A Simple Automatic Hydrogenation Apparatus G . W. H. A. Mansveld, A. P. G. Kieboom, W. Th. M. de Groot,l and Herman van Bekkum Laboratory of Organic Chemistry, Delft University of Technology, The Netherlands
A SIMPLEAPPARATUS has been designed and constructed to record automatically the hydrogen uptake against time for liquid-phase hydrogenations at atmospheric pressure. EXPERIMENTAL
Apparatus. The apparatus is shown schematically in Figure 1. The reaction vessel ( I ) is connected to a stainless steel cylinder containing hydrogen gas and a differential water manometer. The piston of the gas cylinder is driven by a servomotor, which is controlled by an electronic circuit with an electrode in the right-hand leg of the water manometer. A pen, attached to the piston rod, records directly the displacement of the piston against time on a mechanically driven chart. A slight decrease in pressure in the system (caused for instance by hydrogen absorption) causes the level of the water in the right-hand leg of the manometer to fall. As a result, the contact between the electrode and the water is broken,
Present address, Unilever Research Laboratory, Vlaardingen, The Netherlands.
so that the servomotor is operated and the piston of the gas cylinder driven to the left. After the pressure has increased again, the water level will reach the electrode, thus switching off the servomotor automatically. During a hydrogenation reaction, this operation takes place continuously and the displacement of the piston is linearly correlated to the volume of the hydrogen uptake. By using a gas cylinder with a length equal to the width of the recorder paper, the pen records directly the hydrogen uptake against time. In this way, an inexpensive and reliable apparatus is obtained, not necessitating the use of an expensive differential pressure transducer and electronic recorder, as described by Bitner and Dutton ( 2 ) and Rohwedder (3). Procedure. The catalyst and the solvent are placed in the reaction vessel, valves 2 and 3 are closed, and the system is evacuated and filled with hydrogen (1.2 atm) by turning valve 1. This procedure is repeated twice. Atmospheric pressure in the system is obtained by opening valve 2 for a short time, and the manometer is connected by opening valve 3. Subsequently, the electronic control circuit and the stirrer of the (2) E. D. Bitner and H. J. Dutton, J . Amer. Oil Chemists' Soc.,
(1) Cf.H. van Bekkum, A. P. G. Kieboom, and K. J. G. van de Putte, Rec. Truu. Chim., 88, 5 2 (1969).
41, 720 (1964). ( 3 ) W . K. Rohwedder, J. Catalysis, 10,47 (1968).
VACUUM ELECTRONIC C I R C U I T
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Figure 1. Scheme of automatic hydrogenation apparatus Measures given in mm ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
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reaction vessel are switched on. After equilibrating the system for 30 min, the stirrer is switched off again and the substrate is introduced into the reaction vessel with a syringe. The pressure is adjusted by valve 2, and the reaction is initiated by starting the stirrer. The hydrogen uptake is then recorded automatically against time.
gas cylinder and proved to be very useful for small-scale hydrogenations and kinetic measurements. Note. The apparatus can accommodate gas cylinders with a volume up to 1000 ml and is also useful for other gasliquid phase reactions. Full details and design of the apparatus are available from the authors.
RESULTS
The apparatus and procedure described have, for instance, been used for the hydrogenation of benzene, using a 5 x platinum-on-carbon catalyst in acetic acid at 30.0 O C . The reproducibility of the rate of hydrogen uptake of six successive runs was 1.5x. The apparatus was equipped with a 70-ml
ACKNOWLEDGMENT
The authors thank the general service department for building the apparatus. RECEIVED for review December 2, 1969. Accepted February 26, 1970.
A “Do-It-Yourself” Electron Paramagnetic Resonance Cell J. F. Ambrose and D. Dillard Department of Chemistry, Kansas University, Lawrence, Kan. 66044
A. K. Carpenter and R. F. Nelson Department of Chemistry, Sacramento State College, Sacramento, Ca1.f. 95819
AMONGTHE PROBLEMS one enounters in practical EPR spectrometry are the cost and inflexibility of commercial quartz EPR cells. Different types of cells are available for a variety of functions-e.g., aqueous and non-aqueous work, tissue samples, etc.-but the cost in acquiring and replacing these cells is quite high. We have found that a suitable type of EPR cell for some kinds of work can be fashioned from heatshrinkable transparent Teflon (Du Pont) tubing and ordinary glass. Herein, a particular type of cell is described, one that is of use to us, but it appears that other cells could easily be constructed to suit anyone’s individual needs. At present, commercial EPR cells are constructed of quartz rather than borosilicate glass because of the presence of paramagnetic species in the latter. Teflon, unless irradiated, is also free of paramagnetic impurities, so it appears to be a suitable and far less expensive replacement for quartz. This “do-it-yourself”-type cell consists of a short piece of transparent, heat-shrinkable, thin-walled Teflon tubing (a brochure including tubing dimensions and prices is available from Kaufman Glass Co., Plastics Division, 1209-21 French St., Wilmington, Del. ; nominal i.d. tubing dimensions varying from 0.023 to 1.000-inch are available) that is flattened by simply pressing and creasing, leaving a small portion of the tubing at each end still rounded. Application of heat distorted the tubing uncontrollably, so the flattening should be done mechanically. Any kind of glass can be fitted into the tubing; in this case a quartz NMR tube was used, but borosilicate glass would also be perfectly usable since the glass portions are not in the cavity of the spectrometer. The glass is fitted snugly into the Teflon tubing and then sealed in by gentle heating, making sure that the flattened portion is not heated. If the seal is not tight, an epoxy glue can be smeared around the outside to effect a more solvent-tight junction. Studies involving the chemical and electrochemical generation of radical species are of primary interest to us; we have tested this type of cell under these conditions and have found 814
ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
20
GAUSS
,
Figure 1. EPR spectrum of cation radical of p-ethoxyN,N-dimethyl-aniline generated in propylene carbonate-0.1F iodine
it to be very satisfactory. Spectra obtained by chemical and electrochemical generation of radical species are shown in Figures 1 and 2, respectively. These spectra are at least as good as those obtained using the commercial quartz electrolytic cell supplied with the Varian E-3 spectrometer. The signal-to-noise ratio is about the same with both cells (quartz and Teflon) as is the resolution. Note that these studies were conducted in non-aqueous media. This particular cell is not suitable for aqueous work, since the Teflon portion is fairly thick and hence contains a relatively large amount of solution. Due to the high dielectric nature of water, the cell cannot be tuned because of excessive power loss. However, it should be no great problem to produce a cell with a flatter, thinner Teflon portion. If reproducibility of cell dimensions is a necessity, this may also be somewhat of a problem with these cells. Although we did not test the reproducibility in constructing these cells, it would seem to be rather difficult. In addition, because of the nature of the Teflon, cell dimensions may fluctuate somewhat from day to day, albeit slightly. Admittedly, just a “bare-bones”-type cell is presented; the
