Novel and efficient hydrogenative cleavage of azo compounds to amine(s) using chitosan-supported formate and magnesium

Article abstract of DOI:10.1080/00397911.2013.835826

A convenient and efficient method for the hydrogenative cleavage of azo compounds to corresponding amine (s) using chitosan-supported formate as hydrogen donor in conjunction with low-cost magnesium powder is reported. This method was found to be highly facile with selectivity over several other functional groups, such as halogen, alkene, nitrile, carbonyl, ether, amide, methoxy, and hydroxyl groups. Furthermore, this mild, exceedingly efficient, and highly chemoselective method simplifies the handling and separation procedures. Copyright

Full text of DOI:10.1080/00397911.2013.835826

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Novel and Efficient Hydrogenative
Cleavage of Azo Compounds to Amine(s)
Using Chitosan-Supported Formate and
Magnesium
a b
a
a b
a
X. H. Yu
, X. J. Ma , S. P. Jin
& Y. Z. Zhen
a
College of Chemistry and Chemical Engineering, Hexi University ,
Zhangye , China
b
Key Laboratory of Hexi Corridor Resource Utilization of Gansu
Universities , Zhangye , China
Accepted author version posted online: 28 Oct 2013.Published
online: 27 Dec 2013.
To cite this article: X. H. Yu , X. J. Ma , S. P. Jin & Y. Z. Zhen (2014) Novel and Efficient
Hydrogenative Cleavage of Azo Compounds to Amine(s) Using Chitosan-Supported Formate and
Magnesium, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 44:5, 707-713, DOI: 10.1080/00397911.2013.835826
To link to this article: http://dx.doi.org/10.1080/00397911.2013.835826
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1
Synthetic Communications , 44: 707–713, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.835826
NOVEL AND EFFICIENT HYDROGENATIVE CLEAVAGE
OF AZO COMPOUNDS TO AMINE(S) USING
CHITOSAN-SUPPORTED FORMATE AND MAGNESIUM
1
,2
1
X. H. Yu, X. J. Ma, S. P. Jin, and Y. Z. Zhen
1,2
1
1
College of Chemistry and Chemical Engineering, Hexi University,
Zhangye, China
2
Key Laboratory of Hexi Corridor Resource Utilization of Gansu
Universities, Zhangye, China
GRAPHICAL ABSTRACT
Abstract A convenient and efficient method for the hydrogenative cleavage of azo com-
pounds to corresponding amine (s) using chitosan-supported formate as hydrogen donor
in conjunction with low-cost magnesium powder is reported. This method was found to be
highly facile with selectivity over several other functional groups, such as halogen, alkene,
nitrile, carbonyl, ether, amide, methoxy, and hydroxyl groups. Furthermore, this mild,
exceedingly efficient, and highly chemoselective method simplifies the handling and
separation procedures.
Keywords Azo compounds; catalytic transfer hydrogenation; chitosan-supported
formate; magnesium
INTRODUCTION
The reduction of azo compounds to the corresponding amine(s) is a useful
transformation both in the laboratory and in industry because of the fact that aro-
matic amines were essential intermediates for the synthesis of dyes, pharmaceuticals,
[1,2]
and agricultural chemicals.
Catalytic transfer hydrogenation (CTH) using
hydrogen donors is considered to be more safe, cost-effective, selective, rapid, and
environmentally friendly than other methods available for the reduction of azo
[
3–5]
compounds.
compared to other hydrogen donors.
Ammonium formate was found to be more convenient and efficient
However, ammonium formate itself did have
[6,7]
some limitations. This reagent could sublime and block the reaction apparatus, and
it released the gaseous by-products (ammonia and carbon dioxide) through the
Received March 28, 2013.
Address correspondence to X. H. Yu, College of Chemistry and Chemical Engineering, Hexi
University, Zhangye 734000, China. E-mail: yuxinghai455@163.com
7
07

708
X. H. YU ET AL.
Scheme 1. Hydrogenative cleavage of azo compounds using CSF and magnesium in methanol.
decomposition. It gave deposits on the cold surfaces of the reactor lines, which could
create significant problems when performed on a large scale. In addition, the use of
ammonium formate as hydrogen donor often posed complications during isolation
and purification of water-soluble products. For this reason, immobilized formate
on polymeric supports has been developed to solve the problems and offer advantages
over the conventional solution-phase reactions in terms of clean and green processes.
In the past few years, several strategies have been reported to employ the
[
8–10]
polymer-supported formate as hydrogen donors in CTH.
However, most of these
cases have been performed using synthetic polymers, which are unfriendly to the
environment and rather complicated to prepare. Consequently, the development of
biodegradable, nontoxic, and readily and cheaply available catalyst is highly desired.
Chitosan, an abundant and renewable natural polymer, has unique properties
[
11,12]
such as biocompatibility, biodegradability, and nontoxicity.
Recently chitosan
and its derivatives have attracted much attention as polymeric supports in various
fields, especially the supported catalysis that deals with oxidation and reductive
[13–16]
hydrogenation reactions.
In view of the rapid development of chitosan-
supported chemistry over the past few years, papers have very rarely reported
employing the chitosan-supported formate as hydrogen donor in CTH. In this work,
we prepared highly porous chitosan resins used epichlorohydrin (ECH) as
cross-linking agent by reaction with the hydroxyl groups while retaining the amine
groups of chitosan. This prevents the dissolution of CTS in acid and chemicals.
When the cross-linked chitosan resins were treated with a formic acid solution, the
chitosan-supported formate (CSF) were obtained. Our investigations revealed that
the utilization of the CSF as hydrogen donor in conjunction with magnesium to
cleave the azo derivatives into the corresponding amine(s) was cost-effective, rapid,
and simple (Scheme 1).
RESULTS AND DISCUSSION
A series of structurally varied azo compounds underwent reduction by this
methodology and the results are summarized in Table 1.
The reactions were rapid (8–20 min) and high yielding (86–95%) and selectively
reduced azo compounds to the corresponding amine(s). The sensitive functional
groups, such as halogen (Table 1, entries 8 and 9), alkene (Table 1, entry 10), nitrile

HYDROGENATIVE CLEAVAGE OF AZO COMPOUNDS
709
Table 1. Reduction of azo compounds by CSF and magnesium
ꢀ
Melting point ( C)
ꢀ
a
Temp ( C)=
time (min)
Yields
(%)
Entry
Found
Literature
0
b
[18]
[18]
[18]
[19]
[18]
[17]
[18]
[18]
[17]
[18]
[18]
[19]
[18]
1
2
3
4
5
6
7
8
9
R=H, R =H
25=10
25=10
25=12
65=20
25=18
25=12
25=13
25=20
25=15
25=12
25=14
25=17
25=18
94
95
91
89
90
95
92
86
87
92
90
88
90
112
114
125
144
233
57
0
0
0
0
c
c
R=3-CH
R=2-CH
, R =3 -CH
, R =2 -CH
124–125
142–143
3
3
3
3
0
0
d
R=2-C(CH3) 3, R =2 -C(CH3) 3
0 0
R=4-OCH , R =4 -OCH
3 3
R=4-OH, R =4 -OH
R=4-CONH
R=2-Br, R =2 -Br
R=4-Cl, R =4 -Cl
R=4-vinyl, R =4 -vinyl
R=4-CHO, R =4 -CHO
231–232
58–59
0
0
189–191
181
189
183
30
0
0
, R =4 -CONH
2
2
0
0
0
0
28–30
71
72
0
0
d
1
1
1
1
0
1
2
3
242
249
71
0
0
70–71
84–85
98–99
0
0
R=4-CN, R =4 -CN
R=3-COCH
86
0
0
, R =3 -COCH
99
3
3
a
b
c
Yields refer to pure isolated products.
Isolated as acetyl derivative.
Isolated as benzoyl derivative.
d
Boiling point.
(Table 1, entry 12), and carbonyl (Table 1, entries 11 and 13), remained unaffected
under this transfer hydrogenation condition. In addition, many other functional
groups such as amide, methoxy, acid, ether, and hydroxyl are also compatible with
the present system. It is worth noting that we discovered the reactions were sensitive
to the steric and electronic effects of the substituents. The little-substituted azo
compounds were easily reductive to the corresponding amine(s). While the more
sterically azo compounds have been inefficient, good conversion has been obtained
at reflux temperature with longer reaction times (Table 1, entry 4). The results
also revealed that electron-donating groups facilitate the reactions and
electron-withdrawing groups enhance the extent of reaction period.
To obtain optimum reduction conditions, a wide range of solvents were carried
out. Methanol is found to be the best one as far as the solubility of substrate and rate
of reaction is concerned. Furthermore, we observed 3–4 equivalents of CSF and 1–2
equivalents of magnesium were ideal for reduction at room temperature. A control
experiment was carried out using azo compounds with CSF but without magnesium
powder. Remarkably, we found the substrate was unconverted throughout the
experiment, and nothing of reductive products was obtained. This clearly indicates
that magnesium is essential to carry out the reduction.
The separation of products from the reaction mixture is simple and involves, in
most of the reactions, direct removal of the catalyst and resin by filtration and evap-
oration of the solvent under vacuum. The crude product, so isolated, was of excellent
purity for most purposes. Hence, this procedure is highly advantageous to obtain
water-soluble aromatic amines in good yields.
In conclusion, we developed a novel, convenient, and efficient method for the
hydrogenative cleavage of azo compounds using CSF and low-cost magnesium

710
X. H. YU ET AL.
powder. This CTH method combines the advantages of polymer-supported chemistry
with the flexibility of CTH technique, such as cost-effectiveness way, safe reaction
medium, rapidity, and ease of operation. In addition, the use of CSF as hydrogen
source is chemoselectivity to sensitive functional groups and highly helpful to obtain
aromatic amine in pure form with no workup. Further investigations on other useful
applications of this chitosan-supported formate to many other reductive functional
group transformations are in progress and will be the subject of future reports.
EXPERIMENTAL
Chitosan with a deacetylation percentage of approximately 99% was a product
of Shanghai Fuqiang Biochemical Co. Ltd. (China) and was purified before use by
dissolving and precipitating it several times, extracting in Soxhlet apparatus in acet-
ꢀ
one for 24 h, and drying at 40 C under vacuum. Epichlorohydrin and formic acid
were obtained from Shanghai Chemical Ltd. (China). Magnesium powder was pur-
chased from Beijing Chemical Ltd. (China). The other substances were either com-
mercial products used as purchased or were prepared according to literature
procedures. All of the solvents used were analytical grade and purified according
to standard procedures. Thin-layer chromatography (TLC) was carried out on
silica-gel plates obtained from Shanghai Chemical Ltd. (China). The melting points
were determined by using a TX-4 melting-point apparatus and are uncorrected.
Infrared (IR) spectra were taken with KBr pellets on a Perkin-Elmer FTIR 1725
1
13
spectrometer. The H and C NMR spectra were recorded on a Mercury-Plus
00 MHz spectrometer using CDCl as the solvent and tetramethylsilane (TMS) as
internal standard.
4
3
Preparation of Chitosan-Supported Formate
The highly porous chitosan resins were made by an emulsion method using
chitosan powder dissolved in 2.0% acetic acid aqueous and paraffin oil with Span
[
0. A volume of 10 mL of 12.5 mol L ECH was added to the chitosan solution
17]
ꢁ1
8
ꢀ
ꢁ1
and maintained at 60 C for 2 h. Subsequently, 50 mL of 0.1 mol L NaOH was
added dropwise and the system was boiled for 3 h under constant stirring. The pro-
ducts obtained were filtered, washed several times with distilled water and ethanol,
and then dried in a vacuum. Finally, the resins were packed in a column and
exchanged with an excess of 50% solution of formic acid repeatedly to get the
CSF. The resulting resins were washed with water several times, dried under vacuum,
and used directly for catalytic reduction.
General Procedure for the Reduction of Azo Compounds
The experimental procedure for our reduction of azo compounds using CSF
and magnesium is very simple. To a flame-dried flask equipped with a magnetic stir-
rer and condenser, the suspension of appropriate azo compound (5 mmol) in meth-
anol (15 mL), CSF (1 g), and magnesium (5 mmol) were added and stirred under a
nitrogen atmosphere at room temperature. Progress of the reaction was monitored
by TLC until the starting material was consumed completely. Then the catalyst

HYDROGENATIVE CLEAVAGE OF AZO COMPOUNDS
711
and resin were removed by filtration, and the solvent was evaporated under vacuum.
All of the products were purified by silica-gel chromatography eluted with
PE–EtOAc ¼ 5:1 and characterized by comparison of their TLC, melting points,
1
13
IR spectra, H NMR, and C NMR spectra.
ꢁ
1
ꢁ1
ꢁ1
Benzenamine (Entry 1, C H N). Colorless oil. IR (KBr), n (cm ): 3457 cm ,
6
ꢁ1
7
ꢁ
1
345 cm , 3066 cm , 3005 cm , 1618 cm , 1498 cm , 1320 cm , 1274 cm ,
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
2
ꢁ
1
ꢁ1
ꢁ1
1
150 cm , 1025cm , 744 cm . H NMR (400 MHz, CDCl , ppm): d 3.54 (s, br,
H), 6.58–6.63 (m, 2H), 6.72–6.77 (m, 1H), 7.11–7.15 (m, 2H). C NMR (100MHz,
3
13
CDCl , ppm): d 114.9, 116.2, 130.1, 138.2.
3
ꢁ
1
ꢁ1
ꢁ1
m-Toluidine (Entry 2, C H N). Colorless oil. IR (KBr), n (cm ): 3223 cm
,
,
7
9
ꢁ ꢁ1 ꢁ1 ꢁ1 ꢁ1 ꢁ1
1
3
1
2
1
040 cm , 3002 cm , 1623 cm , 1498 cm , 1463 cm , 1306 cm , 1288 cm
ꢁ1
ꢁ1
1
166 cm , 776 cm . H NMR (400 MHz, CDCl , ppm): d 2.25 (s, 3H), 3.52 (s, br,
H), 6.27 (m, 2H), 6.91 (m, 2H). C NMR (100 MHz, CDCl , ppm): d 22.8, 114.5,
3
1
3
3
20.9, 132.1, 146.8;
ꢁ
ꢁ1
1
ꢁ1
ꢁ1
o-Toluidine (Entry 3, C H N). Colorless oil. IR (KBr), n (cm ): 3378 cm
,
,
7
9
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
2
022 cm , 1621 cm , 1586 cm , 1495 cm , 1469 cm , 1302 cm , 1268 cm
ꢁ1
ꢁ1
1
033 cm , 746 cm . H NMR (400 MHz, CDCl , ppm): d 2.19 (s, 3H), 3.56 (s, br,
3
1
3
H), 6.62 (d, J ¼ 7.6 Hz, 1H), 6.69 (t, J ¼ 7.6 Hz, 1H), 6.98–7.04 (m, 2H). C NMR
(
100 MHz, CDCl , ppm): d 17.6, 115.6, 119.1, 123.2, 127.6, 130.8, 144.7.
3
4
-tert-Butylbenzenamine (Entry 4, C H N). Colorless oil. IR (KBr),
10 15
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
,
n (cm ): 3353 cm , 2963 cm , 1627 cm , 1463 cm , 1363 cm , 1266 cm
ꢁ1
ꢁ1
ꢁ1
1
1
(
190 cm , 827 cm , 645 cm
d, J ¼ 6.8 Hz, 12H), 3.58 (s, br, 2H), 6.96–6.72 (m, 2H), 7.14–7.16 (m, 2H).
NMR (100 MHz, CDCl , ppm): d 33.4, 39.7, 116.1, 125.6, 139.1, 143.4.
.
H NMR (400 MHz, CDCl , ppm): d 1.29
3
1
3
C
3
ꢁ
ꢁ1
1
ꢁ1
ꢁ1
p-Anisidine (Entry 5, C H NO). Purple solid. IR (KBr), n (cm ): 3419 cm
,
,
7
9
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
2
348 cm , 3001 cm , 1627 cm , 1509 cm , 1466 cm , 1297 cm , 1239 cm
ꢁ1
ꢁ1
ꢁ1
1
181 cm , 825 cm , 726 cm . H NMR (400 MHz, CDCl , ppm): d 3.44 (s, br,
3
1
3
H), 3.89 (s, 3H), 6.64 (dd, J ¼ 6.8, 2.0 Hz, 2H), 6.78 (dd, J ¼ 6.8, 2.0 Hz, 2H).
C
NMR (100 MHz, CDCl , ppm): d 57.2, 114.4, 116.8, 140.6, 153.0.
3
ꢁ
ꢁ1
1
4
-Aminophenol (Entry 6, C H NO). White solid. IR (KBr), n (cm ):
6
7
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
331 cm , 3274 cm , 3014 cm , 2901 cm , 1612 cm , 1507 cm , 1473 cm ,
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
254 cm , 1237 cm , 1092 cm , 965 cm , 823 cm , 750 cm
.
H NMR
(
2
1
400 MHz, CDCl , ppm): d 4.44 (s, br, 2H), 5.15 (s, 1H), 6.52 (dd, J ¼ 6.0, 2.0 Hz,
3
1
3
H), 7.42 (dd, J ¼ 6.0, 2.0 Hz, 2H). C NMR (100 MHz, CDCl , ppm): d 57.2,
3
16.4, 117.8, 142.6, 149.3.
ꢁ
1
4
-Aminobenzamide (Entry 7, C H N O). White solid. IR (KBr), n (cm ):
7
5
2
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
331 cm , 3274 cm , 3014 cm , 2901 cm , 1612 cm , 1507 cm , 1473 cm
1
,
H NMR
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
254 cm , 1237 cm , 1092 cm , 965 cm , 823 cm , 750 cm
.
(
2
1
400 MHz, CDCl , ppm): d 4.44 (s, br, 2H), 5.45 (s, br, 1H), 6.52 (dd, J ¼ 6.0,
3
1
3
.0 Hz, 2H), 7.02 (dd, J ¼ 6.0, 2.0 Hz, 2H). C NMR (100 MHz, CDCl , ppm): d
3
16.8, 124.6, 129.2, 152.3, 169.3.
ꢁ
1
2
-Bromobenzenamine (Entry 8, C H BrN). Red solid. IR (KBr), n (cm ):
6
6
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
443 cm , 3326 cm , 1605 cm , 1475 cm , 1441 cm , 1298 cm , 1067 cm
,

712
X. H. YU ET AL.
ꢁ
1
ꢁ1
ꢁ1
1
1
2
(
017 cm , 746 cm , 675 cm . H NMR (400 MHz, CDCl , ppm): d 3.79 (s, br,
3
H), 6.35–6.41 (m, 1H), 6.63 (dd, J ¼ 8.8, 2.0 Hz, 1H), 6.90–6.94 (m, 1H), 7.14
1
3
dd, J ¼ 8.8, 2.0 Hz, 1H). C NMR (100 MHz, CDCl , ppm): d 116.9, 118.0,
3
1
20.7, 129.4, 133.3, 148.1.
-Chloroaniline (Entry 9, C H ClN). Yellow solid. IR (KBr), n (cm ):
407 cm , 3309 cm , 2901 cm , 1613 cm , 1494 cm , 1285 cm , 1175 cm ,
ꢁ
ꢁ1
1
4
6
6
ꢁ
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
3
1
ꢁ1
ꢁ1
1
085 cm , 1002 cm , 825 cm , 640 cm . H NMR (400 MHz, CDCl , ppm): d
3
1
3
.66 (s, br, 2H), 6.48 (d, J ¼ 8.0 Hz, 1H), 7.01 (d, J ¼ 8.0 Hz, 1H). C NMR
(
100 MHz, CDCl , ppm): d 118.4, 121.8, 130.4, 147.8.
3
ꢁ
1
4
-Vinylbenzenamine (Entry 10, C H N). White solid. IR (KBr), n (cm ):
8
9
ꢁ1
ꢁ
1
445 cm , 3362 cm , 1623 cm , 1516 cm , 1414 cm , 1284 cm , 1239 cm
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
3
,
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
1
180 cm , 1085 cm , 834 cm , 691 cm . H NMR (400 MHz, CDCl , ppm): d
3
.71 (s, 2H), 5.05 (d, J ¼ 10.8, 1H), 5.56 (d, J ¼ 17.4, 2H), 6.62 (m, 1H), 6.64 (d,
1
3
J ¼ 8.4, 2H), 7.24 (d, J ¼ 8.4 Hz, 2H). C NMR (100 MHz, CDCl , ppm): d
3
1
10.02, 115.03, 127.39, 128.37, 136.58, 146.25.
-Aminobenzaldehyde (Entry 11, C H NO). Yellow solid. IR (KBr), n
cm ): 3050 cm , 2850 cm , 2730 cm , 1705 cm , 1649 cm , 1453 cm ,
4
7
7
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
(
ꢁ
1 1
8
23 cm . H NMR (400 MHz, CDCl , ppm): d 5.78 (s, br, 2H), 6.65 (d, J ¼ 8.4 Hz,
3
1
3
Hz, 2H), 7.60 (d, J ¼ 8.4 Hz, 2H), 9.68 (s, 1H), C NMR (100 MHz, CDCl , ppm):
3
d113.4, 125.5, 132.2, 154.7, 189.6.
ꢁ
1
4
-Aminobenzonitrile (Entry 12, C H N ). White solid. IR (KBr), n (cm ):
7
6
ꢁ1
2
ꢁ
1
465 cm , 3361 cm , 3199 cm , 2914 cm , 2206 cm , 1618 cm , 1593 cm
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
3
1
,
507 cm , 1307 cm , 1164 cm , 830 cm , 689 cm . H NMR (400 MHz, CDCl ,
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
1
3
ppm): d 4.32 (s, br, 2H), 6.72 (dd, J ¼ 6.8, 2.0 Hz, 2H), 7.33 (dd, J ¼ 6.8, 2.0 Hz,
1
3
2
H). C NMR (100 MHz, CDCl , ppm): d 99.8, 117.2, 127.4, 133.7, 149.8.
3
3
-Aminoacetophenone (Entry 13, C H NO). Yellow solid. IR (KBr), n
8
9
ꢁ
1
cm ): 3545 cm , 3455 cm , 2957 cm , 1670 cm , 1634 cm , 1610 cm
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
(
,
,
ꢁ ꢁ1 ꢁ1 ꢁ1 ꢁ1 ꢁ1
1
1
8
2
593 cm , 1501 cm , 1466 cm , 1364 cm , 1334 cm , 1301 cm , 1246 cm
ꢁ
1
ꢁ1
1
89 cm , 781 cm . H NMR (400 MHz, CDCl , ppm): d 2.52 (s, 3H), 4.00 (s, br,
3
1
3
H), 6.86 (dd, J ¼ 8.0, 1.6 Hz, 1H), 7.20–7.29 (m, 3H). C NMR (100 MHz, CDCl3,
ppm): d 27.3, 113.9, 118.5, 119.7, 129.4, 138.1, 147.1, 198.7.
ACKNOWLEDGMENTS
This research was supported by the Foundation of Hexi University (No.
011016) and Key Laboratory of Hexi Corridor Resources Utilization of Gansu
2
Universities (No. 201206).
REFERENCES
1
. Abiraj, K.; Srinivasa, G. R.; Gowda, D. C. Simple and efficient reduction of aromatic
nitro compounds using recyclable polymer-supported formate and magnesium. Aust. J.
Chem. 2005, 58, 149–151.

HYDROGENATIVE CLEAVAGE OF AZO COMPOUNDS
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