Oxidative transformations of cyclohexane, methylcyclopentane, and pentane on treatment with superelectrophiles based on polyhalomethane and aluminum halides

Article abstract of DOI:10.1023/A:1009529302679

Cyclohexane and methylcyclopentane dimerize into dimethyldecalins on treatment with superelectrophilic systems containing polyhalomethanes (CBr₄, CCl₄, CHCl₃) and aluminum halides (AlBr₃, AlCl₃). At 2

Full text of DOI:10.1023/A:1009529302679

Russian Chemical Bulletin, International Edition, Vol. 50, No. 1, pp. 81—87, January, 2001
81
Organic Chemistry
Oxidative transformations of cyclohexane, methylcyclopentane,
and pentane on treatment with superelectrophiles based
on polyhalomethane and aluminum halides
I. S. Akhrem,« I. M. Churilova, and S. V. Vitt
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28, ul. Vavilova, 117813 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. E-mail: cmoc@ineos.ac.ru
Cóñlohexane and methylcyclopentane dimerize into dimethyldecalins on treatment with
superelectrophilic systems containing polyhalomethanes (CBr4, CCl4, CHCl3) and aluminum
halides (AlBr3, AlCl3). At 20 °C, the yields of C12H22 hydrocarbons reach 140 mol.% based on
the superelectrophile. Under the action of CBr4•2AlBr3 at 20 °C in CH2Br2 or without a
solvent, n-pentane is converted predominantly into lower alkanes (mainly, isopentane). In
addition, higher branched C8—C12 alkanes, small amounts of alkylated cyclohexanes,
cycloalkenes, dienes, and alkylbenzenes are formed in a total yield of 20—23 % (w/w) based
on pentane.
Key words: cyclohexane, methylcyclopentane, n-pentane, dimethyldecalins, superelectro-
philes, polyhalomethanes, complexes of aluminum halides, oxidative transformations of satu-
rated hydrocarbons, mass spectra.
Transformations of saturated hydrocarbons (isomeri-
zation, cracking, oligomerization, cyclization, dehydro-
genation, dehydrocyclization, aromatization, etc.) play
an important role in industrial processes.1 As a continu-
ation of our studies dealing with the transformations of
alkanes and cycloalkanes initiated by superelectrophilic
complexes containing polyhalomethanes in combination
with aluminum halides,2,3 we studied the action of these
systems on cyclohexane, methylcyclopentane, and
n-pentane.
Contrary to the publication in which cyclohexane
and methylcyclopentane were reported to remain un-
changed in the presence of 20—30% (w/w) of AlCl3 at
120—150 °C,4 it was shown that these cycloalkanes
dimerize on treatment with aluminum halide-based sys-
tems to give a mixture of dimethyldecalins.5—7 The
formation of the product of cyclohexane dimerization
was first observed5 when it was made to react with
cyclohexyl bromide in the presence of AlCl3. Later, the
hydrocarbon C12H22 was detected upon the reaction of
chlorocamphor with AlBr3 in cyclohexane.6 "Self-alkyla-
tion" (dimerization) of methylcyclopentane on treat-
ment with ButCl and AlCl3 has been observed in a
study,7 in which the reactions mentioned above5—7
were demonstrated to afford the same product, 2,6-di-
methyldecalin. Other examples of cyclohexane and
methylcyclopentane dimerization have also been re-
ported.8—11
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 78—84, January, 2001.
1066-5285/00/5001-0081 $25.00 © 2001 Plenum Publishing Corporation

82
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 1, January, 2001
Akhrem et al.
Table 1. Oxidative dimerization of cyclohexane and methylcyclo-
pentane to dimethyldecalins in the presence of superelectrophiles
(Å) at 20 °C
Superelectrophiles based on polyhalomethanes could
prove to be efficient initiators of the transformations of
cycloalkanes into dimethyldecalins, which are precursors
of adamantanes. The possibility of direct adamantization
or aromatization of C6 cycloalkanes under the action of
the superelectrophiles in question could not be ruled out
either. The transformations of saturated hydrocarbons
(including cyclohexane) into adamantanes8—12 and into
aromatic compounds under rigorous conditions are well
known.13 For example, heating of 10 g of cyclohexane
with 41 g of AlBr3 for 69 h at 110 °C gave rise to 1.9 g of
a mixture of dimethyladamantanes.12
Another investigation object, pentane, presented in-
terest from several standpoints. On the one hand, the
previously observed transformations of cyclopentane3
under the action of these superelectrophiles undoubtedly
include opening of the five-membered ring. Therefore,
certain similarity between the products of transforma-
tions of cyclic and aliphatic C5 hydrocarbons should be
expected. On the other hand, since C5—C18 n-alkanes
are converted into isoalkanes and oligomers with quali-
tatively similar compositions under the action of
superelectrophiles based on polyhalomethanes,2 one
could suggest that the reactions observed for pentane
would also be probable for its higher homologs. The
adamantization of alkanes requires much energy.13
Run
Å
RH
[RH] : [E] τ/h
Yield
(mol.%)
based
on E
1
2
3
4
5a
6
CBr4•2 AlBr3
CBr4•3 AlBr3
CCl4•3 AlBr3
Al2Br6
CBr4•2 AlBr3
CBr4•2 AlBr3
CBr4•2 AlBr3
10 : 1
10 : 1
10 : 1
20 : 1
15 : 1
20 : 1
20 : 1
0.5
0.5
0.5
0.5
2
17
27
25
0
24
24
48
106
138
7
Me
8
9
CCl4•3 AlBr3
CHCl3•3 AlCl3
CCl4•2 AlCl3
5 CCl4•AlBr3
5 CCl4•AlCl3
5 CCl4•AlCl3
5 CCl4•AlCl3
10 : 1
10 : 1
10 : 1
17 : 1
17 : 1
17 : 1
17 : 1
0.5
0.5
48
4
4
2
24
13
97
132
36
150
125
10
11
12
13b
14c
2
a In the presence of CH2Cl2. The other experiments were
performed without a solvent.
b At 40 °C.
c
At 60 °C.
C H2n+2
n
C H2n–4 + 3 H2 – Q
n
dimerization to give isomeric dimethyldecalins (DMD)
and, perhaps, their isomers. The reactions were per-
formed without a solvent at the reactant molar ratio
[RH] : [E] = (10—20) : 1. Although the reaction mixture
is heterogeneous, the yield of C12H22 bicycloalkanes
based on the superelectrophile is ∼25% over a period of
0.5 h; the yield after 2 days is 100—140% (Table 1).
Apart from the CBr4•nAlBr3 and CCl4•nAlBr3 com-
plexes (n = 2 or 3), more readily available systems,
CCl4•2 AlCl3 and CHCl3•2 AlCl3, are also active in
this reaction. However, in the presence of Al2Br6 with-
out CBr4 or CCl4, no C12H22 hydrocarbons can be
found after 1 h at 20 °C.
The products of transformation of cyclohexane and
methylcyclopentane are virtually the same. The C12H22
hydrocarbons formed in these reactions are represented
by a large number of isomers. The first six of them (in
the order of increasing retention times) account for
92—95% of the total amount of bicyclanes; the major
component characterized by the shortest retention time
makes 52—60% of the total mixture of isomers. The
ratios of chromatographic peaks in the order of increas-
ing retention times corresponding either to individual
C12H22 hydrocarbons or to their unseparable mixtures in
run 3 (see Table 1) are 3.3 : 1 : 0.5 : 0.3 : 0.3 : 0.2; in
runs 5 and 10, these ratios are virtually the same,
namely, 4 : 1 : 0.5 : 0.3 : 0.3 : 0.1.
More extensive oxidation of alkanes to aromatic
hydrocarbons is even a more endothermic process,13
unfavorable even at 500 °C.
C H2n+2
n
C H2n–6 + 4 H2 – Q
n
Nevertheless, high-temperature catalytic transforma-
tions of alkanes to aromatic hydrocarbons (aromatiza-
tion or catalytic reforming) are well known and imple-
mented on an industrial scale.1d,14 In terms of the ability
to form aromatic compounds, hydrocarbons of various
classes are arranged in the sequence1d cyclohex-
enes > cyclohexanes > cyclopentanes > alkenes > al-
kanes. Heating dodecane and squalane with excess AlBr3
at 110—130 °C for 2—5 days12b yields small amounts of
alkyladamantanes. On heating solid saturated hydrocar-
bons with aluminum chloride at 210—220 °C for 40 h, a
mixture containing 4 to 46% (w/w) of aromatic hydro-
carbons was formed. The use of anhydrous aluminum
chloride decreases the yields of aromatic hydrocarbons
to 2—6 %.15
The reactions of hydrocarbons with systems contain-
ing polyhalomethanes (CBr4, CCl4, CHCl3) in combina-
tion with aluminum halides (AlBr3, AlCl3) were carried
out in a solution in CH2X2 (X = Cl, Br) or without a
solvent at 20—60 °C for 0.5—48 h. The structures of
products were studied by GC/MS.
On treatment with electrophilic systems CBr4•nAlBr3,
CCl4•nAlCl3, CHCl3•nAlCl3 (E, n = 2 or 3) at 20 °C,
cyclohexane and methylcyclopentane undergo oxidative
The mass spectrum of each isomer contains a rather
intense molecular ion with [M]+ 166 and the same set of
peaks of different intensities corresponding to fragment
ions typical of DMD (m/z 151, 137, 124, 123, 110, 109,

Oxidative transformations of alkanes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 1, January, 2001
83
96, 95, 82, etc.). These fragment ions are produced upon
abstraction of alkyl radicals ranging from CH3 to C6H11
and olefins from C3H6 to C6H12 from the molecular
ion.16 The extent of similarity of the observed mass
spectra to the spectra reported in standard libraries of
mass spectra, NBS 75K and Wiley 138, equals 81—94%.
In our opinion, the major component of the isomer
mixture of hydrocarbons with [Ì]+ 166 having the
minimum retention time is a mixture of cis,cis,trans-2,6-
and cis,cis,trans-2,7-dimethyldecalins. It has been re-
ported16 that the mass spectra of these two isomers are
closely similar to each other; the boiling points of these
compounds coincide and the retention times on squalane
are equal.17 These compounds are characterized by the
shortest retention time among the whole set of geometri-
cal and steric isomers (the only exception is 2,2-DMD;
however, its content in the equilibrium mixture of DMD
is only 4%).17 It was found that cis,cis,trans-2,6- and
cis,cis,trans-2,7-DMD are distinguished by the highest
stability among the geometrical and spatial iso-
mers of DMD.18 The composion of the mixture of
C12H22 bicyclanes formed in these reactions is close
to the calculated equilibrium mixture of DMD,
61% of which is a mixture of cis,cis,trans-2,6- and
cis,cis,trans-2,7-DMD.18 Previously, we showed11 that
2,6- and 2,7-DMD are the main components of the
DMD formed from cyclohexane on treatment with the
superelectrophilic complex AcCl•2 AlBr3. The high de-
gree of similarity of the mass spectra of the C12H22
hydrocarbons under study to the reported DMD, the
fact that the component ratio in the resulting mixtures is
close to the ratio calculated for an equilibrium DMD
mixture, and the enhanced thermodynamic stability of
DMD compared to other isomeric bicyclanes provide
grounds to believe that at least the main bulk of the
C12H22 hydrocarbons are DMD. The minor components
of these hydrocarbons include 2-ethyldecalin, having the
greatest retention index among hydrocarbons with
[Ì]+ 166. The extent of similarity of the mass spectrum
of this compound to the mass spectrum of 2-ethyldecalin
reported in the Wiley 138 library equals 94%. One of the
most intense peaks in its mass spectrum is the peak of an
ion with m/z 137 corresponding to the abstraction of the
ethyl radical from the molecular ion. Note that the
content of 2-ethyldecalin (3%) in the resulting mixture
of C12H22 hydrocarbons is also close to its content in the
equilibrium mixture of DMD.18
[Ì]+ 248, last in retention time, is responsible for an
intense peak with m/z 219, corresponding to the elimi-
nation of an ethyl group from the molecular ion. Appar-
ently, hydrocarbons with [Ì]+ 248 belong to the group
of alkylated tricyclanes C18H32, both tetramethyl-substi-
tuted tricyclanes, present in a predominant amount, and
tricyclanes containing ethyl groups. It should be empha-
sized that oxidative dimerization of cyclohexane and
methylcyclopentane in excess cycloalkane proceeds rather
selectively giving only traces of trimerization products
and other compounds. Conversely, the reaction of cy-
clohexane with CBr4•2 AlBr3 in CH2Br2 with the molar
ratio [RH] : [E] = 5 : 1 results in a low yield of DMD
over a period of 30 min. In this case, the reaction mixture
contains alkylated cyclohexanes cyclo-C6H11CnH2n+1
(M = 98, 126, 140; n = 1—4), isomeric bromides
cyclo-C6H11Br, bicyclic alkenes, and dienes ([Ì]+ 164,
162, 192).
The general scheme of transformations of cyclohex-
ane and methylcyclopentane is presented below.
Scheme 1
Me
Me
CX4•nAlX3
CX4•nAlX3
2
Me
Me
Me
Me
Me
The conjectural mechanism of the observed transfor-
mations of C6 cycloalkanes into bicyclanes C12H22 is
similar to that proposed previously.7—10 It includes the
formation of an active cationic complex (1), generation
of the cycloalkylcarbenium ion from cycloalkane (2),
addition of the cycloalkylcarbenium ion to the conju-
gated cycloalkene to give dicycloalkylcarbenium ion (3),
rearrangement of this product into thermodynamically
stable dimethyldecalinium ion (4), and, finally, the for-
mation of DMD and regeneration of the electrophile (5)
(Scheme 2).
Among other products of transformation of cyclo-
hexane and methylcyclopentane, a hydrocarbon with
[Ì]+ 192 and a series of isomers with a molecular
weight of 248 were detected. The mass spectra of hydro-
carbons with [Ì]+ 248 with shorter retention times
exhibit a set of fragment ions with close intensities,
corresponding to the abstraction of alkyl groups ranging
from CH3 to C7H15 from the molecular ion; the maxi-
mum ion has m/z 233 [Ì+ – CH3]. Other isomers
account for very intense molecular ions. The isomer with
Scheme 2
(1) The formation of the superelectrophilic complex
AlX3
AlX3
–
–
CX4
CX3+AlX4
CX3+Al2X7

84
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 1, January, 2001
Akhrem et al.
(2) Generation of the cycloalkylcarbenium ions and conjugated
alkenes
According to Scheme 2, the formation of one DMD
molecule requires two superelectrophile molecules and
only one of them can be regenerated. In other words,
the maximum possible yield of DMD in the oxidative
dimerization reaction should not exceed 100% based on
the superelectrophile. The formation of DMD in run 7
(see Table 1) in a yield of more than 100% is due to the
fact that CBr4 reacts with cycloalkane to be reduced to
tribromomethane, which is also able (although less effi-
ciently than CBr3+) to generate cycloalkylcarbenium
ions from cycloalkane in the presence of aluminum
halide and thus initiate oxidative dimerization of cyclo-
hexane (Scheme 3).
+
+
CX3
CX3
–CHX3
–CHX3
+
+
Me
or
+
+
–H
–H
Me
Me
(3) The formation of the dicycloalkylcarbenium ion
Scheme 3
+
+
+
AlCl3
AlCl3
–
–
CHBr2+AlCl3Br
CHBr2+Al2Cl6Br
CHBr3
Me
Me
Me
Me
(4) The formation of the dimethyldecalinium ion
Me
+ CH2Br2 + H+
Me
Me
+
2
+ CHBr2
Me
+
+
Me
Me
Activity of CHÕ3•3AlCl3 in the dimerization of
cyclohexane confirms this conclusion.
∼H, ∼Me
To compare the results obtained here with published
data, note that heating of cyclohexane with AlCl3 acti-
vated by the products of isooctane cracking at 40—60 °C
for 15—20 h gives DMD in 10—15% yields.8 The
HF—BF3 system promoted by olefins and isoalkanes
makes it possible to prepare DMD from cyclohexane in
54% yield at 100 °C over a period of 6 h.9 Some
electrophilic systems are active in this reaction at 20 °C;
ButCl—AlCl3,7 Cu(Al2Cl8),10 and AcX•2AlBr311 are ex-
amples. The yields of DMD based on the super-
electrophile are 27% after 2 h,7 33% after 4 h,10 and
100% after 1 h.11
+
Me
Me
(5) The formation of dimethyldecalins and regeneration of electro-
philic species
+
Me
In conformity with Schemes 2 and 3, dimerization of
C6 cycloalkanes is accompanied by the reduction of
initial polyhalomethanes; conversely, aluminum halides
function in these reactions as catalysts. We showed that,
although systems containing an excess of aluminum
halide are more active than equimolar systems, the
reactions are not inhibited even by excess CCl4. The
yield of DMD at the [RH] : [CCl4] : [AlBr3] = 17 : 5 : 1
molar ratio over a period of 4 h at 20 °C is 132% based
on AlBr3; in a similar experiment with AlCl3, the yield
of DMD is only 36% (see Table 1, runs 11 and 12).
The reactions of methylcyclopentane with the
CCl4—AlCl3 system at 40 and 60 °C afford DMD in
150% and 125% yields, respectively, based on AlCl3 (see
Table 1, runs 13, 14). Thus, the catalytic activity of the
CCl4—AlCl3 systems is relatively low. Our attempts to
reproduce the results of a publication10 in which a much
higher activity was reported for this system failed.
Me
CHX3
Me
Me
+
+
+
+
CX3
Me
The overall reaction
Me
Me
+ CHBr3 + HBr
2
+ CBr4
Me

Oxidative transformations of alkanes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 1, January, 2001
85
In this study, we demonstrated that at 20 °C and a
[C5H12] : [CBr4•2 AlBr3] molar ratio of 5 or 10, either
in CH2Br2 or without a solvent, over a period of 30 min
to 1 h, pentane undergoes complex oxidative transfor-
mations. The light volatile products of these transforma-
tions at 20 °C, as has been shown previously,2à are lower
isoalkanes (C4—C6), mainly isopentane. According to
GC/MS data obtained in this study, in addition to these
isoalkanes, the reaction mixture contained higher
branched isoalkanes up to C12H26, alkylated cyclohex-
anes, and unsaturated CnH2n–4 hydrocarbons with
m/z 122, 136, 150, 178, and 192. Comparison of the
mass spectra of unsaturated hydrocarbons with the spec-
tra presented in the NBS 75K and Wiley 138 libraries of
mass spectra allows some of them to be classified as
linear branched trienes and some other, as cyclopenta-
dienes (see examples in Fig. 1). It is worth noting that
the conversion of pentane also gives slight amounts of
CnH2n–6 hydrocarbons, which undoubtedly belong to
the series of alkylated benzenes.19 Table 2 contains the
aromatic hydrocarbons formed from pentane at 20 °C
and at a [C5H12] : [CBr4•2 AlBr3] molar ratio of 5 : 1 in
CH2Br2 over a period of 30 min. According to GLC, the
total yield of all hydrocarbon products (starting from C8)
is 20—23% (w/w) based on the initial pentane and
calculated for a stoichiometric reaction. Thus, n-pen-
tane behaves differently from cyclopentane3 or cyclo-
hexane. When cyclohexane or pentane is treated with an
electrophile, alkylation of the conjugate alkene might be
the main pathway of transformation of the arising
cyclohexyl and pentyl cation.20 However, due to the
the latter undergoes fragmentation to give a lower alkane
and alkene in accordance with the classical scheme. The
subsequent transformations of alkenes give rise to
cycloalkanes and more unsaturated compounds includ-
ing aromatic hydrocarbons (Scheme 4).21
Scheme 4
+
CBr3
+
C5H12
C5H10
C5H11
+
C10H21
R+
+
C
C
+
C10H21
Cycloalkanes,
cycloalkenes,
arenes
Thus, systems containing polyhalomethanes and alu-
minum halides initiate oxidative dimerization of
methylcyclohexane and cyclohexane to DMD in
100—150% yields based on the electrophile. It is signifi-
cant that not only CBr4—AlBr3 systems but also mark-
edly more available CCl4—AlCl3 systems are active in
this reaction.
The products of transformation of pentane in the
presence of CBr4•2AlBr3 under very mild conditions
were found to contain hydrocarbons with different de-
grees of unsaturation: cyclohexanes, cycloalkenes, cyclo-
+
different stabilities of cyclo-C12H21 and C10H21+, fur-
ther transformation pathways are different. The former
isomerizes to give the dimethyldecalinium cation, whereas
C H
C H
n 2n
n 2n–2
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
M+ 126
(86%)
M+ 126
(97%)
M+ 140
(72%)
M+ 140
(80%)
M+ 124
(76%)
C H
n 2n–4
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
M+ 108
(93%)
M+ 136
(95%)
M+ 136
(72%)
M+ 136
(96%)
M+ 136
(91%)
Fig. 1. Cyclic and unsaturated hydrocarbons formed from pentane on treatment with CBr4•AlBr3 at 20 °C. The values in parentheses
are the extents of similarity of the mass spectra to the mass spectra presented in the NBS 75K and Wiley 138 libraries.

86
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 1, January, 2001
Akhrem et al.
Table 2. Aromatic hydrocarbons in the products of conversion of n-pentane in the presence of CBr4•2 AlBr3 (E) ([C5H12] : [E] =
5 : 1, 20 °C, 30 min)*
Aromatic
hydrocarbon
Molecular
ion, [Ì]+
Extent of similarity (%)
(for the Wiley 138
library)
Aromatic
hydrocarbon
Molecular
ion, [Ì]+
Extent of similarity (%)
(for the Wiley 138
library)
Me
Me
120
94
134
148
176
94
97
83
Me
Me
Me
Me
Me
Me
Me
Et
Me
Me
120
120
94
—
Me
Me
Bu
Pr
Me
Me
Me
C7H15
Me
Me
176
190
—
—
134
91
Me
C8H17
Me
* Structures with the most similar mass spectra are presented; in those cases where no data on the extent of similarity are given, we
were unable to choose between the isomers, although the fact that the hydrocarbons are aromatic is beyond doubt. The C3H7—C8H17
radicals correspond to the overall number of alkyl substituents.
cyclohexane (4.1 g, 48.7 mmol) was added at 20 °C with stirring
using a magnetic stirrer. The closed flask with the two-layer
reaction mixture was stirred for 48 h at 20 °C.
dienes (or linear trienes), and aromatic hydrocarbons.
Dehydrocyclization of pentane giving rise to unsaturated
hydrocarbons including arenes under so mild conditions
has not been reported previously.
GC/MS analysis of the reaction mixture (after the standard
workup) showed the presence of several isomers with [Ì]+ 166
and qualitatively similar set of fragment ions differing in inten-
sity. Mass spectrum of the major component with the shortest
retention time m/z (Irel (%)): 166 (27), 151 (20), 137 (1), 124
(0.1), 123 (2), 110 (5), 109 (14), 96 (6), 95 (29), 83 (13), 82
(12), 81 (32). The six major C12H22 isomers accounted for 92%
of the whole sum of isomers; their ratio was 15 : 4 : 2 : 1 : 1 : 0.4.
Virtually no other products were formed. The total yield of
DMD determined by GLC was 0.56 g (3.4 mmol, 140 mol. %
based on CBr4•2 AlBr3).
Reaction of methylcyclopentane with the complex
CCl4•2 AlCl3. The reaction of anhydrous CCl4 (0.34 g,
2.21 mmol), anhydrous AlCl3 (0.59 g, 4.42 mmol), and
methylcyclopentane (1.87 g, 22.1 mmol) gave, after stirring for
48 h at 20 °C, 0.36 g (2.14 mmol) of a DMD mixture (97 mol.%
based on CCl4•2AlCl3). The six major isomers account for 95%
of the total mixture of C12H22 hydrocarbons. The retention time
of the major component is equal to the retention time of the
major component formed in the experiment with cyclohexane;
however, the fragment ions produced from these two compo-
nents differ in intensity; in particular, in the present case, the
ion with m/z 151 is markedly more intense (perhaps, due to the
2,2-DMD impurity). The ratio of the six major isomers is
∼4 : 1 : 0.5 : 0.3 : 0.3 : 0.1. The component with the longest
retention time with [Ì]+ 166, 2-ethyldecalin, is formed in 2%
yield. Trace amounts of a hydrocarbon with [Ì]+ 192 and a
large number of isomers with [Ì]+ 248 were detected.
Experimental
Saturated hydrocarbons, CCl4, CBr4, CH2Br2, and anhy-
drous AlCl3 and AlBr3 (99%) (Aldrich) were used as received;
CH2Cl2 was refluxed and then distilled from P2O5. The reaction
mixtures were analyzed by gas chromatography (GC) on a
Finnigan 9001 chromatograph with a flame ionization detector
(a DB-5.625 30 m½0.3 mm quartz capillary column; helium as
the carrier gas) in the linear temperature programming mode.
The product yields were determined by GLC with an internal
standard (undecane) without a calibration coefficient. GC/MS
analysis was performed with a similar capillary column; mass
spectra were recorded on an AEI MS 1073 instrument (ioniza-
tion energy 70 eV).
General procedure. The calculated amounts of anhydrous
AlBr3 (AlCl3) and polyhalomethane were placed in a round-
bottom flask with a magnetic stirring bar, the required excess of
a cycloalkane was added, and the mixture was stirred in the
closed flask at the specified temperature for the specified period.
The reaction mixture was treated with water and extracted with
ether (10 mL ½ 3), and the organic layer was washed with water
to a neutral reaction and dried with Na2SO4. The reaction
mixture was analyzed by GLC and GC/MS.
Reaction of cyclohexane with the complex CBr4·2 AlBr3.
Carbon tetrabromide (0.81 g, 2.44 mmol) and anhydrous AlBr3
(1.3 g, 4.87 mmol) were mixed in a dry round-bottom flask, and
Reaction of pentane with CBr4•2 AlBr3. A. A mixture of
AlBr3 (1.45 g, 5.4 mmol), CBr4 (0.9 g, 2.7 mmol), and pentane

Oxidative transformations of alkanes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 1, January, 2001
87
(1 g, 13.5 mmol) in 1.5 mL of CH2Br2 was stirred for 0.5 h at
20 °C. After the usual workup, the total yield of hydrocarbons
(according to GLC data) was 0.036 g (20% (w/w) based on
pentane equimolar to the superelectrophile introduced in the
reaction).
2. (à) I. Akhrem, A. Orlinkov, and M. Vol´pin, J. Chem. Soc.,
Chem. Commun., 1993, 671; (b) I. S. Akhrem and A. V.
Orlinkov, Izv. Akad. Nauk, Ser. Khim., 1998, 771 [Russ.
Chem. Bull., 1998, 47, 740 (Engl. Transl.)].
3. I. S. Akhrem, S. V. Vitt, I. M. Churilova, and A. V.
Orlinkov, Izv. Akad. Nauk, Ser. Khim., 1999, 2304 [Russ.
Chem. Bull., 1999, 48, 2299 (Engl. Transl.)].
4. V. Grignard and C. Stratford, Compt. Rend., 1924, 178, 2149.
5. S. D. Nenitzescu and C. N. Ionescu, Ann., 1931, 491, 189.
6. W. E. Doering and E. F. Schoenewaldt, J. Am. Chem. Soc.,
1951, 73, 2333.
7. W. K. Konn and A. Schneider, J. Am. Chem. Soc., 1954,
76, 4578.
B. In a similar experiment with the same amount of initial
compounds, the reaction mixture was treated with water and
extracted with 2 mL of CH2Br2 and the organic layer was
separated. The volatile fraction (b.p. below 100 °C) was distilled
in vacuo into a trap cooled with liquid nitrogen and analyzed.
According to GC/MS (recording of the spectrum started with
C8H18), the volatile fraction contained series of branched ali-
phatic hydrocarbons CnH2n+2 (n = 8—10, [M]+ 114, 128, 142),
cycloalkanes CnH2n (n = 9, 10; [M]+ 126, 140), and unsatur-
ated hydrocarbons including cycloalkenes CnH2n–2 (n = 9,
8. B. T. Gavrilov, V. G. Luksha, Ya. M. Slobodin, and V. E.
Kovyazin, Zh. Org. Khim., 1975, 11, 597 [J. Org. Chem.
USSR, 1975, 11 (Engl. Transl.)].
[M]+ 124, 152) and hydrocarbons CnH2n–4 (n
= 8—14,
[M]+ 136, 150, 164, 178, 192), which are mainly cyclopenta-
diånes, cyclohexadienes, linear trienes, and aromatic hydrocar-
bons. Aromatic hydrocarbons account for 12% of the total
intensity of the ionic current corresponding to the hydrocarbon
products. In addition, compounds with high degrees of
unsaturation, CnH2n–8 (n = 17, 18, 20; [M]+ 230, 244, 272),
were present; apparently, these were alkylated tetralins or poly-
cyclic compounds. The reaction mixture also contained CHBr3
(the product of reduction of CBr4) and small amounts of
1,2-dibromoethane and bromides of cyclohexane and bicyclic
hydrocarbons.
The reaction of pentane with CBr4•2AlBr3 without a sol-
vent. The reaction of AlBr3 (1.1 g, 4.1 mmol), CBr4 (0.68 g,
2.06 mmol), and pentane (1.48 g, 20.6 mmol) at 20 °C over a
period of 1 h gave, after the usual workup, 0.44 g (23% w/w) of
hydrocarbon products, based on pentane equimolar to the
amount of the superelectrophilic complex used in the reaction.
GC/MS analysis of the reaction mixture showed the presence of
alkanes (mainly, branched) CnH2n+2, where n = 8, 9. The
extent of similarity of individual mass spectra of this series of
hydrocarbons to the mass spectra reported in the above-men-
tioned libraries amounts to 60—90%. The mass spectra of the
compounds obtained allow them to be classified unambiguously
as aliphatic hydrocarbons. The reaction mixture contained iso-
mers of alkylated cycloalkanes CnH2n (n = 9, [Ì]+ 126) and
unsaturated hydrocarbons CnH2n–2 (n = 9, [M]+ 122) and
CnH2n–4 (n = 8—14, [M]+ 122, 136, 150, 164, 178, 192). The
mass spectra of some compounds resemble most closely those
reported for cyclic dienes (cyclopentadienes and cyclohexa-
dienes); the spectra of other, less numerous compounds corre-
spond more closely to the mass spectra of linear trienes. The
products contained aromatic hydrocarbons CnH2n–6 (n = 10, 11;
[M]+ 134, 148). Some of the hydrocarbons found in the prod-
ucts of pentane conversion are shown in Fig. 1.
9. (à) Ðàt. Jpn. 74. 01548 (1974); Chem. Abstr., 1974, 80,
145591; (b) Pat. Jpn, 74.01549 (1974), Chem. Abstr., 1974,
80, 145592.
10. J. P. Thoret-Bauchet, A. Mortreux, and F. Petit, J. Mol.,
Catal., 1993, 83, 323.
11. I. S. Akhrem, A. V. Orlinkov, E. I. Mysov, and M. E.
Vol´pin, Tetrahedron Lett., 1981, 22, 3891.
12. (a) P. R. Schleyer, G. J. Gleicher, and C. A. Cupas, J. Org.
Chem., 1966, 31, 2014; (b) M. Nomura and P. R. Schleyer,
J. Am. Chem. Soc., 1967, 89, 3657.
13. Yu. M. Zhorov, Termodinamika khimicheskikh protsessov.
Neftekhimicheskii sintez pererabotki nefti, uglya i prirodnykh
gazov [Thermodynamics of Chemical Processes. Petrochemical
Synthesis of Oil, Coal, and Natural Gas Processing], Khimiya,
Moscow, 1985, 135 (in Russian).
14. (a) P. C. Dulin, P. R. Puiyado, Proizvodstvo aromaticheskikh
uglevodorodov iz szhizhennykh gazov. Neft´, gaz i neftekhimiya
za rubezhom [Production of Aromatic Hydrocarbons from Liq-
uefied Gas. Oil, Gas, and Petrochemistry Abroad], 1989, 9,
68; (b) Å. Å. Davis, USA Pat. 4180689 [RZhKhim., 1983,
15P 167P]; (c) O. V. Bragin, T V. Vasina, and S. A. Isaeva,
Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1, 32 [Bull. Acad.
Sci. USSR, Div. Chem., 1988, 37, 24 (Engl. Transl.)].
15. S. Otin and S. Savencu, Petroleum, 1938, 46, 1 [Chem.
Abstr., 1939, B10].
16. E. S. Brodskii, I. M. Lukashenko, I. A. Musaev, E. Kh.
Kurashova, and P. I. Sanin, Neftekhimiya [Petrochemistry],
1976, 16 (1), 13 (in Russian).
17. E. Kh. Kurashova, I. A. Musaev, V. N. Novikova, and P. I.
Sanin, Neftekhimiya [Petrochemistry], 1975, 15 (2), 190 (in
Russian).
18. S. S. Berman, L. N. Stukanova, and A. A. Petrov,
Neftekhimiya [Petrochemistry], 1970, 10 (5), 635 (in Russian).
19. H. M. Grubb and S. Meyerson, in Mass Spectrometry of
Organic Ions, Ed. F. M. McLafferty, Acad. Press, New
York—London, 1963, 453.
20. (à) F. C. Condon, J. Am. Chem. Soc., 1951, 73, 3939;
(b) A. Schneider and R. M. Kennedy, J. Am. Chem. Soc.,
1951, 73, 5013; (c) A. Jobert-Perol and M. Herlem, Compt.
Rend., 1978, C 287, 187.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 99-03-
33006).
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Received March 24, 2000;
in revised form July 20, 2000