High Pressure Hydrogenations

Revision Date:

6 March 2023

Prepared By:

Benjamin T. King, adopted from Richard Sarpong’s SOP at UC Berkeley.

Lab Supervisor:

Professor Benjamin King

Location:

This procedure is for operations in the King Group room CB327.

Approvals:

Performing a hydrogenation reaction requires training from the PI. Approval from the PI for each and every hydrogenation reaction is required.

Hazards and Precautions:

Hydrogenation reactions pose a significant fire hazard due to the use of flammable solvents. The presence of hydrogen gas increases the risk of explosion. The heating of a closed vessel and the high pressure of hydrogen gas pose an explosion risk. Finely divided, dry palladium can induce the spontaneous ignition of organic solvents in the presence of oxygen (or air).

Engineering Controls:

This procedure should be performed in a fume hood in good working condition. The high pressure reactor must be fitted with an appropriate burst disk. The apparatus must be behind a blast shield.

Administrative Controls/Designated Area:

No special controls or designated area required.

Personal Protective Equipment

a face shield and safety goggles must be worn
a fire-resistant laboratory coat must be worn
a blast shield must be in place before the Parr bomb is pressurized.
Nitrile gloves should be worn when handling solvents and chemicals.

Safety Equipment

A safety shower and eyewash must be readily available when working with these chemicals.

Transport and Storage

Hydrogen cylinders should be transported according to CGA recommendations.

Incident Response

Skin Contact: Immediately flush affected area with cold water using sink or safety shower as appropriate. Remove clothing and jewelry as necessary to reach all affected areas. Seek medical attention if burning or redness is present.
Eye Contact: Immediately flush eyes with cold water using eyewash. Physically hold eyes open if necessary. Seek medical attention immediately.
Minor Spill: Wear the following minimum PPE: goggles, butyl or nitrile chemical resistant gloves, and lab coat. Use spill kit located in lab to clean up spill per CHP instructions or laboratory SOP.
- Minor spills are generally considered to be spills that have a risk equivalent less than that of a spill of one liter of concentrated acid.

Experimental Procedure (indicate if attached):

Flush the glass reaction vessel with inert gas
Weigh out the desired amount of Pd/C and transfer into a glass reaction flask (often an Erlenmeyer flask) under an inert atmosphere blanket using an inverted funnel connected to a Schlenk line..
Wet the catalyst with a small amount of ethyl acetate, dichloromethane, or toluene to the reaction flask, making sure to wash down any Pd/C stuck to the flask walls. All the Pd/C should be submerged at this point.
Carefully add methanol or other solvent via a stream down the side of the flask wall.
Add the reaction substrate either as a solution or neat.
Verify that the temperature probe is affixed to the Parr bomb body and that the heating element is unplugged.
Add a stir bar to the glass reaction vessel, then fit with a septum and a 12 gauge needle to allow gas to flow. Place the glass reaction vessel into the Parr bomb body, set it on a stir plate, and verify that mixture is stirring.
Verify that the top of the Parr bomb assembly is equipped with a burst disk. Place the top of reactor assembly onto the Parr bomb body.
Fit the split-ring clamps onto the Parr bomb assemble. Finger tighten.
Add the clamp ring to hold the split-ring clamps in position. Loosen the clamps.
Purge the vessel with N2 for three minutes.
Using a torque wrench and alternating in a star pattern, tighten the bolts at 5 ft-lb increments to 25 ft-lbs.
Securely clamp the reactor above the stir plate.
Verify that the N2 line is disconnected and the N2 valve is closed. Charge the reactor to 100 psi with H2. Slowly ent the reactor. Repeat the charge/vent cycle a second time.
Place the blast shield.
Charge the reactor to the desired pressure, not to exceed 500 psi.
Verify that the temperature probe is affixed to the reactor and that the heating element is unplugged.
Route the heater through a Variac set to ~65% to a digital temperature controller that is plugged into a GFCI outlet.
Wrap the reactor in insulation
Set the desired temperature, not to exceed 135 °C. Check the temperature at 15 minute intervals to ensure smooth heating.
At the end of the reaction, turn off the heater and allow to cool sufficiently (at least below the boiling point of the solvent!).
After the reaction has cooled, slowly vent the reactor. Rapid venting can cause hydrogen to ignite due to heating in adiabatic expansion.

Prior approval: is prior approval required before performing this procedure?

Yes, prior approval for each and every high pressure hydrogenation reaction must be obtained from Ben King.