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Experimental Skills

Quick Solvent-drying Techniques

When it is not strictly required to use super-dry solvent, one can produce reasonably dry solvent by adding in a generous amount of anhydrous CaCl2 or Na2SO4, shaking the mixture well and then sitting for over an hour.

Reagent-Handling

It is best to prepare the corresponding solution using suitable solvent when handling gases and other substances with difficulties in using.

Active Substances Quenching

When quenching active substances like sodium and CaH, there is a high risk that the reaction mixtures may catch fire.

  • Use freezing mixture to absorb the heat produced during the quenching process.

  • Make sure quenching does not happen in a closed system.

  • Choose quenching reagent wisely. In the case of sodium, one can use Isopropyl alcohol as the quenching reagent instead of H2O or Ethyl alcohol.

  • Quenching should be conducted in the open or where there are no other combustibles and obstacles.

Extraction

If the desired molecules are in a solvent with high polarity, then by adding in a moderate amount of H2O and then using a relatively low-polar solvent to proceed extraction, one can expect the high-polar solvent to stay in the aqueous phase and the product will be kept in the organic phase.

Flash Column Chromatography

  • The types and quantities of silica and developing solvents used should depend on the acidity, polarity and quantity of the desired product. It is necessary to have a test run using thin-layer chromatography beforehand.

  • Make sure there are no air bubbles in the chromatographic column.

  • Using dry or wet sample normally does not affect the result of flash column chromatography, however, one should take the desired molecule’s properties into consideration, that is, generally basic or easily-decomposed compounds should use wet samples.

  • Sample loading should be right in the center of the chromatographic column.

  • After sample loadingļ¼Œone should add a thin layer of Quartz sand to prevent any disturbance coming from solvent loading.

  • Every joint part should be secured by rubber bands or clips.

  • When there are not any other compounds have similar polarity as the desired molecule, one can add more pressure to accelerate the flow rate of the developing solvents.

Recrystallization

Crystals are obtained from the solution of one or more solvents. In the two-solvent system, solvent A and B should be miscible in a relatively low temperature and when solubility is A > B, it is desirable that the boiling point is A < B and the density is A > B. And the slower A evaporates, the bigger the crystals produced are.

Cultivating Single Crystal

The basic rules are the same as in recrystallization and the following are some modification methods.

  • Use a container with a narrow inner diameter and dissolve the sample product in as little solvent A as possible which requires that product has good solubility in A. Then gently and slowly add in another solvent B which should be practically immiscible with product and A so that there is a clear and definite line between the two solvents. Seal the container and place it where low temperature and minimum movement occur. If conducted smoothly, there should be single crystals near the interface after a reasonable period of time.

  • Dissolve sample product in minimum solvent A in container 1 and keep the opening exposed. Put container 1 in container 2 which is filled with a liberal amount of poor solvent B but not enough to submerge the opening of container 1. Seal container 2 and put it where has low temperature and close to non-disturbance. Under ideal conditions, single crystals will be produced in container 1.

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Email:
Tel:1-201-478-8534
1-516-662-5404
Fax: 1-516-927-0118
Address: 2200 Smithtown Avenue, Room 1 Ronkonkoma, NY 11779-7329 USA