Abstract
High loading amino- and diamino-functionalised silicas were prepared
by a simple method; the resultant materials have been shown to be
excellent high capacity scavengers for three representative types
of electrophile with a wide solvent compatibility.
Key words
electrophilic additions - combinatorial chemistry - acylations - silica - scavengers
References
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13 The materials prepared were made by
the templated co-condensation of tetraethoxysilane (TEOS) and a
second functional amine[7], either 3-aminopropyltrimethoxysilane 1 or N -(2′-aminoethyl)-3-aminopropyltrimethoxysilane 2 . The proportion of the functional silane
was kept as high as possible, commensurate with a high yield of
the desired solid product [50 mol% RSi(OMe)3 :
50 mol% TEOS in the case of 1 ,
33 mol% RSi(OMe)3 : 67 mol% TEOS in
the case of 2 ]. The two silanes
were added together but separately (in each case a total of 0.1
mol of silane was added) to a mixture of water, ethanol (50 mL of
each) and 1-aminododecane (5.1 g) at room temperature. After stirring
for 18 h, the white suspension was filtered and the resultant solid
was extracted using a Soxhlet extractor and ethanol as extractant
for 12 hours. The extracted solids were dried at 100 °C
to remove solvent, and were stored in screwtop jars. Yield is typically 10
g. These procedures gave materials with loadings of 5 mmolg-1 aminopropyl(3 ) and 3.7 mmolg-1 of
the diaminosilane respectively(4 ) (Scheme
[1
14 These materials were then evaluated
as scavengers by stirring them with an excess (a mole ratio of 2:1
electrophile: amine group was used) of electrophiles (phenyl isocyanate 5 , benzenesulfonyl chloride 6 ,
and benzoyl chloride 7 ) in a range of solvents.
For 1 g of scavenger 5 mL of solvent was used. After 5 hours, the
solids were removed by filtration, washed with the solvent used
in the reaction, and the quantity of electrophile remaining in solution
was calculated from GC with n -dodecane
as internal standard.
