Chemistry Reference
In-Depth Information
Table 3.4
Solvent-free oxidative dehydrogenation of g-terpinene to p-cymene in the
presence of alumina or quartz sand as milling auxiliary and different
oxidation agents.
a
Yield (%)
Alumina Quartz sand
KMnO
4
99 53
p-Benzoquinone 69 37
I
2
93 52
Oxone 84 8
NaMnO
4
82 73
(NaH
4
)
4
Ce(SO
4
)
4
H
2
O 71 11
NaIO
4
67 41
K
2
Cr
2
O
7
12 7
Na
2
S
2
O
8
11 10
(NH
4
)
2
S
2
O
8
7 7
Urea-H
2
O
2
-adduct (28%) 5 6
a
Batch (per batch): 3.8 g auxiliary, 2 mmol g-terpinene, 6 mmol oxidant, 0.1 g H
2
O.
Oxidant agent
R
KMnO
4
(2 eq)
Al
2
O
3
N
N
(24-93%)
NH
2
b.m. (13.3 Hz)
r.t.; 10 min
R
R
R
O
N
N
(36-87%)
Oxone (1 eq)
Al
2
O
3
R
Scheme 3.4
Solvent-free chemoselective oxidation of anilines either using KMnO
4
to give the corresponding azo-benzenes or with Oxone to give the
respective azoxy compounds. Reactions were performed in a Fritsch
''Pulverisette 7 classic line'' planetary ball mill using 45 mL grinding
beakers (agate or ZrO
2
) and milling balls (6-15 mm; agate or ZrO
2
).
by the migration of the substituent (hydrogen), which is trans to the nitrogen
lone pair, results in the formation of amides. In pathway B, carbinolamine
intermediates are generated after the nucleophilic addition of anilines to
aldehydes, followed by oxidation using Oxone to form the amide products.
Despite the fact that the exact mechanism remains obscure and that both
pathways could well be operating simultaneously, this novel solvent-free and
metal catalyst free procedure makes the synthesis of amides more ecient,
low cost, and eco-friendly as compared to the traditional liquid-phase re-
action. Other oxidants, including K
2
S
2
O
8
and I
2
, were also examined; how-
ever, no reaction was observed (entries 6-11, Table 3.6).
6
In a drive to further deepen the work of Stolle's group on the oxidation
of anilines (using acidic inorganic auxiliaries to direct the formation of
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