McMaster University - Chem2O06 Lab Manual

1997/98


Microscale Laboratory Techniques - Carrying out Reactions


 

A typical assembly for heating a reaction mixture under reflux is shown at the left. While an air condenser is adequate for most applications, a water-jacketed condenser is also supplied, for cases where the solvent is very volatile or where the ambient air temperature is very high. A "spin vane" might also be included for magnetic stirring of the reaction mixture - this is a triangular device coated with teflon, which is shaped to fit the bottom of the conical flask.

Note that the apparatus is clamped at the condenser rather than at the flask, as one would do for a macroscale experiment using conventional ground-glass joint glassware. The apparatus can be clamped in this way because of the screw-cap connection between the condenser and reaction vial, which prevents the connection from falling apart.

Heating is provided by a sandbath atop a magnetic stirrer/heater. A thermometer should be clamped in contact with the sand so as to allow monitoring of the bath temperature. The bath contains slightly more than 1 cm of sand - it is important to have enough to ensure good thermal contact with the reaction vial, but not so much that it is difficult to see the contents.


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wjl; 25-nov-97