942 Ozen
Asian J. Chem.
TABLE-1
OXIDATION OF SUBSTITUTED TOLUONES TO CARBOXYLIC ACID IN THE
PRESENCE OF MOLECULAR OXYGEN WITH PCC IN SUB-CRITICAL WATER
Yield (%) PO2/bar
10 15
80 90
Entry
1
Substrate
Product
(m.p./oC) Ref.
Ac
75
5
20
120-121 (121-123)16
77
90
C6H5Me
C6H5COOH
p-CH3C6H4Me
p-COOHC6H4COOH
2
3
(210-211)16 (dec)
154-156 (155-158)16
(122-124)16
73
70
85
90
88
75
80
82
75
77
80
85
92
90
78
85
85
80
80
92
93
95
95
85
90
85
80
85
95
95
95
95
90
95
90
85
85
95
95
95
95
90
95
90
85
m-BrC6H4Me
m-FC6H4Me
m-BrC6H4COOH
m-FC6H4COOH
4
5
(220-222)16
m-CNC6H4Me
p-CNC6H5CCMe
p-BrC6H4Me
m-CNC6H4COOH
p-CNC6H4CCOOH
p-BrC6H4COOH
p-FC6H4CCOOH
p-ClC6H4COOH
p-CH3OC6H4COOH
6
(217-218)16
7
(252-254)16
8
p-FC6H4CMe
p-ClC6H4Me
(186)16
9
237-239 (238-241)16
(183-184)16
p-CH3OC6H4Me
10
(98-100)16
72
75
80
85
85
o-CH3OC6H4Me
o-CH3OC6H4COOH
11
aDouble equivalents of molecular oxygen, 5 bar, 4.63 × 10-3 mol dm-3; 10 bar, 9.26 × 10-3 mol dm-3; 15 bar, 1.38 × 10-2 mol dm-3; 20 bar, 1.85×10-2
mol dm-3; bRelative yield based on quantitative analysis; cA: Disolved oxygen in water at atmospheric pressure 1.26x10-3 mol dm-3; dAll products
1
were characterized by IR and H NMR and their physical data compared with literature data16. Reactions conditions: Total pressure 60 bar,
temperature 120 oC
Molecular oxygen in
sub-critical water
to the corresponding benzoic acids in excellent yields (entires
4, 5 and 6, 8). Toluenes substituted by electron rich substituents
(entires 2, 10 and 11) also undergo oxidation efficiently.
In conclusion, we developed a practical procedure for the
oxidation of substituted toluenes to their corresponding substi-
tuted carboxylic acid in subcritical water with molecular oxygen
with small amount metal catalysts.
COOH
R
R
PCC (1%)
R: -CN, -F, -Cl,-Br, -CH3, -OCH3
Scheme-I
In the present work, molecular oxygen is used to oxidize
toluenes to their corresponding carboxylic acids in subcritical
water. The dramatic decrease in solvent viscosity and an increase
in substrate solubility suggest that subcritical water may be
useful as a replacement for environmentally unacceptable sol-
vents for a number of organic reactions14.
ACKNOWLEDGEMENTS
The author is greatful to Mersin University Research
Council and TUBITAK (The Scientific and Technical Council
of Turkey) for the supporting this work (Grant No: TBAG-
2235).
The amount of dissolved oxygen in water at atmospheric
pressure was determined according to Henry's Law15 (at 25 °C
the solubulity of O2 is of 1.296.10-3 mol/kg H2O).
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