The reaction is conducted in a 500-ml. round-bottomed flask attached (by a ground-glass joint) to a Pyrex reflux condenser, the top of which is connected to a three-way stopcock leading to (a) a source of nitrogen and a mercury trap and (b) a water aspirator (Fig. 5). The flask and condenser are dried by warming with a free flame while the system is under reduced pressure (stopcock turned to (b) to engage aspirator). Dry nitrogen (Note 1) is then admitted to the apparatus by turning the stopcock slowly to the position indicated in Fig. 5 while nitrogen is bubbling through the mercury trap. The cooled flask is quickly charged with 45 ml. of dry tert-butyl alcohol (Note 2) and 2.15 g. (0.055 g. atom) of potassium (Note 3) and is then reconnected to the apparatus. The flow of nitrogen is stopped, the screw clamp is closed, and the mixture is boiled under reflux until the potassium is dissolved (Note 4), hydrogen being liberated through the mercury trap. The solution is then cooled to room temperature while nitrogen is admitted to equalize the pressure. The flask is quickly disconnected just long enough for the addition of 9.11 g. (0.05 mole) of benzophenone (Note 5) and 13.05 g. (0.075 mole) of diethyl succinate (Note 5). The system is then evacuated (until the alcohol begins to boil) and filled with nitrogen. With the stopcock as shown in Fig. 5 and the screw clamp closed, the mixture is refluxed gently for 30 minutes (Note 6). It is then chilled, acidified with about 10 ml. of cold 1:1 hydrochloric acid, and distilled under reduced pressure (water aspirator) until most of the alcohol is removed. Water is added to the residue, which is extracted thoroughly with ether, and the combined extracts are washed with successive portions of 1N ammonium hydroxide until a test portion gives no precipitate on acidification. The combined alkaline solutions are washed once with a fresh portion of ether and then added slowly with stirring to an excess of cold dilute hydrochloric acid. When the addition is complete the mixture should still be acidic to Congo red. The pale tan crystalline half-ester is separated on a suction funnel, washed well with water, and dried. The yield is 14.0–14.5 g. (92–94%), m.p. 120–124°. If a purer material is desired the product may be recrystallized by dissolving it in about 50 ml. of warm benzene, filtering, and adding an equal volume of petroleum ether (b.p. 40–60°). Upon cooling, 13.0–13.4 g. of almost colorless half-ester crystallizes, m.p. 123–124.5°.