To select the best scavenger for initial screening experiments, do the following steps for each SiliaMetS Metal Scavengers included in the kit. Use 4-8 molar equivalents of each SiliaMetS in respect to the residual metal concentration.
SiliaMetS fixed bed formats are a great alternative for metal removal and are directly scalable. Initial screening investigations can be done using SiliaPrep 2g/6mL SPE cartridges.
If, upon completion of the screening procedure, the scavenging is not completed or you wish to reduce the number of equivalents, or the reaction time, optimization can be undertaken.
Various parameters can be changed one at a time or simultaneously to improve the metal removal efficiency.
Note: you can mix multiple Silia MetS to get superior efficiency.
Number of SiliaMetS Equivalents
| For initial screening experiments we suggest to use 4-8 molar equivalents in respect to the residual metal concentration of each SiliaMetS. Once the preferred scavenger is identified, further optimization can be done to reduce the number of equivalents used (typically down to 2-4 equivalents). Graph represents residual concentration (%) of Pd(AcO)2 with SiliaMetS Thiol in DMR. |
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Subsequent Treatments with SiliaMetS
In some particular cases (equilibrium process or the presence of multiple species), multiple treatments with SiliaMetS could be suitable instead of one single treatment with a larger amount. For optimal results, filtration between each treatment can allow for a higher scavenging efficiency.
Reaction time
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In some particular cases, where increasing the temperature is impossible, longer contact time with the scavenger can allow higher scavenging efficiency. Conditions: Pd(AcO)2, THF, SiliaMetS Thiol, RT. |
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Temperature In initial screening, we suggest to run the scavenging experiments at room temperature. Usually, metal scavenging is completed after one hour or so. However, if the timescale is too long for your need, higher scavenging rates can be achieved by increasing the temperature. SiliaMetS can be safely used at elevated temperature without degradation and can be added either at room temperature or directly to warm solution. Mixing Rate SiliaMetS are mechanically stable and offer excellent scavenging efficiency in batch processes agitated with overhead and magnetic stirrers, as well as orbital shaking under low to moderate agitation rate. pH of Aqueous Solution When the scavenging is done in aqueous solution, it is possible to use SiliaMetS in a pH range of 2 to 12. Furthermore, depending on the nature of the SiliaMetS, pH can modify the nature of functional groups present on the scavengers by charging them. Scavenging can be affected (i.e.: amine groups in acidic conditions). Solvent SiliaMetS can safely be used in a wide range of organic and aqueous solvents commonly used in laboratory and in process, such as DMF, DMSO, THF, 2-butanone, alcohols, ethers, chlorinated solvent, etc. As demonstrated in the graphs below, the nature of the solvent does sometimes influence the scavenging efficiency. If scavenging or kinetic are too slow, changing solvent or co-solvent addition should be considered. SiliaMetS Format (Mode Used) One advantage of SiliaMetS is their great compatibility with various technologies. They can be used in batch, in fixed bed (SPE or Flash cartridges), in flow chemistry, or in microwave. Scavenging efficiency can be improved by changing the mode used. |
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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