Thermal decomposition reaction of 3,3,6,6-tetramethyl- 1,2,4,5-tetroxane in 2-methoxy- ethanol solution

Article abstract of DOI:10.1007/s10593-010-0449-6

The thermal decomposition study of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (acetone cyclic diperoxide) was carried out in 2-methoxyethanol solution in the 130-166 °C temperature range. The overall reaction follows a first-order kinetic law up to at least 75% diperoxide conversion. The activation parameters (ΔH^# = 22.5 ± 0.7 kcalmol^-1 and ΔS^# = -25.6 ± 0.5 calmol^-1K ^-1) for the unimolecular rupture of the O-O bond in the diperoxide molecule were obtained by measuring the remnant diperoxide at different reaction times by the CG technique. Acetone was detected by GC as the major organic product of the reaction.

Full text of DOI:10.1007/s10593-010-0449-6

Chemistry of Heterocyclic Compounds, Vol. 45, No. 12, 2009
THERMAL DECOMPOSITION
REACTION OF 3,3,6,6-TETRAMETHYL-
1,2,4,5-TETROXANE IN 2-METHOXY-
ETHANOL SOLUTION
1
2
2
3
L. A. C. Leiva , J. M. Romero , N. L. Jorge , L. F. R. Cafferata ,
2
3
M. E. Gómez Vara , and E. A. Castro *
The thermal decomposition study of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (acetone cyclic diperoxide)
was carried out in 2-methoxyethanol solution in the 130-166ºC temperature range. The overall reaction
follows a first-order kinetic law up to at least 75% diperoxide conversion. The activation parameters
#
–1
#
–1 –1
(
∆H = 22.5 ± 0.7 kcal⋅mol and ∆S = -25.6 ± 0.5 cal⋅mol ⋅K ) for the unimolecular rupture of the O–
O bond in the diperoxide molecule were obtained by measuring the remnant diperoxide at different
reaction times by the CG technique. Acetone was detected by GC as the major organic product of the
reaction.
Keywords: acetone cyclic diperoxide, diacetone diperoxide, tetroxane, thermolysis.
Peroxides have wide commercial use as bleaching agents and polymerization catalysts [1]. Due to the
weak O−O bond, peroxides undergo facile thermal decomposition to produce radicals. Many peroxides are
shock sensitive and their overall decompositions are exothermic so that special handling precautions must be
taken [2, 3]. Depending on the molecular stoichiometry of the peroxide, its decomposition may be explosive.
Most peroxides, such as the commonly used dibenzoyl peroxide or di-t-butyl peroxide, contain too much carbon
to be true explosives; but they have been rated as having a 2,4,6-trinitrotoluene (TNT) equivalence of 25 and
3
0%, respectively [4]. At the same time, the stoichiometry of hydrogen peroxide is perfect to allow it to act as an
explosive; albeit, it does so only in concentrations exceeding those at which it is commonly available [5].
This study examines the decomposition behavior of multiperoxidic triacetone triperoxide (TATP) and
compares it with that of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (acetone cyclic diperoxide, ACDP), both of which
exhibit explosive behavior. In recent years, TATP has been used as an improvised explosive because its
_
*
______
To whom correspondence should be addressed, e-mail: castro@quimica.unlp.edu.ar.
1
Laboratorio de Química Física, Departamento de Química, Facultad de Ciencias Exactas, Naturales y
Agrimensura, Universidad Nacional del Nordeste. Avenida Libertad Nº 5460 (3400), Corrientes, Argentina.
Laboratorio LADECOR, Facultad de Ciencias Exactas, UNLP (1900) calle 47 esq 115, La Plata, República
2
Argentina.
3
INIFTA, Theoretical Chemistry Division, Suc. 4, C.C. 16, La Plata 1900, Buenos Aires, Argentina.
_
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1806-1811, December, 2009.
Original article received December 5, 2008; revised version received August 10, 2009.
009-3122/09/4512-1455©2009 Springer Science+Business Media, Inc.
0
1455

precursor chemicals are readily obtained and its synthesis is straightforward. The analysis and detection of one
class of peroxide explosives have become particularly important in forensic investigations due to the emergence
of terrorist threats and crimes in which these explosives were applied. Peroxide explosives are organic
compounds that contain one or more peroxide functional groups (−O−O−), often in a cyclic form. In general,
these compounds are powerful explosives, extremely sensitive to flame, heat, impact, and friction. Peroxide
explosives can be generally prepared from hydrogen peroxide and a few other well-known chemicals such as
ketones or aldehydes. A small amount of sulfuric or hydrochloric acid is added as a catalyst. Most of these
ingredients can be obtained easily from local pharmacies.
The unusual reactivity of peroxides is generally attributed to weakness of the O−O bond, and it is
expected that their thermal decomposition would be initiated by homolytic dissociation of the peroxide bond.
Intuitively, it is expected that the peroxide-based explosives would liberate much energy upon decomposition,
and their energy content depends on the carbon/oxygen ratio [6].
In this work a kinetic study of the thermal decomposition reaction of ACDP in 2-methoxyethanol (MOET) is
presented.
Me
O
Me
O
O
Me
Me
O
ACDP
The thermal decomposition reaction of ACDP was studied in MOET solution at the temperature ranges
–
2
of 130 to 166°C (Table 1, Fig. 1) and initial concentration ca. 2·10 M. It was found that the kinetic behavior of
this system is, according to the first-order kinetic law, up to at least ca. 75% of organic diperoxide conversions.
It seems that under the experimental conditions of the present work, there are no contributions from the second-
order processes inducing the ACDP decomposition at higher conversions.
t, h
–
2
Fig. 1. Kinetics of ACDP thermal decomposition reaction (2.0⋅10 mol/l) in MOET
solution at different temperatures: 1 – 130, 2 – 140, 3 – 150, 4 – 166°C.
1
456

TABLE 1. Rate Constant Values for the Thermolysis of ACDP in MOET
Solution
2
5
–1
T, ºC
[ACDP]⋅10 , mol/l
kexp⋅10 ⋅s
1
1
1
1
30
40
50
66
0.20
0.20
0.20
0.10
1.61
2.69
5.79
14.23
14.17
14.12
0
0
.20
.30
The temperature effect on the experimental rate constant values (k ) for the unimolecular reaction
exp
investigated can be represented by the following Arrhenius equations (Eq. (1)), where the errors shown are
standard deviations from the least-mean-squares data treatment [11] and the activation energy is expressed in
–
1
cal⋅mol :
–
1
ln k ⋅s = (17.9 ± 0.5) – (23343 ± 700)/RT
(1)
exp
The Arrhenius equation plot is linear (r = 0.997) in a relatively large temperature range (ca. 78°C),
which suggests that the calculated activation parameter values for the ACDP reaction belong to a single process,
which could be unimolecular thermal cleavage of the O–O bond.
.
.
Me
Me
Me
O
O
O
Me
Me
Me
.
O
.
O
O
O
O
O
Me
Me
Me
Me
O
Me
Me
O
O
cage solvent
The rate-determining step is the biradical formation, which further decomposes by either C–C, C–O, or O–
O bond ruptures, leading to final organic products like acetone and molecular oxygen.
Fig. 2. Eyring plot corresponding to the thermal decomposition reaction of ACDP in MOET
solution.
1
457

In the previous works it was demonstrated that the O–O bond dissociation energy is influenced by solvent
12], substituents [13], and ring size [14]. In the special case of these studies in different solvents, it was concluded
[
that the activation parameters are higher in the more nonpolar solvents and the rate constant values are the lowest.
#
–1
#
–1 –1
The activation parameter values (∆H = 22.5 ± 0.7 kcal⋅mol and ∆S = -25.6 ± 0.5 cal⋅mol ⋅K ) (Fig. 2)
corresponding to the unimolecular thermal decomposition reaction of ACDP in 2-methoxyethanol are in the order of
those values obtained for other cyclic peroxides in polar solvents like methanol and 2-propanol [7, 14].
The thermolysis of ACDP in MOET solution follows the first-order kinetic law up to at least 75% diperoxide
conversion. The activation parameters mentioned correspond to the initial homolysis of the O–O bond of the
diperoxide molecule. Analysis of the reaction products is insufficient for proposing a complete mechanism of
thermolysis of ACDP.
.
Me
Me
O
O
Me
Me
.
O
O
O
O
2MeOMe + O2
Me
Me
Me
Me
O
O
The high negative value of the change in entropy would explain the existence of a transition state. Such
a result allows one to suppose the existence of an adduct, as was proposed for the kinetics of ACDP
decomposition in 2-propanol [15].
EXPERIMENTAL
Analysis by gas chromatography was performed using a GC Hewlett-Packard instrument, series II plus
(
a capillary column HP5, 30 m×0.25 mm (i.d.), methylphenylsilicone stationary phase) with nitrogen as a carrier
gas and flame ionization detection. The oven temperature was maintained at 40ºC for 3 min, then programmed
at a rate of 30º/min to 150ºC.
IR absorption spectra at room temperature from 1 cm diameter pellets made of the compound diluted in
spectroscopic grade KBr were recorded on an IR Nicolet infrared spectrometer using the diffuse reflectance
−1
technique between 400-4000 cm .
3
,3,6,6-Tetramethyl-1,2,4,5-tetroxane (ACDP) was prepared by dropwise addition of acetone (5 ml,
6
8.1 mmol) in acetonitrile (20 ml) to a vigorously stirred, cooled (-20°C) solution of 69.7% hydrogen peroxide
(
2.3 ml, 73.61 mmol) and sulfuric acid (5 ml, 18 M). After stirring at -20°C for 1 h, filtration, thorough water
washing, and drying, the crude product (71% yield) was purified by recrystallization from ethyl acetate until a
constant melting point of 133°C was attained. The product purity was also checked by GC and IR analyses
–
1
(
nujol), ν, cm : 2910 (s), 2850 (s), 1200 (m), 940 (w), 860 (w), 814 (w), 682 (w) [7, 8].
The 2-Methoxyethanol used as solvent was purified with the appropriate techniques [9, 10] and its purity
was checked by GC analysis.
Pyrex glass tubes (7 cm×6 mm o.d.) half filled with the appropriate ACDP solution were thoroughly
degassed under vacuum at -196ºC and then sealed with a flame torch. To perform the runs the ampoules were
immersed into the thermostatic silicone oil bath (±0.1ºC) and withdrawn after predetermined times, and the
reaction was stopped by cooling them in an ice-water bath (0ºC). The ACDP remaining and the reaction
products were determined by quantitative analysis by gas chromatography.
The qualitative determination of the organic reaction products was performed by GC. The corresponding
first-order rate constant values were calculated from the slope of the line obtained by the mean-squares treatment
of the reaction data when plotting the values of ln [ACDP] concentration vs reaction times. The activation
parameters were calculated according to the Eyring equation, and the errors were worked out by the Arrhenius
equation method using the mean-squares data treatment [11].
1458

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