Double manifold

A Schlenk apparatus, illustrated in Fig. 3 and similar to that employed by Collman et al., is used for the reaction sequence. Vacuum and argon sources are provided by a double manifold, to which the stopcocks of the apparatus are attached. Prepurified nitrogen can be used in place of argon. 

If sufficient resources are available each bench should have a medium or high vacuum pump, connected to a double manifold, but in many labs vacuum pumps are considered to be communal equipment (see Chapter 8 for more details about vacuum pumps). 

If you wish to carry out reactions under dry and/or inert conditions as a matter of routine, the double manifold is perhaps the single most useful item of equipment that will enable you to do this. We recommend that this be a standard item of equipment, permanently fitted to every individual bench and connected to the laboratory inert gas supply by PVC (Tygon) tubing. The manifold consists of two glass barrels, one evacuated and one filled with an inert gas. An outlet is supplied by either barrel of the manifold via a two-way double oblique tap (see Figs. 4.4 and 4.5). Thus, at the turn of the tap, equipment connected to the manifold can be alternately evacuated or filled with inert gas. 

These are so universally useful that we suggest you have at least three of the B14 size and two of the B24 size as part of your personal bench set. They are particularly useful when used in conjunction with a double manifold. With the inert gas from the manifold connected to the horizontal inlet and the tap in position A (Fig. 4.10), a reaction flask can be kept under a slight positive inert gas pressure. If the gas flow is increased and the tap is turned to position B, liquids can be introduced via the vertical inlet, whilst maintaining an inert atmosphere (see Chapters 6 and 9 for more details). Another simple use is for connecting flasks to a high vacuum system for removal of last traces of solvent. 

For liquids with a high boiling point, or which decompose on heating, distillation under reduced pressure is the usual method of purification. Again it is convenient and effective to use a one-piece distillation apparatus in conjunction with a double manifold for this type of distillation. The procedure is described in more detail in Chapter 11, and some examples of reagents which can be distilled under reduced pressure are given in Table 6.2. 

When the distillation is complete the heat is turned off and the two-way tap on the double manifold is slowly turned to the inert gas position. The flask containing the distillate will then be conveniently under an inert atmosphere and should be quickly removed and fitted with a tightly fitting septum (see Section 6.4.1 for more details about storing and transferring reagents under inert conditions). 

For some experiments the dispersion can be used without separating out the oil. To do this simply weigh it into a pre-dried reaction flask and place it under inert atmosphere by sequentially evacuating, then purging the flask with an inert gas. A 3-way Quickfit tap connected to a double manifold is ideal for this purpose. 

Weigh the dispersion in a flask (do not forget to take the oil into account) and place it under inert atmosphere. Use a double manifold connected by a 3-way Quickfit tap if possible (Fig. 6.18a). 

A medium vacuum of about 10-12mmHg is ideal for a variety of tasks including rotary evaporation, distillations, and for serving double manifold-type inert gas lines. 

Alternatively, a piece of high vacuum tubing can be used to connect the traps to a distillation apparatus, a double manifold (Fig. 4.4, Chapter 4), or any other piece of equipment. 

A fast flow is used when filling a system, but once the reaction is set up, one bubble every 5-10s is adequate. A piece of apparatus which is very useful when used in conjunction with a double manifold is a Quickfit 3-way tap, which is also described in more detail in Chapter 4. 

Although we recommend using the double manifold techniques described above, reactions can also be kept under inert atmosphere by using a balloon filled with inert gas (Fig. 9.10). This can prove particularly useful if a... 

Dry all the glass apparatus in an oven, or with a heat gun under vacuum, and purge with inert gas whilst cooling. This is most easily accomplished by connecting the apparatus to a double manifold/bubbler system (see Chapter 4). Although Quickfit distillation assemblies can be used, we prefer one piece type apparatus, as shown in Figs. 11.8 and 11.9b. 

Fig. 2.2 Double manifold system designed to provide a source of inert gas and reduced pressure.

After about 30 min, the gas inlet is removed and the system placed under a blanket of inert gas using the double manifold and the sodium dodecylsulfate (1.0 g) is added. The mechanical stirrer is then started and vigorous stirring is maintained. The solution is heated to 50°C for 2-4 h. ... 

While the apparatus is still hot, set up the two-necked flask with a septum cap and magnetic stirrer bar. Connect to the double manifold with a gas inlet adapter, evacuate the flask and then fill with nitrogen. Allow the flask to cool to room temperature. ... 

While the apparatus is still hot, a two-necked round-bottomed flask (250 ml) is equipped with a Teflon-coated magnetic stirrer bar, a rubber septum on one neck whilst the second neck is connected to the double manifold. 

Into a dry two-necked, round-bottomed flask (100 mL) equipped with a magnetic stirrer bar, a septum cap, and a nitrogen gas inlet attached to the double manifold, add lithium chloride (0.02 g, 0.5 mmol) under a flow of nitrogen. Freshly distilled THF (50 mL) is added directly via a gas-tight syringe through the side-arm of the flask. 

Kryptofix (0.012 g, 0.03 mmol) is placed in a two-necked round-bottomed flask (50 mL) fitted with a rubber septum and connected to the double manifold by a gas-inlet tube. The flask is then heated to 60°C for a further 2 h and then cooled to room temperature and immediately prior to polymerization, the minimum volume of THF is added to dissolve the ligand. 

The monomer is prepared for addition by cooling to -1S°C in the presence of a portion of MAO. A two-necked round-bottomed flask (100 mL) fitted with a rubber septum is attached to the double manifold by means of a gas-inlet tube and flushed with argon. 1-Hexene (2 mL, 16 mmol) and MAO (0,7 mL, 12 mmol with respect to aluminium) are added using gas-tight syringes of appropriate sizes. The flask is then place in a dry ice/acetone bath and allowed to stand at 78°Cfor30 min. 

To a single-necked round-bottomed flask equipped with a condenser, a Teflon-coated magnetic follower and inlet to the double manifold is added a mixture of 4,4 -difluorobenzophenone (15.0 g, 68 mmol), sodium hydroxide (5.44 g, 136 mmol), water (35 ml), and DMSO (150 ml). 

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