DIETHYLKETONE TRIPEROXIDE DECOMPOSITION
of DEKT were about 0.02 M and 1% naphthalene was added as an
internal standard to perform quantitative analyses. The appro-
priate solution of DEKT in acetone–toluene and acetone–1-
propanol mixtures were placed in a Pyrex glass ampoule (10 cm
long ꢀ 4 mm OD), thoroughly degassed under vacuum at
ꢁ196 8C and then sealed with a flame torch. These ampoules
were immersed in a thermostated silicone oil bath (ꢂ0.1 8C), at
150 8C. After predetermined times (15, 30, 60 and 120 min) the
reaction in the ampoule was stopped by cooling at 0 8C in an
ice-water bath. The concentrations of DEKT remaining in the
solution were determined by quantitative GC analysis (internal
standard method) in an Rtx-5MS capillary column (5% biphenyl–
95% dimethyl polysiloxane, 30 m, 0.25 mm ID, 0.25 mm film
thickness) installed in a Thermo Quest Trace 2000 GC model gas
chromatograph with helium as carrier gas (0.5 mL minꢁ1), FID
detection (250 8C) and injection port in split mode at 150 8C. The
experiments were carried out under programmed conditions
(80 8C, 5 min, 10 8C minꢁ1, 160 8C, 20 min). Retention time of DEKT
is ca. 15.7 min.
Table 1. Pseudo first order rate coefficient values (kobs) of the
thermal decomposition reaction of DEKT at 150 8C in acetone–
toluene binary mixtures and its refractive indexes
Toluene mole
fraction (XT)
Refractive
index (h)
a
ETNð30Þ
kobs (10ꢁ4 sꢁ1
)
0
1.3596
1.3714
1.3837
1.4071
1.4217
1.4477
1.4764
1.4970
0.355
0.349b
0.343
0.327
0.309
0.275
0.241
0.099
2.55
2.28
2.30
2.19
2.17
1.85
1.69
1.52c
0.05
0.10
0.20
0.30
0.50
0.70
1
a From Reference 12.
b Interpolated values from data in Reference 12.
c From Reference 3.
The corresponding pseudo first-order rate coefficient values,
in sꢁ1, were calculated from the slope of the straight line
obtained by plotting the values of ln[DEKT]t versus reaction
time at 150 8C; correlation coefficients (r) obtained by a
least-mean-square program were better than 0.996 for all kinetic
runs.
Identification of the reaction products was done by GC analysis
by comparing the retention time of each product in a sample
prepared with the corresponding reagents with the retention
time of that compound in the reaction mixture. The identification
was checked by co-chromatography.
microsphere of solvation, the so-called cybotatic region, which is
different from the composition of the bulk solvent.
Up to now, few systematic studies in mixed solvents have been
carried out with DEKT. In a first attempt to systematize the study
of the solvent effects in binary mixtures, we reported the kinetic
data in acetone–water mixtures of different composition.[8] In the
present work, it was of interest to evaluate the solvent effects of
some reported non-synergetic and synergetic binary mixtures on
the thermal decomposition of diethylketone cyclic triperoxide.
We now report the study of the above reaction in binary mixtures
of acetone–toluene (aprotic þ aprotic solvent system) and
acetone–1-propanol (aprotic þ protic solvent systems) in order
to investigate the influence on the rate of this reaction with the
continuous change of the polarity of the medium and the
microenvironment of the reactants. The results are interpreted in
terms of preferential solvation (PS) alternatively referred as a
solvent sorting, in which one or more solvation shells significantly
differ in molar composition from the bulk solvent mixture.
Solvation of solute and transition state will contribute to a change
in the intrinsic barrier of the reaction. In other words, changes in
the rate of reaction may be evaluated since the solute and/or the
transition state are species with different charge distributions,
each one having in its microenvironment, a higher amount of one
kind of solvent of the mixture than the other.
Refractive index (h) determinations
A standard ABBE refractometer was used to measure the
corresponding refractive index of each mixture at ambient
temperature.
RESULTS AND DISCUSSION
General considerations of the selected solvent systems
Acetone–toluene system
The aprotic non-polar co-solvent toluene possesses a small
permanent dipole moment (m ¼ 0.36 D) and a p-electron system
which contains neither an electron pair donor centre nor an
electron pair acceptor centre. Acetone is an aprotic mildly
polar solvent (m ¼ 2.88 D, e25 ¼ 20.7) which may participate in
donor–acceptor interactions. Acetone weakly interacts with
toluene[12] but they are both miscible in all concentrations.
The ET(30) parameter for aprotic þ aprotic binary solvent systems
with acetone as solvent and toluene as co-solvent, have been
reported by Mancini et al. in 1995. There is a relatively large
increase in ET(30) values when small amounts of acetone are
added to toluene (Table 1) providing strong evidence for PS by
acetone. Acetone–toluene mixtures yield non-synergetic effects
on the ET(30) polarity parameter.[12] The normalized ETNð30Þ
polarity parameter values of each mixture for binary mixtures of
acetone–toluene (Table 1) were worked out from an equation
using tetramethylsilane (ETN ¼ 0) and water (ETN ¼ 1) as extreme
reference solvents.[1]
MATERIALS AND METHODS
Materials
DEKT was prepared by methods described elsewhere[9] (m.p.
59–60 8C) and its purity was checked by GC. The acetone (Merck,
analytical grade) was purified following methodologies described
in the literature[10] (b.p. 56 8C). The toluene (b.p. 110.0–111.0 8C)
and 1-propanol (b.p. 97 8C) solvents were purified by standard
methods.[11] Sublimed naphthalene (Mallinckrodt AR) was
employed as an internal standard in quantitative GC determi-
nations of DEKT concentration.
Kinetic methods
Pure solvent was mixed by volume to give binary solvent
mixtures of various mole fraction compositions. Kinetic solutions
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 96–100