56 JOURNAL OF CHEMICAL RESEARCH 2013
Table 1 Hydrogenative cleavage of azo compounds using chitosan-supported formate and zinc
Entry
Temp/ °C
/Time/min
Yield/%a
M.p./ °C
Found
Lit.
1
2
R=H, R’=H
R= 3-CH3, R’= 3’-CH3
25/8
95
95
93
91
90
96
94
87
89
93
90
89
91
96
95
112b
124–125c
142–143c
231–232d
58–59
189–191
181
11426
12526
14426
23327
5726
25/8
3
R= 2-CH3, R’= 2’-CH3
25/10
65/15
25/13
25/10
25/12
25/15
25/12
25/10
25/12
25/13
25/15
25/9
4
R= 2-C(CH3)3, R’= 2’-C(CH3)3
R= 4-OCH3, R’= 4’-OCH3
R= 4-OH, R’= 4’-OH
5
6
18926
18326
3026
7
R= 4-CONH2, R’= 4’-CONH2
R= 2-Br, R’= 2’-Br
8
28–30
71
9
R= 4-Cl, R’= 4’-Cl
7226
10
11
12
13
14
15
R= 4-vinyl, R’= 4’-vinyl
R= 4-CHO, R’= 4’-CHO
R= 4-CN, R’= 4’-CN
242d
24926
7126
70–71
84–85
98–99
50
8627
R= 3-COCH3, R’= 3’-COCH3
1,2-di(naphthalen-1-yl)diazene
1,1’-(diazene-1,2-diyl)bis(naphthalen-2-ol)
9926
5028
5128
25/10
50
a Yield refer to pure isolated products.
b Isolated as acetyl derivative.
c Isolated as benzoyl derivative.
d Boiling point.
powder did not yield the reduced compound. The results
showed that the combination of CSF and zinc powder is essen-
tial to carry out the reduction. The probable reduction mecha-
nism proceeded through the degradation of CSF into hydrogen
which induced the reduction of azo compounds. Furthermore,
it is worth noting that the CSF could be regenerated and reused
for further hydrogenolysis processes. In most of the reactions,
we found the reaction yields retained the typical values
throughout six successive recycle runs.
We thank the Key Laboratory of Resources and Environment
Chemistry of West China, and Hexi University for the financial
assistance. We are also grateful to Dr G. R. Yue for his encour-
agement.
Received 31 October 2012; accepted 27 November 2012
Paper 1201600 doi: 10.3184/174751912X13553360452222
Published online: 15 January 2013
In conclusion, the use of CSF and zinc powder provides a
very simple and efficient procedure for the smooth hydrogena-
tive cleavage of azo compounds to the corresponding amine(s).
The method combines the advantages of polymer-supported
chemistry with the flexibility of the CTH technique, including
a cost effective safe reaction medium, rapidity, ease of
operation, and a simple recovery of the hydrogen donor. This
distinguishes this procedure from others catalytic transfer
hydrogenation and will hopefully prove to be of wide use in
organic synthesis.
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