Vaporization and thermal decomposition of B,B',B''-tribromoborazine

Article abstract of DOI:10.1134/S0036023612040110

Vapor pressure as a function of temperature above solid and liquid (BrBNH)₃ and the thermody-namic parameters of (BrBNH)₃ sublimation and vaporization have been determined using static tensimetry with membrane null-manometer. The thermal decomposition of tribromoborazine has been studied in the saturated and unsaturated vapor regions. Irreversible decomposition occurred at noticeable rates at temperatures higher than 343 K and was accompanied by HBr evolution. In the unsaturated vapor region, thermal decomposition has far lower rates than in the saturated vapor region because of diffusion limitations. The activation energy of condensed-phase thermal decomposition of B,B',B''-tribromoborazine is 65 ± 3 kJ/mol, and this value proves that tribromoborazine decomposition at low temperatures is not accompanied by opening of the boron-nitrogen cycle.

Full text of DOI:10.1134/S0036023612040110

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 4, pp. 557–563. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © I.V. Kazakov, A.Yu. Timoshkin, 2012, published in Zhurnal Neorganicheskoi Khimii, 2012, Vol. 57, No. 4, pp. 621–627.
PHYSICAL METHODS
OF INVESTIGATION
Vaporization and Thermal Decomposition
of B,B',B''ꢀTribromoborazine
I. V. Kazakov and A. Yu. Timoshkin
Chemistry Department, St. Petersburg State University, St. Petersburg, Russia
Received January 20, 2011
Abstract—Vapor pressure as a function of temperature above solid and liquid (BrBNH)3 and the thermodyꢀ
namic parameters of (BrBNH)3 sublimation and vaporization have been determined using static tensimetry
with membrane nullꢀmanometer. The thermal decomposition of tribromoborazine has been studied in the
saturated and unsaturated vapor regions. Irreversible decomposition occurred at noticeable rates at temperaꢀ
tures higher than 343 K and was accompanied by HBr evolution. In the unsaturated vapor region, thermal
decomposition has far lower rates than in the saturated vapor region because of diffusion limitations. The
activation energy of condensedꢀphase thermal decomposition of B,B',B''ꢀtribromoborazine is 65
3 kJ/mol,
and this value proves that tribromoborazine decomposition at low temperatures is not accompanied by openꢀ
ing of the boron–nitrogen cycle.
DOI: 10.1134/S0036023612040110
Boron and nitrogen compounds have been used cold part of the system at room temperature and then
since long ago as precursors for the synthesis of inorꢀ purified by repeated vacuum resublimation at 318–
ganic polymers and boron nitride for use in industries 328 K. The compound was obtained as colorless
and microelectronics. For example, cubic boron needlelike crystals. In view of the irreversible reaction
nitride is used as a diamond substitute in drilling and of (BrBNH)3 with atmospheric moisture, all manipuꢀ
cutting tools. Hexagonal BN is one of the few anaꢀ lations (purification, packing, and sampling) were carꢀ
logues of graphite.
ried out in wholeꢀsealed evacuated glass systems,
which were fully airꢀtight.
B,B',B''ꢀTrihaloborazines are suitable precursors
for both boron nitride and various boron–nitrogen
inorganic polymers. This is due to the good volatility
and sufficient thermal stability of trihaloborazines.
Their use as precursors in vapor phase deposition reacꢀ
tions opens ample opportunities for preparing nanoꢀ
structured BN and inorganic polymers as thin
grapheneꢀlike surface films [1], catalysts [2], ceramic
coatings [3], matrices [4], and nanotubes [5]. Howꢀ
ever, the processes involved in trihaloborazine heating
that yield diverse inorganic polymers and boron
nitride, yet remain poorly studied. Here, we study the
volatility and thermal decomposition of B,B',B''ꢀtriꢀ
bromoborazine.
The massꢀspectrometric study of the vapor over triꢀ
bromoborazine was carried out on an MXꢀ1321
instrument; the ionizing electron energy was 30 and
70 eV, and the vaporizer temperature was 393 K.
The (BrBNH)3 vapor pressure was measured as a
function of temperature by static tensimetry method
with a glass membrane nullꢀmanometer [8, 9]. The
instruments were made of molybdenum glass. Pressure
was measured on an MChRꢀ3 mercury gage accurate
to 0.1 mmHg. Temperature was monitored by two
thermocouples (Chromel–Alumel); thermoꢀemf was
measured on a Shchꢀ1516 digital voltmeter; the temꢀ
perature measurement accuracy was 0.05 K. The volꢀ
ume of the membrane chamber was found as the difꢀ
ference between the weights of the waterꢀfilled and
empty system. The volume measurement error was
0.02 mL, which amounts (for the instrument volume
of 18.86 and 37.28 mL) to 0.1 and 0.05% for the first
and second set of runs, respectively.
EXPERIMENTAL
We chose to study B,B',B''ꢀtribromoborazine
(hereafter, tribromoborazine). (BrBNH)3 was preꢀ
pared using the hot tube method [6] by reaction (1) at
473–493 K.
3NH4Br(s) + 3BBr3(g) = (BrBNH)3(g) + 9HBr(g). (1)
RESULTS AND DISCUSSION
Tribromoborazine vaporization processes. A repreꢀ
sentative mass spectrum of vapor above tribromoboraꢀ
zine is displayed in Table 1. The major process is the
vaporization of (BrBNH)3 in the form of monomeric
Nitrogen was used as a carrier gas. Ammonium
bromide (pure grade) was resublimed under vacuum
before use. Boron tribromide was synthesized and
purified using routine procedures [7]. The tribromobꢀ
orazine produced by reaction (1) was condensed in the molecules accompanied by partial thermal dissociaꢀ
557

558
KAZAKOV, TIMOSHKIN
Table 1. Mass spectrum of B,B',B''ꢀtribromoborazine
recorded with 30ꢀeV ionizing electron energy and a vaporꢀ
izer temperature of 393 K
function of temperature in the heating–exposure–
cooling mode. The heating rate was ~2 K/min. Expoꢀ
sure lasted 2–3 h for each set of measurements; the
exposure temperature was increased systematically
from set to set. Cooling was slow (for several hours). In
experiments designed in this way, a considerable porꢀ
tion of (BrBNH)3 underwent irreversible thermal
decomposition, which manifested itself as an irreversiꢀ
ble increase in pressure in the system. Noticeable triꢀ
bromoborazine decomposition rates were found at
temperatures above 343 K.
In the second run, to a system of 37.28 mL in volꢀ
ume, 37.7 mg tribromoborazine was placed under vacuꢀ
um. The first sets of measurements in the second run
were carried out in the heating–rapid cooling mode.
The heating rate was ~2 K/min. Rapid cooling was
provided by withdrawing the instrument from the furꢀ
nace. In experiments designed in this way, (BrBNH)3
decomposition occurred to a small extent.
Ion
m
/
z
I
rel, %
+
+
+
73–78
11.2
B N H
B3N3H3, B3N3H2,
3
3
+
79, 81
80, 82
39.9
*
Br
+
HBr
+
129–133
22.3
Br2B2NH2
+
155–160
218–223
233–241
313–321
34.8
9.4
BrB3N3H3
+
Br2B3N2
+
84.4
Br2B3N3H3
+
100.0
BrBNH
(
)
3
For the reason that, in each set of measurements,
equilibrium volatilization of tribromoborazine was to
some extent accompanied by its irreversible thermal
decomposition, the overall pressure in the system
increased from set to set. For deriving the (BrBNH)3
saturated vapor pressure versus temperature depenꢀ
dence, it is necessary to subtract the partial pressure of
* The ion peak intensity noticeably exceeds the overall intensity of
+
(BrBNH)3 peaks.
tion with hydrogen bromide evolution (with a vaporꢀ
izer temperature of 393 K). The hydrogen bromide
peak intensity noticeably exceeds the overall intensity decomposition products from the overall pressure. On
of ion peaks that refer to a molecular ion as judged the assumption that hydrogen bromide was the only
from their weightꢀtoꢀcharge ratios. The other ions in volatile decomposition product, its partial pressure
was estimated from the thermal gas expansion line at
low temperatures (within 343 K), where the tribroꢀ
moborazine saturated vapor pressure was less than
0.1 mmHg [10]. The vapor pressure of HBr estimated
from the thermal expansion line was further refined by
the consecutive approximations method [9]. The
resulting log plot of tribromoborazine saturated vapor
pressure versus reciprocal temperature is shown in Fig. 1.
For comparison, the same figure displays data taken
from [10]; there is a satisfactory agreement between
these data. We appreciably expanded the temperature
range of tribromoborazine vaporization relative to that
used in [10].
the mass spectrum are likely fragments of the
+
molecular ion. Thus, HBr is the major volꢀ
BrBNH
(
)
3
atile product of tribromoborazine decomposition.
Two runs were carried out to study tribromoboraꢀ
zine vaporization. In the first run, to a system of 18.86
mL in volume, 24.7 mg tribromoborazine was placed
under vacuum. Then, the instrument was transferred
to a furnace and vapor pressure was measured as a
–2
–3
–4
–5
–6
–7
The enthalpies and entropies of sublimation and
vaporization were derived from the measured vapor
pressure versus temperature relationship as follows
P
A
T
ΔH 0 ΔS 0
(2)
ln( ) = − + B = −
+
.
P 0
RT
R
The combined data of five sets of the two runs were
treated in a similar way; the resulting thermodynamic
parameters of sublimation and vaporization are listed
in Table 2.
Thermal decomposition of tribromoborazine was
studied both in the saturated and unsaturated vapor
regions.
Determination of composition of the condensed
phase. Assuming that HBr is the only volatile product
of thermal decomposition of tribromoborazine, we
–8
2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
1000/T
, K–1
P
1
T
Fig. 1.
for sublimation (triangles) and
ln( ) = f ( )
P 0
vaporization (squares) of tribromoborazine (white symbols
refer to this work, and black symbols are data taken from
[10]).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

VAPORIZATION AND THERMAL DECOMPOSITION
559
Table 2. Parameters of Eq. (2) and the thermodynamic parameters of (BrBNH)3 vaporization and sublimation
Sublimation
Vaporization
Parameter
this work
8.65 0.37
[10]
this work
[10]
A
B
Δ
Δ
10.35 0.07
22.31 0.18
86.1 0.6
185.5 1.5
30
5.76 0.48
10.52 1.13
47.9 4.0
87.4 9.4
36
5.64 0.61
10.53 1.61
46.9 5.0
87.6 13.4
5
17.61 1.12
71.9 3.5
146.4 9.3
65
H
H
°
t, kJ/mol
t, J/mol K
°
Number of datapoints
Temperature range, K
347–405
342 – 402
411–450
407.3
402–415
399.8
T
T
, K
triple
boil, K*
548
536 42
Note: *Obtained by extrapolation.
may write the following reaction equations for from Eq. (5); the evolved HBr amount was found from
(BrBNH)3 decomposition in the condensed phase (3) Eq. (6); and х was found from Eq. (7).
and in the vapor phase (4).
P
T
P'
T
V
R
(5)
(6)
(7)
Δn(BrBNH)
=
(BrBNH)3 − (BrBNH)3
,
(
)
3
n(BrBNH)3(cond) = (BrxB3N3Hx)n
(cond)
+
n
(3 –
х
)HBr(g),
(3)
)HBr(g). (4)
in Eqs. (3) and (4) characterizes
P
T
P'
V
R
ΔnHBr
=
HBr − HBr
,
)
(
T
n
(BrBNH)3(g) = (BrxB3N3Hx)n
+ n(3 – х
(cond)
ΔnHBr
The parameter
х
x = 3 −
.
Δn
(BrBNH)3
the composition of the nonvolatile product of thermal
decomposition of tribromoborazine (BrxB3N3Hx)n
The value varies from three for pure tribromoboraꢀ
.
The results of
tions are listed in Table 3.
In run 1, we studied (BrBNH)3 thermal decompoꢀ
sition in the saturated vapor region (in the presence of
a condensed tribromoborazine phase in the system).
x determination for various condiꢀ
х
zine to zero for complete (BrBNH)3 decomposition to
boron nitride.
In this work, х was calculated on the basis of variaꢀ
tions in hydrogen bromide and tribromoborazine
amounts in the system. Measurements in the unsaturꢀ
ated vapor region (where all tribromoborazine is volaꢀ
tilized) allow the hydrogen bromide and tribromoboꢀ
razine amounts in the system to be calculated from the
In this case, the variation of
х
in each set of measureꢀ
0.50
P'
T
P'
T
ꢀꢀꢀ
ꢀꢀꢀ
HBr + (BrBNH)
3
0.45
P
T
nR
V
Mendeleev–Clapeyron equation:
The HBr
.
=
0.40
amount was derived from the thermal gas expansion
line in the lowꢀtemperature region (below 343 K),
where the tribromoborazine saturated vapor pressure
is less than 0.1 mmHg. The total HBr and (BrBNH)3
amount was determined immediately after the yield to
unsaturated vapor.
P'
T
ꢀꢀꢀ
HBr
0.35
0.30
0.25
0.20
P
T
P
T
ꢀꢀ(BrBNH)
3
ꢀꢀ
HBr
The
P/T versus temperature plot for two consecuꢀ
tive sets of measurements is shown in Fig. 2. Initial
270
320
370
, K
420
470
P
T
P
T
T
and
values were calculated in the
HBr
(BrBNH)3
P'
P'
first set of measurements;
and
(BrBNH)3
HBr
Fig. 2. Example determination of tribromoborazine and
hydrogen bromide in the unsaturated vapor region from
P/T versus temperature curve. Circles refer to the first set
of measurements and triangles to the second set of meaꢀ
surements. For explanations, see the text.
T
T
values after temperatureꢀcontrolled exposure were
calculated from the subsequent set of measurements.
The decomposed tribromoborazine amount was found
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

560
KAZAKOV, TIMOSHKIN
Table 3. Determination of the composition of a condensed phase (parameter
tion (4))
x
) for tribromoborazine decomposition (reacꢀ
ΔnHBr
Δ
n
(BrBNH) ,
mmol
Δ
n
(HBr),
3
Run no.
T
,
K
t
, h
x
mmol
Δn
(BrBNH)3
1.74 0.06
2.68 0.03
a
1
1
2
353–443
12
99
0.046 0.002 0.080 0.002
1.26 0.06
0.32 0.03
b
c
660
573
5
4
0.078 0.002
0.209 0.002
a
6.5
0.042 0.002 0.073 0.002
0.055 0.001 0.105 0.001
0.083 0.002 0.179 0.001
1.74 0.09
1.91 0.05
2.16 0.04
2.17 0.04
1.26 0.09
1.09 0.05
0.84 0.04
0.83 0.04
13.2
37.1
39.8
0.095 0.002 0.206 0.001
a
b
c
Note: Overall exposure time. Until
system.
P/
T
in the system ceases to increase. At the end of the run, there is no tribromoborazine in the
ments cannot be determined. However, after the meaꢀ ment was taken off the furnace and rapidly cooled in
surements in the saturated vapor region are over (the air. Then, a second rapid heating and exposure were
total exposure time is longer than 12 h at temperatures carried out.
of 353–443 K), the system was heated to yield to
unsaturated vapor; this allowed us to determine to be
1.26 0.06. Thus, when tribromoborazine is decomꢀ
posed in a condensed phase at temperatures up to 443 K,
the composition of the solid decomposition product is
formulated as (Br1.26B3N3H1.26)n, which indicates its
polymeric nature.
In run 2, we studied the decomposition of gaseous
tribromoborazine; the measurement protocol was as
follows: rapid heating –exposure–rapid cooling. The
heating rate was 4–5 K/min; the exposure temperaꢀ
ture was chosen such that (BrBNH)3 fully vaporized
(the unsaturated vapor region). Two consecutive sets
of measurements were carried out as follows: the sysꢀ
tem was rapidly heated to a certain temperature and
then exposed for several hours, after which the instruꢀ
Noteworthy, in run 2 sets of measurements were
carried out prior to unsaturated vapor measurements,
to measure saturated vapor pressure as a function of
х
temperature; for this reason, the initial х value in run 2
was 1.26 0.09. This value well agrees with the value of
1.26 0.06, which was obtained after condensedꢀ
phase tribromoborazine decomposition (in run 1).
Interestingly, shortꢀtime borazine thermolysis (for 30
min or less) at 613–653 K yields a compound of comꢀ
position (H1.2B3N3H1.2)n as a nonvolatile product; this
compound has a polymeric nature [11].
Noteworthy, at a fixed temperature (573
value depends on the exposure time (Table 3) and
4 K) the
х
given logꢀtern exposure, it approaches some constant
value of ~0.8.
According to the results of measurements, the
amounts of evolved HBr and decomposed (BrBNH)3
are linear functions of time (Fig. 3), and their ratio also
changes with time (Table 3). Thus, the evolved HBr
amount increases with time from 1.74 to 2.17 mol per
tribromoborazine mole. In our opinion, the increased
amount of HBr evolved per (BrBNH)3 mole is due to
the slow thermal decomposition of condensed
(BrxB3N3Hx)n with hydrogen bromide evolution:
0.25
0.20
0.15
0.10
0.05
(BrxB3N3Hx)n(cond)=(Brx–yB3N3Hx–y)n
+ nyHBr(g).(8)
(cond)
Thus, hydrogen bromide appears in the system due
to at least two processes: rapid borazine decomposiꢀ
tion (reactions (3), (4)) and a relatively slow decomꢀ
position (aging) of the polymer (process (8)). Even
after 39.8 h of exposure at 573 K, a noticeable amount
of undecomposed tribromoborazine (22.6% of the iniꢀ
tial weight) remains in the system.
0
10
20
30
40
50
t
, h
Fig. 3. Evolved HBr amount (circles) and consumed triꢀ
bromoborazine amount (rhombs) versus time at an expoꢀ
The complete conversion of gaseous tribromoboraꢀ
zine to boron nitride in a closed system is hardly
sure temperature of 573
4 K.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

VAPORIZATION AND THERMAL DECOMPOSITION
561
achievable even at elevated temperature. Exposure at
660 K for 99 h (until HBr evolution ceases) in the
first run yields a condensed phase of composition
(Br0.32B3N3H0.32 but not pure boron nitride. Tribroꢀ
moborazine is completely decomposed in the course
of the run. This behavior is typical of borazine, too:
exposure of (HBNH)3 for 48 h at 748 K (until hydroꢀ
gen evolution ceases) yields a condensed phase of
–7
–9
5
)
n
–11
composition (H0.45B3N3H0.45) [11]. For tribromoboꢀ
razine, similar conversion is achieved at a temperature
90 K lower than for borazine.
n
–13
2.2
2.4
2.6
2.8
1000/
T
, K–1
Kinetics of tribromoborazine decomposition. Static
tensimetry method with membrane nullꢀmanometer
is usable for kinetic studies of processes in which the
Fig. 4. Log conventional rate versus reciprocal temperature
for tribromoborazine decomposition in a liquid phase (triꢀ
angles) and solid phase (squares).
number of gas moles changes. The volume
system is a fixed value during the run; therefore, a conꢀ
ventional reaction rate may be taken to be an
V of the
υ
conv
slowed down and was virtually independent of decomꢀ
position temperature. Our estimate of the activation
energy of gasꢀphase tribromoborazine decomposition
P
T
increment in the quotient in unit time, which is
directly proportional to the increase in hydrogen broꢀ
in the range 473–573 K is
5
2 kJ/mol, indicating that
Δ(P T)
the reaction rate is controlled by tribromoborazine diffuꢀ
sion to the walls of the vessel. An estimate of 2.5 kJ/mol
was obtained for the activation energy with diffusion
rate control from the diffusivity versus temperature
dependence at the temperatures of our runs [12].
mide concentration in the system:
υconv
=
.
Δt
The HBr evolution rate from (BrxB3N3Hx)n(cond) at
573 K is relatively low; therefore, we may state that
hydrogen bromide evolution by reaction (8) will be
insignificant at low temperatures. This allows using
the initial rates method for estimating the activation
energy of the condensedꢀphase thermal decomposiꢀ
tion of tribromoborazine at relatively low temperaꢀ
tures (353–443 K). In using the initial rates method
for (BrBNH)3 thermal decomposition in the saturated
vapor region, we made the following assumptions: the
tribromoborazine concentration in condensed phase
remains practically unchanged during the run; the
Suggested decomposition scheme. The small value
of the activation energy of condensedꢀphase thermal
decomposition of tribromoborazine (65
3 kJ/mol)
suggests that, unlike for borazine, tribromoborazine
thermal decomposition preserves the B3N3 heterocyꢀ
cle core. Tribromoborazine thermal decomposition is
likely a polycondensation reaction, where polymer
compounds (BrxB3N3Hx)n
are formed at the first
(cond)
stage to slowly loss hydrogen bromide in the course of
further crosslinking of polymeric fragments. Our sugꢀ
gested scheme of tribromoborazine decomposition is
displayed in Fig. 5. This scheme comprises the rapid
addition of tribromoborazine molecules to a growing
polymer network and a slower release of hydrogen broꢀ
mide upon further polymer crosslinking.
product (BrxB3N3Hx
)
does not experience furꢀ
n(cond)
ther decomposition at noticeable rates; and the contriꢀ
bution of gasꢀphase tribromoborazine decomposition
is negligible and ignored. Five sets of vapor pressure
measurements as a function of time have been carried
out at 353, 384, 404, 419, and 443 K; the log plot of the
conventional rate versus reciprocal temperature is seen
in Fig. 4. We note that points referring to the decomꢀ
position of solid and liquid tribromoborazine fall on
one straight line. According to this work, the activaꢀ
tion energy of the condensedꢀphase thermal decomꢀ
In summary, we used static tensimetry method to
determine saturated and unsaturated vapor pressures
of (BrBNH)3 as a function of temperature, and the
parameters of tribromoborazine sublimation and
vaporization have been determined. Noticeable rates
of tribromoborazine decomposition with HBr gas evoꢀ
lution are observed at temperatures higher than 343 K.
The other decomposition products are nonvolatile and
have a polymeric nature. At 573 K polymers continue
releasing hydrogen bromide, may be, due to the
crosslinking of polymer chains. We failed to provide
complete HBr release even upon a longꢀterm exposure
of the closed system at 660 K. Likely, complete
position of (BrBNH)3 (process (3)) is 65
3 kJ/mol.
Data from [11] give an estimate of 220 kJ/mol for the
activation energy of thermal decomposition of boraꢀ
zine, implying the greater ease of (BrBNH)3 decomꢀ
position relative to (HBNH)3. In our opinion, the reaꢀ
son for this is the easier elimination of HBr compared
to Н2 due to the greater negative charge on the broꢀ
mine atom.
After (BrBNH)3 was completely evolved to the gas removal of HBr at these temperatures is achievable
phase, the decomposition reaction rate substantially only under unequilibrium conditions. Our estimate of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

562
KAZAKOV, TIMOSHKIN
x
= 3
x
= 2.5
x = 2.25
HN
BBr
HN
B
–2HBr
+2(BrBNH)
HN
B
HN BBr
NH
HN BBr
BBr
NH
BBr
HN BBr
BBr
NH
BBr
HN BBr
BBr
HN
BBr
NH
–HBr
3
BrB
BrB
N
BrB
N
N
B
B
HN
HN
HN
HN BBr
HN BBr
HN
BBr
BBr
N
–HBr
x
= 2
BrB
HN
NH
BBr
HN
HN BBr
BBr
HN
BBr
NH
BBr
B
BrB
N
N
B
N
B
HN
HN BBr
B
x
= 2
N
–2HBr
+2(BrBNH)
–2HBr
+2(BrBNH)
HN
BrB
BBr
NH
B
3
BrB
HN
NH
BBr
3
x
= 2
HN
HN
HN BBr
BBr
HN
BBr
NH
BBr
HN
HN BBr
BBr
HN
B
BBr
N
N
B
BBr
NH
BBr
B
BrB
N
N
B
N
B
B
BrB
N
N
B
HN
HN BBr
B
B
HN
HN BBr
N
BBr
HN
N
HN BBr
N
B
B
NH
BBr
BrB
N
HN BBr
HN
BrB
HN
NH
N
BBr
BrB
NH
–HBr
HN
BBr
HN
BrB
BBr
NH
–3HBr
x
= 1.83
N
B
x
= 1.5
HN
B
HN
B
HN BBr
BBr HN
B
HN BBr
BBr
HN
N
BBr
NH
BBr
BBr
NH
BBr
BrB
N
N
B
BrB
HN
N
N
B
B
N
B
N
B
HN
N
HN BBr
B
N
B
BBr
HN
N
N
B
N
B
BrB
HN
B
NH
NH
BBr
BrB
HN
N
BBr
N
B
N
B
BrB
HN
NH
BBr
x
= 1.34
HN
BrB
N
BBr
NH
x
= 1
HN BBr
HN BBr
HN BBr
B
BrB
N
B
N
B
NH
N
BBr
HN
B
N
BBr
N
N
B
N
B
N
N
B
B
N
B
N
B
B
B
N
N
N
N
B
N
BrB
NH
BBr
HN
BrB
HN
HN
B
N
BBr
HN
B
B
N
N
B
B
H
B
B
N
B
N
B
B
B
BrB
HN
NH
BBr
N
N
B
N
NH
BBr
BrB
N
B
B
N
N
B
n
HN
B
N
B
N
B
BrB
N
NH
B
HN BBr HN BBr
Fig. 5. Suggested scheme of tribromoborazine thermolysis: the initial polycondensation step (top), and formation of 2D sheets
(left) and linear polymers (right). The value is given for each structure.
x
the activation energy for tribromoborazine thermal
decomposition in a condensed phase is 65 kJ/mol,
which is an indirect indication of the preservation of
ACKNOWLEDGMENTS
3
The authors appreciate the financial support
from St. Petersburg State University (grant
the heterocycle core upon the thermal decomposition. no. 12.37.139.2011).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

VAPORIZATION AND THERMAL DECOMPOSITION
563
7. Handbuch der praeparativen anorganischen Chemie, Ed.
by G. Brauer (Ferdinand Enke, Stuttgart, 1975–1981;
Mir, Moscow, 1985).
REFERENCES
1. K. B. Shelimov and M. Moskovits, Chem. Mater. 12
,
250 (2000).
8. A. V. Suvorov, The Thermodynamic Chemistry of Vapor
State (Khimiya, Leningrad, 1970) [in Russian].
2. G. Postole, M. Caldararu, N. I. Ionescu, et al., Therꢀ
mochim. Acta 434, 150 (2005).
3. K. N. Chaitanya, R. Schaeffer, and R. T. Paine, J. Am.
Chem. Soc. 109, 5556 (1987).
4. K. J. L. Paciorek, S. R. Masuda, and H. Rainhold,
9. E. I. Davydova, T. N. Sevastianova, A. V. Suvorov, and
A. Y. Timoshkin, Coord. Chem. Rev. 254, 2031 (2010).
10. A. W. Laubengayer and C. W. J. Scafie, J. Chem. Eng.
Data 11, 172 (1966).
11. A. W. Laubengayer, P. C. Jr. Moews, and R. F. Porter,
Chem. Mater.
5. F. Müller, K. Stöwe, and H. Sachdev, Chem. Mater. 17
3464 (2005).
3, 88 (1991).
,
J. Am. Chem. Soc. 83 (6), 1337 (1961).
6. C. A. Brown and A. W. Laubengayer, J. Am. Chem. 12. B. P. Nikol’skii, Physical Chemistry (Khimiya, Leninꢀ
Soc. 77, 3699 (1955). grad, 1987) [in Russian].
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012