Highly efficient amination of benzene to aniline mediated by bromine with metal oxide as cataloreactant

Article abstract of DOI:10.1246/cl.2006.1358

We report a highly efficient and versatile two-step process for the amination of benzene to aniline that is mediated by bromine and metal oxides as cataloreactants. The process under mild condition (e.g. below 200°C) offers an overall yield of ca. 90% and selectivity of ca. 95% for aniline production based on benzene converted. Copyright

Full text of DOI:10.1246/cl.2006.1358

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358
Chemistry Letters Vol.35, No.12 (2006)
Highly Efficient Amination of Benzene to Aniline Mediated by Bromine
with Metal Oxide as Cataloreactant
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Hesheng Zhai, Haiqiang Lin, Xin Lu, and Xing-Hua Xia
Nano-Science & Technology Center, Xiamen University, Xiamen 361005, P. R. China
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College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China
(Received August 4, 2006; CL-060888; E-mail: xhxia@nju.edu.cn)
We report a highly efficient and versatile two-step process
for the amination of benzene to aniline that is mediated by bro-
mine and metal oxides as cataloreactants. The process under
mild condition (e.g. below 200 C) offers an overall yield of
ca. 90% and selectivity of ca. 95% for aniline production based
on benzene converted.
no loss of bromine and metal oxide in this step. The second step
is the ammonolysis of bromobenzene over a metal oxide catalo-
reactant. In addition to the production of aniline, ammonia-coor-
dinated metal bromide compound is produced, which releases
ammonia upon heating. Oxidation of the metal bromide gives
rise to Br2 with regeneration of the metal oxide cataloreactant.
So in a cycle, only the raw materials such as ammonia and ben-
zene are consumed, whereas bromine and the metal oxide cata-
loreactants can be recycled with ideally no loss. This is certainly
superior to the Dow process in which the reaction intermediate
of copper chloride is not easy for recycle.
ꢀ
Aniline (C6H5NH2) is an important intermediate for the syn-
thesis of many commodity chemicals in pharmaceutical and
chemical industries. Industrially, aniline has mainly been pro-
duced by reduction of nitrobenzene (C6H5NO2) in the presence
of Fe/HCl or fixed bed hydrogenation over a nickel sulfide cat-
The bromination of benzene catalyzed by metal (e.g. Fe or
FeBr3) has been well documented. However, in our experiments,
we have tested two types of catalysts, i.e., Fe powders and ZrO2.
Gas chromatography analyses of the liquid-phase products from
1
alyst. However, such industrial processes suffer drawbacks in-
cluding high cost of raw materials and difficulty in recycling
of catalysts. Alternative to this is the ammonolysis of phenol
4
reaction of bromine with excessive benzene catalyzed by Fe
powder show that bromobenzene is produced with a yield of
(
neous catalysts. For example, the amination of phenol over
C6H5OH) and chlorobenzene (C6H5Cl) using suitable heteroge-
2
ca. 97% and selectivity of >97% based on benzene converted.
5
2
c,2d
modified alumina catalysts has been applied to practical use,
For the bromination catalyzed by ZrO2 (pretreated by sulfuric
but its cost is higher than that of the reduction of nitrobenzene. In
addition to these industrial processes that convert derivatives of
benzene into aniline, direct amination of benzene to aniline also
acid), a selectivity of >95% and yield of >95% are obtained
for the production of bromobenzene based on benzene con-
sumed.
3
has been attempted. These processes displayed either too low
The ammonolysis of bromobenzene was performed in a
stainless steel autoclave with the use of CuO/TiO2 mixture as
conversion of benzene or too low selectivity to aniline to be at-
tractive targets for commercialization. Here, we report a highly
efficient and versatile two-step process for the amination of ben-
zene to aniline that is mediated by bromine and metal oxide cat-
aloreactants. The cataloreactants can be readily regenerated
upon oxidation of the used ones with no loss of cataloreactivity.
Our synthetic approach is schematically shown in Figure 1.
The first step is the bromination of benzene, which produces bro-
mobenzene (C6H5Br) and HBr. HBr can be collected with metal
oxide or metal hydroxide; further oxidation of the solid mixture
gives rise to Br2 and metal oxide with yields >99%. So there is
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cataloreactants. Table 1 lists the conversion of bromobenzene
and selectivity of aniline in the reactions of bromobenzene with
liquid ammonia over pristine CuO/TiO2 cataloreactant under
different conditions. Under an optimized condition, we obtained
a bromobenzene conversion of 97.6% and a selectivity of ca.
95% to aniline, in addition to little amount of benzene (by-prod-
uct). This corresponds to a yield of ca. 90% for aniline produc-
tion relative to benzene consumed, indicating that the two-step
process concerned is highly efficient for synthesis of aniline
from benzene. It is also noteworthy that the ammonolysis of
bromobenzene can be completed within 5 h under a much mild
Table 1. Margin specifications
Quantity Quantity Quantity
Ta of catalo- of bromo-
Conversion
of bromo-
benzene
/%
Estimated
Pressureb
Selectivity
of aniline
/%
of
beneze ammonia
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/
C
reactant
/atm
/g
/mL
/mL
1
2
1
2
80c
00d
80d
00d
13
11
13
11
10
10
10
10
20
20
20
10
65–80
70–80
57–75
34–37
97.6
87.0
87.4
62.0
94.7
92.0
90.0
69.3
aThe reactions were carried out at the specified temperature for 4 h. bIn
closed autoclaves, the pressure increases automatically to the estimated
range upon heating and gasification of the reactants. cReaction in an auto-
Figure 1. Mechanism for the animation of benzene to aniline
mediated by bromine and metal oxide cataloreactants.
d
clave with a Teflon inner wall. Reaction in a stainless steel autoclave.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.12 (2006)
1359
Table 2. Conversion and product selectivities in the amination
of bromobenzene over pristine and regenerated CuO/TiO2 cata-
loreactants
benzene that can be recycled for the synthesis of bromobenzene.
It should be emphasized that the two-step process for the
synthesis of aniline could be versatile for the production of de-
rivatives of aniline. This target could be readily approached by
using various derivatives of benzene, e.g., toluene (C6H5CH3),
instead of benzene in the first step or using various primary or
secondary amines, e.g., methylamine and dimethylamine,
instead of ammonia in the second step. The high efficiency,
simplicity, and versatility of such a two-step process for the
production of aniline (or its derivatives) from benzene (or its
derivatives) offer its readiness and overwhelming attractiveness
for commercialization.
Conversion of
bromobenzene
Selectivity of
aniline
Cycle No.
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2
3
4
5
6
7
99%
100%
99%
92%
90%
92%
91%
92%
91%
93%
100%
100%
100%
100%
References and Notes
1
K. Weissermei, H. J. Arpe, Industrial Organic Chemistry,
VCH Publishers, 1993, Chap. 13.
2
a) C. D. Chang, P. D. Perkins, Zeolites 1983, 3, 298. b) D. G.
Jones, U.S. Patent 3231616, 1966. c) M. Yashuhara, F.
Matsunaga, Mitsui Petrochemical Industries Ltd., Eur. Pat.
Int. 321 275 A2, 1989. d) A. A. Shutz, L. A. Cullo, Aristech
Chemical Corp., PCT Pat. WO 9305010A1, 1993. e) N.
Katada, S. Kuroda, M. Niwa, Appl. Catal., A 1999, 180, L1.
a) J. P. Wibaut, Berichte 1917, 50, 541. b) Thomas, et al.,
Canadian Patent 553 988, 1958. c) L. Schmerling, U.S. Patent
Figure 2. Mechanism for the hydrolysis of bromobenzene to
phenol mediated by metal oxide cataloreactants.
3
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condition, i.e., at a temperature of ca. 190 C, meaning that the
energy cost is moderate.
2
,948,755, 1960. d) J. Becker, W. F. H o¨ lderich, Catal. Lett.
1998, 54, 125. e) W. F. H o¨ lderich, et al., German Pat. Appl.
DE 19634110 A1, 1998. f) S. A. Axon, PCT Int. Appl. WO
9
0
D. M. Lowe, C. Lugmair, D. M. Poojary, H. Turner, H.
Weinberg, X. Zhou, R. Armbrust, G. Fengler, U. Notheis,
Catal. Today 2003, 81, 319. i) N. Hoffmanh, M. Muhler,
Cataly. Lett. 2005, 103, 155.
In addition to liquid ammonia, (NH4)2CO3 or aqueous
ammonia can also be used as amino-source for the amination
of bromobenzene with comparable bromobenzene conversion
9/10311, 1999. g) H. E. Stitt, PCT Int. Appl. WO 00/
9473, 2000. h) P. Desrosiers, S. Guan, A. Hagemeyer,
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and aniline selectivity, e.g., in the amination of bromobenzene
that uses aqueous ammonia as amino-source and pure CuO as
cataloreactant, the yield and selectivity to aniline was >95%
at a bromobenzene conversion of 100%. Little amount of
benzene and phenol were found as by-products.
In catalytic reactions that make use of cataloreactants, of
practical important is the regeneration of cataloreactant. This
is not problem in the present case. Heating the final products
of the ammonolysis of bromobenzene, we obtain separately,
ammonia both unreacted and released from the ammonia-coordi-
nated metal bromide, unreacted bromobenzene, benzene,
aniline, and solid residue. The solid residue is definitely solid
metal bromide. Upon oxidation of the solid residue in a muffle
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Typical reaction was carried out in 20 mL of benzene mixed
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with 0.5 g of Fe powder and 4 mL of Br at 60 C for 4 h.
2
Typical reaction was carried out in 20 mL of benzene mixed
with 0.5 g of ZrO2 (pretreated with sulfuric acid) and 4 mL
of Br2 at 105 C for 4 h.
The CuO/TiO2 cataloreactant was prepared as follows. 75.6 g
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of oxalic acid was dissolved in 300 mL of water. The solution
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was heated to 60 C with slow addition of 68 mL of
Ti(OC4H9)4. A transparent solution (designated as Ti-sol)
was obtained and diluted to 400 mL with water. In a separate
flask, 40 mL of polyacrylic acid (30%) solution was mixed
with ca. 20 mL of Cu(NO3)2 solution (12 g of Cu(NO3)2.
H2O + 20 mL of water). Upon addition of 100 mL of Ti-sol
into the mixture, an aqua-colored colloid was obtained and
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at 350 C for several hours, we obtained Br2 and the metal oxide
mixture with the yields larger than 99%. Br2 thus obtained can
be reused for the production of bromobenzene, whereas the re-
generated metal oxide mixture can be reused in the ammonolysis
of bromobenzene. The cataloreactivity of the as-regenerated cat-
aloreactants in a long run has been examined and compared with
that of the pristine cataloreactant. Table 2 gives the conversions
of bromobenzene and selectivities of anilines in a series of
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heated at 110 C for 5 h. The colloid was dried and calcinated
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at 500 C for several hours, giving rise to a dry, sage green
solid of CuO/TiO2.
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Typical reaction in an autoclave (100 mL) with a Teflon inner
wall was carried out using 5 mL of bromobenzene, 5 mL of
aqueous ammonia (20% NH3) and 6 g of CuO at 190 C for
3 h. The estimated pressure in the autoclave is ca. 17 atm dur-
ing the reaction.
Reactions were carried out at 210 C for 4 h in stainless steel
autoclaves (2.5 mL) fed with 0.45 g of (NH4)2CO3, 0.25 mL
of bromobenzene, and 0.25 g of pristine or regenerated CuO/
TiO2.
Typical reaction was carried out at 240 C for 4 h in a stainless
steel autoclave (2.5 mL) fed with 1.0 mL of water, 0.3 mL of
bromobenzene, and 0.5 g of pristine CuO/TiO2.
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reactions over the pristine and regenerated cataloreactants. It
is clear from Table 2 that even after 7 cycles the regenerated
cataloreactant displayed slightly higher cataloreactivity than that
of the pristine cataloreactant. Hence, we believe the CuO/TiO2
cataloreactant will keep its cataloreactivity in a long run.
The two-step process shown in Figure 1 can be extended for
the synthesis of phenol, another important commodity chemical
in industry, by simply modifying the second step, as shown in
Figure 2. Using water rather than ammonia, we found that the
hydrolysis of bromobenzene affords a phenol yield of ca. 17%
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at a bromobenzene conversion of ca. 33%. The by-product is
Published on the web (Advance View) November 4, 2006; doi:10.1246/cl.2006.1358