.03 × 104
6.10 × 1010
5.96
3.53 × 10
1.85 × 10
2.15 × 10
6.03
6. 2-mf f C2H2 + C2H4 + CO
7. 2-mf f CH3CO + C3H3
8. 2-mf f HCO + CHdCHCHdCH2
9. 2-mf f 2-mfuryl + H
1.18 × 10-2 1.35 × 1011
1.48 × 10
6.74 × 1014
10. 2-mf + H f 2-mfuryl + H2
11. 2-mf + CH3 f 2-mfuryl + CH4
12. 2-mf + C3H3 f 2-mfuryl + p-C3H4
13. 2-mf + C3H3 f 2-mfuryl + a-C3H4
14. 2-mf + C3H5 f 2-mfuryl + C3H6
15. 2-mf + C4H3 f C4H4 + 2-mfuryl
16. 2-mf + H f furan + CH3
9.00 8.01 × 1012 8.08 × 108
5.19
10.0
2.68 × 1010 5.18 × 107
1.43 × 1010 5.43 × 109
1.43 × 1010 1.65 × 1010
-1.39
-0.144
-1.18
-1.15
-0.158
2.52
48.2
49.3
56.0
45.0
44.1
46.4
47.4
79.1
10.0
10.0
12.0
6.38 × 109
1.19 × 1010
8.00 3.19 × 1010 3.80 × 107
8.00 2.00 × 1013 1.07 × 1011
17. furan f p-C3H4 + CO
75.0
77.5
100.5
64.0
71.0
64.0
64.0
76.7
65.0
65.0
65.0
65.0
94.0
111.0
1.38 × 102
1.41 × 10
1.20 × 10
18. furan f C2H2 + CH2CO
1.83 × 104
19. furan f C3H3 + HCO
1.08 × 10-1 2.91 × 109
20. 2-mfuryl f CO + CH2dCdCHCH2
21. 2-mfuryl f CO + CHdCHCHdCH2
22. 2-mfuryl f CH2CO + C3H3
23. 2-mfuryl f HCO + C4H4
2.59 × 104
8.70 × 102
1.46 × 104
1.46 × 104
1.28 × 102
1.30 × 102
1.30 × 102
1.30 × 102
1.30 × 102
6.95 × 104
8.48 × 104
1.37 × 108
1.52 × 1010
9.34 × 108
2.04
52.1
65.1
80.9
-7.89
-12.8
-4.9
-0.769
94.2
24. 2-mfuryl f C2H2 + C2H3 + CO
25. CH3CtCCH3 f CH2dCHCHdCH2
1.95
26. CH2dCdCHCH3 f CH2dCHCHdCH2 3.00 × 1013
1.66
-1.56
-3.51
0.357
38.1
27. CH2dCdCHCH3 f CH3CtCCH3
28. CHtCsCH2CH3 f CH2dCdCHCH3
29. CH3CtCCH3 f CH2sCtCCH3 + H
30. CH2dCHCHdCH2 f
1.06 × 102
7.96 × 10
17
estd
estd
2.21 × 10-1 3.20 × 1012
1.57 × 10-4 3.19 × 1013
33.0
111.6
CHdCHCHdCH2 + H
31. CH2dCHCHdCH2 f
CH2dCdCHCH2 + H
32. CH2dCdCHCH3 f
CH2CtCsCH3 + H
33. CH2dCdCHCH3 f
0
0
0
103.0
89.0
91.0
1.97 × 10-3 1.10 × 1013
2.76 × 10-1 3.25 × 1012
3.70 × 10-1 2.64 × 1013
33.8
34.6
32.3
103.7
89.3
90.9
estd
estd
estd
CH2dCdCHCH2 + H
34. CHtCCH2CH3 f CHtCCHCH3 + H
0
0
0
0
0
72.0
101.0
79.0
5.17 × 102
5.37 × 1015
34.9
35.5
38.2
38.5
10.4
89.5
101.1
79.2
78.4
-12.7
estd
estd
estd
estd
estd
35. CHtCCH2CH3 f CHtCCH2CH2 + H 3.00 × 1015
6.60 × 10-3 5.41 × 1012
36. CH2dCdCHCH3 f C3H3 + CH3
37. CHtCCH2CH3 f C3H3 + CH3
38. CH3CtCCH3 + H f
CH2CtCCH3 + H2
1.00 × 1016
1.00 × 1016
6.00 × 1014
1.54 × 102
5.04 × 1012
78.0
2.31 × 102
4.62 × 1012
6.80 3.88 × 1013 1.24 × 109
6.80 2.59 × 1013 1.16 × 1013
6.80 1.29 × 1013 1.60 × 1011
6.80 6.47 × 1012 1.69 × 108
6.80 1.94 × 1013 3.07 × 109
6.80 1.29 × 1013 2.97 × 108
6.80 1.94 × 1013 3.52 × 1010
39. CH2dCHCHdCH2 + H f
CHdCHCHdCH2 + H2
4.00 × 1014
2.00 × 1014
1.00 × 1014
3.00 × 1014
2.00 × 1014
3.00 × 1014
6.00 × 1013
4.00 × 1013
2.00 × 1013
1.00 × 1013
3.00 × 1013
2.00 × 1013
3.00 × 1013
3.00 × 1013
2.00 × 1013
1.00 × 1013
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5.38
6.20
4.74
-3.16
-17.5
-15.9
-17.4
-5.82
-13.5
-4.05
3.85
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
estd
40. CH2dCHCHdCH2 + H f
CH2dCdCHCH2 + H2
41. CH2dCdCHCH3 + H f
CH2CtCCH3 + H2
6.94
42. CH2dCdCHCH3 + H f
CH2dCdCHCH2 + H2
4.64
43. CHtCCH2CH3 + H f
CHtCCHCH3 + H2
7.29
44. CHtCCH2CH3 + H f
CHtCCH2CH2 + H2
7.89
45. CH3CtCCH3 + CH3 f
CH4 + CH2CtCCH3
11.5
5.86 × 1011 3.59 × 108
3.90 × 1011 9.25 × 1010
1.95 × 1011 1.68 × 1012
9.76 × 1010 4.88 × 107
2.93 × 1011 8.86 × 108
1.95 × 1011 8.59 × 107
2.93 × 1011 1.02 × 1010
2.93 × 1011 3.53 × 1010
3.87
46. CH2dCHCHdCH2 + CH3 f
CH4 + CH2dCdCHCH2
11.5
11.5
11.5
11.5
11.5
11.5
11.5
19.0
12.0
-0.377
-1.20
0.358
-1.94
0.716
1.32
47. CH2dCHCHdCH2 + CH3 f
CH4 + CHdCHCHdCH2
48. CH2dCdCHCH3 + CH3 f
CH4 + CH2CtCCH3
-18.4
-16.8
-18.3
-6.7
49. CH2dCdCHCH3 + CH3 f
CH4 + CH2dCdCHCH2
50. CHtCCH2CH3 + CH3 f
CH4 + CHtCCHCH3
51. CHtCCH2CH3 + CH3 f
CH4 + CHtCCH2CH2
52. CH3CtCCH3 + C3H3 f
p-C3H4 + CH2CtCCH3
5.12
1.14
53. CH2dCHCHdCH2 + C3H3 f
p-C3H4 + CH2dCdCHCH2
54. CH2dCHCHdCH2 + C3H3 f
p-C3H4 + CHdCHCHdCH2
9.53 × 109
7.98 × 1010 1.35 × 1014
4.44 × 1011
0.872
0.052
10.6
18.5

Decomposition of 2-Methylfuran
J. Phys. Chem. A, Vol. 101, No. 6, 1997 1025
kr(1250 K) ∆Sr°(1250 K) ∆Hr°(1250 K) ref
TABLE 3 (Continued)
reaction
A
n
E
kf(1250 K)
55. CH2dCdCHCH3 + C3H3 f
p-C3H4 + CH2CtCCH3
5.00 × 1012
0
12.0
3.99 × 1010 3.92 × 109
1.20 × 1011 7.12 × 1010
7.98 × 1010 6.90 × 109
1.20 × 1011 8.17 × 1011
1.61
-0.693
1.97
-3.76
-2.16
-3.62
7.98
estd
estd
estd
estd
56. CH2dCdCHCH3 + C3H3 f
p-C3H4 + CH2dCdCHCH2
1.50 × 1013
1.00 × 1013
1.50 × 1013
2.00 × 1013
1.48 × 1013
4.05 × 1017
4.70 × 1017
2.00 × 1013
2.00 × 1013
7.00 × 1012
1.00 × 1014
1.00 × 1014
1.00 × 1014
1.00 × 1014
1.00 × 1014
0
0
0
12.0
12.0
12.0
57. CHtCCH2CH3 + C3H3 f
p-C3H4 + CHtCCHCH3
58. CHtCCH2CH3 + C3H3 f
p-C3H4 + CHtCCH2CH2
2.57
59. CH2dCHCHdCH2 f C4H4 + H2
60. a-C3H4 f p-C3H4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
75.0
60.4
75.0
80.0
1.55
2.88 × 106
1.34 × 102
1.24 × 1018
5.83 × 1017
33.88
1.03
34.0
49.6
-1.47
91.6
17
8
12
19
20
20
estd
estd
estd
estd
estd
estd
17
12
21
13
12
13
13
22
20
20
12
23
estd
estd
estd
estd
estd
estd
estd
estd
estd
12
estd
estd
13
13
13
4.08 × 102
3.13 × 104
4.85 × 103
61. a-C3H4 + Ar f C3H3 + H + Ar
62. p-C3H4 + Ar f C3H3 + H + Ar
63. p-C3H4 + H f C3H5
33.0
93.1
2.40 7.61 × 1012 1.36 × 103
-24.7
-23.7
-27.2
25.4
25.4
24.8
28.5
27.7
32.7
-57.9
-59.4
-53.7
53.4
54.3
41.8
44.8
52.7
40.4
64. a-C3H4 + H f C3H5
2.40 7.61 × 1012 4.49 × 102
65. p-C3H4 + C3H3 f C6H6 + H
66. CHtCCHCH3 f H + C4H4
67. CH2CtCCH3 f H + C4H4
68. CHtCCH2CH2 f H + C4H4
69. CHdCHCHdCH2 f H + C4H4
70. CH2dCdCHCH2 f H + C4H4
10.0
1.25 × 1011 4.35 × 107
74.0
54.0
42.0
45.0
53.0
66.0
41.1
66.0
1.16 × 10
3.62 × 104
4.54 × 106
1.36 × 106
5.42 × 104
3.47 × 10
4.05 × 106
2.89
7.35 × 109
3.31 × 1013
3.66 × 1013
5.64 × 1012
8.18 × 1012
2.98 × 106
1.01 × 102
2.78 × 1012
71. CH2dCHCHdCH2 f C2H2 + C2H4 1.20 × 1013
72. C2H2 + C2H2 f C4H4
73. C2H2 + C2H2 f C4H3 + H
74. CH3 + C2H2 f C3H5
6.20 × 1013
1.00 × 1012
6.03 × 1011
2.50 × 1015
8.00 × 1013
3.92 × 1011
7.23 × 1013
2.50 × 1014
1.13 × 1015
3.62 × 1012
1.00 × 1014
2.00 × 1014
3.92 × 1011
1.00 × 1013
8.10 × 1013
3.00 × 1014
1.00 × 1013
5.00 × 1013
5.00 × 1011
5.00 × 1011
5.00 × 1014
1.50 × 1013
3.50 × 1014
1.33 × 106
6.63
-30.3
-35.5
71.9
2.68
7.70 2.71 × 1010 2.51 × 103
-30.3
23.8
-3.83
-10.4
-40.4
25.2
30.9
24.9
24.2
33.0
-10.0
-1.24
-3.45
5.34
0.014
-11.0
-9.17
-11.1
34.8
-49.4
37.4
-69.5
-70.4
-102.4
17.7
14.3
38.3
38.6
107.4
-69.2
-0.34
-68.3
0.549
14.3
75. C2H3 + Ar f C2H2 + H + Ar
76. C2H3 + H f C2H2 + H2
77. C2H3 + CH3 f C2H2 + CH4
78. C2H3 + CH3 f C3H6
79. HCO + Ar f H + CO + Ar
80. CH3CO + Ar f CH3 + CO + Ar
81. C2H5 f C2H4 + H
82. C4H3 f C4H2 + H
83. C4H4 f C4H3 + H
33.6
0
0
3.34 × 109
7.41 × 1015
8.00 × 1013 3.92 × 102
3.92 × 1011 3.68 × 10
7.23 × 1013 6.07 × 10-1
2.78 × 1011 1.07 × 1014
7.99 × 1012 4.42 × 1013
0
16.9
12.3
37.2
40.0
103.0
0
15.0
0
12.0
15.0
15.0
0
1.14 × 106
1.02 × 107
2.07 × 1012
3.03 × 1013
1.97 × 10-4 7.55 × 1012
3.92 × 1011 4.94 × 10
2.39 × 1010 3.88 × 1010
8.10 × 1013 5.33 × 102
2.39 × 1012 2.03 × 1011
2.39 × 1010 7.62 × 1012
1.19 × 1011 6.25 × 1012
5.00 × 1011 2.89 × 10
5.00 × 1011 8.41
84. C4H3 + CH3 f C4H2 + CH4
85. C4H4 + CH3 f CH4 + C4H3
86. C4H3 + H f C4H2 + H2
87. C4H4 + H f C4H3 + H2
88. C4H4 + C3H3 f p-C3H4 + C4H3
89. C4H3 + C2H3 f C6H5 + H
90. C4H3 + C2H3 f C4H4 + C2H2
91. C4H3 + C2H3 f C4H2 + C2H4
92. C6H5 f C4H3 + C2H2
-3.94
-70
0
0
0
0
2.53
3.70
0
0
0
0
38.0
0
-75.5
41.4
1.14 × 108
4.81 × 1012
93. C3H3 + C3H3 f C6H6
1.50 × 1013 4.34 × 10-5
-60.1
-146.8
-11.7
7.25
6.37
-22.5
34.2
94. C3H6 + H f CH3 + C2H4
95. C2H4 + H f C2H3 + H2
96. C2H4 + CH3 f C2H3 + CH4
97. C2H4 + CH3 f nC3H7
9.00 9.35 × 1012 6.28 × 109
5.12
12.2
6.59 × 1011 2.58 × 1011
9.50 4.16 × 1010 3.12 × 1011
7.70 1.49 × 1010 5.77 × 107
7.67
1.09
3.31 × 1011
1.80 × 1014
1.24 × 1014
-29.9
24.8
8.05
-40.3
98. n-C3H7 f C3H6 + H
99. C2H6 + H f C2H5 + H2
100. CH3 + CH3 f C2H6
38.2
3.77 × 107
1.45 × 1013
12
12
13
9.60 2.60 × 1012 7.06 × 109
-4.62
-90.5
1.01 × 1015 -0.64
0
1.05 × 1013 9.80
a ∆Hr° are expressed in units of kcal/mol and ∆Sr° in units of cal/(K mol), respectively. Rate constants are expressed as k ) ATn exp(-E/RT)
•
in units of cm3, s, mol, and cal. 2-mf is 2-methylfuran. 2-mfuryl is (C4H3O)sCH2 .
SCHEME 5
C2H4 in the second channel. Were the two channels completely
equivalent, the second channel should have produced acetylene
with methylketene, but as has been mentioned before we did
not identify methylketene in the postshock mixtures and we thus
believe that the latter immediately decomposes to ethylene and
carbon monoxide.
CH3(CH)CdO f CO+C2H4
∆Hr°(298K) ) 11.1 kcal/mol
There are two additional unimolecular decomposition chan-
nels of 2-methylfuran. They involve the cleavage of other CsC
bonds in the ring following the aforementioned 1,2 H-atom and
1,2 methyl group migrations (Scheme 5). These channels exist
also in furan but owing to the symmetry of the molecule they
appear as one channel.
This observation is in complete agreement with the results of
the computer simulation as the concentrations of C2H4 and C2H2
could not be accounted for without this channel. This will be
discussed later.
b. Initiation of Free Radical Reactions. Free radical
reactions are involved in the production of a large number of
products such as CH4, C2H6, and others. The CsH bond in
the methyl group is the weakest bond in the molecule. It
The two channels in 2-methylfuran yield C3H4 (propyne and
allene) with ketene in one channel and acetylene with CO and

1026 J. Phys. Chem. A, Vol. 101, No. 6, 1997
Lifshitz et al.
is an sp3 bond which is somewhat weakened by the â-γ
double bond bond of the ring, DCH sH ∼ 90 kcal/mol. The
2
ejection of H-atom from the methyl group is thus the major
initiator of free radical reactions. In addition to this process,
as has been assumed in the past in similar 5-membered rings,10,11
cleavage of the ring without H-atom or methyl group migrations
can also take place. The three initiation reactions are reactions
7-9 in the reaction scheme, which is shown in Table 3.
In Figure 6 we compared the rates for total decomposition
of 2-methylfuran and furan,1 where the rate in 2-methylfuran
is somewhat higher. We believe that this is the result of faster
initiation of free radical reactions and faster H-atom abstractions
owing to the existence of an sp3 CsH bond in the methyl group.
An equivalent CsH bond in furan does not exist.
c. Reaction Scheme and Computer Modeling. In order
to account for the observed product distribution, we have
constructed a reaction scheme containing 36 species and 100
elementary reactions. The scheme is shown in Table 3. The
rate constants listed in the table are given as k ) ATn exp(-
E/RT) in units of cm3, mol, s, and cal. The Arrhenius parameters
for the reactions in the scheme are based on experimentally
deduced parameters and are estimated or taken from various
literature sources, mostly from the NIST Kinetic Data Base.12
The parameters for each reaction taken from the NIST Kinetic
Data Base are the best fit to a large number of entries. (In
view of the very large number of citations involved they are
not given as references in the article.) Parameters for reactions
which could not be found in available compilations are estimated
by comparison with similar reactions for which the rate
parameters are known.
•
•
•
Figure 9. Calculated profiles of CH3 , C3H3 , H•, and C2H3 at
1250 K.
The thermodynamic properties of the species involved were
taken from various literature sources13-16 or estimated with
(SP).9 We have performed sensitivity analysis with respect to
variations (or rather uncertainties) in the ∆Hf° of species whose
thermodynamic properties were estimated or are not known
accurately enough. Incorrect values of the thermodynamic func-
tions result in erroneous values for the rate constants of the back-
reactions. In several sensitivity tests that were performed on
the thermodynamic functions, we found that the results of the
simulation were very insensitive to the estimated values.
Figure 10. Experimental and calculated mole percents of the reactant
2-methylfuran.
The reactions that appear in the scheme, in addition to the
unimolecular decompositions of 2-methylfuran, enter into
several categories, among them radical-radical recombina-
tions, abstraction and displacement reactions, unimolecular
decomposition of unstable intermediates isomerizations, and
others.
CHtCCH2CH3 f CH2dCHCHdCH2
CHtCCH2CH3 f CH3CtCCH3
cannot take place by simple rearrangements and do not appear
in the scheme.
In the stage of constructing the scheme, we calculated the
free radical profiles in order to determine which ones should
be introduced into the scheme in abstraction and other reactions.
The radical profiles of the final reaction scheme are shown in
As has been mentioned before, the rate parameters for all of
the reactions were either taken from various sources or were
estimated. In the process of estimating rate parameters, we
followed very strict rules such as, for example, A factors for
recombinations and abstractions decrease as the size of the
radicals increase, starting at ∼1014 cm3 mol-1 s-1 for H-atoms
and decreasing to ∼1010-1011 cm3 mol-1 s-1 for large radical
species. Free radical dissociation is associated with stiff
transition states and hence low A factors, etc.
Figure 10 shows the experimental and the calculated mole
percent of 2-methylfuran corresponding to its overall decom-
position. Figures 11-15 show experimental and calculated
mole percents of products found in the decomposition of
2-methylfuran. The overall agreement seems to be quite
satisfactory.
•
•
Figure 9. CH3 and C3H3 have the highest concentrations
among the free radicals in the system. In the H-atom abstraction
reactions that appear in the scheme, particularly from the
different C4H6 isomers and several other high-concentration
•
•
products, we have considered only reactions of CH3 , C3H3 ,
and H•.
The reaction scheme contains four unimolecular steps that
produce carbon monoxide and four C4H6 isomers (1-4), two
unimolecular steps that produce other stable molecules (5
and 6), and three unimolecular dissociations that produce
unstable species (7-9). The latter initiate free radical reac-
tions in the system. The scheme contains also four (out
of six) interisomerizations of the various C4H6 isomers.17 The
reactions
Table 4 (a and b) shows the sensitivity spectrum of the
reaction scheme at 1150 and at 1300 K, respectively. The
sensitivity factor Si,j is defined in the table as ∆(log Ci)/∆(log

Decomposition of 2-Methylfuran
J. Phys. Chem. A, Vol. 101, No. 6, 1997 1027
TABLE 4: Sensitivity Analysis (k Changed by a Factor of 3)
Reaction CO CH4 C2H4 C2H6 C2H2 C3H6 a-C3H4 p-C3H4 CH2CO 1,3-butadiene 2-butyne 1,2-butadiene 2-butyne C4H4 C4H2 furan C6H6
(a) At 1150 K
1
2
3
4
5
6
7
9
0.98
0.42
0.35
0.22
0.98
0.84
0.97
0.83
0.20
0.69
0.27
0.98
0.97 0.71
0.27 0.36
0.20
0.42
0.40
0.81
-0.35
-0.81
0.18 0.41
0.55 0.99 0.60 0.63
0.61 0.31
10
11
12
13
14
16
20
22
23
24
36
74
75
78
85
87
88
93
94
96
100
0.19
-0.24 0.29
0.52
-0.20 0.20
-0.26
0.28 0.19 0.20 0.44
-0.58
-0.60
0.66
0.39
0.20
0.27
-0.32
0.26
-0.25
-0.23 0.42
0.23 0.29 0.18 -0.54
-0.30 -0.25 -0.20 0.86
0.22 0.32 0.17 -0.34
0.34
0.35
0.18
0.20
-0.24
0.36
0.70
0.22
0.40
0.51
-0.20
0.20
0.20
-0.29
0.37
-0.32
-0.30
(b) At 1300 K
1
2
3
0.41
0.18
-0.45
-0.48 -0.27 -0.29 -0.25
0.63
-0.21
0.26
0.34
-0.29
0.59
4
5
6
7
-0.30
0.59
-0.21 0.29
-0.25
0.44
0.42
0.59
0.73
0.22 0.55
0.26
-0.21
0.21
0.24
-0.24
0.22
9
-0.20
-0.23
0.38 0.27
10
14
16
17
22
25
26
27
28
37
38
44
45
46
51
71
72
75
78
85
87
88
96
100
0.18
0.20
-0.91
0.25
0.23
0.23
0.27
-0.29
-0.31
0.28
0.21
-0.24
-0.25
-0.23
0.17
-0.58
-0.41
-0.32
0.19
-0.32
-0.20
0.22
0.39
-0.58 -0.39
-0.21
0.35
0.36
0.58
0.33
0.29
-0.24
-0.23
0.27
kj) at t ) 2 ms. The sensitivity factors Si,j were evaluated by
changing kj by a factor of 3. Reactions that show no effect on
the production rate of all of the products both at high and at
low temperatures were not included in the tables.
Most of the sensitivity factors that appear in Table 3 are self-
explanatory and appear in many systems of the same nature.
The sensitivity factors for reactions 7 and 100, for example,
show the competition on methyl radicals which expresses itself
in the production rates of methane vs ethane. The sensitivity
factors for C2H2 and C2H4, as can be seen in Table 4, are high
for reaction 6, which indicates that it is the main source for
their production. The reaction has, however, only a mild effect
on the production of CO because the latter also formed directly
from the ring by other faster channels.
Table 4 shows that only a relatively small number of
elementary steps affect the product distribution in the sense that
variation of their rates by a factor of 3, for example, affects at
least the production rate of one of the products. The majority
of the elementary reactions that compose the scheme do not
affect the distribution at all. They are left in the kinetic scheme
for the sake of completeness and applicability beyond the
temperature range of the present experiments.
d. Existence of 1,2-Methyl Group Migration. After
performing the computer simulation, we can better understand

1028 J. Phys. Chem. A, Vol. 101, No. 6, 1997
Lifshitz et al.
Figure 14. Experimental and calculated mole percents of methane and
ethane.
Figure 11. Experimental and calculated mole percents of the four C4H6
isomers.
Figure 15. Experimental and calculated mole percents of 1-butyne
with and without reaction 4. Isomerizations alone cannot account for
the observed mole percent of 1-butyne.
Figure 12. Experimental and calculated mole percents of CO, C4H4,
C6H6, and C4H2.
for reactions 4 and 6. As has been shown, both can take place
only after 1,2 methyl group migration from C(2) to C(3) in the
ring has occurred. In reaction 4, 1-butyne is formed, and in
reaction 6 acetylene and methylketene are formed, where the
latter decomposes to carbon monoxide and ethylene.
1-Butyne. Since the four isomers of C4H6 can interisomer-
ize,17 it is possible, at least in principle, that 1-butyne is formed
as a product of isomerization rather than directly from the
2-methylfuran ring. In order to clarify this point, we ran the
kinetic scheme by eliminating reaction 4. The results are shown
in Figure 15. It can readily be seen that, just by isomerization
alone, 1-butyne cannot be obtained in large enough concentra-
tions to match the experimental observation. This is particularly
true at the lower temperature end. At high temperatures the
concentrations of the isomers is high enough to produce the
observed concentration of 1-butyne. These results are solid
proof for the existence of the methyl migration channel.
C2H2 and C2H4. We ran the scheme without reaction 6. The
results are shown in Figures 16 and 17. It can readily be seen
that reaction 6 is necessary to produce enough C2H2 and C2H4.
If this reaction is eliminated, the concentrations of C2H2 and
C2H4 are too small as compared to the experimental values.
Figure 13. Experimental and calculated mole percents of propyne and
allene.
and answer the question of whether the 1,2-methyl group
migration from C(2) to C(3) in the ring is really necessary to
explain the observed product distribution. This process accounts
A byproduct of this observation is that methylketene decom-

Decomposition of 2-Methylfuran
J. Phys. Chem. A, Vol. 101, No. 6, 1997 1029
azole.18 On the other hand, Melius has recently expressed his
inability to identify transition states involving 1,2 methyl group
migrations in methyl cyclopentadienes.24
V. Conclusions
The decomposition pattern of 2-methylfuran is similar to that
of furan. The loss of symmetry in the molecule opens more
reaction channels which involve, in addition to hydrogen atom
migration, a migration of the methyl group. The ring opening
steps have high preexponential factors which point to the
existence of biradical mechanisms. The computer modeling
shows that the product distribution cannot be explained without
assuming that a methyl group migration from position 2 to
position 3 in the ring does takes place.
References and Notes
(1) Lifshitz, A.; Bidani, M.; Bidani, S. J. Phys. Chem. 1986, 90, 5373.
(2) Laskin, A.; Lifshitz, A. Proceedings of the 20th International
Symposium on Shock Tubes and WaVes; in press.
Figure 16. Experimental and calculated mole percents of C2H2 with
and without reaction 6. Without this reaction which produces acetylene
by a direct dissociation of the 2-methylfuran ring, its calculated mole
percent is far below the experimental value.
(3) Grela, M. A.; Amorebieta, V. T.; Collusi, A. J. J. Phys. Chem.
1985, 89, 38.
(4) Lifshitz, A.; Moran, A.; Bidani, S. Int. J. Chem. Kinet. 1987, 19,
61.
(5) Rogers, A. S.; Ford, W. G. F. Int. J. Chem. Kinet. 1973, 5, 965.
(6) Eight Peak Index of Mass Spectra; Mass Spectrometry Data Centre,
The Royal Society of Chemistry, The University of Nottingham: Notting-
ham, U.K., 1983; ISBN 0-85186-407-4.
(7) Lifshitz, A.; Bidani, M.; Agranat, A.; Suslensky, A. J. Phys. Chem.
1987, 91, 6043.
(8) Lifshitz, A.; Frenklach, M.; Burcat, A. J. Phys. Chem. 1975, 79,
1148.
(9) Stein, S. E.; Rukkers, J. M.; Brown, R. L NIST-Standard Reference
Data Base 25; National Institute of Standards and Technology: Washington,
DC.
(10) Lifshitz, A.; Wohlfeiler, D. J. Phys. Chem. 1992, 96, 4505.
(11) Lifshitz, A.; Wohlfeiler, D. J. Phys. Chem. 1992, 96, 7367.
(12) Westly, F.; Herron, J. T.; Cvetanovic, R. J.; Hampson, R. F.;
Mallard, W. G. NIST-Chemical Kinetics Standard Reference Data Base
17, Ver. 5.0; National Institute of Standards and Technology: Washington,
DC.
(13) Tsang, W.; Hampson, R. F. Phys. Chem. Ref. Data 1986, 15, 1087.
(14) Melius, K. BAC-MP4 Heats of Formation; Sandia National Lab-
oratories: Livermore, CA, March 1993.
(15) Pedley, J. B.; Taylor, R. D.; Kirby, S. P Thermochemical Data of
Organic Compounds; Chapman and Hall: London, 1986.
(16) Burcat, A.; McBride, B.; Rabinowitz, M. Ideal Gas Thermodynamic
Data for Compounds Used in Combustion; TAE 657 Report; Technion-
Israel Institute of Technology: Haifa, Israel, 1994.
(17) Hidaka, Y.; Higashihara, T.; Ninomiya, N.; Oshita, H.; Kawano,
H. J. Phys. Chem. 1993, 97, 10977.
Figure 17. Experimental and calculated mole percents of C2H4 with
and without reaction 6. Without this reaction, the relatively high mole
percent of C2H4 cannot be accounted for.
(18) Lifshitz, A.; Wohlfeiler, D. J. Phys. Chem. 1995, 99, 11436.
(19) Hidaka, Y.; Nakamura, T.; Miyauchi, A.; Shiraishi, T.; Kawano,
H. Int. J. Chem. Kinet. 1989, 21, 643.
(20) Warnatz, J. In Rate Coefficients in the C/H/O System Combustion
Chemistry; Gardiner, W. C., Jr., Ed.; Springer-Verlag: New York, 1984; p
197.
(21) Benson, S. W. Int. J. Chem. Kinet. 1989, 21, 233.
(22) Fahr, A.; Laufer, A.; Klein, R.; Braun, W. J. Phys. Chem. 1991,
95, 3218.
(23) Weissman, M.; Benson, S. W. Int. J. Chem. Kinet. 1984, 16, 307.
(24) Melius, C. F. 26th Symposium (International) on Combustion,
Naples; The Combustion Institute: Pittsburgh, PA, 1996; paper 236.
poses completely and very fast to CO and C2H4 at the temp-
erature range of this investigation.
1,2-Methyl group migrations have been shown to exist in
other cyclopentadiene type rings, and the results obtained in
this investigation are in complete agreement with them. 1,2-
Methyl group migration from position 5 to position 4 in
5-methylisoxazole, which is isoelectronic to methylfuran, to
produce CO and C2H5CN has recently been observed.11
similar migration has also been observed in 3,5-dimethylisox-
A