SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai
Triphenyl (3-sulfopropyl) phosphonium functionalized PWA on Silica catalyzed
Hosomi-Sakurai reaction
Sumit B. Kamble, Chandrashekhar V. Rode*
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Chemical Engineering & Process Development Division, CSIR-National Chemical Laboratory, Pune-411008, India.
E-mail: s.kamble@ncl.res.in; cv.rode@ncl.res.in
1. Introduction:
Acid catalyzed Hosomi-Sakurai mono-allylation of acetal with allyl-TMS is one of the most important C-C bond forming
reactions which is a key step in natural product synthesis. Commercially available Lewis and Brønsted acid catalysts have
been reported in homogeneous medium having the known serious drawbacks. In this work, we prepared silica supported,
non-leachable, triphenyl (3-sulfopropyl) phosphonium functionalized phosphotungstic acid (PWA) catalysts for the
selective mono-allylation of acetals to homoallylethers up to 93 – 99% yields (scheme 1).
Scheme 1. Hosomi-Sakurai mono-allylation of acetals using 30PW-Si/TPSP
2. Methods and materials:
Various catalysts were prepared by sequential loading of PWA ( H3PW12O40) in the range of 10 - 30%, on silica (w/w) (1030PW-Si) by wet impregnation method followed by the abstraction of protons by TPSP (10-30PW-Si/TPSP). The prepared
catalysts were thoroughly characterized by XRD and FT-IR (Figure 1) confirming the retention of PWA, and for acid
strength and type measurement by NH3-TPD (Figure 2) and Py-IR, respectively. ‘Si’ and ‘P’ solid state NMR were also
studied for different interactions (Figure 3). TGA for thermal stability, BET for surface area. In a typical procedure, 0.05 g
of the catalyst (30PW-Si/TPSP) was added to the solution of benzaldehyde-dimethylacetal (1mmol, 0.152 g) and
allyltrimethylsilane (1.5 mmol, 0.237 mL) in acetonitrile (2 mL). The mixture was stirred at room temperature under
nitrogen till the reaction was completed as monitored by TLC. Products were characterized using NMR, IR and GC-MS etc.
Si-NMR
Figure 1. FT-IR samples
Figure 2. NH3-TPD of samples
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SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai
Figure 3. Solid state NMR
3. Significant Results and Discussion:
After the characterization, catalyst optimization study was carried out using different commercial and the prepared solid
acid catalysts in various solvents and catalyst loadings. Among these, 30PW-Si/TPSP catalyst (0.05 g) having 30 % PW on
silica showed the highest activity in acetonitrile which was then further extended to react with various dimethyl and –
diethyl acetals in presence of allyl-TMS with different electronic substituents to synthesise homoallyl ethers up to 93 – 99
% yields. Our catalyst, 30PW-Si/TPSP was truly heterogeneous as evidenced by its efficient five recycling experiments
(Fig. 4).
Figure 4. Recycling study of 30PW-Si/TPSP
4. Conclusion:
In summary, we have prepared a new triphenyl (3-sulfopropyl) phosphonium (TPSP) functionalized
phosphotungstic acid on a silica support as an efficient Brønsted solid acid catalyst for selective mono -allylation of
acetals via Hosomi - Sakurai reaction. The catalyst was systematically characterized by XRD, FT-IR, solid state
NMR and BET surface area. The acidic strength and Brønsted acidic sites of the catalyst were determined by the
ammonia-TPD and pyridine FT-IR studies and the order of acidity was observed as follows: PW > PW-TPSP >
30PW-Si/TPSP. The versatility of our catalyst was demonstrated by achieving quantitative yields in H -S reaction
using a wide variety of acetals with excellent yields up to 99 %. The stability of this new heterogeneous acid
catalyst was established by its successful recycle runs for five times.
5. References:
1.
2.
3.
S. Kamble, S. Shinde, C. Rode, Catal. Sci. technol., 5, (2015), 4039-4047.
A. Hosomi, M. Endo, and H. Sakurai, Chem Lett, (1976), 941-942.
D. Kampen, B. List, SYNLETT, 16, (2006), 2589-2592.
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