Carbon tetrabromide - A new brominating agent for alkanes and arylalkanes

Article abstract of DOI:10.1023/A:1020889209717

Quantitative catalytic bromination of alkanes, cycloalkanes, and arylalkanes with carbon tetrabromide as brominating agent was accomplished for the first time.

Full text of DOI:10.1023/A:1020889209717

Russian Journal of Organic Chemistry, Vol. 38, No. 7, 2002, pp. 962 966. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 7, 2002,
pp. 1004 1008.
Original Russian Text Copyright
2002 by Smirnov, Zelikman, Beletskaya, Golubeva, Tsvetkov, Levitskii, Kazankova.
Carbon Tetrabromide A New Brominating Agent
for Alkanes and Arylalkanes*
V. V. Smirnov, V. M. Zelikman, I. P. Beletskaya, E. N. Golubeva, D. S. Tsvetkov,
M. M. Levitskii, and M. A. Kazankova
Department of Chemistry, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia
Received December 28, 2001
Abstract Quantitative catalytic bromination of alkanes, cycloalkanes, and arylalkanes with carbon tetrabromide as
brominating agent was accomplished for the first time.
The present communication describes catalytic
bromination of alkanes (decane and dodecane), cyclo-
alkanes (cyclohexane and adamantane), haloalkanes
(butyl chloride) and arylalkanes (toluene, p- and
m-xylenes, and mesitylene) by the action of CBr4 in
the presence of metal-complex catalyst. The process
follows the equation
molecular bromine [4]. Synthetic utilization of this
procedure is complicated by the necessity of using
twofold excess of aluminum bromide and by sen-
sitivity of the brominating agent to moisture. Like-
wise, the bromination of alkanes with methylene
bromide in the presence of SbF5 [5] requires relatively
large amounts of metal halide (molar ratio of CH2Br2
to SbF5 is about 2). Presumably, a high concentration
of catalyst is a general feature of the halogenation
of alkanes in the presence of Lewis acids; this makes
such processes less attractive from the preparative
viewpoint. The goal of the present study was to effect
selective bromination of alkanes and arylalkanes with
CBr4 in the presence of a catalytic amount of transi-
tion metals.
As catalysts we used copper complexes formed by
reaction of CuBr or CuBr2 with quatenary ammonium
bromides, e.g., CuBr Bu4NBr (1:1) (Ia), CuBr2
Bu3(PhCH2)NBr (1 : 4) (Ib), polymetalphenyl-
siloxanes of the general formula {[PhSiO1.5]2CuO}n
(IIa, metal concentration in the heterogeneous catalyst
0.11%), and {[PhSiO]6CuO]}n (IIb, metal concentra-
tion 0.3%), as well as related nickel derivative
{[H2N(CH2)3SiO1.5]2NiO}n (III, 0.16% of Ni). Pre-
viously, copper chloride complexes analogous to I
and silica-immobilized polymetalorganosiloxanes
(PMOS) with phenyl, alkyl, and aminoalkyl substit-
uents on the silicon (analogous to catalysts II and III)
were examined as catalysts of C Cl and C H bond
metathesis in the systems CCl4 alkane [6 8]. These
catalytic systems are advantageous due to their stabil-
ity, high activity, and simplicity of the synthetic
procedure. Reactions with CCl4 in the presence of
such catalysts ensured preparation of chloroform and
monochloroalkanes with a selectivity of 98 99%, the
conversion of the initial alkane being 50 80%.
(1)
This reaction can be regarded as metathesis of
C H and C Br bonds in saturated compounds.
Reaction (1) in the presence of transition metal
complexes has not been studied previously. We
showed in [1] the possibility for preparation of bromo
derivatives of aromatic hydrocarbons by heating the
corresponding arenes with CBr4 for a long time at
150 180 C in the absence of a catalyst and solvent.
The yield of the products was 30 70%, but our
attempts to use CBr4 as brominating agent for alkanes
was unsuccessful. Schreiner et al. [2] reported on
the bromination of alkanes and cycloalkanes with
carbon tetrabromide in combination with sodium
hydroxide in a two-phase system in the presence of
phase-transfer catalyst [2]. However, this process is
low effective: the reaction time is as long as 90 h, and
the yield of the products does not exceed 30 70%.
Vol’pin et al. [3] used carbon tetrabromide in the
form of a catalytic complex with AlBr3 to brominate
alkanes and cycloalkanes; the complex CBr4 2AlBr3
itself can act as brominating agent in the absence of
____________
*
This study was financially supported by the Russian Founda-
tion for Basic Research (project nos. 00-03-32 211 and
00-03-32813).
1070-4280/02/3807-0962$27.00 2002 MAIK Nauka/Interperiodica

CARBON TETRABROMIDE
A NEW BROMINATING AGENT
963
Table 1. Bromination of alkanes with carbon tetrabromide
Run
no.
Molar ratio
RH: CBr4
Temperature, Yield of RBr, %
Alkane (RH)
Catalyst
Time, h
C
(with respect to CBr4)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
C12H26
C10H22
C12H26
cyclo-C6H12
C10H22
C10H22
C10H22
C12H26
C12H26
C12H26
C12H26
C12H26
C10H22
cyclo-C6H12
PhCH3
m-(CH3)2C6H4
m-(CH3)2C6H4
Adamantane
10: 1
5: 1
Iaa
Ia
Ia
2.5
8
5
10
0.5
1
2
2.5
5
180
160
180
180
150
150
150
160
150
150
130
98
150
150
150
150
150
150
67
93
95
86
62
88
10: 1
10: 1
10: 1
10: 1
10: 1
10: 1
10: 1
2.2: 1
10: 1
10: 1
10: 1
10: 1
10: 1
10: 1
10: 1
4: 1d
Ia
Iba
Ib
Ib
98
IIab
IIa
IIa
IIa
IIa
IIa
IIa
IIa
IIb
IIb
IIb
130c
68
61
55
28
60
48
99
5
10
10
5
8
1.5
1
87
2
1.5
110c
95
(all isomers)
91
19
20
21
22
23
24
Mesitylene
C12H26
cyclo-C6H12
PhCH3
PhCH3
p-(CH3)2C6H4
10: 1
10: 1
10: 1
10: 1
5: 1
IIb
IIIe
III
III
III
III
1
2.5
10
10
10
5
150
150
150
150
150
150
155c
67
160c
145c
135c
10: 1
a
b
c
d
e
Equimolar mixture of CuBr (or CuBr2)+Bu4NBr [or Bu3(PhCH2)NBr], 10 wt % relative to the reactants.
Polycopperphenylsiloxane on Silochrome, 1 g per 10 ml of solution; copper concentration in the catalyst 0.11 wt % (IIa) or 0.3%.
Yields greater than 100% arise from participation of more than one bromine atom from CBr4 molecule.
In chlorobenzene at a dilution of 1:10.
Polynickelsiloxane on Silochrome (III, 0.16% of Ni), 10 wt % relative to the reactants.
Reactions of carbon tetrabromide with alkanes
isomers while analyzing the GC MS data. We can
only state that the yields of all secondary bromo-
alkanes are comparable. For example, the bromination
of dodecane at 150 C in the presence of catalyst Ia
yields five isomeric secondary bromododecanes at
and cycloalkanes. Reactions of CBr4 with alkanes
and cycloalkanes in the presence of catalysts I III
occur in the temperature range from 150 to 180 C and
give the corresponding monobromo derivatives in
quantitative or nearly quantitative yield (calculated on a ratio of 1.3:1.2:1.0:1.4:0.9 ( 0.1); this means
the initial CBr4). No induction period is observed.
Table 1 contains the yields of the products obtained
under various conditions. The reaction is highly selec-
tive: cyclohexane gives rise exclusively to cyclohexyl
bromide; secondary bromoalkanes are formed from
that the selectivity with respect to particular isomers
ranges from 16 to 24% ( 2%), no 1-bromododecane
being formed. In the reaction with adamantane, the
bromination occurs mainly at position 1, and the ratio
of 1- and 2-bromoadamantanes at 150 C is 9.5:1.
decane and dodecane; neither 1-bromoalkanes nor Quantitative yields of bromoalkanes above 150 C are
dibromo derivatives were detected (or they were
present in trace amounts). The mass spectra of
isomeric linear secondary bromoalkanes are similar;
therefore, we failed to assign ion peaks to particular
attained in several hours; the conversion of CBr4 in
the reaction with adamantane is complete in 1.5 2 h.
At 98 130 C, the reaction rate falls down but remains
measurable (Table 1, run nos. 11 and 12). This is
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 7 2002

964
SMIRNOV et al.
a distinctive feature of the reaction under study, in
contrast to analogous processes with participation of
carbon tetrachloride, which proceed very slowly at
temperatures below 150 C. As follows from the data
in Table 1 (run nos. 9, 10, 23, and 24), initial reactant
ratio has no significant effect on the product yield.
Undoubtedly, metathesis in the presence of copper
complexes follows a radical mechanism. In keeping
with the data of [6 10] on reactions involving CCl4
and CCl3Br, the process with participation of carbon
tetrabromide may be represented by the following
scheme:
With m-xylene and ethylbenzene as examples, the
data in Table 2 illustrate how the composition of the
reaction mixture obtained in the present of catalyst
IIb changes over a period of 10 h. It is seen that the
alkylation of m-xylene becomes appreciable when
the time of contact reaches 4 h and longer, i.e., after
quantitative consumption of CBr4. Analogous pattern
was observed for toluene, p-xylene, and mesitylene.
Therefore, preparative bromination of methylbenzene
is not strongly hampered by the alkylation process due
to a large difference in the rates of these reactions.
Another situation is typical of compounds containing
more active secondary or tertiary hydrogen atoms in
the -position relative to the aromatic ring. In this
case the rate of alkylation is so high that the bromina-
tion product could not be obtained in high yield (cf.
data for ethylbenzene in Table 2). Likewise, carbon
tetrabromide reacts with cumene.
Reaction of carbon tetrabromide with butyl
chloride. Introduction of a halogen atom considerably
reduces the reactivity of substrates in the bromination
with CBr4. Under the conditions described above for
the bromination of alkanes and arylalkanes, the yield
of the bromination products of butyl chloride in the
presence of catalysts IIa and III was 28 and 22%,
respectively (150 C, 10 h). The ratio of isomeric
bromochlorobutanes almost does not depend on the
catalyst and is as follows (the yield of 4-bromo-1-
chlorobutane is assumed to be equal to unity):
(2)
(3)
(4)
Here, {Cu(I)} and {Cu(II)Br} stand for bromide
copper complexes. The mechanism of activation of
halogen derivatives by nickel complexes remains
unclear. The data of Gossage et al. [11] on related
processes with participation of CCl4 suggest that
the reaction is accompanied by change of the metal
valence [Ni(II)
Ni(III)].
On the whole, the catalytic character of the reaction
under study originates from reaction (5) which gives
the final product and simultaneously regenerates the
active form of the catalyst.
4-Br-1-Cl
1
3-Br-1-Cl
10
2-Br-1-Cl
6
1-Br-1-Cl
4
(5)
Specific features of the reactions carried out
in the presence of heterogeneous PMOS. Reactions
of carbon tetrabromide with alkanes, adamantane,
and methylbenzenes in the presence of homogeneous
catalyst I exclusively follow Eq. (1) provided that
the conversion does not exceed 50%. Presumably,
heterogeneous catalysts II and III give rise to forma-
tion of measarable amounts of hydrogen bromide
(in some cases, up to 20 50% of the initial CBr4)
and (at higher conversion) of methylene bromide. In
the reactions of active hydrocarbons (higher alkanes
and alkylbenzenes) in the presence of catalysts II and
III more than 1 mol of monobromoalkane can be
obtained from 1 mol of the initial CBr4 (runs nos. 5,
12, 14, 17, and 19 21; Table 1). This fact, as well as
the formation of CH2Br2 and 10 20% excess of the
yield of bromoalkanes over the yield of bromoform
(which was observed in some experiments carried out
with catalyst I), is explained by participation of
CHBr3 in the process. Presumably, the following
Reactions of carbon tetrabromide with aryl-
alkanes. The bromination of arylalkanes, such as
p- and m-xylenes, mesitylene, and ethylbenzene,
proceeds at a high rate, and at 150 C carbon tetra-
bromide is consumed almost completely in 1.5 h.
However, the process is accompanied by alkylation.
The role of CBr4 itself as alkylating agent may be
neglected in the first approximation (traces of tri-
bromomethyl derivatives are usually present in the
reaction mixtures), whereas the contribution of alkyla-
tion of arylalkanes with monobromoalkyl derivatives
is appreciable:
R , R = CH3, H.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 7 2002

CARBON TETRABROMIDE
A NEW BROMINATING AGENT
965
Table 2. Variation of the composition of the reaction mixture (% of the initial CBr4) in the systems CBr4 arylalkane
catalyst IIb; temperature 150 C, RH CBr4 ratio 10: 1a
Component
RH = m-Xylene
RH = Ethylbenzene
1 h
2 h
4 h
10 h
1 h
2 h
4 h
10 h
CBr4
14
86
2
99
Traces
75
0
70
82
15
12
85
55
25
Traces
11
0
8
0
Traces
17
CHBr3
RBr
87
110
90
48
29
62
R R (alkylation
product)
Traces
4.5
9.5
40
76
a
Experimental values are given. The apparent disbalance with respect to bromine is likely to result from further transformations
of the alkylation products and bromoform with formation of unidentified high-molecular-weight products.
reactions occur in the system containing CBr4 and
catalyst II or III:
80 m2/g) favors the known disproportionation of tri-
bromomethyl radicals [2] according to reaction (6):
(6)
(4a)
(3a)
Polymerization of C2Br4 is a possible way of
formation of the polymeric product. Thermal dissocia-
tion of bromine molecule could give rise to atomic
bromine and hydrogen bromide:
The contribution of reactions (4a) and (3a) rises as
the conversion of CBr4 and hence the CHBr3 :CBr4
ratio increases. As a result, at high conversions the
yield of bromoform over catalysts II and III is lower
by 30 50% than the yield of monobromoalkane.
Special experiments, in which a mixture of CBr4 with
CHBr3 was used instead of CBr4, showed that bromo-
form is in fact consumed in the presence of CBr4.
From a mixture of dodecane, CHBr3, and CBr4 at
a molar ratio of 10:3.5:1 (150 C, reaction time 1.5 h)
we obtained a mixture of secondary monobromodo-
decanes in 59% yield (calculated on the initial CBr4),
and the final RH:CHBr3 :CBr4 ratio was 9.4:3.2:0.7
instead of 9.4:3.5:0.4 expected for the process
involving no bromoform. Another proof for the
participation of CHBr3 in the reaction is that its
concentration passes through a maximum during the
process (see Table 2). In the absence of CBr4 and
brominated arylalkanes, i.e., compounds possessing
weakened C Br bonds and capable of chain initiating
according to reaction (2), bromoform reacts with
alkanes and arylalkanes very slowly. It should be
noted that CBr4 does not affect alkylation of aryl-
alkanes by their bromination products.
(7)
(8)
Reactions (6) (8) do not contribute much to the
overall yield of RBr, for an equivalent amount of
bromine atoms [and hence of molecules of the mono-
bromo derivatives; reactions (4) and (8)] is formed
by reaction (7) instead of those consumed by reac-
tion (6) on the catalyst surface.
Our results show that the reaction with carbon
tetrabromide provides an efficient and convenient
method for functionalization of alkanes and aryl-
alkanes. It is advantageous due to high conversion
of initial CBr4, high selectivity in the bromination
of alkanes, cycloalkanes, and methylbenzenes, and
no need of using hazardous and toxic reagents.
EXPERIMENTAL
Carbon tetrabromide of pure grade was thrice re-
crystallized from ethanol. Dodecane, decane, cyclo-
hexane, bromoform, and dodecyl bromide were dis-
tilled and thoroughly dried. Copper(I) bromide of
pure grade was used without additional purification.
One more specific feature of the reactions occurring
in the presence of immobilized PMOS is formation of
an unidentified polymeric product. Probably, a highly
developed surface of the heterogeneous catalyst (about
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 7 2002

966
SMIRNOV et al.
Tetrabutylammonium bromide was synthesized from
tributylamine and butyl bromide and was purified by
azeotropic drying followed by double recrystallization
71, 85, 113). The absence of 1-bromododecane among
the products unambiguously follows from the lack
of C4H8Br+ ion peak (m/z 135, 137) which is typical
from benzene. The catalytic complex was prepared of all 1-bromoalkanes [14].
from CuBr and Bu4NBr by dissolving the components
in the reaction mixture on heating to 40 50 C.
The amount of hydrogen bromide liberated during
the bromination process was determined by acid base
titration.
Oligomeric cage-like PMOS were synthesized as
described in [12, 13]. Their structure was confirmed
by the presence in their vibrational spectra of bands
REFERENCES
1
typical of Si O Si (1030 1100 cm ; II, III),
1
1
Si O Cu (950 980 cm , II), Ph Si (1130 cm ,
1. Hunter, W.H. and Edgar, D.E., J. Am. Chem. Soc.,
1
II), and NH2 groups (750, 3380 cm ; III); the elec-
1932, vol. 54, p. 2025.
tron absorption spectra of IIa and IIb contained
a characteristic absorption at 750 nm due to d d
transitions in Cu(II) ion. The silicon-to-metal ratio
in all compounds was close to 2, in keeping with
the assumed structure; found for PMOS precursor
of IIa: Cu 18.2%; Si 16.4%; C 45.3%; H 2.7%.
C12H10Si2O4Cu. Calculated: Cu 18.8%; Si 16.6%;
C 45.6%; H 3.0%; for precursor of III: Ni 19.0%;
Si 18.5%; C 24.7%; H 5.0%. C6H16N2Si2O4Ni. Cal-
culated: Ni 19.9%; Si 18.9%; C 24.4%; H 5.4%. The
silica-immobilized catalysts (silokhrom S-80) were
prepared by adsorption of PMOS from a solution in
toluene or toluene DMF with subsequent separation
by decanting, removal of the residual solvent by
evacuation, and heating of the solid catalyst at 160 C
under reduced pressure.
2. Schreiner, P.R., Lauenstein, O., Kolomitsyn, I.V.,
Nadi, S., and Fokin, A.A., Angew. Chem., Int. Ed.
Engl., 1998, vol. 37, p. 1895.
3. Vol’pin, M.E., Akhrem, I.S., and Orlinkov, A.V.,
New J. Chem., 1989, vol. 13, p. 771.
4. Akhrem, I.S., Orlinkov, A.V., Afanas’eva, L.V.,
and Vol’pin, M.E., Izv. Ross. Akad. Nauk, Ser.
Khim., 1996, p. 1208.
5. Olan, G.A., Wu An-Hsiang, and Farooq, O., J. Org.
Chem., 1989, vol. 54, p. 1463.
6. Golubeva, E.N., Kokorin, A.I., Zubareva, N.A.,
Vorontsov, P.S., and Smirnov, V.V., J. Mol.
Catal. A, 1999, vol. 146, p. 434.
7. Smirnov, V.V., Golubeva, E.N., Zagorskaya, O.V.,
Nevskaya, S.M., Levitskii, M.M., and Zuf-
man, V.Yu., Kinet. Katal., 2000, vol. 41, pp. 439
442.
Alkanes were brominated with carbon tetrabromide
in sealed ampules. An ampule was charged with
required amounts of a solution of CBr4 in alkane
with a specified concentration and components of
complex I (2 mol % with respect to the hydrocarbon)
or heterogeneous catalyst (1 g per 10 ml of the reac-
tion solution). The mixture was deoxygenated by
repeated freezing evacuation (to a residual pressure
8. Smirnov, V.V., Levitskii, M.M., Tarkhanova, I.G.,
Kokorin, A.I., and Lanin, S.N., Kinet. Katal., 2001,
vol. 42, p. 737.
9. Russel, G.A., Deboel, C., and Desmond, K.M.,
J. Am. Chem. Soc., 1963, vol. 85, p. 365.
10. Tadder, M. and Watson, R.A., Trans. Faraday. Soc.,
3
1966, vol. 62, p. 1215.
of 10 mm) heating procedures. The ampule was
then sealed and kept at a constant temperature as long
as necessary. The thermostat was equipped with
a setup for rotating an ampule at a variable rate in
various directions. Samples were analyzed by GLC.
Isomeric composition of the bromination products
(with dodecane as an example) was determined by gas
chromatography mass spectrometry using a Finnigan
MAT-212 instrument coupled with a Varian 3740
chromatograph. The mass spectra of monobromo-
dodecanes characteristically contained peak of the
[M Br]+ ion formed by elimination of bromine from
the molecular ion (m/z 169) and a set of ion peaks
typical of fragmentation of alkyl chain (m/z 43, 57,
11. Gossage, R.A., van de Kuil, L.A., and van Koten, G.,
Acc. Chem. Res., 1998, vol. 31, p. 423.
12. Zhdanov, A.A. and Levitskii, M.M., Uspekhi v
oblasti sinteza elementoorganicheskikh polimerov
(Advances in the Field of Synthesis of Organometal-
lic Polymers), Korshak, V.V., Ed., Moscow: Nauka,
1988, pp. 143 231.
13. Igonin, V.A., Shchegolikhina, O.I., Lindeman, S.V.,
Levitsky, M.M., Struchkov, Yu.T., and Zhda-
nov, A.A., J. Organomet. Chem., 1992, vol. 423,
p. 351.
14. NIST/EPA/NIH Mass Spectral Database. Version 4.5,
02.1994.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 7 2002