Filtering cannula

Fig. 1.12. Assembly of a filter cannula or Green filter. (a) A piece of glass capillary tubing, which has been blown open and fire-polished to form a lip on one end, is attached to the cannula with epoxy cement, (b) Filter paper is folded over the glass capillary and secured with wire.

The checkers note that, when carrying out this preparation on a Schlenk line, filtration through Celite on a glass frit is preferred to filtration with a filter cannula. Owing to the presence of large amounts of solid, filtration through a filter cannula is very slow and usually leads to oxidative decomposition of the product. 

Attach a 5 cm circle of filter paper over the glass end of the filtering cannula with wire as shown in Fig. 3.1. Briefly remove the septum from the reaction flask and push the metal end of the cannula through the bottom of the septum. Pull the cannula through and replace the septum such that the filter paper-covered glass end of the filtering cannula is now inside the reaction flask. 

To wash the product, first pull the glass end of the filtering cannula back to... 

Filter the solvent from the crystalline product using a filter cannula (Chapter 7, Protocol 4). 

Wash the crystals of 1 with cold, dry nitrogen-saturated hexane (2 x 40 mL) injected by syringe, remove using a filter cannula, and dry under vacuum for 2 h. The yield of 1 is typically 120-140 g, 60-70% for the three steps and the material displays the appropriate spectroscopic data. The dry solid is stable indefinitely in air. A further portion (5-10%) may be obtained by concentration of the filtrate. 

Transfer the resulting yellow solution into the empty Schlenk tube via a filter cannula. If any decomposition is seen at this stage, the solution may be filtered through a small bed of Kieselguhr. 

Separate the yellow crystals from the mother liquor by filtration using a filtering cannula and collect the mother liquor in a Schlenk tube. 

Separate the yellow crystals from the mother liquor by filtration using a filter cannula and collect the mother liquor in a Schlenk tube under nitrogen (Chapter 7, Protocol 3). Wash the crystals with cooled nitrogen-saturated petroleum ether and remove the supernatant solution. 

Filter into a Schlenk tube via a filtering cannula and concentrate using the vacuum line to give an orange residue. 

Transferring liquids from one Schlenk tube to another via a cannula or filtering cannula... 

Ensure that Schlenk tube B and the cannula (or filtering cannula) are clean and have been dried for at least an hour in a 100°C oven before use. 

Allow the cannula (or filtering cannula) to cool to room temperature. If using a filtering cannula, place and wire a piece of filter paper around the glass filtering device as illustrated in Fig. 3.1. 

Lower the tip of the cannula (or filtering cannula) into Schlenk tube A until it is just below the level of the liquid to be transferred. 

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