Organic Syntheses, Coll. Vol. 5, p.734 (1973); Vol. 43, p.71 (1963).
A "Vycor" tube 550 mm. long and 25 mm.
in outside diameter is packed for 500 mm. of its length with 6-mm. × 6-mm. quartz rings
and mounted vertically so that the upper section is encased in a tube furnace 150 mm. long and the lower section is encased in a tube furnace 300 mm. long. The upper furnace, which serves as a preheater, is monitored by a thermocouple placed between the tube and the furnace heating elements. The temperature of the lower furnace is monitored by a thermocouple
located in the center of the lower packed section. The upper end of the pyrolysis tube is fitted with a Y-tube
carrying the thermocouple well and a graduated addition funnel with a pressure-equalizing arm. The lower end is attached through one 500-ml. trap
and two 200-ml. traps
, each immersed in a mixture of solid carbon dioxide
, to a regulated vacuum source. One gram of hydroquinone
is placed in the first trap.
The pyrolysis tube is flushed with nitrogen
, the lower section is heated to 600° and the upper section to 300° (Note 1)
, and the pressure is regulated at 25 mm. Then 184 g. (1.00 mole) (Note 2) of dimethyl 3-methylenecyclobutane-1,2-dicarboxylate3
is admitted over a period of 3 hours (Note 3)
. The product, which amounts to 172–177 g., collects in the traps. It is distilled through a 13-mm. × 1.2-m. Nester spinning-band
First there is 41–47 g.
) of methyl acrylate
1.4010, b.p. 34–36°/150 mm.
, then 39–43 g.
) of methyl butadienoate
1.4635 (Note 4)
, b.p. 59–60°/52 mm.
or 48–49°/26 mm.
By continuing the distillation, 20–30 g. of starting material, b.p. 125–150°/25 mm.
, can be recovered.
The temperature of the lower section is quite critical and should be maintained within the range 590–610°. However, the preheater section is needed only to volatilize the ester, so any temperature between 200° and 400° is satisfactory.
Since an estimated 3–5 g. of carbon
is deposited in the tube during the pyrolysis, it is advisable to pyrolyze only 1 mole of ester at a time and to burn out the carbon
with a slow stream of air at 600° between pyrolyses.
The space velocity is approximately 125 l. of standard gas per l. of free space per hour, and the contact time is approximately 0.3 second.
The checkers used a 10-mm. × 0.76-m. Nester spinning band still and obtained material having nD25
1.4620 that could not be purified by redistillation. Analysis by vapor-phase chromatography (silicone gum rubber, 20% w/w on firebrick, 120-cm. × 6-mm. outside diameter column
at 125°) showed this material to be 95% methyl butadienoate
contaminated by small amounts of two other materials.
4. Merits of the Preparation
This procedure gives a product free of acetylenic groups. It illustrates the synthesis of an olefinic compound by cracking a cyclobutane
into two fragments.
This preparation is referenced from:
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