SiliaMetS®- Metal Scavengers Typical Experimental Procedures
Screening in Batch Reactor Mode (Bulk)
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.
- 1. Dissolve the crude product to be treated in a suitable solvent (or use directly the crude reaction mixture) and prepare vials containing the same solution volume.
- 2. Directly, add to these vials the amount needed for each SiliaMetS included in the kit. Note: no pre-wetting of the SiliaMetS is required. See Calculation of the amount of SiliaMetS to use.
- 3. For initial tests, stir the solution for at least one hour at room temperature.
- 4. Scavenging progress can be followed by normal analytical techniques. The scavenging progress can be estimated by looking at the color of the solution as demonstrated in the figure. When the scavenging is almost completed, the solution is less colored and SiliaMetS becomes colored. In some occasional cases, if all the samples are still coloured, let them react for a longer time and/or add more equivalents of the SiliaMetS and/or increase the temperature of the reaction.
- 5. At the end of the scavenging, filter off the SiliaMetS using a fritted funnel or filtration device.
- 6. Wash the SiliaMetS with additional solvent for total recovery of the API (or compound of interest) and concentrate the solution under vacuum.
- 7. Analyze the residual metal concentration of each vial to identify the most efficient SiliaMetS Metal Scavenger. Note: you can choose more than one scavenger.
- 8. If you are satisfied with the scavenging efficiency of the best SiliaMetS, direct scale-up is possible. Otherwise, scavenging optimization can be done with SiliaMetS identified in #7 (see next section).
Screening with SiliaMetS Fixed Bed Mode (SPE or Flash Cartridges)
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.
- 1. Condition the cartridge with 3-4 cartridge volume using the same solvent as the solution to be treated.
- 2. Add to the top of the cartridge the solution containing the API and the metal and let it pass through the cartridge under gravity
Note: if needed, a slight positive pressure on the top of the cartridge or a light vacuum can be applied to speed up the flow rate.
- 3. As shown by the picture on the right, a dark coloured band will be observed on the top of the silica bed most of the time.
- 4. If the residual solution is still coloured, multiple passes through the same cartridge can be done.
- 5. Once the scavenging is completed, wash the cartridge using at least 3 column volumes of solvent to insure total API (or compound of interest) recovery. Note: in some particular cases, additional washing may be required.
Experiment Optimization with SiliaMetS
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.
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.
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.
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.
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.
If required, mixing rates can be increased to get better scavenging results. With faster stirring, you improve SiliaMetS dispersion in solution.
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).
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.
Leaching & Stability Studies
Metal Scavengers Calculation