|
II. ACTIVATED ALUMINA
Aldrich offers various grades of Al2O3, four of which are products designed for column chromatography and adsorptive filtration: acidic, basic and neutral activated aluminas from Camag (Brockmann I grade). Highly porous in nature, aluminas can be effective desiccants and have numerous applications in catalysis as well. Fieser and Fieser’s Reagents for Organic Synthesis² give examples of synthetic applications of activated aluminas.
A.
Conversion of Brockmann I to Brockmann IIV grades
Although Camag aluminas are the adsorbents of choice in a wide range of uses in column chromatography and adsorptive filtration, chemists have yet to exploit the ease with which Brockmann I grades can be converted to grades of lower activity simply by adding water.
Taking the precautions to shake well (to disintegrate lumps) and to allow the material to equilibrate in a closed vessel for at least overnight, one can use the following guide to prepare modest quantities of Brockmann IIV grades of alumina simply by adding the appropriate amount of water to the respective Brockmann I grade.
|
Grade
designation
|
Brockmann
Number
|
Amount
of water to be
added to Brockmann I grade
(%)
|
Approx.
water content
(%,
Karl Fischer method)
|
|
5016-A-II,
507-C-II
|
II
|
3
|
4-4.5
|
|
5016-A-III,
507-C-III
|
III
|
6
|
7-7.5
|
|
5016-A-IV,
507-C-IV
|
IV
|
10
|
11-11.5
|
|
5016-A-V,
507-C-V
|
V
|
15
|
16-16.5
|
B.
Typical particle-size distribution (mesh analysis)of all grades of activated alumina
|
Table
4
|
|
Sieve
opening (mm)
|
Mesh
size
|
%
Retained
|
|
0.25
|
60
|
0.1
(max.)
|
|
0.20
|
~
75
|
25
|
|
0.15
|
100
|
1520
|
|
0.10
|
~
150
|
5565
|
|
0.07
|
~
210
|
7285
|
|
0.04
|
~
360
|
9598
|
|
Table
5
|
|
Properties
and Characteristics of Camag Standard Grades of Activated
Alumina
|
|
Catalog
Number
|
|
|
|
|
|
Brockmann
Number
|
1
|
1
|
1
|
1
|
|
Grade
|
5016-A-I
|
507-C-I
|
504-C-I
|
504-C-I
|
|
Type
|
basic
|
neutral
|
acidic
|
weakly
acidic
|
|
pH
(5%
stirred aq. suspension)
|
9.5
± 0.3
|
7.5
± 0.5
|
4.5 ± 0.5
|
6.0
± 0.5
|
|
Aprrox.
particle size (mesh)
|
150
|
150
|
150
|
150
|
|
Sureface
area (m2/g)
|
150
|
150
|
150
|
150
|
|
Pore
diameter (Å)
|
58
|
58
|
58
|
58
|
|
Cl-
(mval/g)
|
—
|
0.03
|
0.14
|
0.06
|
|
Na2O
(%)
|
0.4
|
0.4
|
0.4
|
0.4
|
|
Fe2O2
(%
max.)
|
0.02
|
0.02
|
0.02
|
0.02
|
|
SiO2
(%
max.)
|
0.02
|
0.02
|
0.02
|
0.02
|
|
H2O
(%,
approx.)
|
1.5
|
1.5
|
1.5
|
1.5
|
|
