Asian Journal of Chemistry; Vol. 27, No. 6 (2015), 2341-2342
A
SIAN
J
OURNAL OF HEMISTRY
C
NOTE
Regioselective Catalyzed Nitration of Toluene by Zeolites
1,*
XIONGZI DONG1,2 and XINHUA PENG
1School of Chemical Engineering, Hefei University of Technology, Hefei 230009, P.R. China
2School of Chemistry and Chemical Engineering, Hefei Normal University, Hefei 230601, P.R. China
*Corresponding author: Tel/Fax: +86 551 62901468; E-mail: orgpeng@163.com
Received: 26 March 2014;
Accepted: 27 May 2014;
Published online: 17 March 2015;
AJC-17025
The nitration of toluene with nitric acid and nitrogen dioxide as nitration agent was studied. The effect of zeolite catalysts was also
discussed. By using zeolite as catalysis, the yield of nitro-toluene was improved with nitric acid as nitration agent. The conversion of
toluene and yield of nitro-toluene were both greatly enhanced with nitrogen dioxide as nitration agent.
Keywords: Nitration, Toluene, Nitric acid, Nitrogen dioxide, Zeolite.
The nitration of aromatic compounds is an important
process in both industrial and academic research for the widely
uses of nitro-arene as pharmaceuticals, dyes, explosives and
plastics1. Conventional nitration processes are carried out by
employing a mixture of nitric acid and sulfuric acid, which
have the major defects such as corrosion, over-nitration, oxida-
tion and poor selectivity2.
To overcome these problems, many researchers have
reported their findings in nitration of arene. The gained signifi-
cant progresses are mainly focused on the selection of nitrifying
agents and catalysts. Liquid nitrogen dioxide3 and nitric acid
with anhydride4 were used to nitrify a series of aromatic com-
pounds and good yield was obtained. Better selectivity was
obtained when the nitration was catalyzed with ionic liquids5
and zeolites6.
Nitration of toluene with nitric acid: Dichloromethane
(5 mL), zeolite (0.1 g) and toluene (0.319 mL, 3 mmol) were
added in a round-bottomed flask under stirring at 0 °C. Then
nitric acid (95 %, 0.660 mL, 15 mmol ) was added dropwise.
The mixture was stirred for 12 h. The organic layers was
washed with water ( 10 mL × 2 ), NaHCO3 solution ( 10 %,
10 mL) and water (10 mL × 2), dried with MgSO4. A certain
amount of p-nitro-chlorobenzene was added as internal stan-
dard. Then the solution was analyzed by gas chromatography.
Nitration of toluene with nitrogen dioxide: Dichloro-
methane (5 mL), zeolite (0.1 g, calcined in air at 550 °C for
2 h) and toluene (0.319 mL, 3 mmol) were added in a round-
bottomed flask under stirring at 0 °C. Then a certain amount
of liquid nitrogen dioxide was added dropwise. The mixture
was stirred for 12 h under an oxygen almosphere. The organic
layers was washed with water (10 mL × 2), NaHCO3 solution
(10 %, 10 mL) and water (10 mL × 2), dried with MgSO4. A
certain amount of p-nitro-chlorobenzene was added as internal
standard. Then the solution was analyzed by gas chromato-
graphy.
Generally, the nitration reaction occurs with an inter-
mediate nitronium ion. The presence of sulfuric acid can
greatly strengthen the nitric acid dissociation process to form
nitronium ion. However, the strongly corrosive spent acid can
pollute the environment. To avoid the use of sulfuric acid, we
carried the nitration of toluene with 1 equivalent nitric acid.
However, poor conversion and yield were obtained (Table-1,
entry 1). To enhance the conversion and yield, we increased
the amount of nitric acid. The results are listed in Table-1.
With the increasing amount of nitric acid, the conversion
of toluene increased. When 15 mmol nitric acid was used, the
maximum conversion 100 % and yield 80.4 % were obtained.
For some consumption of toluene occurred double nitration
and dinitro-toluene was produced, the yield of nitro-toluene
was decreased to 72.1 % with the further increasing of nitric
acid to 24 mmol. So the 15 mmol nitric acid was used in the
sequence reaction.
Zeolites are attractive catalysts which were widely used
in catalysis reaction. Some progresses in catalyzed nitration
with zeolites have been reported7,8. To enhance the yield of
nitro-toluene, a series of zeolites were used to catalyze nitration
of toluene. The reaction without zeolite was carried for compa-
rison. The results are listed in Table-2.