Modified Silica Sulfuric Acid

4 Silica Gel-Supported Aluminum Chloride (Si02-AICl3) 

---

Zolfigol et al. (2011) have synthesized a modified silica sulfuric acid (MSSA) as a new type of heterogeneous catalyst for the conjugated addition of pyrrole, indole, and thiols to Michael acceptors. This catalyst has the advantages of being a stable, nonvolatile, inexpensive, and safe for handling source of acid (Figure 1.2). 

FIGURE 1.2 Modified silica sulfuric acid (MSSA). 

Zolfigol, M.A., Veisi, H., Mohanazadeh, F., Sedrpoushan, A. 2011. Synthesis and application of modified silica sulfuric acid as a solid acid heterogeneous catalyst in Michael addition reactions. Journal of Heterocyclic Chemistry 48 977-986. 

Modified silica sulfuric acid (MSSA), as a new type of silica sulfuric acid, was effectively used in the conjugate addition of indoles with Michael acceptors under mild conditions at room temperature (Scheme 2.13) (Zolfigol et al. 2011). 

BDE 17, 28, 47, 66, 85, 99, 100, 153, 154 183 Palm oil Palm oil Extraction by dialysis in hexane using a semi-permeable membrane. Purification thorugh multilayer column filled with neutral silica, silica modified with sulfuric acid (44%, w/w), and silica modified with KOH. Gas Chromatography (VF-5MS Factor Four, Varian) IT-MS 0.07-1.3 pg (instrumental limit of detection) [42]... 

Khodaei, M.M., Khosropour, A.R. and Fattahpour, R 2005. A modified procedure for the Dakin-West reaction An efficient and convenient method for a one-pot synthesis of P-acetamido ketones using silica sulfuric acid as catalyst. Tetrahedron Lett. 46(12) 2105-2108. 

Kumar, G.G., Kim, A.R., Nahm, K.S., and Elizabeth, R. (2009) Nation membranes modified with silica sulfuric acid for the elevated temperature and lower humidity operation of PEMFC, Int. J. Hydrogen Energ., 34, 9788-9794. 

Exposure of keto acids 286 to ozone at low temperature followed by purging with excess ozone and the addition of silica gel and aqueous sulfuric acid led, over several days, to the clean formation of the desired tetracyclic artemisinin analogs 287 modified at C-3 and C-9 (Equation 35 Table 25) <1996JME2900>. 

Zolfigol, M. A., Shirini, E., Choghamarani, A. G., Mohammadpoor-Baltork, I. Silica modified sulfuric acid/NaN02 as a novel heterogeneous system for the oxidation of 1,4-dihydropyridines under mild conditions. Green Chem. 2002,4, 562-564. 

The first supported molten salt catalyst systems date from 1914, where BASF filed a patent on a silica-supported V20s-alkali pyrosul te sulfur dioxide oxidation catalyst [48], which even today - as a slightly modified catalyst system - is still the preferred catalyst for sulfuric acid production [49]. However, it took many years to realize in the 1940s [50,51], that the catalyst system actually was a molten salt SLP-type system which is best described by a mixture of vanadium alkah sulfate/hydrogensulfate/pyrosulfate complexes at reaction conditions in the temperature range 400-600 °C with the vanadium complexes playing a key role in the catalytic reaction [49]. 

Regeneration Physically or chemically modified cellulose can be regenerated in suitable solvents (for instance xanthates in sulfuric acid) leading to pure cellulose Relative density (pr) The ratio between the aerogel bulk density and the bulk glass density (e.g., for silica 2.2 g/cm )... 

Cannabinoids in cannabis preparations have been measured using an ODS-modified silica column with ED (presumably GCE, +1.2V vs Ag/AgCl). " The eluent was acetonitrile-methanol-aq. sulfuric acid (10mmolL ) (16 + 7 + 6). Bourquin and Brenneisen used a similar system to measure 11-carboxy-A -tetrahydro-cannabinol (THC-COOH) in hydrolysed urine. Cannabinol was the internal standard. The reason such a high potential was used in these reports is not clear (no voltammogram was given) since THC-COOH contains a phenolic hydroxyl... 

To estimate the content of dihydro-2,5-dihydroxy-6-methyl-4//-pyran-4-one (DDMP) saponin and saponin B in selected pea cultivars, an HPTLC method was developed [35]. Silica gel 60 F254 plates were prewashed with methanol and activated at 100°C prior to development in automated multiple development chamber AMD2 using chloroform-methanol-water (55 37 8, v/v). Densitometry, after postchromato-graphic derivatization with anisaldehyde-sulfuric acid, revealed the prevalence of saponin B over DDMP saponin in all pea cultivars. The identities of the two com-ponnds were determined by coupling HPTLC directly to ESI-MS and additionally by offline MALDI-TOF/TOF-MS by application of a purified extract/matrix mixture onto a standard steel MALDI plate. HPTLC plates intended for MS analysis were developed with a modified developing solvent chloroform-methanol-water (6.5 3.5 0.9, v/v). The analytes were eluted from the plates with 0.1% formic acid-acetonitrile (40 60, v/v) by means of TLC-MS interface (CAMAG) and transferred into the ESI-MS system, which operated in positive-ion mode. 

---