An Automatic Atmospheric Pressure Hydrogenator A simple, inexpensive apparatus for we in atmospheric pressure hydrogenations has heen described in the literature1dnd is found in many laboratories. Typically, it is employed to reduce functional groups such as olefins, aldehydes, and ketones. The apparatus in- ' cludes a mercury manometer, a hydrogen reservoir, and a leveling bulb. During the course of a reaction, the hydrogen is constantly consumed and the oressure stesdilv decreases. To comDensate for this pre3sure decrease, the leveling bulh must he manually adjusted to return :he pressure tu the dexiwd \,aIw. Although accurate kinetic dala may be obtained through uaeof the hylnrgrnator, it can easily he understood that data accumulation can be a rather tedious process. In this report, we wish to report on the design and operation of an inexpensive apparatus that will automatically keep the pressure constant a t one atmosphere of hydrogen. This automatic hydrogenation aooaratus allows the lahoratorv, oersonnel to onrsue other activities during the mwsc of the hydrogenation. The progress of the l gen consumed. reaction is simply follwed try periudically monitoring the volume of h) n e ~It. differs ~ from that previously described' The hydrogenator shown in the figure is similar in design to that c en reservoir (31are substituted for the leveling in two main areas. First, a 12-V solenoid valve (11, a switch (61, and a ni I the new design. The first electrode is located bulb. Second, the mercury manometer contains two platinum electrod re1 with the switeh in position b. When hydrogen below the mercury level while the s a n d is approximately 1mm above th is consumed bv the reaction. the mercurv level will rise and make contad.wit h the upper platinum electrode. This completes the circuit bet&en the 12-V power suppiy and the solenoid valve and the vahie ODens. . Nitroeen then oressurizes the reservoir 13) and the oil level in the reservoir rises. This rise compresses the hydrogen and thereby increases the pressure. At this point, the mercury level decreases, the circuit opens and causes closure of the solenoid valve. This cycle enables the pressure to be kept constant to within 1mm of mercury during the course of a hydrogenation. This automatic hydrogenation system has been used extensively for over a year in our laboratory with essentially no mechanical or operational difficulties. Systematic studies have been performed in which catalysts such as Raney nickel and nickel boride (NizB) have been employed in the hydrogenation of various functional groups. Some typical reactions are listed below. ~
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The reaction flask containing reactant, solvent, and catalyst is attached at stopcock D, and switch 161is put in position a. This action causes the solenoid valve Ill to open, and nitrogen flows into the nitrogen reservoir (31, applying pressure to the oil. Stopcock A is then opened to vent the pressurized gas in the hydrogen reservoir (5).When the oil level bas reached Stopcock A, it is closed to the reservoir, and switch 161is placed in position b. At this point, it should he verified that Stopcocks B, C, and D are open to the three possible directions. The entire system, including the reaction vessel, is then evacuated and filled with hydrogen. This procedure is repeated twice to ensure that the system is properly purged. After the third cycle, the vent valve (41and then Stopcock A are opened, allowing hydrogen to fill the reservoir. When the oil level reaches the zero mark, the hydrogen supply is shut off. The vent valve 141is then closed and Stopcock A is opened to connect the hydrogen reservoir only to the hydrogenator reaction flask. Next, Stopcock C is turned 180' so that one side of the manometer is isolated from the remainder of the system. After the power supply has been energized, the reaction can be initiated. The progress of the reaction can then he monitored by following the volume change in the reservoir 15) as a function of time. Acknowledgment The authors gratefully acknowledge the financial support of Ventron Corporation for making this work possible.
' Langrebe. J. A.. "Theory and Practice in the Organic Laooratory." Heath and Co.. Lexington, Massachusetts. 1977.
Jones. L.. Master's Thesis. College of Engineering. University of South Florida. 1976. J. A. Schrelfels, W. E. Swartz, Jr., and P. C. Maybury University Of Soulh Florida Tampa, FL 33620
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Journal of Chemical Education
