A
250-mL, one-necked, round-bottomed flask is equipped with a
magnetic stirrer and a
reflux condenser protected by a
calcium chloride drying tube. Into the flask are placed
30.0 g (0.14 mol) of di-tert-butyl malonate (Note
1),
8.4 g (0.28 mol) paraformaldehyde (Note
2),
1.4 g (0.014 mol) of potassium acetate,
1.4 g (0.007 mol) of cupric acetate monohydrate, and
70 mL of glacial acetic acid. The resulting green–white suspension is placed in an
oil bath preheated to 90–100°C and stirred for 2 hr (Note
3). The reaction mixture is allowed to cool to room temperature, and the reflux condenser is replaced with a short-path distillation apparatus, the vacuum outlet of which is connected in sequence to a
trap cooled in acetone–dry ice, a
potassium hydroxide trap, another trap cooled in acetone–dry ice, and a
vacuum pump. The
receiving flask is cooled in acetone–dry ice, and the system is evacuated over approximately 1 hr to remove
acetic acid and other volatile material (Note
4). The bath temperature is increased to 40–50°C for 15 min and then is rapidly raised to 140–150°C to drive over crude product, which is collected over a boiling-point range of 60–82°C (Note
5). When distillate ceases to come over, the bath temperature is increased to 170°C and distillate is collected over the same boiling-point range until the reaction mixture turns from blue to green–brown. The total amount of crude product collected is
24.3 g. This material is dissolved in
50 mL of ether and washed with saturated aqueous
sodium bicarbonate solution (4 × 20 mL) and water (25 mL). The combined aqueous fractions are extracted with
50 mL of ether, and the combined
ether extracts are dried over
magnesium sulfate for 10 min (Note
6). Filtration and evaporation on a
rotary evaporator give
20.0 g of crude product, which is distilled through an
8-cm Vigreux column. The
di-tert-butyl methylenemalonate is collected at
60–67°C/0.1 mm and weighs
15.3 g (
48%) (Note
7). The product is somewhat unstable and should be stored in Pyrex in the
refrigerator.