Synthesis of energetic compounds via the metathesis reaction of 4-methylenespiro[2,3]hexane

Article abstract of DOI:10.1134/S0965544108040099

Transformations of methylenespiro[2,3]hexane (MSH) on a heterogeneous rhenium-alumina metathesis (disproportionation) catalyst were studied. It was found that, owing to a significant difference in the stability of carbenic complexes of methylene and disubstituted carbenes, MSH undergoes isomerization to 4-methylspiro[2,3]hex-4-ene followed by their cometathesis yielding bis(spiro[2,3]hexylidene-4). The feasibility of selective cometathesis of MSH and dicyclobutylidene on the rhenium-alumina catalyst resulting in the formation of 4-cyclobutylidenespiro[2,3]hexane was shown.

Full text of DOI:10.1134/S0965544108040099

ISSN 0965-5441, Petroleum Chemistry, 2008, Vol. 48, No. 4, pp. 309–313. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © S.V. Kotov, S.P. Chernykh, E.Sh. Finkel’shtein, B.S. Strel’chik, V.A. Tyshchenko, V.I. Milovantseva, 2008, published in Neftekhimiya, 2008, Vol. 48, No. 4,
pp. 306–310.
Synthesis of Energetic Compounds via the Metathesis Reaction
of 4-Methylenespiro[2,3]hexane
S. V. Kotova, S. P. Chernykhb, E. Sh. Finkel’shteinc, B. S. Strel’chikd,
V. A. Tyshchenkoa, and V. I. Milovantsevae
a OAO Middle-Volga Research Institute of Oil Processing, Novokuibyshevsk, Samara oblast, Russia
b All-Russia Institute of Organic Synthesis, Moscow, Russia
c Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, Russia
d ZAO Novokuibyshevsk Petrochemical Company, Novokuibyshevsk, Samara oblast, Russia
e Petroleum Analyst, Samara Branch, Novokuibyshevsk, Samara oblast, Russia
Received July 20, 2007
Abstract—Transformations of methylenespiro[2,3]hexane (MSH) on a heterogeneous rhenium–alumina met-
athesis (disproportionation) catalyst were studied. It was found that, owing to a significant difference in the sta-
bility of carbenic complexes of methylene and disubstituted carbenes, MSH undergoes isomerization to
4-methylspiro[2,3]hex-4-ene followed by their cometathesis yielding bis(spiro[2,3]hexylidene-4). The feasibil-
ity of selective cometathesis of MSH and dicyclobutylidene on the rhenium–alumina catalyst resulting in the
formation of 4-cyclobutylidenespiro[2,3]hexane was shown.
DOI: 10.1134/S0965544108040099
The development of some kinds of rocketry oxide was ineffective. To establish the feasibility of
demands new liquid propellants with a high specific metathesis for compound I, acetylenic compounds
impulse. 4-Methylenespiro[2,3]hexane (I), the product were removed from the olefin via a preparative proce-
of the cyclopropanation of one double bond in dimeth- dure with the Ilosvay reagent [1].
ylenecyclobutane (allene dimer), is a promising semi-
Compound I did not undergo any transformations
product for the synthesis of energetic materials. The
during the treatment with the reagent, which represents
presence of cyclobutane and cyclopropane rings in the
copper complexes. After purification, I had a 99 wt %
molecule of compound I ensures a high energy density
purity. Being cleaned of acetylenic hydrocarbons, com-
of this olefin. Therefore, the products of both its met-
pound I reacted fairly well in the presence of a hetero-
athesis and cometathesis with unsaturated compounds
geneous rhenium–alumina catalyst promoted with
containing strained carbocycles are of great interest.
êbEt4 or SnBu4. In accordance with the traditional met-
athesis scheme, ethylene and bis(spiro[2,3]hexylidene-4)
(II) had to be formed as the reaction products.
RESULTS AND DISCUSSION
However, according to the gas chromatography–
A crude allene dimer is a mixture of two isomeric
mass spectrometry data, the molecular masses of the
four-membered carbocycles, 1,2- and 1,3-dimethyle-
heavy products of the transformation of I were 188, not
necyclobutane. As a consequence, the product of the
160 as it must be in the case of compound II. For iden-
cyclopropanation of the dimers is also a mixture of two
tification, one of the products was isolated by prepara-
isomers, namely, compound I and 5-methyle-
tive chromatography with a purity of 97 wt %. On the
nespiro[2,3]hexane. The ratio of isomers is 9–10 to 1,
basis of IR, 1H NMR, and mass spectral data (table), the
respectively.
isolated compound was identified as diene (III):
Compound I with a purity of higher than 98 wt %,
isolated via fractional distillation from the reaction
CH2
CH2
mixture after the reduction of 2,2-dichloromethyle-
nespiro[2,3]hexane contained metathesis-catalyst poi-
sons as impurities. By gas chromatography–mass spec-
trometry and Fourier-transform IR spectroscopy, it was
found that the distillate of compound I contains hydro-
carbons with a molecular mass of 96 having a triple car-
CH2
C CH CH2
C
C
CH3
(III)
CH2 CH2
CH2 CH2
Other heavy products of the transformation of com-
bon–carbon bond, mainly in the α position. According pound I are its isomers that differ in the position of
to the IR data, the adsorption purification of I for the cyclopropane rings. It is easy to see a certain resem-
removal of these poisons by activated γ-aluminum blance of structures of this hydrocarbon and the previ-
309

310
KOTOV et al.
PETROLEUM CHEMISTRY Vol. 48 No. 4 2008

SYNTHESIS OF ENERGETIC COMPOUNDS
311
ously described 2-methyl-5-cyclobutylidenepentene-1
[2], one of the products of 1-methylcyclobutene comet-
athesis with methylenecyclobutane (IV), a structural
analog of I. This similarity suggests that diene III is
formed according to the following schemes:
The question of why diene III is formed instead of
compound II is of considerable theoretical and practical
interest. In terms of the carbene mechanism of metathe-
sis, the transformation of I to II requires the transition
from one carbene complex (V) to another carbene com-
plex (VI) in accordance with scheme (3):
CH2
CH3
(1)
Re
CH2
Re
CH
+
2
(VI)
(3)
+
CH2
(V)
CH2
CH C CH3
However, such a transition seems to be difficult
because of the substantial difference in the stability of
complexes V and VI. According to published data
[3, 4], the carbene complex of methylene is one of the
least stable complexes. In contrast, complex V must be
considerably more stable, since it is a complex of a sec-
ondary carbene [3] and contains a three-membered ring
capable of conjugation. At the same time, cometathesis
reaction (2) shown above includes the transition of V to
a structurally close complex of 1,1-disubstituted car-
bene (VII), which also has a three-membered ring capa-
ble of conjugation:
+
(2)
H2C
C
CH3
However, the mechanism of the formation of
4-methylspiro[2,3]hexane remains unclear. It is likely
that this compound is formed via a route similar to the
isomerization of IV into 1-methylcyclobutane on
γ-Al2O3. But it may also be assumed that the isomeriza-
tion occurs in the coordination sphere of the rhenium
ion, which is the active center of metathesis.
(V)
Re
Re
H2C
Re
+
+
(4)
H3C
C
C
CH
CH3
C
C
CH
CH2
CH2
H3C
(VII)
Note that this reaction differs from the cometathesis
of IV with 1-methylcyclobutene; in the latter case, two
variants of coordination of 1-methylcyclobutene to the
Re
HC
H2C
C
C
CH3
carbene complex Re
were realized and two
isomeric cometathesis products, 5-cyclobutylidenehex-
ene-1 and 5-cyclobutylidene-2-methylpentene-1, were
formed [2]. In our case, the single variant of the coordi-
nation depicted in scheme (4) was realized. The cause
of this fact can be both steric hindrance to the formation
of the alternative complex and a lower stability of the
monosubstituted carbene (VIII) formed from this com-
plex at the next stage.
(VIII)
These facts suggest that the low reactivity of I in the
metathesis is due to a high-energy barrier to the trans-
formation of highly stable, relatively unreactive car-
bene complex V into the less stable complex VI. The
reaction proceeds via another, energetically more
favorable route involving the isomerization of I fol-
lowed by the formation of carbene complex VII, which
seems to be close in energy to complex V.
PETROLEUM CHEMISTRY Vol. 48 No. 4 2008

312
KOTOV et al.
Yield of IX, mol %
50
40
30
20
10
0
10
20
30
40
50
60
Time, min
Kinetic curve for the formation of compound IX.
These speculations are confirmed by the effective cometathesis of compound I with dicyclobutylidene accord-
ing to scheme (5):
CH2
CH2
+
+
(5)
(IX)
In this case, the reaction requires the conversion of ene complex VI should be produced at one of the reac-
complex V to the structurally similar complex tion steps in this case:
Re
CH2
Re
and there is no need of the involvement of
(VI)
Re
CH2
energy-rich methylene carbene. The cometathesis was
conducted in the liquid phase at 35°ë in the presence of
the êbEt4- or SnBu4-promoted rhenium–alumina cata-
lyst. The selectivity of the transformation of I into IX
was about 90%. The kinetic curve of the process
depicted in the figure indicates that, although the reac-
tion initially proceeds at a high rate, the composition of
the reaction mixture stops changing after approxi-
mately 20 min. This invariance can be explained by the
thermodynamic constraints on the process.
+
(6)
(V)
(IV)
(IX)
The
same
transformations
of
methyle-
nespiro[2,3]hexane were observed under the conditions
of its cometathesis with IV as those in the absence of
IV, i.e., the isomerization of I to 4-methyle-
nespiro[2,3]hex-4-ene and their metathesis.
4-Cyclobutylidenespiro[2,3]hexane (IX), the prod-
uct of the cometathesis of compound I with dicyclobu-
tylidene, was isolated by vacuum rectification to have a
purity of 97 wt %. The structure of the product was con-
firmed by IR, 1H NMR, and mass spectral data (table).
EXPERIMENTAL
Analytical Methods
The gas-chromatographic/mass-spectrometric anal-
ysis of hydrocarbon mixtures and individual com-
We failed to synthesize compound IX via the alter- pounds was carried out with an LKB-2091 instrument
native cometathesis of I and IV according to scheme (6). (ion-source and molecular-separator temperatures of
It is likely that the failure is due to the fact that methyl- 250°ë, an ionization energy of 70 eV, an emission cur-
PETROLEUM CHEMISTRY Vol. 48 No. 4 2008

SYNTHESIS OF ENERGETIC COMPOUNDS
313
rent of 50 µA) on a 70000 × 0.25-mm capillary column compound IV, 89.69 wt %; unidentified impurities,
coated with Apiezon L, as well as with a Kratos instru- 0.26. During the reaction, which lasted 2 h, ethylene
ment on a 2000 × 3-mm column packed with 3% SE-30- was released. According to GLC data, liquid products
coated Chromaton). The proton NMR spectra were contained unreacted compounds IV and I, as well as
recorded on a JEOL (100 MHz) instrument. The IR dicyclobutylidene resulting from metathesis, product
spectra were recorded with a Specord spectrophotome- III, and its isomers. The yield of diene III and its iso-
ter in a 5% CCI4 solution, as well as in the solvent-free mers calculated on the basis of reactant I fed was
mode.
21.63 mol % and that calculated on the basis of reactant
I converted was 78.16 mol %. The yield of dicyclobu-
tylidene calculated on the basis of reactant IV fed was
17.37 mol %, and the selectivity for dicyclobutylidene
was 78.92 mol %.
Transformations of Methylenespiro[2,3]hexane (I)
on Promoted Rhenium–Alumina Catalysts
The rhenium–alumina catalyst was prepared
according to the conventional procedure [2]. The reac-
tion was carried out at 35°ë in a thermostated batch
reactor equipped with a stirrer. A catalyst (0.78 g) pre-
liminary activated at 580°ë in a flow of air for 1 h and
in a flow of nitrogen for 1 h was placed into the reactor.
After thermostating, the catalyst was promoted with
1.3 wt % tetraethyl lead. Then, 3.9 ml (3.1 g) of com-
pound I cleaned of acetylenic compounds was added.
The reaction was accompanied by heat evolution. After
2 h, according to GLC data (SE-30, l = 3 m), the reac-
tion mixture had the following composition (wt %):
unreacted I, 53.88; diene III and its isomers, 38.86; and
unidentified hydrocarbons, about 7.26. The yield of
diene III and its isomers calculated in terms of reactant
I taken was 39.25 mol %, and the selectivity of the con-
version of I into these products was 86.13 mol %. Prod-
uct III was isolated by preparative chromatography
with a purity of 97 wt % (a PEG 1000 column; l = 3 m;
and column and evaporator temperatures of 200 and
200°ë, respectively). The structure of III and its physi-
cochemical and spectral characteristics are given in the
table. A mixture of the isomers of III was isolated with
a purity of 95 wt %. The IR, 1H NMR, and mass spec-
tral data for diene III are given in the table.
Synthesis of 4-Cyclobutylidenespiro[2,3]hexane
The 10% Re2O7/Al2O3 catalyst activated in a nitro-
gen flow at 580°C was placed into a reactor similar to
the one described above. After cooling, the catalyst was
promoted with tetraethyl lead (1.3 wt %). The reactor
was thermostated at 35°ë, and a mixture of I (14.73 wt %)
with dicyclobutylidene (83.56 wt %) was added to the
reactor. The reaction was run at a constant temperature
of 35°ë with stirring for 2 h. Neither gas emission nor
heat evolution was observed. According to GLC data,
the resultant mixture contained unreacted compound I,
dicyclobutylidene; compounds IV and IX as comet-
athesis products; and unidentified hydrocarbon impuri-
ties. The yield of IX on a fed reactant I basis was
45.29 mol %, the selectivity of the transformation of I
was 96 mol %. The yield of IX on the fed dicyclobutyl-
idene basis was 100 mol %. The desired product
4-cyclobutylidenespiro[2,3]hexane was isolated to
have a 97 wt % purity via vacuum rectification followed
by preparative chromatography under the aforemen-
tioned conditions. Its physicochemical and spectral
characteristics are given in the table. The kinetics of the
cometathesis reaction of compound I with dicyclobu-
tylidene is illustrated in the figure.
Transformation of a Mixture of I and IV
REFERENCES
on PbEt4-Promoted Rhenium–Alumina Catalyst
1. Houben-Weyl. Methoden der organischen Chemie
(Georg Thieme, Stuttgart, 1953; Khimiya, Moscow,
1967).
The reaction was carried out at 35°ë in a batch sys-
tem composed of a thermostated reactor equipped with
a stirrer and an arrangement for the withdrawal of the
ethylene produced. The 10% Re2O7/Al2O3 catalyst acti-
vated at 580°ë was loaded into the reactor and pro-
moted with tetraethyl lead (1.3 wt %) after cooling.
Then, a mixture of I and IV was added. The mixture had
the following composition (wt %): compound I, 10.05;
2. E. Sh. Finkel’shtein, B. S. Strel’chik, S. V. Kotov, et al.,
Neftekhimiya 25, 41 (1985).
3. B. A. Dolgoplosk, K. L. Makovetskii, and E. I. Tinyak-
ova, Dokl. Akad. Nauk SSSR 228, 1109 (1976).
4. B. A. Dolgoplosk, E. I. Tinyakova, and V. A. Yakovlev,
Dokl. Akad. Nauk SSSR 232, 1075 (1977).
PETROLEUM CHEMISTRY Vol. 48 No. 4 2008