High-Pressure Apparatus and Experimental Procedures

Many kinds of flexible sample tubes have been devised. Four different kinds of sample containers are shown in Fig. 3. In all cases, either polyte-trafluoroethylene (PTFE) or metal bellows are used, and there is at least one threaded hole for withdrawal. For high-pressure reactions at temperatures of up to ca. 60 °C, several kinds of commercially available syringes and polyethylene tubes have also been used. 

In most preparative experiments under high pressure, the procedure is as follows pressure is applied at room temperature (rt) to a sample tube containing the reagents and, if necessary, catalysts and solvent, before the temperature is raised, if required. After a suitable time, the heater is switched off. After cooling to rt, the pressure is carefully released, and the sample tube is removed from the vessel. When the reaction at high pressure does not take place at ambient temperature, according to GC, TLC, NMR, or other analytical techniques, an increase of pressure and/or temperature might be effective. In certain cases, the use of a catalyst may lead to success. 

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