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COOH
COOH
NH
2
Ball mill
80 °C, vacuum
-H
2
O
+
(HCHO)
n
NH
S
HS
18
19
20
NH
2
O
O
+
N
O
O
O
21
22
23
H
N
NH
2
S
N
C
S
N
C
S
N
H
+
S
N
N
N
H
C
Ar
S
N
C
S
R
H
R
24
25
26
R = 4-Cl, 4-OH, 2-NH
2
Scheme 1.34 Mechanochemical reactions of amines with carbonyl compounds and
isothiocyanates.
R''
R"
R'
R'
N
NH
2
O
ball mill
1 h
+
+
H
2
O
R
NH
2
R
N
O
R"
R''
100%
Scheme 1.35 Mechanochemical synthesis of quinoxaline derivatives.
R'
O
O
N
NH
2
OH
O
N
+
-2H
2
O
R
NH
2
O
OH
OH
100%
Scheme 1.36 Mechanochemical synthesis of benzo[a]phenzin-5-ol.
milling.
33
The condensation of substituted o-phenylenediamines and
benzil produced the corresponding quinoxaline derivatives within 1 h
(Scheme 1.35). Similarly, condensation between 2-hydroxy-1,4-naphthoquinone
and o-phenylenediamine furnished the benzo[a]phenazin-5-ol within 15 min at
70 1C (Scheme 1.36). The yields are almost quantitative in all these reactions.
Kaupp and co-workers also investigated the solid state condensation of
o-phenylenediamine with oxoglutaric acid, oxalic acid, 1,4-dihydroquinoxa-
line-2,3-dione and parabanic acid and found that in each case the corres-
ponding products were obtained in high yields (Scheme 1.37).
33
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