A.
Methyl 2-iodo-3-nitropropionate. A dry,
5-l., three-necked, round-bottomed flask is fitted with a mineral oil-containing liquid-sealed
mechanical stirrer, a
gas-inlet tube connected to a
drying tower containing 1:1 sodium hydroxide–Drierite, and an open neck that will later be connected to a
rubber septum. The flask is flushed gently by passing dry
nitrogen through the drying tower and gas-inlet tube as
methyl acrylate (298.4 g., 331 ml., 3.47 moles) (Note
1) and anhydrous
diethyl ether (2500 ml.) (Note
1) are added through the open neck. The flask is fitted with the rubber septum and then cooled to 0° by covering three-fourths of the flask with ice in a large
ice bath made from a picnic cooler insulated on top with glass wool. The gas-inlet tube is removed just long enough to permit the addition of
iodine (250 g., 0.98 mole) (Note
1). The mixture is stirred for about 15 minutes and then
dinitrogen tetroxide (76.6 ml., 1.24 moles) (Note
1) and (Note
2) is introduced rapidly with a syringe (Note
3) through the rubber septum. The reaction solution is stirred at 0° for 30 hours. The solution is divided into three batches of about 1-l., which are cooled in a freezer to −4°. One batch at a time is removed and added to a
2-l. separatory funnel where it is washed with
80 ml. of aqueous 70% saturated sodium sulfite solution that had been precooled to −4° (Note
4). The ethereal solutions are washed alternately so that each batch is exposed to room temperature for the minimum time. The
sodium sulfite washes are repeated two or three times on each batch until the color of the ethereal solution remains light yellow when kept at −4° (Note
5). The cooled ethereal solutions are then dried by washing each with precooled (to −4°) aqueous solutions containing
80 ml. of saturated sodium chloride and
15 ml. of saturated sodium sulfite. The ethereal solutions are then combined in a
4-l. Erlenmeyer flask and dried over anhydrous
sodium sulfate at −4° overnight in a freezer. The dried solution is then filtered to remove the
sodium sulfate, and concentrated by evaporating it in portions in a
1-l. round-bottomed flask on a
rotating evaporator fitted with a
cold-finger condenser containing a dry-ice bath (Note
6). The solution should be concentrated until it contains approximately equal volumes of product and
ether. The solution is then cooled to −78° for 30 minutes (Note
6) and (Note
7), causing the separation of 403.5–409 g. of ether–wet crystals. The crystals are filtered and stored in a
freezer, and the filtrate is eluted through a chromatographic column containing
700 g. of silica gel (Baker Analyzed, 60–200 mesh, 7-cm. column diameter), using
30% diethyl ether/petroleum ether (b.p.
30–60°) as eluent. The solution containing the first band to be eluted, which is yellow, is evaporated on a rotating evaporator fitted with a cold finger condenser cooled with dry ice as described above. This gives a residue of 35–54.5 g. of yellowish crystals, which are a 7:3 mixture of
methyl 2-iodo-3-nitropropionate and
methyl (E)-3-nitroacrylate. The
ether-wet product from the original filtration and the eluted product are combined in a 1-l. round-bottomed flask and dried at 0° under a vacuum (0.3–0.5 mm.) for 3–4 hours, giving
396–401 g. (
78–79%), m.p.
32–35°, of
methyl 2-iodo-3-nitropropionate containing a small amount of
methyl (E)-3-nitroacrylate. This mixture may be used directly in the next step. The product can be recrystallized from
30% ether/petroleum ether (b.p.
30–60°) to obtain thermally unstable white plates, m.p.
33–35° (Note
8).