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In the original project, the period of prolonged reflux was carried out using a two-litre glass reaction vessel with three Quickfit taper necks (24/29), fitted with an efficient double surface condenser (Fig 20.1). A heating mantle and a means of stirring the mixture and monitoring the temperature were also required. To protect the reacting substances from atmospheric moisture, calcium chloride guard tubes were used. To remove excess alcohol in the final stage, the double-surface condenser was attached to the reactor vessel by means of a distillation head. The alcohol that was distilled was collected in a glass receiving vessel that was also fitted with a calcium chloride guard tube (Fig 20.4). An accurate chemical balance, capable of measuring to 0.1g, was required to weigh out the necessary reactants.
In the subsequent ‘Single Shot’ project, a specialised stainless steel pressurised reaction vessel (autoclave) was employed. This replaced the glassware and the reflux condenser. This sealed stainless steel vessel (autoclave) allowed the reaction to take place under pressure, shortened reaction time and reduced the problem of contamination from atmospheric moisture (Fig 20.2). Pressure was read directly from the gauge with the temperature in the reaction vessel read via a thermocouple (with an infrared thermometer used as backup).
To remove the substituted malonates from the reaction vessel a condenser was employed. This was made from stainless steel tubing surrounded by a water jacket. Connected to a receiving vessel of stainless steel this was then vented using a calcium chloride guard tube and placed under reduced pressure in the distillation process using a water tap vacuum attachment.