M. Khosravi M. et al. / Polyhedron 62 (2013) 18–25
19
The surface of elemental aluminum is covered by a oxide layer,
thus it is thought HgCl will activate this surface and accelerate the
reaction kinetics [30]. The HgCl initially reacts with aluminum to
produce the Al ion, which then reacts with the alcohol to form
the alkoxide adduct. We have optimized the process by lowering
Table 1
Synthesis conditions to produce APh, AH, and AIP.
2
2
Product Aluminum
mole
Alcohol mole
HgCl2
mole
Reflux time
(h)
Solvent
3
+
APh
AH
AIP
1
1
1
4.3 (Phenol)
0.001
24
11
9
THF
–
–
the reaction time and the concentration of HgCl
2
to obtain
7.9 (Hexanol) 0.001
8.3 0.001
Isopropanol)
improvements in yield, which now allows for a complete charac-
terization of these useful products. Optimum conditions include
use of excess alcohol and a lower amount of mercuric chloride
catalyst [9,21,28,29]. The work presented herein includes a gener-
alized preparation and characterization of divergent aluminum
(
We used ICP-MS (Elan 6000, Perkin Elmer) to determine the levels
of Hg impurity in the synthesized alkoxides. 2% nitric acid was
used to dilute and dissolve the alkoxides followed by 30 min son-
icating using a Branson 1510 sonicator.
alkoxide structures including aluminum isopropoxide (R = C
aluminum phenoxide (R = C ), and aluminum n-hexyloxide
R = C 13). Notably, the approach allows for the first generalized
3 7
H ),
6 5
H
(
6
H
synthesis and characterization of aluminum n-hexyloxide. Synthe-
sis of aluminum n-hexyloxide from 1-hexanol is significant in that
this alkoxide possesses low water, high stability, and efficient reac-
tivity for the production of aluminum oxide nanomaterials. We se-
lected aluminum isopropoxide, aluminum phenoxide, and
aluminum n-hexyloxide, as a general representation of steric bulk
effects since the A-values of the attached alkyl groups are different
for each group. Isopropyl = 2.15 kcal/mol, phenyl = 2.7 kcal/mol,
and ethyl (analogue of n-hexyl) = 1.75 kcal/mol [33]. The effect of
ligand environment on the physiochemical properties of aluminum
alkoxides influences the properties of the alumina [3,11,34]. The
structure and properties of aluminas produced from these alumi-
num alkoxides with different steric characteristics can now be pro-
duced and studied using the reported method.
2
2
.3. Synthesis
.3.1. General procedure
To ensure an anhydrous environment, solvent and alcohols
were dried over molecular sieves. The flask was fitted with a con-
denser and a CaCl tube. A sand bath and heat regulator were used
2
to provide homogenous heating for the reactions. One mole of alu-
minum was treated with excess alcohol in the presence of catalytic
mercuric chloride (0.001 mole) and refluxed. Vacuum distillation
was applied to remove un-reacted alcohol and solvent in the case
of APh and un-reacted alcohol in the case of AIP and AH. AIP was
purified by further vacuum distillation. However, APh and AH were
collected without further vacuum distillation since they were
shown to decompose upon heating. Experimental conditions to
synthesis aluminum alkoxides are shown in Table 1.
2
. Experimental
2.1. Materials
2.3.2. Aluminum n-hexyloxide (AH)
Al (1 mole) was added to excess 1-hexanol (7.9 mole) and
The aluminum n-hexyloxide (AH) was prepared from the reac-
(0.001 mole) HgCl in a flask. The mixture was refluxed for 11 h un-
2
tion of aluminum (granular, Spectrum, 99.6%) and 1-hexanol
anhydrous, Alfa-Aesar, 99.0%) in the presence of HgCl (Fischer,
00.0%) as a catalyst. Aluminum phenoxide (APh) was prepared
from aluminum (granular, Spectrum, 99.6%) and phenol (detached
crystals, Alfa-Aesar, >99%) in the presence of HgCl (Fischer,
00.0%) as catalyst and dried THF (EMD, 99.99%) as solvent. Alumi-
der N atmosphere with stirring then the solution was allowed to
cool overnight without stirring. Since AH decomposed on vacuum
distillation, it was collected from the top layer of the flask and vac-
2
(
1
2
uum filtered with a Buchner funnel using filter paper (Fischer, P ).
4
1
2
H NMR (C D ): d 0.8 (t, 3H, JCH = 6.97, 7.22 Hz, CH ), 1.1 (m, 6H,
CH ), 1.3 (m, 2H, CH ), 3.2 (m, 2H, CH ). C NMR (C D ): d 13.87
2 2 2 6 6
6
6
3
1
3
1
num isopropoxide (AIP) was prepared from aluminum (granular,
Spectrum, 99.6%) and isopropyl alcohol (Sigma-Aldrich, >99.8%)
3 2 2 2
(s, CH ), 22.64 (s, CH ), 25.44 (s, CH ), 31.62 (s, CH ), 32.77 (s,
2
7
CH ), 62.34 (s, CH ). Al NMR (C D ): d 56.5 (s, 4 or 5 coordinated
2
2
6 6
in the presence of HgCl
EMD, 70%-Omni Trace) was used to dissolve samples for the
ICP-MS experiment.
2
(Fischer, 100.0%) as catalyst. HNO
3
Al). XRD (c alumina at 1000 °C): 2h 25.7, 35.2, 37.9, 43.5, 52.6, 57.6,
ꢀ1
ꢀ1
(
60.1, 61.5. IR (nujol, Al–O–C, cm ): 1055.80 cm .
2
.3.3. Aluminum phenoxide (APh)
Al (1 mole) was added to excess phenol (4.3 mole), in 2 L dried
THF (solvent) and (0.001 mole) HgCl in a flask [9]. The mixture
was refluxed for 24 h under a N atmosphere with stirring. Solvent
2
.2. Equipment
2
AH, AIP and APh were characterized by IR, XRD, NMR, ICP and
2
and alcohol were removed by vacuum distillation. Aluminum
phenoxide was not extracted by further vacuum distillation since
it decomposes on heating and was collected from the flask [9].
elemental analysis. To obtain the IR spectra, nujol mulls of the solid
alkoxides were analyzed with a Nicolet (Avatar 360) spectropho-
tometer. Elemental analysis was performed (Galbraith Laboratory)
for AH, APh and AIP separately using a C, H, O combustion method.
The structure of the synthesized alkoxids were determined by
Powder X-ray diffraction (XRD) using a Panalytical X’Pert Pro
1
H NMR (DMSO and methanol): d 6.73 (m, 3H, CH), 7.12 (m, 2H,
1
3
CH).
1
C NMR (DMSO and methanol): d 115.55 (s, 2H, CH),
1
27
19.22 (s, 2H, CH), 129.77 (s, H, CH), 157.63 (s, qC). Al NMR
(
DMSO and methanol): d 56.5 (s, 4 or 5 coordinated Al). XRD (
c
X-ray diffractometer with Cu K
scanning rate of 0.02 s in the 2h ranges from 10° to 90°. The
a
radiation (k = 0.15418 nm) at a
ꢀ1
and
a
alumina at 1000 °C): 2h 25.7, 35.2, 37.9, 43.5, 52.6, 57.6,
1
13
6
0.1, 61.5, 19.5, 32, 37.7, 39.5, 45.8, 60.5. IR (nujol, Al–O–C,
XRD power source was (40 kV, 40 mA). H NMR, C NMR and
ꢀ
1
ꢀ1
2
7
cm ): 1070.75 cm
.
Al NMR were collected on a Varian NMR-S 500 MHz instrument
1
using a pfg-enabled dual-broadband probe. The H NMR, gCOSY,
1
3
27
C NMR and Al NMR spectrum of aluminum isopropoxide
AIP) and aluminum n-hexyloxide (AH) were recorded with ben-
2.3.4. Aluminum isopropoxide (AIP)
(
Al (1 mole) was added to excess isopropyl alcohol (8.3 mole)
zene-d6 as solvent. The spectrum of aluminum phenoxide (APh)
was recorded with DMSO-d6 and methanol-d4 as solvent. All sam-
ples were prepared and measured at ambient temperature 25 °C.
and (0.001 mole) HgCl
9 h under N atmosphere with stirring. Afterward, vacuum distilla-
tion was applied to remove the un-reacted alcohol. Further
2
in a flask. The mixture was refluxed for
2