Now that our SiliaMetS Metal Scavengers are being used by many pharmaceutical and biotechnological companies, each SiliaMetS manufactured by SiliCycle is submitted to an extensive washing procedure which ensures a product with extremely low levels of extractables and leachables.
SiliCycle has implemented a quality control procedure regarding possible leaching that includes loading and reactivity determination, as well as leachables and extractables analysis (silica gel purity ≥ 99.995%). The solution must be free of contaminants for the product to successfully pass the rigorous quality control tests.
To address the end users concerns for potential leaching of impurities into reaction mixtures using SiliaMetS, we have performed three typical metal containing reactions. We then investigated the detection, identification, and quantification of possible impurities resulting from the scavengers used.
The following three transition metal catalyzed reactions were performed:
Experimental Procedure
Crude reaction mixtures (8 mL) were placed in a standard polypropylene tube equipped with a 20 µm frit and filled with 1 g of the appropriate SiliaMetS Metal Scavenger and mixed for 4 h at either room temperature or 80°C. Solutions were then filtered through a 0.02 µm filter prior to analysis.
Leaching Analysis
For each SiliaMetS, silanes leaching was analyzed by ICP-OES which has proven to be very sensitive for silicon quantification (detection limit in solution is 0.125 ppm). Traces of non-silicon containing impurities were also analyzed by GC-MS and 1H NMR Analysis. Only results for SiliaMetS Thiol and DMT are shown. However, no evidence of any impurities was found for allSiliaMetS. Contact us to get the complete study.
Gel Purity Calculation Example
Results shown in the table below for SiliaMetS Thiol & DMT confirm that minimal leaching occurs with SiliCycle SiliaMetS.
Note: concentration given are in ppm and represent mg of silicon leached per kg of SiliaMetS.
| Stability of SiliaMetS in Suzuki, Stille and Ring-Closing Metathesis reactions | |||||
| Reaction (solvent) | Temperature | SiliaMetS Thiol | SiliaMetS DMT | ||
| [Silicon] | Gel Purity | [Silicon] | Gel Purity | ||
| Suzuki (Toluene) | 22°C | 2 ppm | 99.9998 % | 1 ppm | 99.9999 % |
| 80°C | 2 ppm | 99.9998 % | 2 ppm | 99.9998 % | |
| Stille (1,4-Dioxane) | 22°C | 2 ppm | 99.9998 % | 1 ppm | 99.9999 % |
| 80°C | 1 ppm | 99.9999 % | 3 ppm | 99.9997 % | |
| Ring-Closing Met (DCM) | 22°C | 2 ppm | 99.9998 % | 2 ppm | 99.9998 % |
| Note: Very low levels of silicon were detected in most experiments, giving products purity higher than 99.995 %. | |||||
| Gas chromatography-mass spectrometry (GC-MS) | 1H NMR Analysis (d6-dmso) |
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Compared to the silica blank spectrum (bare silica in solvent), neither experiment showed evidence of any impurities for either SiliaMetS Thiol or DMT.
Note: each experiment was ran on a 1 g aliquote of SiliaMetS and was shaken for one hour at room temperature. In GC-MS spectrum, peak at 8.5 minutes is the internal standard (1-fluoronaphthalene, 100 ppm). In NMR spectrum, peaks at 2.4 and 3.4 ppm are, respectively, d6-dmso and water contained in deuterated solvent.
| SiliCycle certifies that SiliaMetS Metal Scavengers stored under recommended conditions in an undamaged container are guaranteed to perform for over two years from the manufacturing date without loss of performance, prouved by results at right. |
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SiliaMetS® Thiol (Si-Thiol) is a robust metal scavenger for a variety of metals including Pd, Pt, Cu, Ag and Pb under a wide range of conditions. It has been used in pharmaceutical processes up to the pilot plant scale. It is our most versatile metal scavenger and is the preferred metal scavenger for Pd(II), Cu, Ag, and Hg.
SiliaMetS® Thiourea (Si-THU) is a versatile metal scavenger for all forms of palladium and is widely used in the pharmaceutical industry. It works particularly well in organic solvents. It can also be used to scavenge Ag, Pt, Ru, Rh and Hg. Once complexed with a transition metal, it has been reported as being an effective catalyst.
SiliaMetS® Cysteine (Si-Cys) is the silica bound equivalent of the amino acid Cysteine. By attaching the molecule to the backbone via the amino group, the thiol group remains free and accessible for higher metal scavenging efficiency. It is a versatile metal scavenger for a variety of metals including Pd, Sn, Ru, Pt, Cu, Rh, Cd and Sc under a wide range of conditions and the preferred metal scavenger for tin residues.
SiliaMetS® DMT (Si-DMT) is the silica bound equivalent of 2,4,6-trimercaptotriazine (trithiocyanuric acid). It is a versatile metal scavenger for a variety of metals including Cd, Co, Ni, Pd, Pt, Rh, and Ru under a wide range of conditions and the preferred metal scavenger for ruthenium catalysts.
TMT has been reported to efficiently remove palladium and heavy metals by precipitation. Unfortunately, its solubility in organic solvents causes problem. SiliaMetS DMT solves this issue and almost all solvents can now be used.
SiliaBond® Amine (Si-NH2) is an effective scavenger of acid chlorides, sulfonyl chlorides, isocyanates and other electrophiles. Si-NH2 has been shown to be effective metal scavenger and catalyst for Knoevenagel reactions. SiliaBond Amine is also used in chromatography as normal phase sorbent.
SiliaBond® Amine (Si-NH2) is an effective scavenger of acid chlorides, sulfonyl chlorides, isocyanates and other electrophiles. Si-NH2 has been shown to be effective metal scavenger and catalyst for Knoevenagel reactions. SiliaBond Amine is also used in chromatography as normal phase sorbent.
SiliaMetS® Diamine (Si-DIA) is a proven scavenger for metals and electrophiles. It scavenges acids, acid chlorides, anhydrides, aldehydes, isocyanates, and chloroformates as well as Pb, Ni, and Cd.
SiliaMetS® Triamine (SiliaMetS WAX-3, Si-TRI) is effective for scavenging metals such as Pb, Co, Ru and Pd. Our screening studies have shown it to be the preferred scavenger for Pb. It can also be used as a scavenger for acid chlorides, isocyanates and other electrophiles.
SiliaMetS® Imidazole (Si-IMI) is a versatile metal scavenger for a variety of metals including Cd, Co, Cu, Fe, Ni, Pd, and Rh under a wide range of conditions and the preferred metal scavenger for iron catalysts.
SiliaMetS Imidazole can also be used as an amine base in systems that are generally sensitive to basic conditions compared to other SiliaMetS supported bases.
SiliaMetS® TAAcOH (SiliaMetS Triaminetetraacetic Acid) is a silica bound metal scavenger for Pd(0), Ni(0) and Cu. It is the supported version of EDTA in its free form. It is an effective scavenger for metals in low or zero oxidation states, which includes many of the most synthetically useful catalysts such as tetrakis-(triphenylphosphine)palladium(0).
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