The Heterogenation Of Saccharin, Melamine And Sulfonic Acid Onto Rice Husk Ash Silica And Their Catalytic Activity In Esterification Reaction
Loading...
Date
2010-12
Authors
Mohammed Hello, Kasim
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Sodium silicate from rice husk ash (RHA) was functionalized with 3–
(chloropropyl)triethoxysilane (CPTES), 3–(mercaptopropyl)trimethoxysilane and
3–(aminopropyl)triethoxysilane to give RHACCl, RHAPrSH and RHAPrNH2 via a
simple one–pot synthesis. The 29Si MAS NMR of RHACCl showed the presence of
T2, T3, Q3 and Q4 silicon centres, while the T1, T2, T3, Q2, Q3 and Q4 silicon centres
were present in both RHAPrSH and RHAPrNH2. The 13C MAS NMR showed that
RHACCl had three chemical shifts at 10.37, 26.70 and 47.69 ppm, which was
attributed to the three carbon atoms of the CPTES moiety. RHAPrNH2 had chemical
shifts at 16.59, 32.73 and 14.58, while RHAPrSH showed only two signals at 26.13
and 47.87 ppm instead of the expected three signals. This was due to the
superimposition of two signals on each other. The combination of elemental and
EDX analysis showed the presence of chlorine in RHACCl, sulfur was found in
RHAPrSH and nitrogen was found in RHAPrNH2 as well as the presence of carbon
and silicon in the samples confirmed that the silylating agents were incorporated
onto RHA silica. Saccharine (Sac) and Melamine (Mela) were immobilized onto
RHACCl to form RHAC-Sac and RHAPrMela. Both 29Si MAS NMR spectra of
RHAC-Sac and RHAPrMela showed similar chemical shifts to the RHACCl. The
13C MAS NMR showed that RHAC-Sac had a series of chemical shifts consistent
with the presence of the aromatic and lactam ring. Two chemical shifts at 161.52 and
169.67 ppm with double spinning side bands were seen in the 13C MAS NMR of
RHAPrMela, indicating that the three carbon atoms in the melamine ring were not
equivalent. The functionalized –CH2–SH group in RHAPrSH was oxidized to
sulfonic acid, –CH2–SO3H with hydrogen peroxide at room temperature. The 29Si
MAS NMR showed similar chemical shifts to the RHAPrSH. No overlapping of the
C3 and C2 chemical shifts in the 13C MAS NMR was observed after the
transformation to RHAPrSO3H. RHAC-Sac, RHAPrMela, RHAPrSO3H, RHA–
Blank (as control) as well as homogenous Sac and homogenous Mela were used as
catalysts in the esterification reaction. The catalytic activity of the catalysts toward
the respective esters was found to follow the sequence below.
Description
Keywords
The heterogenation of saccharin, melamine and sulfonic acid , onto rice husk ash silica and their catalytic activity in esterification reaction