One-step synthesis of tolunitriles by heterogeneously catalyzed liquid-phase ammoxidation

Article abstract of DOI:10.1080/00397910500278214

Tolunitriles have been efficiently synthesized by selective ammoxidation of corresponding xylene over silica-supported Co-Mn-Mg-Ni catalysts, without solvent for the first time in a one-pot procedure. The selectivity for mono-nitriles is almost 100%. Copyright Taylor & Francis, Inc.

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One‐Step Synthesis of
Tolunitriles by Heterogeneously
Catalyzed Liquid‐Phase
Ammoxidation
Yuan Liu a , Min Zhong a , Wei Yu a & Yu‐Long Ma a
a Department of Chemistry , Wuhan University ,
Wuhan, China
Published online: 21 Aug 2006.
To cite this article: Yuan Liu , Min Zhong , Wei Yu & Yu‐Long Ma (2005) One‐Step
Synthesis of Tolunitriles by Heterogeneously Catalyzed Liquid‐Phase Ammoxidation,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 35:23, 2951-2954
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Synthetic Communicationsw, 35: 2951–2954, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500278214
One-Step Synthesis of Tolunitriles
by Heterogeneously Catalyzed
Liquid-Phase Ammoxidation
Yuan Liu, Min Zhong, Wei Yu, and Yu-Long Ma
Department of Chemistry, Wuhan University, Wuhan, China
Abstract: Tolunitriles have been efficiently synthesized by selective ammoxidation of
corresponding xylene over silica-supported Co-Mn-Mg-Ni catalysts, without solvent
for the first time in a one-pot procedure. The selectivity for mono-nitriles is almost
100%.
Keywords: Ammoxidation, liquid-phase ammoxidation, tolunitrile, xylene
INTRODUCTION
Mononitriles are of widespread use in fine chemical production. They can be
converted into commercially interesting and valuable intermediates for the
synthesis of pharmaceuticals, plastics, resins, fibers, dyestuffs, and so on.[1,2]
Traditionally, tolunitrile was mainly synthesized from diazotization of
methylbenzamine,[3] catalysis of benzoate ions in the presence of
ammonia,[4] dehydration of methylbenzamide[5] or aldoxime,[6] and
cyanation of aryl chloride[7] or toluic acid.[8] These methods usually employ
expensive feedstock or cause serious pollution and are not suitable for
large-scale production. The vapor-phase ammoxidation of xylenes based on
vanadium-containing catalysts has considerable importance as the commercial
method for producing tolunitrile and dicyanobenzenes.[9,10] However, the
temperature is usually greater than 673 K, and the yield and selectivity for
tolunitriles are very low, because two methyl groups in xylene are identical.
Address correspondence to Yu-Long Ma, Department of Chemistry, Wuhan
University, Wuhan 430072, China.
2951

2952
Y. Liu et al.
Scheme 1. One-step synthesis of tolunitriles.
Another method for the synthesis of tolunitriles is the selective ammoxidation
of methylbenzyl chlorides.[11] However, the drawbacks of this process are the
use of a large amount of chlorine and the generation of large amounts of
poisonous effluents.
To the best of our knowledge, there are no reports about heterogeneously
catalysed ammoxidation of xylene to tolunitrile. By comparison, cobalt oxides
possess an extremely high oxidative reactivity, and manganese and
magnesium oxides have a lower, although still high, activation ability in the
liquid-phase ammoxidation. After being used five times, the catalyst still
demonstrates good activity. The main by-products of this reaction are tolu-
aldehyde and toluic acid, and their content increases with the time. Taking
into account the optimal selectivity, we choose 5 h as the reaction time.
In conclusion, we have showed an efficient synthesis of mono-nitriles
from xylene (Scheme 1).The mild reaction conditions coupled with high selec-
tivity makes this methodology a valuable tool to generate tolunitrile. The
absence of solvent and the recyclability of the catalyst make this an environ-
mentally friendly methodology amenable to scaling.
The position of the second substituent (methyl) on the toluene molecule
greatly influenced the yield and the selectivity of the reactivity under compar-
able conditions. As shown in Table 1, the 4-isomer revealed the highest con-
version and selectivity to the desired nitrile, whereas the data significantly
declined for the 3- and 2-isomers (4 . 3 . 2). This row mirrors the
different accessibility and reactivity depending on the position of the substitu-
ent methyl. It may be attributed to an electronic effect on the aromatic ring
Table 1. Result of liquid-phase ammoxidation of xylene
Metal
weight Selectivity Yield
Isomer
Catalyst
Molar ratio
(wt%)
(%)
(%)
o-
Co/Mn/Mg/Ni 1 : 0.946 : 1.188 : 0.056
Co/Mn/Mg/Ni 1 : 1.397 : 1.527 : 0.016
Co/Mn/Mg/Ni 1 : 1.012 : 1.224 : 0.081
6.9
9.3
9.9
99.6
99.3
99.7
14.0
18.3
28.7
m-
p-

One-Step Tolunitrile Synthesis
2953
related to the addition of Me groups, although steric hindrance also appeared
to be responsible for the consistently low rates of o-xylene ammoxi-
dation.[12,13] We also prepared p-tertbutyl benzonitrile by p-tertbutyl toluene
under the same conditions.[14] In the case of p-tertbutyl toluene, a
35.92 mol% conversion with 99.8 mol% selectivity to p-tertbutyl benzonitrile
was obtained, which exhibits higher activity and selectivity than xylene.
Possibly due to the electron effect, tertbutyl is more electron-donating
compared with methyl group, thus stimulating H-extraction of methyl,
which is the control step of the reaction.[15]
EXPERIMENTAL
Xylenes and reagents from which catalysts were prepared were analytically or
chemically pure. Products were characterized by 1H NMR and IR spectra. The
IR spectrum was recorded on an Avatar 360 infrared spectrophotometer. The
1
1H NMR spectra were measured on a Varian Mercury VX-300 H NMR
spectra with (CH3)4Si as internal standard. The purity of products was
tested with a 102G gas chromatograph.
Catalyst Preparation
The catalyst was prepared by using a commercially available silica (grain
diameter 125–425 mm) as support. The support was impregnated with an
aqueous solution of mixed cobalt, manganese acetates, magnesium, and nickel
chloride. The mole ratio of metal salts and their wt% on silica were demonstrated
in Table 1. After being impregnated, the mixture was first calcined 2 h at 573 K
and then 5 h at 773 K in a muffle to afford the oxides. Compared to the three-
component catalyst we reported before,[15] the catalyst composed of
magnesium chloride performed a more efficient catalytic activity.
Preparation of Tolunitrile by Liquid Ammoxidation
The catalytic ammoxidation reactions were carried out in an 300-ml autoclave
that was equipped with a magnetic-type stirrer (Dalian Instrument, China). In
the typical experiment, xylene (150 g) and catalyst (1.0 g) were added, and the
mixture was stirred at a constant speed of 500 rpm. After the mixture was
heated to 363 K, the oxygen and ammonia were injected into the reactor
and the reaction pressure was maintained at 0.5 MPa. The ratio of oxygen
and ammonia was modulated to 5 : 1 by rotor flowmeter. The reaction was ter-
minated by charging the cool water through the cooling coil inside. When the
reaction was finished, the catalyst was filtered and the residue mixture was
distilled under the condition of decompression. Product samples were

2954
Y. Liu et al.
collected and analyzed by gas chromatography (Shanghai 102G gas chromato-
graph). Only a trace amount of tolualdehyde was detected, because when
tolualdehyde was contacted with ammonia on the surface of catalyst, the cor-
responding tolunitrile was produced.
Now, a detailed investigation is under way to prepare the optimized
catalyst and to increase the yield of tolunitrile.
Spectral Data of the Products
Benzonitrile, 4-methyl-: FT-IR gmax (KBr, cm21): 2229, 1609, 1509, 1178,
1
817, 64; H NMR dH (CDCl3, 300 MHz): 7.23–7.47 (m, 4H, PhH), 2.41
(S, 3H, CH3).
Benzonitrile, 3-methyl-: FT-IR gmax (KBr, cm21): 2230, 1585, 1485, 789,
667; 1H NMR dH (CDCl3, 300 MHz): 7.34–7.47 (m, 4H, PhH), 2.39 (S, 3H,
CH3).
Benzonitrile, 2-methyl-: FT-IR gmax (KBr, cm21): 2226, 1487, 761, 712,
469; 1H NMR dH (CDCl3, 300 MHz): 7.26–7.53 (m, 4H, PhH), 2.54 (S, 3H,
CH3).
ACKNOWLEDGMENTS
Financial support from the National Natural Science Foundation of China
(Project 20376064) is gratefully acknowledged.
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