Hydroxylation of Phenol Catalyzed by Oxovanadium(IV)
229
encapsulated in zeolite-Y were used as catalysts for
hydroxylation reaction of phenols [24].
J = 6.95), 6.82–7.31 (m, 10H, Ar–H), 8.68 (s, 2H, HC=N),
13.53 (s, 2H, OH).
In continuation of our efforts to study the catalytic activity
of oxovanadium(IV)-based catalyst, we report herein the
preparation and characterization of two oxo-vanadium(IV)
complexes abbreviated, VO-(EtOsalphen) and VO-(EtO-
salnaph). These complexes are derived from tetradentate
0
2.3.1.2 B. N,N -1,8-Naphthylenebis(3-Ethoxysalicylidene-
aminate) (EtOsalnaph) 1,8-Diaminonaphthaline (0.158 g),
and 3-ethoxysalicylaldehyde (0.332 g) were dissolved in
absolute ethanol (20 mL) and refluxed for 2 h. A brown
solid obtained on recrystallization from cyclohexane. Yield
0
Schiff base ligand of type ONNO; N,N -1,2-phenylenebis
0
-1
(
3-ethoxysalicylideneaminate) (EtOsalphen) and N,N -1,
-naphthylene-bis(3-ethoxysalicylideneaminate) (EtOsal-
36%; m.p. 142–144 °C; IR (KBr, cm ), 3358 m(OH), 1614
m(C=N), 1269 m(C–N), 1114 m(C–O), 3044–3098 m(C–H
8
naph). The catalytic activity of these complexes was tested
for hydroxylation of phenol and the suitable reaction con-
ditions have been optimized to get maximum hydroxylation.
arom), 2861–2990 m(C–H aliph.). E1-mass (m/z), 455 (66)
[M ? 1] , 454 (82) M , 436 (25), 391 (44), 304 (97), 290
?
?
1
(15), 247 (100); H-NMR d ppm (500 MHz, d -DMSO),
6
1.37 (t, 6H, CH , J = 6.88 Hz), 4.08 (q, 4H, CH , J =
3 2
6.9), 5.71 (s, 2H, OH), 6.54–7.19 (m, 12H, Ar–H), 8.80 (s,
2
Experimental Section
2H, HC=N).
2
.1 Materials
2.3.2 Preparation of the Oxavanadium(IV) Complexes
Vanadyl sulfate trihydrate was obtained from Fluka,
,2-diamino benzene, 1,8-diaminonaphthaline and 3-eth-
oxysalicylaldehyde were obtained from Merck. Phenol and
8%, H O were of AR grade and all other chemical reagents
The two complexes were prepared according to the fol-
lowing procedure. An aqua solution (10 mL) of
VOSO ꢀ3H O (0.217 g, 1 mmol), was added drop wise to
1
4
2
2
the hot ethanolic solution (10 mL) of the Schiff base ligand
(1 mmol). The mixture was heated under reflux for 5–6 h.
The precipitated solid which was obtained, filtered, washed
with hot water then ethanol and finally dried at 110 °C.
2
2
were used as such. Solvents were used after being purified
according to the standard method.
2
.2 Physical Methods and Analysis
2
.3.2.1 A. VO-(EtOsalphen) Green solid, m.p. [ 300 °C,
-1
Infrared spectra were recorded as KBr pellets on BUCK-
1
00 FT-IR spectrometer. H-NMR spectra were recorded
IR (KBr, cm ); 3064–3098 m(C–H arom), 2861–2980
5
m(C–H aliph.), 1602 m(C=N), 1600 and 1546 m(C=C), 1252
1
on a Bruker 500 (500 MHz) using d6-DMSO or CDCl as a
3
m(C=N), 1103 m(C–O), 987 m(V=O). H-NMR (d -DMSO);
6
solvent and TMS as internal standard. GC-Mass spectra
were recorded on Hewlett Packard E1 at 70 eV. Elemental
analysis was performed on Euro Vectro EA 3000A. All
catalyzed reactions products were analyzed using Shima-
dzu gas chromatography (GC-14 B) fitted with FID
detector.
1.57 (t, 3H, CH ), 4.52 (q, 2H, CH ), 6.8 (m, 10H, Ar–H),
3
2
9.5 (s, 1H, HC=N). Anal. calc. for C H N O V: C, 61.4,
4 22 2 5
2
H, 4.71, N, 5.96, found: C, 61.09, H, 4.48, N, 6.21.
2.3.2.2 B. VO-(EtOsalnaph) Green solid, m.p. [ 300 °C,
-
1
IR (KBr, cm ); 3041–3102 m(C–H arom), 2867–2988
m(C–H aliph.), 1604 m(C=N), 1600 and 1546 m(C=C), 1247
2
2
2
.3 Preparation
m(C–N), 1100 m(C–O), 976 m(V=O). 1H-NMR (d -DMSO);
6
1.37 (t, 3H, CH ), 3.35 (q, 2H, CH ), 6.9–7.26 (m, 12H,
3 2
.3.1 Preparation of the Ligands
Ar–H), 10.1 (s, 1H, HC=N). Anal. calc. for C H N O V:
28 24 2 5
C, 64.74, H, 4.65, N, 5.39. found: C, 64.02, H, 4.36, N,
5.82.
0
.3.1.1 A. N,N -1,2-Phenylenebis(3-Ethoxysalicylideneami-
nate) (EtOsalphen) A mixture of 1,2-diaminobenzene
0.108 g, 0.001 mol) and 3-ethoxysalicylaldehyde (0.332 g,
.002 mol) in 20 mL absolute ethanol were refluxed with
(
2.3.3 Catalytic Activity Study
0
stirring for 2 h. An orange solid was obtained which
The catalytic hydroxylation of phenol was carried out in a
50 mL flask fitted with a water condenser. In a typical
reaction, an aqueous solution of 28% H O (6.07 g,
recrystallized from ethanol. Yield 68%; m.p. 122–124 °C;
-
1
IR (KBr, cm ), 3343 m(OH), 1625 m(C=N), 1264 m(C–N),
2
2
1
116 m(C–O), 3048–3094 m(C–H arom), 2890–2971 m(C–H
aliph.). E1-mass (m/z), 405(12) [M ? 1], 404(18) M ,
0.05 mol) and phenol (4.7 g, 0.05 mol) were mixed in
2 mL of MeCN and the reaction mixture was heated at
70 °C with continuous stirring in an oil bath. An appro-
priate amount of catalyst (0.007 g) was added to the
?
1
254(51), 239(100), 197(72). H-NMR d ppm (500 MHz,
CDCl ): 1.56 (t, 6H, CH , J = 7.0 Hz), 4.20 (q, 4H, CH ,
3
3
2
123