Robert M Rioux, Pennsylvania State University, University Park, PA

The use of gases in a synthetic chemistry laboratory is essential for carrying out a variety of highly facile and atom economical transformations. Reactions such as hydrogenation, oxidation, and amination require the use of gases like hydrogen, oxygen, and ammonia. Due to the poor solubility of these gases in typical reactant solutions, high pressures are necessary to achieve a meaningful reaction rate. Not only are these gases highly reactive, the use of high pressures makes these operations fairly hazardous. The biggest challenge in the use of high pressure is the containment of the high-pressure gas for the entire duration of the reaction, with close monitoring of the pressure and temperature, to avoid the formation of explosive mixtures and runaway reactions.

These reactions are typically carried out using thick-walled pressure vessels. The pressurized vessel allows for operation at high pressure with appropriate safety concerns abated. Figure 1 demonstrates the various parts of a typical pressure vessel, used to conduct high-pressure reactions. The following protocol highlights the procedure for the safe operation of these high-pressure reactor vessels.

Figure 1. (a) Parts of the high pressure reactor vessel. (b) Assembled high pressure reactor vessel.

The operation of the high-pressure Parr reactor (or equivalent) can be roughly broken down into 3 steps.

1. Charging

1. Select an appropriate secondary reaction vessel based on the scale of the reaction. Test tubes, Erlenmeyer flasks, or round-bottom flasks are some examples of appropriate reaction vessels. Make sure to keep enough head space above the solvent level in the flask as the solvent tends to bubble up during pressure venting.
2. Place the reactants, along with a stir

The manipulation of gases at high pressure can be done with the use of a Parr reactor (or equivalent) vessel. Proper safety precautions should be observed while operating these vessels as they present an explosion hazard.